Aviation Weather HandbookFAA-H-8083-28B
Chapter 26
Advisories
34 pagesPages 26-1–26-34
26.1 Introduction
The third of five types of aviation weather information contained in this handbook are advisories. For this handbook, advisories include the following:
1. Significant Meteorological Information (SIGMET):
Inside the CONUS:
o Non-Convective.
o Convective.
Outside the CONUS.
2. Airmen’s Meteorological Information (AIRMET):
Inside the CONUS.
Outside the CONUS.
3. Center Weather Advisory (CWA).
4. Volcanic Ash Advisory (VAA).
5. Tropical Cyclone Advisory (TCA).
6. Space Weather Advisory.
7. Wind Shear Alerts.
8. Airport Weather Warning (AWW).
26.2 Significant Meteorological Information (SIGMET)
A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations. SIGMETs are issued in text format and intended for dissemination to all pilots in flight to enhance safety. SIGMETs are issued as soon as practical to give notice to operators and aircrews of potentially hazardous en route conditions. Although the areas where the SIGMETs apply may be shown graphically, a graphical depiction of the SIGMET area is not the entire SIGMET. Additional information regarding the SIGMET may be contained in the text version.
26.2.1 SIGMET Issuance
SIGMETs are issued from MWOs. The United States has three MWOs: the AWC, the AAWU, and the WFO Honolulu.
The AWC is responsible for:
Twenty domestic ARTCC FIRs covering the CONUS and adjacent coastal waters. CONUS SIGMETs, except for Convective SIGMETs, are grouped into six areas (see Figure 26-1).
The New York, Houston, Miami, and San Juan Oceanic FIRs (see Figure 26-2).
The Oakland Oceanic FIR north of 30°N latitude and the portion east of 140° W longitude, which is between the Equator and 30°N latitude (see Figure 26-3).
The AAWU is responsible for the Anchorage Continental FIR and the Anchorage Oceanic FIR (see Figure 26-3).
WFO Honolulu is responsible for the Oakland Oceanic FIR south of 30°N latitude and between 140°W and 130°E longitude (see Figure 26-3).
Figure 26-1. AWC SIGMET Areas of Responsibility—CONUS
Figure 26-2. AWC SIGMET Areas of Responsibility—Atlantic Basin
Note that KKCI refers to the AWC that is in Kansas City, MO.
Figure 26-3. SIGMET Areas of Responsibility—Pacific Basin
26.2.2 SIGMET Identification
U.S. SIGMETs (other than Convective SIGMETs) are assigned a series identifier:
AWC for the CONUS:
o NOVEMBER, OSCAR, PAPA, QUEBEC, ROMEO, UNIFORM, VICTOR, WHISKEY, XRAY, and YANKEE. Note that SIERRA and TANGO are excluded.
AWC for the Oakland Oceanic FIR:
o ALFA, BRAVO, CHARLIE, DELTA, ECHO, FOXTROT, GOLF, and HOTEL.
Honolulu MWO for the Oakland Oceanic FIR:
o NOVEMBER, OSCAR, PAPA, QUEBEC, ROMEO, SIERRA, TANGO, UNIFORM, VICTOR, WHISKEY, XRAY, YANKEE, and ZULU.
AAWU for the Anchorage FIR:
o INDIA, JULIET, KILO, LIMA, and MIKE.
A number is assigned sequentially with each issuance until the phenomenon ends. At 0000 UTC each day, all continuing SIGMETs are renumbered to one, regardless of a continuation of the phenomena (e.g., YANKEE 1, YANKEE 2, YANKEE 3).
26.2.3 SIGMET Standardization
SIGMETs follow these standards:
All heights or altitudes are referenced to above MSL, unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 ft, the level is preceded by “FL” (e.g., FL180).
References to latitude and longitude are in whole degrees and minutes following the model: Nddmm or Sddmm, Wdddmm, or Edddmm with a space between latitude and longitude and a hyphen between successive points (e.g., N3106 W07118—N3011 W7209).
Messages are prepared in abbreviated plain language using contractions from FAA Order JO 7340.2, Contractions, for domestic products, and from ICAO Doc 8400, ICAO Abbreviations and Codes, for international products issued for Oceanic FIRs. A limited number of non-abbreviated words, geographical names, and numerical values of a self-explanatory nature may also be used.
26.2.4 Inside the CONUS
26.2.4.1 Non-Convective SIGMET
26.2.4.1.1 Non-Convective SIGMET Issuance Criteria—CONUS
A SIGMET may be issued in the CONUS when any of the following conditions affect, or, in the judgment of the forecaster, are expected to affect an area judged to have a significant impact on the safety of aircraft operations:
Severe or greater turbulence (SEV TURB).
Severe icing (SEV ICE).
Widespread dust storm (WDSPR DS).
Widespread sandstorm (WDSPR SS).
Volcanic ash (VA).
26.2.4.1.2 Non-Convective SIGMET Issuance Time and Valid Period—CONUS
A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a four-hour period. A SIGMET can have a valid period up to, but not exceeding, four hours. SIGMETs for continuing phenomena will be reissued at least every four hours as long as SIGMET conditions continue to occur in the area of responsibility.
26.2.4.1.3 Non-Convective SIGMET Format and Example—CONUS
The content and order of elements in the SIGMET are as follows:
Series name and number.
Valid beginning and ending time (UTC).
List of states affected by the phenomena.
Location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time.
Phenomena description (e.g., SEV ICE).
Vertical extent (base and top), if appropriate.
Movement, if appropriate.
Intensity change (INTSF—intensifying, WKN—weakening, NC—no change).
Indication that the weather condition will continue during the four hours beyond the valid time of the SIGMET.
SFOR UWS 100130 SIGMET ROMEO 1 VALID UNTIL 100530 OR WA FROM SEA TO PDT TO EUG TO SEA SEV TURB BTN FL280 AND FL350. CONDS CONTG BYD 0530Z.
Figure 26-4. Non-Convective SIGMET for the CONUS—Example
Table 26-1. Decoding a Non-Convective SIGMET for the CONUS
| Line | Content | Description |
|---|---|---|
| 1 | SFO | SIGMET area identifier |
| R | SIGMET series | |
| UWS | Product identifier | |
| 100130 | Issuance date/time UTC | |
| 2 | SIGMET | Product type |
| ROMEO | SIGMET series name | |
| 1 | Series issuance number | |
| VALID UNTIL 100530 | Ending valid date/time UTC | |
| 3 | OR WA | Phenomenon location (states) |
| 4 | FROM SEA TO PDT TO EUG TO SEA | Phenomenon location (high-altitude VOR coordinates) |
| 5 | SEV TURB BTN FL280 AND FL350. CONDS CONTG BYD 1000Z | Phenomenon description |
The SIGMET in Figure 26-4 is decoded as the following:
(Line 1) SIGMET ROMEO series issued for the San Francisco area at 0130 UTC on the 10th day of the month.
(Line 2) This is the first issuance of the SIGMET ROMEO series and is valid until the 10th day of the month at 0530 UTC.
(Line 3) The affected states within the San Francisco area are Oregon and Washington.
(Line 4) From Seattle, WA; to Pendleton, OR; to Eugene, OR; to Seattle, WA.
(Line 5) Severe turbulence between FL280 and FL350. Conditions continuing beyond 0530Z.
26.2.4.1.4 Non-Convective SIGMET Cancellations—CONUS
A CONUS Non-Convective SIGMET is cancelled when the phenomenon is no longer occurring, no longer expected to occur, or has moved out of the area of responsibility.
