5-53 Figure 5-30. NCWF Hazard Scale
5.6.5.2.2 One-Hour Extrapolated Forecast Polygons.
One-hour extrapolated forecast polygons are high-resolution polygons outlining areas expected to be filled by selected Convective hazard fields in 1 hour. Extrapolated forecasts depict new locations for the Convective hazard fields based on their past movements. Extrapolation forecasts do not forecast the development of new Convective hazard conditions or the dissipation of existing conditions. Forecasts are provided only for Convective hazard scale Levels 3 or higher. The forecast polygons do not depict specific forecast hazard levels. In Figure 5-29, the light blue polygon denotes the location of the 1-hour forecast Convective hazard field.
5.6.5.2.3 Forecast Speed and Direction.
Forecast speed and direction are assigned to current Convective hazard fields having a 1-hour extrapolated forecast. A line (or arrow on the AWC JavaScript product) is used to depict the direction of movement. The speed in knots is depicted by the first group of two numbers located near the current Convective hazard field. The second group of three numbers identifies echo tops.
Forecast speed and direction is only updated every 10 minutes. The larger update time interval (compared to five-minute updates for the NCWF) smooths erratic forecast velocities. In Figure 5-29, the forecast direction (depicted by an arrow) is pointing to the southeast, and the speed is 25 kts.
5.6.5.2.4 Echo Tops.
Echo tops are assigned to current Convective hazard fields having a 1-hour extrapolated forecast. Echo tops are depicted by a group of three numbers located near the current Convective hazard field and are plotted in hundreds of feet MSL. In Figure 5-31, NCWF One-Hour E xtrapolated Forecast Polygon, Forecast Movement Velocity and Echo Tops—Examp le, the echo tops are 45,000 ft MSL.
5-54 Figure 5-31. NCWF One-Hour Extrapolated Forecast Polygon, Forecast Movement Velocity and Echo Tops—Example
5.6.5.2.5 Past Performance Polygons.
Past performance polygons are magenta polygons displaying the past hour’s extrapolated forecast polygons with the current Convective hazard fields. A perfect forecast would have the polygons filled with Convective hazard scale Levels 3 or higher data. Levels 1 and 2 would be outside the polygons. The display of past performance polygons allows the user to review the accuracy of the past hour’s forecast.
Figure 5-32, NCWF Past Performance Polygons—Example, depicts current Convective hazard fields and past performance polygons (magenta) valid at 1500Z. The past performance polygons are the 1-hour extrapolated forecasts made at 1400Z. Although the polygons do not perfectly match the current Level 3 and higher hazard fields, the forecasts are still fairly accurate.
Newly developed Convective hazard Levels 3 and higher do not have past performance polygons. Extrapolated forecasts do not forecast developing hazardous Convective.
5-55 Figure 5-32. NCWF Past Performance Polygons—Example
5.6.5.3 St rengths and Limitations.
5.6.5.3.1 Strengths.
Strengths of the NCWF include:
• Convective hazard fields that agree very well with radar and lightning data;
• Updates every five minutes;
• High-resolution forecasts of Convective hazards; and
• Well-forecasted long-lived Convective precipitation.
5.6.5.3.2 Limitations.
Limitations of the NCWF include:
• Initiation, growth, and decay of Convective precipitation are not forecast;
• Short-lived or embedded convection may not be accurately displayed or forecast;
• Low-topped convection that contains little or no lightning may not be depicted;
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• Erroneous motion vectors are occasionally assigned to storms; and
• Convective hazard field scales are not identified within the forecast polygons.
5.6.5.4 Uses of the NCWF.
The purpose of the NCWF is to produce a Convective hazard field diagnostic and forecast product based on radar data, echo top mosaics, and lightning data. The target audience includes the FAA and other government agencies, pilots, aircraft dispatchers, aviation meteorologists, and other interested aviation users in the general public.
5.7 Products for Tropical Cyclones.
The NWS issues SIGMETs, Convective SIGMETs, and CWAs to inform the aviation community about the potential or existence of tropical cyclones. These above-listed products are the primary source of information. The NWS also issues other products pertaining to tropical cyclones. Tropical cyclones have a sustained wind speed of 34 kts or greater and are called tropical storm, hurricane, typhoon, and cyclone, depending on their intensity or region of the world.
5.7.1 Tropical Cyclone Advisory (TCA).
The TCA is intended to provide tropical cyclone forecast guidance, through 24 hours, for international aviation safety and routing purposes. TCAs are issued by the World Meteorological Organization’s (WMO) TCACs for all ongoing tropical cyclone activity in their respective AORs. There are seven TCACs worldwide, with two in the United States, the NWS’ National Hurricane Center (NHC) in Miami, Florida, and the NWS’s Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii.
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.
5.7.1.1 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.
