SFC ALG 20NNW HUH.30SSE HUH.60S SEA 50NW LKV.60WNWOAL.30SW OAL 040 ALG 40W HUH.30W HUH.30NNW SEA.40N PDX.20NNW DSD 080 ALG 160NW FOT.80SW ONP.50SSW EUG 40SSE OED.50SSE CZQ.60E EHF.40WSW LAS ....
3.9.3.7 Graphical AIRMETs (G.AIRMETs)
a) G.AIRMETs found on the Aviation Weather Center webpage at http://aviationweather.gov, are graphical forecasts of en.route weather hazards valid at discrete times no more than 3 hours apart for a period of up to 12 hours into the future (for example, 00, 03, 06, 09, and 12 hours). Additional forecasts may be inserted during the first 6 hours (for example, 01, 02, 04, and 05). 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. Forecasts valid at 06 through 12 hours correspond to the text bulletin outlook. G.AIRMET depicts the following en route aviation weather hazards:
1) Instrument flight rule conditions (ceiling < 1000’ and/or surface visibility <3 miles)
2) Mountain obscuration
3) Icing
4) Freezing level
5) Turbulence
6) Low level wind shear (LLWS)
7) Strong surface winds
b) G.AIRMETs are snap shots at discrete time intervals as defined above. The text AIRMET is the result of the production of the G.AIRMET but provided in a time smear for a 6hr valid period. G.AIRMETs provide a higher forecast resolution than text AIRMET products. Since G.AIRMETs and text AIRMETs are created from the same forecast “production” process, there exists perfect consist-ency between the two. Using the two together will provide clarity of the area impacted by the weather hazard and improve situational awareness and decision making.
Interpolation of time periods between G.AIRMET valid times: Users must keep in mind when using the G.AIRMET 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 weathercondition is occurring between the snap shots 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.
EXAMPLE.
See FIG GEN 3.5.8 for an example of the G.AIRMET graphical product.
3.9.3.8 Severe Weather Watch Bulletins (WWs) and Alert Messages (AWWs)
a) WWs define areas of possible severe thunder-storms or tornado activity. The bulletins are issued by the Storm Prediction Center (SPC) in Norman, OK. WWs are unscheduled and are issued as required.
b) A severe thunderstorm watch describes areas of expected severe thunderstorms. (Severe thunder-storm criteria are 3/4.inch hail or larger and/or wind gusts of 50 knots [58 mph] or greater.)
c) A tornado watch describes areas where the threat of tornadoes exists.
d) In order to alert the WFOs, CWSUs, FSSs, and other users, a preliminary notification of a watch called the Alert Severe Weather Watch bulletin (AWW) is sent before the WW. (WFOs know this product as a SAW).
EXAMPLE. Example of an AWW:
MKC AWW 011734 WW 75 TORNADO TX OK AR 011800Z.020000Z AXIS..80 STATUTE MILES EAST AND WEST OF A LINE..60ESE DAL/DALLAS TX/ . 30 NW ARG/ WALNUT RIDGE AR/ ..AVIATION COORDS.. 70NM E/W /58W GGG . 25NW ARG/ HAIL SURFACE AND ALOFT..1 3/4 INCHES. WIND GUSTS..70 KNOTS. MAX TOPS TO 450. MEAN WIND VECTOR 24045.
e) Soon after the AWW goes out, the actual watch bulletin itself is issued. A WW is in the following format:
1) Type of severe weather watch, watch area, valid time period, type of severe weather possible, watch axis, meaning of a watch, and a statement that persons should be on the lookout for severe weather.
2) Other watch information; i.e., references to previous watches.
3) Phenomena, intensities, hail size, wind speed (knots), maximum cumulonimbus (CB) tops, and estimated cell movement (mean wind vector).
4) Cause of severe weather.
5) Information on updating Convective Outlook (AC) products.
EXAMPLE. Example of a WW:
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