26.2.4.1.5 Non-Convective SIGMET Amendments—CONUS
Amendments to CONUS Non-Convective SIGMETs are not issued. Instead, a new SIGMET is issued using the next series number.
26.2.4.1.6 SIGMET (Non-Convective) Corrections—CONUS
Corrections to CONUS Non-Convective SIGMETs are issued as necessary. The corrected SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time.
26.2.4.2 Convective SIGMET
Convective SIGMETs are issued for the CONUS instead of SIGMETs for thunderstorms. Any Convective SIGMET implies severe or greater turbulence, severe icing, and LLWS.
Although the areas where the Convective SIGMETs apply may be shown graphically, such a graphical depiction, the Convective SIGMET polygon is a “snapshot” that outlines the area (or line) of thunderstorms at the issuance time of 55 minutes past each hour. During the valid time of the SIGMET, the area/line will move according to the movement vector given in the SIGMET. For fast-moving areas or lines, they will very likely end up outside the SIGMET polygon by the end of the hour. Slow-moving or stationary areas or lines will likely remain in or very close to the original polygon. For additional clarification, the movement “MOV FROM...” within the Convective SIGMET describes the current movement of the SIGMET area or line. In cases when cell movements are different within the area, the SIGMET will include an additional line that states “CELL MOV FROM.” Detailed information regarding the Convective SIGMET depiction should be compared to the textual version for storm movement, velocity, cloud tops, and several other important elements. Users should exercise caution as areas of convection and their associated polygons can change and should only be used for strategic planning.
26.2.4.2.1 Convective SIGMET Routine Issuance Criteria
A Convective SIGMET will be issued when any of the following conditions are occurring, or, in the judgment of the forecaster, are expected to occur:
A line of thunderstorms at least 60 mi long with thunderstorms affecting at least 40 percent of its length.
An area of active thunderstorms judged to have a significant impact on the safety of aircraft operations covering at least 40 percent of the area concerned and exhibiting a very strong radar reflectivity intensity or a significant satellite or lightning signature.
Embedded or severe thunderstorm(s) expected to occur for more than 30 minutes during the valid period, regardless of the size of the area.
26.2.4.2.2 Convective SIGMET Special Issuance Criteria
A special Convective SIGMET may be issued when any of the following criteria are occurring or, in the judgment of the forecaster, are expected to occur for more than 30 minutes of the valid period:
Tornado, hail greater than or equal to ¾ in (at the surface), or wind gusts greater than or equal to 50 kt (at the surface) are reported.
Indications of rapidly changing conditions if, in the forecaster’s judgment, they are not sufficiently described in existing Convective SIGMETs.
Special issuance is not required for a valid Convective SIGMET.
26.2.4.2.3 Convective SIGMET Issuance Time and Valid Period
Convective SIGMET bulletins for the eastern, central, and western regions of the CONUS (see Figure 26-5) are issued on a scheduled basis, hourly at 55 minutes past the hour. Each bulletin contains all valid Convective SIGMETs within the region. Convective SIGMETs are valid for two hours or until superseded by the next hourly issuance. A Convective SIGMET bulletin must be transmitted each hour for each region. When conditions do not meet or are not expected to meet Convective SIGMET criteria within a region at the scheduled time of issuance, a “CONVECTIVE SIGMET...NONE” message is transmitted.
Figure 26-5. AWC Convective SIGMET Areas of Responsibility
26.2.4.2.4 Convective SIGMET Format and Example
Each Convective SIGMET bulletin includes one or more individually numbered Convective SIGMETs for the region. The content and order of each bulletin is as follows:
Convective SIGMET series number and region letter (E, W, or C).
Valid ending time (UTC).
List of states affected by the phenomena.
Location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time.
Phenomena description (e.g., AREA SEV EMBD TS).
Movement (e.g., MOV FROM 26030KT).
Cloud top (e.g., TOPS ABV FL450).
Remarks (e.g., TORNADOES...HAIL TO 2.5 IN...WIND GUSTS TO 70KT POSS). Note: Tropical cyclone information will be added to the remarks section of the CONUS Convective SIGMETs when appropriate.
Figure 26-6. Convective SIGMET—Example
Table 26-2. Decoding a Convective SIGMET for the CONUS
| Line | Content | Description |
|---|---|---|
| 1 | MKC | Issuing office (AWC) |
| C | Region (East, Central, or West) | |
| WST | Product identifier | |
| 221855 | Issuance date/time (DDHHMM) | |
| 2 | CONVECTIVE SIGMET | Product type |
| 20 | Issuance number | |
| C | Region (East, Central, or West) | |
| 3 | VALID UNTIL 2055Z | Valid ending time (UTC) |
| 4 | ND SD | States/areas affected |
| 5 | FROM 90W MOT-GFK-ABR-90W MOT | Phenomenon location (high-altitude VOR coordinates) |
| 6 | INTSFYG AREA SEV TS MOVG FROM 24045KT. TOPS ABV FL450. WIND GUSTS TO 60KTS RPRTD. TORNADOES…HAIL TO 2 IN… WIND GUSTS TO 65KTS POSS ND PTN | Phenomenon description, movement, cloud top, remarks |
The Convective SIGMET in Figure 26-6 is decoded as the following:
(Line 1) Convective SIGMET issued for the central portion of the United States on the 22nd day of the month at 1855Z.
(Line 2) This is the 20th Convective SIGMET issued on the 22nd day of the month for the central United States as indicated by “20C.”
(Line 3) Valid until 2055Z.
(Line 4) The affected states are North Dakota and South Dakota.
(Line 5) From 90 NM west of Minot, ND; to Grand Forks, ND; to Aberdeen, SD; to 90 NM west of Minot, ND.
(Line 6) An intensifying area of severe thunderstorms moving from 240° at 45 kt (to the northeast). Thunderstorm tops above FL450. Wind gusts to 60 kt reported. Tornadoes, hail with diameter of two inches, and wind gusts to 65 kt possible in the North Dakota portion.
26.2.4.2.5 Convective SIGMET Outlook
Each Convective SIGMET bulletin includes a two- to six-hour outlook at the end of the bulletin. The content and order of each bulletin is as follows:
Beginning and ending valid times.
Location of expected Convective SIGMET issuances delineated by high-altitude VOR coordinates for the outlook valid time.
26.2.4.2.6 Convective SIGMET Cancellations
Convective SIGMETs are not cancelled but are superseded by the next Convective SIGMET in the series.
26.2.4.2.7 Convective SIGMET Amendments
Amended Convective SIGMETs are not issued. Instead, a new Convective SIGMET is issued for that region.
26.2.4.2.8 Convective SIGMET Corrections
Corrections to Convective SIGMETs are issued as necessary. The corrected Convective SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time.
26.2.5 Outside the CONUS
26.2.5.1 SIGMET Issuance Criteria—Outside the CONUS
U.S. SIGMETs outside the CONUS are issued when any of the following conditions affect or, in the judgment of the forecaster, are expected to affect an area judged to have a significant impact on the safety of aircraft operations:
Thunderstorm—of type below:* o Obscured (OBSC TS).
o Embedded (EMBD TS).
o Widespread (WDSPR TS).
o Squall line (SQL TS).
o Isolated severe (ISOL SEV TS).
Severe turbulence (SEV TURB).
Severe icing (SEV ICE); with freezing rain (SEV ICE (FZRA)).
Widespread dust storm (WDSPR DS).
Widespread sandstorm (WDSPR SS).
Volcanic ash (VA).
Tropical cyclone (TC).
