Chapter 26, Advisories 26-22
• 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
ZDV ARTCC identification
2 Phenomenon number (single digit, 1–6)
CWA Product type (CWA)
032140 Beginning and/or issuance UTC date/time
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
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
Chapter 26, Advisories 26-23
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.
Chapter 26, Advisories 26-24
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 VAAC s as well as other
weather information sources.
Chapter 26, Advisories 26-25
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.
Chapter 26, Advisories 26-26
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.
Chapter 26, Advisories 26-27
26.6.2 TCA Content
TCAs list the current tropical cyclone position, motion, and intensity, and 3-, 9-, 15-, 21-, and 2 7-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.
Chapter 26, Advisories 26-28
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.