5.7.1.2 Content.
TCAs list the current tropical cyclone position, motion, and intensity, and 6-, 12-, 18-, and 24-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 Department of Defense (DOD).
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5.7.1.3 Format.
The format of the Aviation Tropical Cyclone Advisory is as follows:
FKaa2i cccc ddhhmm (ICAO communication header) (TROPICAL CYCLONE TYPE) (NAME)ICAO ADVISORY NUMBER ## (ISSUING OFFICE CITY STATE) BBCCYYYY time UTC day of week mon dd yyyy TEXT $$
5.7.1.4 Aviation Tropical Cyclone Advisory (TCA) Example.
FKNT25 KNHC 210900 TCANT5 TROPICAL STORM ICAO ADVISORY NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092007 0900 UTC SUN OCT 21 2007
TC ADVISORY DTG: 20071021/0900Z TCAC: KNHC TC: ERNESTO NR: 027 PSN: N3000 W08012 MOV: N 13KT C: 0998HPA MAX WIND: 045KT FCST PSN + 06 HR: 211200 N3106 W07951 FCST MAX WIND + 06 HR: 045KT FCST PSN + 12 HR: 211800 N3206 W07930 FCST MAX WIND + 12 HR: 050KT FCST PSN + 18 HR: 220000 N3321 W07903 FCST MAX WIND + 18 HR: 045KT
5-58 FCST PSN + 24 HR: 220600 N3436 W07836 FCST MAX WIND + 24 HR: 040KT
RMK THE FORECAST POSITION INFORMATION IN
THIS PRODUCT IS INTERPOLATED FROM OFFICIAL FORECAST DATA VALID AT 0000...
0600...1200...AND 1800Z.
NXT MSG: 20071021/1500Z $$
5.7.1.5 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 graphic format. For more information on these public forecasts, see the websites of NHC, CPHC, WFO Guam, and WFOs along the Gulf Coast and the East Coast.
5.8 Volcanic Ash Forecasts.
In addition to SIGMETs, the NWS issues forecasts to notify the aviation community of volcanic ash clouds.
5.8.1 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, World Area Forecast Centers (WAFC), 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 5-33, Volcanic Ash Advisory Centers (VAACs)). 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.
5-59 Figure 5-33. Volcanic Ash Advisory Centers (VAACs)
AORs for VAACs include Anchorage, Montreal, Washington. Wellington (New Zealand), Buenos Aires (Argentina), London, Toulouse (France), Tokyo, and Darwin.
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 National Environmental Satellite, Data, and Information Service (NESDIS) Satellite Analysis Branch (SAB) and the NWS National Centers for Environmental Prediction (NCEP) Central Operations (NCO). The Anchorage VAAC is managed by the NWS’s AAWU. The AORs for each VAAC are:
• Washington VAAC.
o FIRs in CONUS and adjacent coastal waters.
o The Oakland Oceanic FIR over the Pacific Ocean.
o The New York FIR over the western Atlantic Ocean.
o FIRs over and adjacent to the Caribbean and Central and South America north of 10 degrees south latitude.
• Anchorage VAAC.
o The Anchorage FIR.
o Russian FIRs north of 60 degrees north latitude and east of 150 degrees east longitude.
5.8.2 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.
5-60 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.
5.8.2.1 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 6 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.
5.8.2.2 VAA Format.
The VAA format conforms to the “Template for advisory message for volcanic ash” included in ICAO Annex 3.
5.8.2.3 VAA 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 OBSERVEDAND 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.
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5.8.2.4 VAA Graphic Example.
Figure 5-34. Volcanic Ash Advisory in Graphical Format
5.9 G raphical Forecast for Aviation (GFA).
The GFAs are a set of Web-based displays which are expected to provide the necessary aviation weather information to give users a complete picture of the weather that may impact flights in the CONUS. These displays are updated continuously and provide forecasts, observational data, and warnings of weather phenomena that can be viewed from 14 hours in the past to 15 hours in the future. This product covers the surface up to FL420 (or 42,000 ft MSL). Wind, icing, and turbulence forecasts are available in 3,000-ft increments from the surface up to 18,000 ft MSL, and in 6,000-ft increments from 18,000 ft MSL to FL420. Turbulence forecasts are also broken into low (below 18,000 ft MSL) and high (above 18,000 ft MSL) graphics. A maximum icing graphic and maximum wind velocity graphic (regardless of altitude) are also available. The graphic below is an example of an aviation forecast for clouds.