*Tornado (TDO), funnel cloud (FC), waterspout (WTSPT), and heavy hail (HVY GR) may be used as further descriptions of the thunderstorm, as necessary.
26.2.5.2 SIGMET Issuance Time and Valid Period—Outside the CONUS
A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a four-hour period. A SIGMET outside the CONUS can have a valid period up to, but not exceeding, four hours, except for volcanic ash (VA) and tropical cyclone (TC), which can be valid up to six hours. SIGMETs for continuing phenomena will be reissued at least every four (or six) hours as long as SIGMET conditions continue to occur in the area of responsibility.
26.2.5.3 SIGMET Format and Example—Outside the CONUS
SIGMETs outside the CONUS contain the following information, related to the specific phenomena and in the order indicated:
Phenomenon and its description (e.g., SEV TURB).
An indication whether the information is observed, using “OBS” and/or “FCST.” The time of observation will be given in UTC.
Location of the phenomenon referring to, where possible, the latitude and longitude and FLs (altitude) covering the affected area during the SIGMET valid time. SIGMETs for volcanic ash clouds and tropical cyclones contain the positions of the ash cloud, tropical cyclone center, and radius of convection at the start of the valid time of the SIGMET.
Movement toward or expected movement using 16 points of the compass, with speed in knots, or stationary, if appropriate.
Thunderstorm maximum height as FL.
Changes in intensity, using, as appropriate, the abbreviations for intensifying (INTSF), weakening (WKN), or no change (NC).
Forecast position of the volcanic ash cloud or the center of the tropical cyclone at the end of the validity period of the SIGMET message.
Figure 26-7. SIGMET Outside the CONUS—Example
Table 26-3. Decoding a SIGMET Outside of the CONUS
| Line | Content | Description |
|---|---|---|
| 1 | WSPA07 | ICAO communication header |
| PHFO | Issuance MWO | |
| 010410 | Issuance UTC date/time | |
| 2 | SIGPAT | NWS AWIPS communication header |
| 3 | KZAK | Area control center |
| SIGMET | Product type | |
| TANGO | SIGMET series | |
| 2 | Issuance number | |
| VALID 010410/010800 | Valid period UTC date/time | |
| PHFO | Issuance office | |
| 4 | OAKLAND OCEANIC FIR | FIR |
| FRQ TS OBS AND FCST WI 200NM N3006 W14012 - N2012 W15016 CB TOP FL400 MOV W 10KT WKN. | Phenomenon description |
The SIGMET in Figure 26-7 is decoded as the following:
(Line 1) The WMO product header is WSPA07. Issued by the Honolulu MWO on the first day of the month at 0410 UTC.
(Line 2) The NWS Advanced Weather Interactive Processing System (AWIPS) communication header is SIGPAT.
(Line 3) For the Oakland ARTCC (KZAK). This is the second issuance of SIGMET Tango series, valid from the 1st day of the month at 0410 UTC until the 1st day of the month at 0800 UTC, issued by the Honolulu MWO.
(Line 4) Concerning the Oakland Oceanic FIR, frequent thunderstorms observed and forecast within 200 NM of 30° and 6 minutes north; 140° and 12 minutes west; to 20° and 12 minutes north, 150° and 16 minutes west, cumulonimbus tops to FL400 moving west at 10 kt, weakening.
26.2.5.4 SIGMETs for Volcanic Ash (VA)—Outside the CONUS
A SIGMET for a volcanic ash cloud is issued for volcanic eruptions. A volcanic eruption is any volcanic activity, including the emission of volcanic ash, regardless of the eruption’s magnitude. Initial volcanic ash SIGMETs may be issued based on credible PIREPs in the absence of a VAA but are updated once a VAA is issued. Volcanic ash SIGMETs will continue to be issued until the ash cloud is no longer occurring or expected to occur.
SIGMETs for a volcanic ash cloud are valid up to six hours and provide an observed or forecast location of the ash cloud at the beginning of the SIGMET. A six-hour forecast position for the ash cloud, valid at the end of the validity period of the SIGMET message, is also included.
26.2.5.5 SIGMETs for Tropical Cyclone (TC)—Outside the CONUS
SIGMETs for a tropical cyclone (which includes a hurricane, typhoon (western Pacific), and tropical storm) may be issued for non-frontal synoptic-scale cyclones meeting the following criteria:
Originates over tropical or subtropical waters with organized convection and definite cyclonic surface wind circulation.
Wind speeds reach 35 kt independent of the wind averaging time used by the TCAC. SIGMETs for tropical cyclones will be valid up to six hours. SIGMETs for tropical cyclones will include two positions. The first position will be the observed position of the center of the tropical cyclone, taken from the TCA. The second position will be the forecast position of the center of the tropical cyclone valid at the end of the SIGMET period, which will coincide with the six-hour forecast position in the TCA.
In addition to the two storm positions, SIGMETs will include associated convection when applicable. SIGMETs will be reissued at least every six hours while the tropical cyclone winds remain or are expected to remain above 34 kt.
26.2.5.6 SIGMET Cancellation—Outside the CONUS
SIGMETs are cancelled when the phenomenon is no longer occurring or expected to occur.
26.2.5.7 SIGMET Amendments—Outside the CONUS
SIGMET amendments will not be issued. Instead, the next SIGMET in the series is issued to accomplish the update. The valid time of the new SIGMET is reset to reflect the new four-hour valid period (six-hour period for volcanic ash and tropical cyclone SIGMETs).
26.2.5.8 SIGMET Corrections—Outside the CONUS
Corrections to SIGMETs are issued as necessary. This is done by issuing a new SIGMET in the series, which advances the SIGMET number and cancels the previous SIGMET.
26.2.5.8.1 SIGMET for Volcanic Ash Example—Outside the CONUS
- WVNT06 KKCI 082030
- TJZS SIGMET FOXTROT 2 VALID 082030/090230 KKCI-
- SAN JUAN FIR VA FROM SOUFRIERE HILLS LOC 1642N06210W
- VA CLD OBS AT 2030Z WI N1730 W06400 - N1700 W06300 - N1650 W06300 - N1710 W06400
- - N1730 W06400. SFC/060. MOV W 15KT. FCST 0230Z VA CLD APRX N1730 W06500 - N1700
W06300 - N1650 W06300 - N1710 W06500 - N1730 W06500.
The ICAO communication header for this product is WVNT06. It is a SIGMET issued by the AWC (KKCI) in Kansas City, MO, on the eighth day of the month at 2030 UTC. This is the second issuance of SIGMET series Foxtrot valid from the 8th day of the month at 2030 UTC until the 9th day of the month at 0230 UTC. Within the San Juan Oceanic FIR, volcanic ash from the Soufriere Hills volcano located at 16°/42 minutes north, 62°/10 minutes west. Volcanic ash cloud observed at 2030 UTC within an area bounded by 17°/30 minutes north, 64°/00 minutes west to 17°/00 minutes north, 63°/00 minutes west to 16°/50 minutes north, 63°/00 minutes west to 17°/10 minutes north, 64°/00 minutes west to 17°/30 minutes north, 64°/00 minutes west. From the surface to 6,000 ft MSL. Moving to the west at 15 kt. Forecast at 0230 UTC, volcanic ash cloud located approximately at 17°/30 minutes north, 65°/00 minutes west to 17°/00 minutes north, 63°/00 minutes west to 16°/50 minutes north, 63°/00 minutes west to 17°/10 minutes north, 65°/00 minutes west to 17°/30 minutes north, 65°/00 minutes west.
26.2.5.8.2 SIGMET for Tropical Cyclone Example—Outside the CONUS.
- WSNT03 KKCI 081451
- SIGA0C
- KZNY SIGMET CHARLIE 11 VALID 081500/082100 KKCI-
- NEW YORK OCEANIC FIR TC KYLE OBS N3106 W07118 AT 1500Z CB TOP FL500 WI 120NM OF
- CENTER MOV WSW 5 KT NC FCST 2100Z TC CENTER N3142 W07012
The ICAO communication header for this product is WSNT03. It is a SIGMET issued by the AWC (KKCI) in Kansas City, MO, on the eighth day of the month at 1451 UTC. The NWS AWIPS communication header for this product is SIGA0C. This is the eleventh issuance of SIGMET series Charlie valid from the eighth day of the month at 1500 UTC until the eighth day of the month at 2100 UTC. Within the New York Oceanic FIR, Tropical Cyclone Kyle observed at 31°/6 minutes north, 71°/18 minutes west at 1500 UTC, cumulonimbus tops to FL500 (approximately 50,000 ft MSL), within 120 NM of the center, moving from west-southwest at 5 kt, no change in intensity is forecast, at 2100 UTC the tropical cyclone center will be at 31°/42 minutes north, 70°/12 minutes west.
26.3 Airmen’s Meteorological Information (AIRMET)
An AIRMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations. AIRMETs are intended to inform all pilots, especially VFR pilots and operators of sensitive aircraft, of potentially hazardous weather phenomena. AIRMETs contain details about IFR, extensive mountain obscuration, moderate turbulence, strong surface winds, moderate icing, and freezing levels.
AIRMETs are intended for dissemination to all pilots in the preflight and en route phases of flight to enhance safety. En route, AIRMETs are available over Flight Service frequencies. Over the CONUS, AIRMETs are also available on equipment intended to display weather and other non-ATC-related flight information to pilots using the FIS-B. In Alaska and Hawaii, AIRMETs are broadcast on air traffic frequencies.
AIRMETs are issued for the CONUS, Alaska, and Hawaii. No AIRMETs are issued for U.S. Oceanic FIRs in the Gulf of America, Caribbean, and Western Atlantic and Pacific Oceans.
26.3.1 AIRMET Issuance
AIRMETs are issued from the three U.S. MWOs located at the AWC, the AAWU, and the WFO Honolulu. Their areas of responsibility are:
AWC: The CONUS and adjacent coastal waters.
AAWU: Alaska and adjacent coastal waters.
WFO Honolulu: Hawaii and adjacent waters.
26.3.1.1 AIRMETs Over the CONUS
AIRMETs over the CONUS are displayed graphically (sometimes known as G-AIRMETs) on websites such as https://aviationweather.gov and https://www.1800wxbrief.com and equipment receiving FIS-B information. AIRMETs over the CONUS provide a higher forecast resolution than AIRMETs issued in text format. AIRMETs over the CONUS are valid at discrete times no more than three hours apart for a period of up to 12 hours into the future (e.g., 00, 03, 06, 09, and 12 hours). Additional forecasts may be inserted during the first six hours (e.g., 01, 02, 04, and 05). A forecast at 00-hour represents the initial conditions, and the subsequent graphics depict the area affected by the particular hazard at that valid time. Forecasts valid at 00 through 06 hours correspond to the text AIRMET bulletin.
AIRMETs over the CONUS depict the following en route aviation weather hazards:
IFR conditions (ceiling <1,000 ft and/or surface visibility <3 mi).
Widespread mountain obscuration.
Moderate icing.
Freezing levels.
Moderate turbulence.
Non-convective LLWS potential below 2,000 ft AGL.
Sustained surface winds greater than 30 kt.
Interpolation of time periods between AIRMETs over the CONUS valid times: Users should keep in mind when using the AIRMET over the CONUS that if a 00-hour forecast shows no significant weather and a 03-hour forecast shows hazardous weather, they must assume a change is occurring during the period between the two forecasts. It should be taken into consideration that the hazardous weather starts immediately after the 00-hour forecast, unless there is a defined initiation or ending time for the hazardous weather. The same would apply after the 03-hour forecast. The user should assume the hazardous weather condition is occurring between the snapshots unless informed otherwise. For example, if a 00-hour forecast shows no hazard, a 03-hour forecast shows the presence of hazardous weather, and a 06-hour forecast shows no hazard, the user should assume the hazard exists from the 0001-hour to the 0559-hour time period.
26.3.1.2 AIRMETs Over Alaska and Hawaii
AIRMETs over Alaska and Hawaii are in text format. The hazard areas are described using well-known geographical areas. AIRMETs over Alaska are issued for three Alaska regions corresponding to Alaska area forecasts.
AIRMETs over Alaska are valid up to eight hours. AIRMETs over Hawaii are valid up to six hours. Unscheduled issuances contain an update number for easier identification. There are three AIRMET categories: Sierra, Tango, and Zulu.
AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations.
AIRMET Tango describes moderate turbulence, sustained surface winds of 30 kt or greater, and/or non-convective LLWS.
AIRMET Zulu describes moderate icing and provides freezing level heights.
26.3.1.3 AIRMET Issuance Criteria
An AIRMET may be issued when any of the following weather phenomena are occurring or are expected to occur:
Ceiling less than 1,000 ft and/or visibility less than 3 SM (IFR). o Weather phenomena restricting the visibility including, but not limited to, precipitation (PCPN), smoke (FU), haze (HZ), mist (BR), fog (FG), and blowing snow (BS).
Widespread mountain obscuration (MTN OBSCN).
o Weather phenomena causing the obscuration are included, but not limited to, clouds (CLDS), precipitation (PCPN), smoke (FU), haze (HZ), mist (BR), and fog (FG).
Moderate turbulence (MOD TURB).
o Top and bottom of MOD TURB layer are specified.
Sustained surface wind greater than 30 kt (STG SFC WND).
Moderate icing (MOD ICE).
o Top and bottom of MOD ICE are specified.
o The range of freezing level altitudes is given when the bottom altitude of MOD ICE is the freezing level (FRZLVL).
o Areas with multiple freezing levels are specified.
o Range of freezing levels over the area is specified.
o Lowest freezing levels AGL at intervals of 4,000 ft MSL (or surface (SFC) as appropriate) are specified.
Non-convective LLWS potential below 2,000 ft AGL (LLWS POTENTIAL).
26.3.2 AIRMET Standardization
All AIRMETs follow these standards:
All heights or altitudes are referenced to above MSL, unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 ft, the level is preceded by “FL” to represent flight levels (e.g., FL180).
Messages are prepared in abbreviated plain language using contractions from Order JO 7340.2. A limited number of non-abbreviated words, geographical names, and numerical values of a self-explanatory nature may also be used.
Weather and obstructions to visibility are described using the weather abbreviations for surface weather observations (METAR/SPECI). Refer to Federal Meteorological Handbook No. 1, Surface Weather Observations and Reports, or Section 24.3 of this handbook.
26.3.3 AIRMET Issuance Times and Valid Periods
AIRMETs are issued following the schedule listed in Table 26-4. AIRMETs are issued four times a day except for those in Alaska, which are issued three times a day. Unscheduled AIRMETs are issued when conditions are occurring or expected to occur but were not forecast.