Figure 5-35. Aviation Forecast for Clouds-Example Aviation Forecasts • Clouds SURVEY INFO CIG/VIS PCPN/WX +3hr 2300 UTC Mon 13 Jun 2016 Obs/Warn Settings 00Z 012 02Z 032 042 052 062 072 082 092 10Z TOP 090 OVC080 o BKNOO TOP O05 LYRD. LY 0079 avE CI ABV CI AB TOP 090 OVCOZO OVC110
• I 5 TO 02 10015 TO Scale C085 TOF 020 Cirrus 500 km Ans Cirrus ONC 500 mi VERAP Cloud Fraction at Low [20160613_18_F05] Coverage <FL180 SKY FEW SCT BKN OVC SKY Coverage Below FL180) OSKC OFEW OSCT OBKN •ovC AIRMETS OBSCN MInOR MTN SIGMETS SI Thunder Storm Cyclonel Trop Volcanic Ash
5.9.1 Time Selection and Slider.
Available weather product tabs are configured based on the time selection. Users may choose between Forecast and Observations/Warnings (Obs/Warn). The specific hour may then be chosen by the time slider.
Figure 5-36. Time Selection and Slider orecast Obs/Warn Settings 162 17Z 18Z 19Z 20Z 21Z 22Z 23Z 00Z 01Z 02Z 03Z 04Z 05Z 06Z
5.9.1.1 Forecast Weather Products Tabs.
Weather products with forecast information are available by selecting one of the tabs at the top of the display above the time selector. The selected product will be highlighted. The default is TAF.
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5-63 Figure 5-37. Forecast Weather Products Tabs
5.9.1.2 Forecast Weather Product Elements Tabs.
The following table shows which weather elements are displayed on each forecast product tab. The acronyms in this table are decoded for each product by clicking the products tab to review the NWS Hazard and Code and the AWC SIGMET and Code charts found at https://www.aviationweather.gov/gf a/help?page=products.
Table 5-11. Weather Elements on Forecast Product Tabs Product Gridded Product Weather Data Overlay SIGMET NWS Warnings AIRMET Vertical Levels TAF - - All All - - CIG/VIS LAMP Flight Category, Ceiling, or Visibility NDFD Precipitation/ Weather Type and Intensity Symbol
C-SIG TC TS BD BS VA WS BZ Sierra (IFR) - Clouds RAP Model Cloud Coverage, Tops, or Bases RAP Model Cloud Base, Layers, and Tops C-SIG TC TS VA - Mountain Obscuration -
PCPN/WX NDFD Precipitation/ Weather Type and Likelihood NDFD Precipitation/ Weather Type and Intensity
C-SIG TC TS BD BS VA
TO TS WS BZ
IS LS ST
- -
TS NDFD Thunderstorm Coverage NDFD Thunderstorm Type and Intensity
C-SIG TC TS TO TS - - Winds RAP/NDFD Wind Speed RAP/NDFD Wind and Gust Barb
C-SIG TC TS WS BZ IS ST GA HW LLWS, Strong Surface Winds
SFC, MAX, every 3,000 ft from FL030 to FL300; every 6,000 ft from FL300 to FL480 Turb Graphical Turbulence Guidance (GTG)
- C-SIG TC TS TB - Turbulence LO, HI, every 3,000 ft from FL030 to FL300; every 6,000 ft from FL300 to FL480
5-64 Product Gridded Product Weather Data Overlay SIGMET NWS Warnings AIRMET Vertical Levels Ice FIP @ “SFC” NDFD Winter Precipitation/ Weather Type and Likelihood @ “SFC” NDFD Winter Precipitation/ Weather Type and Intensity C-SIG TC TS IC @ “SFC” WS
BZ IS LS Icing SFC, MAX, every 3,000 ft from FL030 to FL300; every 6,000 ft from FL300 to FL480
5.9.1.3 Observations/Warnings (Obs/Warn).
The Observation/Warning option provides an option to display weather data for the current time and the previous fourteen hours (rounded to the nearest hour). Users may advance through time using the arrow buttons or by clicking on the desired hour.
Figure 5-38. Observations/Warnings Tab
5.9.1.4 Observations/Warnings Weather Product Tabs.
The following table shows what is displayed on each Observations/Warnings weather product tab. Each product in this menu is overlaid on an infrared (IR) satellite image with a radar loop of the five most recent images up to the selected hour.
Table 5-12. Products Displayed on Observations/Warnings Weather Products Tab Product Weather Data Overlay SIGMET NWS Warnings Vertical Levels METAR METAR Station Plot All All - PCPN/WX METAR Precipitation Weather Symbol
C-SIG TC TS BD BS VA
TO TS WS BZ IS LS ST - CIG/VIS FLT CAT: Non-VFR Color-Coded METAR Flight Category Symbol CIG: Number (ft/100) VIS: Number (SM)
C-SIG TC TS BD BS VA
WS BZ - PIREP PIREP symbols All - ALL, every 3,000 ft from FL030 to FL300;
every 6,000 ft from FL300 to FL480 RAD/SAT - All All -
5.9.2 GFA Static Images.
Some users with limited Internet connectivity may access static images via the AWC at https://www.aviationweather.gov/gfa/plot. There are two static graphical images