Table 26-4. AIRMET Issuance Schedule
| Product Type | Issuance Time | Issuance Frequency |
|---|---|---|
| AIRMETs over the CONUS | 0245, 0845, 1445, 2045 UTC | Every 6 hours |
| AIRMETs over Alaska | 0115, 1315, 2115 UTC (Standard Time) 0415, 1215, 2015 UTC (Daylight Saving Time) | Every 8 hours |
| AIRMETs over Hawaii | 0400, 1000, 1600, 2200 UTC | Every 6 hours |
AIRMETs are valid for six hours except for those in Alaska, which are valid for eight hours. The valid period of an AIRMET message cannot exceed the valid time of the AIRMET bulletin. However, note that each AIRMET contains remarks concerning the continuance of the phenomenon during the six hours following the AIRMET ending time. Also, AIRMET bulletins can contain a separate outlook when conditions meeting AIRMET criteria are expected to occur during the six-hour period (eight-hour for Alaska) after the valid time of the AIRMET bulletin.
26.3.4 AIRMET Formats and Examples
The AWC’s website provides several options to display AIRMETs over the CONUS. There is an interactive display, as well as snapshots that may be viewed as static (single), combined, and looped images using the tools provided on the website.
An AIRMET message for Alaska and Hawaii includes the following information as appropriate and in the order indicated:
Reference to appropriate active SIGMETs affecting the area at the time of AIRMET issuance (e.g., SEE SIGMET BRAVO SERIES).
Beginning time of the AIRMET phenomenon if different from the AIRMET beginning valid time.
AIRMET name (SIERRA, TANGO, or ZULU), update number, weather phenomenon, and ending valid time. (Note: The AIRMET number is reset to 1 after 0000 UTC each day.) o AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations. Hawaii AIRMETs for mountain obscuration may be issued for an area less than 3,000 mi2. o AIRMET Tango describes moderate turbulence, sustained surface winds of 30 kt or greater, and non-convective LLWS.
o AIRMET Zulu describes moderate icing and provides freezing-level heights.
Fixed geographic locations (Alaska and Hawaii, see Figure 27-3 and Error! Reference source not found.).
Description of phenomenon for the AIRMET issuance.
Vertical extent (bases and tops), as appropriate.
Ending time of phenomenon if different from the AIRMET ending time.
For Alaska AIRMETs: Intensity change remarks (INTSF, WKN, IMPR, or NC) concerning the continuance of the phenomenon following the valid period.
For Hawaii AIRMETs: A separate AIRMET outlook is included in the AIRMET bulletin when conditions meeting AIRMET criteria are expected to occur during the six-hour period after the valid time of the AIRMET bulletin.
26.3.4.1 Example of AIRMET Sierra Issued for the Southeast Alaska Area
- WAAK47 PAWU 241324
- WA7O
- JNUS WA 241315
- AIRMET SIERRA FOR IFR AND MT OBSC VALID UNTIL 242115
.
LYNN CANAL AND GLACIER BAY JB
MTS OBSC BY CLDS/ISOL PCPN. NC.
.
CNTRL SE AK JC
MTS OCNL OBSC IN CLDS. NC.
.
SRN SE AK JD
PAWG-PAKT LN W OCNL CIGS BLW 010/VIS BLW 3SM BR. IMPR. .
SRN SE AK JD
MTS OCNL OBSC IN CLDS. NC.
.
ERN GLF CST JE
OCNL CIGS BLW 010/VIS BLW 3SM BR/-RA BR. DTRT. .
ERN GLF CST JE
MTS OBSC IN CLDS/ISOL PCPN. DTRT.
.
SE AK CSTL WTRS JF
MTS OCNL OBSC IN CLDS. NC.
.
- =JNUT WA 241315
- AIRMET TANGO FOR TURB/STG SFC WINDS VALID UNTIL 242115
.
- ERN GLF CST JE
- OFSHR ICY BAY W SUSTAINED SFC WND 30 KTS
OR GTR. SPRDG E. INTSF.
.
- =JNUZ WA 241315
- AIRMET ZULU FOR ICING VALID UNTIL 242115
.
ERN GLF CST JE
16Z TO 19Z ALG CST W ICY BAY OCNL MOD ICEIC 080-160. FZLVL 045 EXC 015 INLAND. WKN.
26.3.4.2 Example of AIRMET Tango Issued for Hawaii FA Area
- WAHW31 PHFO 241529
- WA0HI
- HNLS WA 241600
- AIRMET SIERRA UPDATE 2 FOR IFR VALID UNTIL 242200
.
NO SIGNIFICANT IFR EXP.
- =HNLT WA 241600
- AIRMET TANGO UPDATE 3 FOR TURB VALID UNTIL 242200
.
AIRMET TURB...HI
OVER AMD IMT S THRU W OF MTN.
TEMPO MOD TURB BLW 070.
COND CONT BEYOND 2200Z.
- =HNLZ WA 241600
- AIRMET ZULU UPDATE 2 FOR ICE AND FZLVL VALID UNTIL 242200
.
NO SIGNIFICANT ICE EXP.
26.3.5 AIRMET Updates and Amendments
AIRMETs are issued over the CONUS by the AWC every six hours and are updated/amended as necessary. If an AIRMET issued for Alaska or Hawaii is amended, “AMD” is added after the date/time group. The issuance time of the AIRMET bulletin is updated to reflect the time of the amendment. The ending valid time remains unchanged.
26.4 Center Weather Advisory (CWA)
A CWA is a concise description of the occurrence or expected occurrence of specified weather phenomena that meet or approach in-flight advisory (e.g., AIRMET, SIGMET, or Convective SIGMET) criteria. A CWA is issued for hazardous weather when there is no existing in-flight advisory from the AWC or the AAWU.
26.4.1 CWA Issuance
CWAs are issued by the NWS CWSU. CWSU areas of responsibility are depicted in Figure 26-8.
Figure 26-8. CWSU Areas of Responsibility
CWAs are valid for up to two hours and may include forecasts of conditions expected to begin within two hours of issuance. If conditions are expected to persist after the advisory’s valid period, a statement to that effect is included in the last line of the text. Additional CWAs will subsequently be issued as appropriate. Notice of significant changes in the phenomenon described in a CWA is provided by a new CWA issuance for that phenomenon. If the forecaster deems it necessary, CWAs may be issued hourly for convective activity.
26.4.2 CWA Criteria
CWAs may be issued for the following situations:
There is no existing AWC or AAWU advisory in effect or any of the following conditions occur: o Conditions meeting Convective SIGMET criteria;
o Icing—moderate or greater;
o Turbulence—moderate or greater;
o Heavy and extreme precipitation;
o Freezing precipitation;
o Conditions at or approaching LIFR;
o Surface wind gust at or above 30 kt;
o LLWS (surface–2,000 ft); or o Volcanic ash, dust storms, or sandstorms.
When a hazard has grown significantly outside of the boundary defined by the AWC or the AAWU advisory.
To upgrade a thunderstorm advisory to include severe thunderstorms.
To upgrade an AIRMET to include isolated severe turbulence or icing. If greater than isolated severe turbulence or icing is occurring, then a new CWA should be issued.
To define a line of thunderstorms within a larger area covered by the AWC or the AAWU advisory.
To better define hazards expected at a major terminal already within an AWC or an AAWU advisory.
Anything that in the judgment of the CWSU forecaster will add value to an existing advisory.
If in the forecaster’s judgment the conditions listed above, or any others, may adversely impact the safe flow of air traffic.
26.4.3 CWA Format and Example
Figure 26-9. CWA—Example
Table 26-5. Decoding a CWA
| Line | Content | Description |
|---|---|---|
| 1 | ZDV | ARTCC identification |
| 2 | Phenomenon number (single digit, 1–6) | |
| CWA | Product type (CWA) | |
| 032140 | Beginning and/or issuance UTC date/time | |
| 2 | ZDV | ARTCC identification |
| CWA | Product type | |
| 2 | Phenomenon number (single digit, 1–6) | |
| 02 | Issuance number (issued sequentially for each phenomenon number) | |
| VALID TIL 032340Z | Ending valid UTC date/time | |
| 3 | FROM FMN TO 10N FMN TO 20NE FMN TO 10E FMN TO FMN | Phenomenon location |
| 4 | ISOLD SEV TS NR FMN MOVG NEWD 10KTS. TOP FL410. WND GSTS TO 55KTS. HAIL TO 1 INCH RPRTD AT FMN. SEV TS CONTG BYD 2340Z | Phenomenon description |
The CWA in Figure 26-9 is decoded as follows:
(Line 1) CWA issued for the Denver ARTCC (ZDV) CWSU. The “2” after ZDV in the first line denotes this is the second meteorological event of the local calendar day. This CWA was issued/begins on the third day of the month at 2140 UTC.
(Line 2) The Denver ARTCC (ZDV) is identified again. The “202” in the second line denotes the phenomena number again (2) and the issuance number (02) for this phenomenon. This CWA is the valid until the third day of the month at 2340 UTC.
(Line 3) From Farmington, NM, to 10 NM north of Farmington, NM, to 20 NM northeast of Farmington, NM, to 10 NM east of Farmington, NM, to Farmington, NM.
(Line 4) Isolated severe thunderstorms near Farmington moving northeastward at 10 kt. Tops to FL410. Wind gusts to 55 kt. Hail to one inch reported at Farmington. Severe thunderstorms continuing beyond 2340 UTC.
26.5 Volcanic Ash Advisory (VAA)
The VAA is advisory information on volcanic ash cloud issued in abbreviated plain language, using approved ICAO abbreviations and numerical values of self-explanatory nature. A graphical (e.g., chart) version of the VAA is also produced and is sometimes referred to as “VAG.” The VAG contains the same information as in the VAA but in a four-panel chart format.
26.5.1 Volcanic Ash Advisory Center (VAAC)
A VAAC is a meteorological office designated by an ICAO regional air navigation agreement to provide advisory volcanic ash information to MWOs, WAFCs, area control centers, flight information centers, and international operational meteorological (OPMET) data banks regarding the lateral and vertical extent and forecast movement of volcanic ash in the atmosphere following a volcanic eruption. There are nine VAACs worldwide (see Figure 26-10). The duties of a VAAC include:
Monitoring relevant geostationary and polar-orbiting satellite data to detect the existence and extent of volcanic ash in the atmosphere in the area concerned;
Activating the volcanic ash numerical trajectory/dispersion model in order to forecast the movement of any ash cloud that has been detected or reported; and
Issuing advisory information regarding the extent and forecast movement of the volcanic ash cloud.
Areas of responsibility for VAACs include Anchorage, Montreal, Washington, Wellington (New Zealand), Buenos Aires (Argentina), London, Toulouse (France), Tokyo, and Darwin.
Figure 26-10. Volcanic Ash Advisory Centers
The United States has two VAACs with responsibilities defined in ICAO Annex 3, Meteorological Service for International Air Navigation. The Washington VAAC is jointly managed by the NESDIS SAB and the NWS NCO. The Anchorage VAAC is managed by the NWS AAWU.
The Washington VAAC areas of responsibility are:
FIRs in the CONUS and adjacent coastal waters.
The Oakland Oceanic FIR over the Pacific Ocean.
The New York FIR over the western Atlantic Ocean.
FIRs over and adjacent to the Caribbean and Central and South America north of 10° S latitude. The Anchorage VAAC areas of responsibility are:
The Anchorage FIR.
Russian FIRs north of 60°N latitude and east of 150°E longitude.
26.5.1.1 VAA Issuance
Each VAAC issues VAAs to provide guidance to MWOs for SIGMETs involving volcanic ash. VAAs are issued as necessary, but at least every six hours until such time as the volcanic ash cloud is no longer identifiable from satellite data, no further reports of volcanic ash are received from the area, and no further eruptions of the volcano are reported.
VAAs in both text and graphical format are available from the websites of the VAACs as well as other weather information sources.
26.5.1.2 VAA Format
The VAA format conforms to the template included in ICAO Annex 3, Table A2-1, Template for Advisory Message for Volcanic Ash.
26.5.1.3 VAA Text Example
- FVAK21 PAWU 190615
- VOLCANIC ASH ADVISORY
- ISSUED: 20030419/0615Z
- VAAC: ANCHORAGE
- VOLCANO: CHIKURACHKI, 900-36
- LOCATION: N5019 E15527
- AREA: KAMCHATKA NORTHERN KURIL ISLANDS
- SUMMIT ELEVATION: 7674 FT (2339 M)
- ADVISORY NUMBER: 2003-02
- INFORMATION SOURCE: SATELLITE
- AVIATION COLOR CODE: NOT GIVEN
ERUPTION DETAILS: NEW ERUPTION OCCURRED APPROX 190500 UTC.
HEIGHT IS ESTIMATED AT FL300. ESTIMATE IS BASED ON OBSERVED AND MODEL WINDS. MOVEMENT APPEARS TO BE E AT 75 KTS.
OBS ASH DATA/TIME: 19/0500Z
OBS ASH CLOUD: VA EXTENDS FM NEAR VOLCANO EWD TO N50 E160.
FCST ASH CLOUD +6HR: 30NM EITHER SIDE OF LN FM NIPPI N49 E159 - N50 E175. FCST ASH CLOUD +12HR: 30NM EITHER SIDE OF LN FM N50 E168 - N50 E180. FCST ASH CLOUD +18HR: 30NM EITHER SIDE OF LN FM N51 E175 - N50 E185.
NEXT ADVISORY: 20030419/1500Z
REMARKS: UPDATES AS SOON AS INFO BECOMES AVAILABLE.
26.5.1.4 VAA Graphic Example
Figure 26-11. VAA in Graphical Format
26.6 Aviation Tropical Cyclone Advisory (TCA)
The aviation TCA is intended to provide tropical cyclone forecast guidance, through 24 hours, for international aviation safety and routing purposes. TCAs are issued by the WMO’s TCAC for all ongoing tropical cyclone activity in their respective areas of responsibility. Two of the world’s TCACs are in the United States: the NWS NHC in Miami, FL, and the NWS CPHC in Honolulu, HI. The NHC is responsible for all ongoing tropical cyclone activity in the Atlantic and eastern Pacific, north of the Equator, while the CPHC is responsible for the central Pacific, north of the Equator. TCAs are available on their respective websites.
26.6.1 TCA Issuance
The NHC and CPHC issue TCAs at 0300, 0900, 1500, and 2100 UTC and are valid from the time of issuance until the next scheduled issuance or update. The forecast position information in the TCA is interpolated from the official forecast data, which is valid at 0000, 0600, 1200, and 1800 UTC.
26.6.2 TCA Content
TCAs list the current tropical cyclone position, motion, and intensity, and 3-, 9-, 15-, 21-, and 27-hour forecast positions and intensities. It is an alphanumeric text product produced by hurricane forecasters and consists of information extracted from the official forecasts.
This forecast is produced from subjective evaluation of current meteorological and oceanographic data as well as output from Numerical Weather Prediction (NWP) models, and is coordinated with affected NWS offices, the NWS national centers, and the DOD.
26.6.3 TCA Example
- FKNT22 KNHC 151436
- TCANT2
- TROPICAL STORM BILL ICAO ADVISORY NUMBER 5
- NWS NATIONAL HURRICANE CENTER MIAMI FL
- 1500 UTC TUE JUN 15 2021
- AL022021
- TC ADVISORY
- DTG: 20210615/1500Z
- TCAC: KNHC
- TC: BILL
- ADVISORY NR: 2021/005
- OBS PSN: 15/1500Z N4030 W06200
- MOV: NE 33KT
- INTST CHANGE: NC
- C: 0998HPA
- MAX WIND: 050KT
- FCST PSN +3 HR: 15/1800Z N4225 W05939
- FCST MAX WIND +3 HR: 050KT
- FCST PSN +9 HR: 16/0000Z N4425 W05722
- FCST MAX WIND +9 HR: 050KT
- FCST PSN +15 HR: 16/0600Z N4628 W05507
- FCST MAX WIND +15 HR: 045KT
- FCST PSN +21 HR: 16/1200Z N//// W/////
- FCST MAX WIND +21 HR: ///KT
- FCST PSN +27 HR: 16/1800Z N//// W/////
- FCST MAX WIND +27 HR: ///KT
- RMK: SOME FORECAST INFORMATION IN THIS PRODUCT IS INTERPOLATED FROM OFFICIAL
FORECAST DATA.
NXT MSG: 20210615/2100Z
$$
26.6.4 Additional Tropical Cyclone Information Products The NHC, CPHC, and select WFOs issue many public tropical storm and hurricane/typhoon information products. Many are in web-based graphical format. For more information on these public forecasts, see the websites of the NHC, CPHC, WFO Guam, and WFOs along the Gulf Coast and the East Coast.
26.7 Space Weather Advisory
ICAO implemented a Space Weather Advisory program in late 2019. Under this program, ICAO designated four global space weather service providers:
The United States, which is done by the NOAA SWPC.
The Australia, Canada, France, and Japan (ACFJ) consortium, comprising of space weather agencies from Australia, Canada, France, and Japan.
The Pan-European Consortium for Aviation Space Weather User Services (PECASUS), comprising of space weather agencies from Finland (lead), Belgium, the United Kingdom, Poland, Germany, Netherlands, Italy, Austria, and Cyprus.
The China-Russian Federation Consortium (CRC) comprising of space weather agencies from China and the Russian Federation.
26.7.1 Space Weather Advisory Issuance
The SWPC, ACFJ consortium, PECASUS consortium, and CRC consortium serve as four global space weather centers that share the responsibility to issue global Space Weather Advisories, on a rotating basis, when there are impacts to HF COM, SATCOM, satellite-based navigation and surveillance systems (GNSS), or when heightened radiation occurs above FL250.
A Space Weather Advisory is issued whenever space weather conditions exceed predefined ICAO thresholds for both moderate impacts (MOD) and severe impacts (SEV) as given in Table 26-6.
Table 26-6. Space Weather Advisory Issuance Criteria
| Effect | Sub-Effect | Parameter Used | Thresholds | Impact within Advisory Area | ||
|---|---|---|---|---|---|---|
| MOD | SEV | MOD | SEV | |||
| GNSS | Amplitude Scintillation | S4 (dimensionless) | 0.5 | 0.8 | Possible degraded service | Possible unreliable service |
| GNSS | Phase Scintillation | Sigma-phi (radians) | 0.4 | 0.7 | ||
| GNSS | Vertical Total Electron Content (TEC) | TEC units | 125 | 175 | ||
| RADIATION | Effective dose (micro-Sieverts/hour)* | 30 | 80 | Possible increased dose rates above normal levels | ||
| HF COM | Auroral Absorption (AA) | Kp index | 8 | 9 | Possible degraded service | Possible unreliable service |
| HF COM | Polar Cap Absorption (PCA) | dB from 30 MHz riometer data | 2 | 5 | ||
| HF COM | Shortwave Fadeout (SWF) | Solar X rays (0.0–0.8 NM) (W-m⁻²) | 1×10⁻⁴ (X1) | 1×10⁻³ (X10) | ||
| HF COM | Post-Storm Depression | Maximum Usable Frequency (MUF) | 30% | 50% | ||
| SATCOM | No threshold has been set for this effect | Possible degraded service | Possible unreliable service | |||
*MOD advisories will only be issued when the MOD threshold is reached between FL250 and FL460. SEV advisories will be issued when the SEV threshold is reached at any FL above FL250. For context, the background effective dose rate at FL370 at very high latitudes is approximately 9 micro-Sieverts/hour during solar minimum and 6 micro-Sieverts/hour during solar maximum. These rates decrease progressively toward the equatorial regions to values approximately one quarter of what is observed at very high latitudes. Note: SEV radiation is a rare event with only a few short-lived events occurring during an 11-year solar cycle.
26.7.2 Space Weather Advisory Format
The Space Weather Advisory provides an observed or expected location for the impact and 6-, 12-, 18-, and 24-hour forecasts. The advisory describes the affected part of the globe in one of three ways:
Six pre-defined latitude bands of width 30° shown in Table 26-7 (multiple bands may be given in one advisory), followed by a longitude range in 15-degree increments;*
The term “DAYLIGHT SIDE,” meaning the extent of the planet that is in daylight; or
A polygon using latitude and longitude coordinates.
Note: *E18000-W18000 (or E180-W180) is used when the entire band is affected.
Table 26-7. Latitude Bands Used in Space Weather Advisories
| Latitude Bands Used in Space Weather Advisories | |
|---|---|
| High latitudes northern hemisphere (HNH) | N90 to N60 |
| Middle latitudes northern hemisphere (MNH) | N60 to N30 |
| Equatorial latitudes northern hemisphere (EQN) | N30 to equator |
| Equatorial latitudes southern hemisphere (EQS) | Equator to S30 |
| Middle latitudes southern hemisphere (MSH) | S30 to S60 |
| High latitudes southern hemisphere (HSH) | S60 to S90 |
By design, the vertical and temporal resolutions of the advisory are very coarse. The use of 30° latitude bands, 15-degree longitude increments, 1,000-ft vertical increments (for radiation), and six-hour time intervals will at times result in over-forecasting the affected airspace. In addition, while an entire latitude band may be forecast to have MOD or SEV space weather, there will often be times that the effect does not cover the entire width of the band or is intermittent or temporary. Users should refer to the remarks section of the advisory for additional information. Users can also go to the center’s website, where a graphical depiction of the space weather event may be provided along with additional information. Changes to the Space Weather Advisory content and format are possible in the coming years as experience is gained with the use of this product.
The Space Weather Advisory is not a replacement for the SWPC’s other products or the NOAA Space Weather Scales, which continue to be provided by the SWPC. Refer to the SWPC’s website for information on these products and the scales.
Table 26-8. Format of the Space Weather Advisory
| Format | Explanation | Examples |
|---|---|---|
| Communication header | Product’s coded identification for the issuing centers. KWNP is the SWPC, LFPW and YMMC are the ACFJ, EFKL and EGRR are the PECASUS, and ZBBB and UUAG are the CRC.FNXX01 is for GNSS, FNXX02 is for HF COM, FNXX03 is for Radiation, and FNXX04 is for SATCOM. | FNXX01 KWNP FNXX01 LFPW FNXX01 YMMC FNXX01 EFKL FNXX02 EGRR FNXX03 UUAG FNXX04 ZBBB |
| SWX ADVISORY | Space Weather (SWX) Advisory. | SWX ADVISORY |
| STATUS: | Status indicator (optional) for test or exercise. | TEST EXER |
| DTG: | Date and time of origin, in YYYYMMDD/HHMMZ. | 20190418/0100Z |
| SWXC: | Name of the Space Weather Advisory Center (SWXC). | ACFJ PECASUS SWPC CRC |
| ADVISORY NR: | Advisory number (NR). | 2019/9 |
| NR RPLC: | Advisory number being replaced by this advisory (optional). | 2019/8 |
| SWX EFFECT: | Space weather effect. | HF COM MOD HF COM SEV SATCOM MOD SATCOM SEV GNSS MOD GNSS SEV RADIATION MOD RADIATION SEV |
| OBS (or FCST) SWX: | Observed (OBS) or expected (FCST) space weather effect date/time, location, and altitudes (altitudes are only used in the radiation advisory). | 18/0100Z EQN W18000-W12000 18/0100Z HNH HSH E180-W180 ABV FL370 18/0100Z DAYLIGHT SIDE 18/0100Z NO SWX EXP |
| FCST SWX +6 HR: | 6-hour forecast. Date/time, location, and altitudes. | Same as above |
| FCST SWX +12 HR: | 12-hour forecast. Date/time, location, and altitudes. | Same as above |
| FCST SWX +18 HR: | 18-hour forecast. Date/time, location, and altitudes. | Same as above |
| FCST SWX +24 HR: | 24-hour forecast. Date/time, location, and altitudes. | Same as above |
| RMK: | Remarks (RMK). | Additional information |
| NXT ADVISORY: | Date/time when the next (NXT) scheduled advisory will be issued. | 2010418/0700Z |
26.7.3 Space Weather Advisory Examples
26.7.3.1 Example Space Weather Advisory—GNSS
Note: “GNSS” is the acronym for Global Navigation Satellite System, which is the term for all the world’s navigation satellites, which includes the United States’ Global Position Satellites.
- FNXX03 KWNP 020100
- SWX ADVISORY
- DTG: 20190502/0100Z
- SWXC: SWPC
- ADVISORY NR: 2019/59
- NR RPLC: 2019/58
- SWX EFFECT: GNSS MOD
- OBS SWX: 02/0100Z HNH HSH E18000-W18000
- FCST SWX + 6 HR: 02/0700Z HNH HSH E18000-W18000
- FCST SWX + 12 HR: 02/1300Z HNH HSH E18000-W18000
- FCST SWX + 18 HR: 02/1900Z NO SWX EXP
- FCST SWX + 24 HR: 03/0100Z NO SWX EXP
- RMK: IONOSPHERIC STORM CONTINUES TO CAUSE LOSS-OF-LOCK
- OF GNSS IN AURORA ZONE. THIS ACTIVITY IS
- EXPECTED TO SUBSIDE IN THE FORECAST PERIOD
- NXT ADVISORY: 20190502/0700Z=
26.7.3.2 Example Space Weather Advisory—RADIATION
- FNXX02 EFKL 190300
- SWX ADVISORY
- DTG: 20190219/0300Z
- SWXC: PECASUS
- ADVISORY NR: 2019/20
- SWX EFFECT: RADIATION MOD
- OBS SWX: 19/0300Z HNH HSH E18000-W18000 ABV FL370
- FCST SWX + 6 HR: 19/0900Z NO SWX EXP
- FCST SWX + 12 HR: 19/1500Z NO SWX EXP
- FCST SWX + 18 HR: 19/2100Z NO SWX EXP
- FCST SWX + 24 HR: 20/0300Z NO SWX EXP
- RMK: RADIATION AT AIRCRAFT ALTITUDES ELEVATED
- BY SMALL ENHANCEMENT JUST ABOVE PRESCRIBED
- THRESHOLD. DURATION TO BE SHORT-LIVED
- NXT ADVISORY: NO FURTHER ADVISORIES=
26.7.3.3 Example Space Weather Advisory—HF COM
- FNXX01 YMMC 020100
- SWX ADVISORY
- DTG: 20190202/0100Z
- SWXC: ACFJ
- ADVISORY NR: 2019/10
- SWX EFFECT: HF COM MOD
- OBS SWX: 02/0100Z DAYLIGHT SIDE
- FCST SWX + 6 HR: 02/0700Z DAYLIGHT SIDE
- FCST SWX + 12 HR: 02/1300Z DAYLIGHT SIDE
- FCST SWX + 18 HR: 02/1900Z NO SWX EXP
- FCST SWX + 24 HR: 03/0100Z NO SWX EXP
- RMK: LOW END OF BAND HF COM DEGRADED
- ON SUNLIT ROUTES. NEXT 12 HOURS
MOST POSSIBLE, DECLINING THEREAFTER.
NXT ADVISORY: 20190202/0700Z=
26.8 Low-Level Wind Shear (LLWS)/Microburst Advisories
When LLWS/microburst is reported by pilots or the integrated terminal weather system (ITWS), or detected on wind shear detection systems, such as the LLWS Alert System, the weather systems processor (WSP), or the TDWR, ATC issues the alert to all arriving and departing aircraft. ATC will continue providing the alert to aircraft until it is broadcast on the ATIS and pilots indicate they have received the appropriate ATIS code. A statement is included on the ATIS for 20 minutes following the last report or indication of the wind shear/microburst.
At facilities without the ATIS, ATC broadcasts wind shear/microburst information to all arriving and departing aircraft for 20 minutes following the last report or indication of the wind shear/microburst.
26.9 Airport Weather Warning (AWW)
The AWW addresses weather phenomena that can adversely impact airport ground operations. Information contained in this product may be useful to airport managers, fixed-based operators, airline ground personnel, and others responsible for the safety of ground operations. Ground decisions supported by the AWW information may include fueling delays during thunderstorms, deicing frequency, and other similar ground operations. AWWs are not intended for use by in-flight operations. Note: The AWW is not to be confused with the Aviation Watch Notification Message (see Section 27.17.4.1), which the NWS refers to as “SAW,” but is also known by “AWW” on the websites of some weather provider services. The Aviation Watch Notification Message was formerly known as the Alert Severe Weather Watch Bulletin as well as the Severe Weather Forecast Alert.
26.9.1 AWW Issuance
The AWW is issued for select larger airports and is available on NWS WFOs’ websites who have responsibility for issuing the TAFs for that airport. The AWW is not available on the AWC’s website. Issuance criteria are established according to local airport requirements. Some examples of criteria are strong surface winds, freezing rain, heavy snow, and lightning within five miles of the airport.
26.9.2 AWW Format and Example
The AWW is written in a plain language, free-text format.
- WWUS82 KJAX 112212
- AWWJAX
- FLZ025-112315-
- AIRPORT WEATHER WARNING FOR JACKSONVILLE INTERNATIONAL AIRPORT
- NATIONAL WEATHER SERVICE JACKSONVILLE FL
- 612 PM EDT WED MAR 11 2015
- ...AN AIRPORT WEATHER WARNING HAS BEEN ISSUED FOR JACKSONVILLE
- INTERNATIONAL AIRPORT FOR STRONG WINDS AND POSSIBLE WINDSHIFT
VALID UNTIL 700 PM...
- A CLUSTER OF THUNDERSTORMS WILL MOVE EASTWARD AT 12 KNOTS AND
- AFFECT JACKSONVILLE INTERNATIONAL AIRPORT BY 620 PM. WIND GUSTS
- OVER 35 KNOTS ARE LIKELY WITH THESE STORMS...AS WELL AS CLOUD-
TO-GROUND LIGHTNING AND REDUCED VISIBILITIES FROM HEAVY RAIN.
WINDSHIFTS ACCOMPANYING THE THUNDERSTORMS MAY ALTER THE RUNWAY
LANDING PATTERN WITH SOME STRONG WESTERLY WIND GUSTS. $$