Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 270520
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1020 PM MST WED NOV 26 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 416 PM MST WED NOV 26 2014

SNOW SHOWERS CONTINUE THIS AFTERNOON ACROSS THE NEBRASKA PANHANDLE
ALONG THE LEADING EDGE OF LOW TO MID-LEVEL WAA MOVING IN FROM WEST
TO EAST. LAPS SOUNDINGS SHOWS LLVL LAPSE RATES ARE ALSO A BIT
STEEP...WHICH IS LIKELY CONTRIBUTING TO SHOWER DEVELOPMENT AS
WELL. MODELS SHOW THIS ACTIVITY STEADILY WANING AROUND
SUNSET...ALTHOUGH A FEW SHOWERS MAY PERSIST THROUGH ABOUT 03Z.
WINDS OVER THE SOUTHERN LARAMIE RANGE ARE INCREASING ALTHOUGH THE
SFC FRONT IS SLOWER TO SHIFT EAST THAN PREVIOUS THOUGHT SO
WIDESPREAD HIGH WINDS HAVE NOT QUITE MATERIALIZED. SIMILARLY FOR
BORDEAUX...WINDS ARE STILL OUT OF THE SOUTHEAST AT THIS HOUR. IT
APPEARS PRESSURE FALLS OVER THE MOUNTAINS OF COLORADO HAVE KEPT
THE FRONT FROM SHIFTING EAST OUT INTO THE PLAINS...BUT EXPECTING
THESE PRESSURE FALLS OVER THE MOUNTAINS TO EASE OVER THE NEXT FEW
HOURS WHICH SHOULD ALLOW THE FRONT TO FINAL TREK EAST.
THEREFORE...STILL THINKING THAT HIGH WINDS WILL DEVELOP AT LEAST
FOR A SHORT PERIOD OVER THE SOUTHERN LARAMIE RANGE IN THE EVENING
AND AT BORDEAUX LATER TONIGHT...AND SO WILL KEEP THE WARNING IN
PLACE FOR THE NEAR TERM. EXTENDED IT THROUGH THURSDAY AFTERNOON AS
THE POSSIBILITY EXISTS FOR STRONG WINDS TO PERSIST THROUGH THE
DAY.

THE CAG-CPR GRADIENT REMAINS STRONG THROUGH THURSDAY...AND REALLY
THROUGH FRIDAY AS WELL...WITH WINDS OF 50+ KTS PROGGED TO BE JUST
OFF THE SURFACE THROUGH THIS TIME WITH STRONG ZONAL FLOW SETTING
UP OVERHEAD. THE OVERALL PATTERN REMAINS VERY FAVORABLE FOR A LONG
DURATION HIGH WIND EVENT THROUGH FRIDAY FOR THE WIND PRONE AREAS
ALONG AND WEST OF I-25...HOWEVER AM CONCERNED ABOUT MODELS SHOWING
A STRONG AND PERSISTENT INVERSION NEAR THE SURFACE WHICH COULD
PREVENT THESE STRONGER WINDS FROM REACHING THE SURFACE. WAA WITH
RISING HEIGHTS ALOFT IN ZONAL FLOW COMBINED WITH A SHARP MIDLEVEL
THERMAL GRADIENT DEVELOPING ALONG THE ROCKIES ARE CONTRIBUTING TO
THIS INVERSION. THE INVERSION WILL BE COMPETING WITH DEEP LAYER
SUBSIDENCE ON THE ANTICYCLONIC SIDE OF THE JET AND WITH AN ACTIVE
MOUNTAIN WAVE IN PLACE TOMORROW AND FRIDAY. SO...TOUGH CALL WHAT
TO DO EXACTLY WITH HIGH WIND HIGHLIGHTS EXACTLY. FEEL MORE
CONFIDENT THAT THE ARLINGTON AREA WILL SEE PERSISTENT STRONG WINDS
THROUGH THURSDAY AND FRIDAY BEING A HIGHER ELEVATION SITE AND
CLOSER TO MOUNTAIN WAVE/GAP INFLUENCES...BUT FURTHER EAST AT
BORDEAUX AND MAYBE EVEN THE SOUTHERN LARAMIE RANGE/FOOTHILLS...THE
INVERSION MAY HOLD STRONG ENOUGH TO KEEP THE WINDS ALOFT. SO FOR
NOW...MAINTAINED THE HIGH WIND WARNING THROUGH TOMORROW AFTERNOON
FOR ALL WIND PRONE ZONES AS ITS DEFINITELY NOT OUT OF THE QUESTION
THAT THE STRONG WINDS WILL BE FORCED TO THE SURFACE IN THE MORNINGAND
AGAIN IN THE AFTERNOON. WILL REEVALUATE ON LATER SHIFTS FOR THE
NEED FOR FURTHER HIGHLIGHTS THROUGH FRIDAY. TEMPERATURES WILL WARM
BACK INTO THE 40S AND 50S FROM WEST TO EAST...WITH EVEN A FEW 60S
EXPECTED ACROSS THE PLAINS ON FRIDAY.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 416 PM MST WED NOV 26 2014

A WARM START TO THE EXTENDED FCST PERIOD WITH FLAT/ZONAL FLOW ALOFT
IN PLACE OVER MUCH OF THE NORTHERN CONUS. WITH ANY NOTABLE WEATHER
FEATURES WELL TO THE NORTH...BOTH GFS AND ECMWF SHOW ANOTHER DAY OF
H7 TEMPS AS WARM AS 4 DEG C AT 18Z SAT ALONG AND SOUTHEAST OF A LINE
FROM CHEYENNE TO ALLIANCE. WESTERLY DOWNSLOPE FLOW WOULD MOST LIKELY
ENHANCE WARMING WHICH GIVES CREDENCE TO MOS GUIDANCE IN THE LOW
TO MID 60S OVER MUCH OF THE PLAINS. BUMPED UP HIGHS SEVERAL
DEGREES ON SAT AS BOTH THE MEX AND ECM SHOWED TEMPS SOME 3-5 DEG F
WARMER THAN THE PREVIOUS FCST. STRONG WINDS COULD BE LINGERING IN
THE WIND PRONE AREAS THROUGH AT LEAST EARLY SUN AS 850 AND 700 MB
CAG-CPR GRADIENTS LOOK TO REMAIN AROUND 60 METERS PER THE GFS
ALONG WITH RATHER STRONG FLOW ALOFT AT H75. STRONG MID LEVEL
SHORTWAVE DIGS INTO THE PACIFIC NORTHWEST LATE SAT AND INTO
NORTHERN WY ON SUN. THIS FORCES A STRONG SFC COLD FRONT SOUTHWARD
INTO THE NORTHERN ZONES AND GIVES WAY TO A SLIGHT COOLING TREND BY
LATE IN THE WEEKEND. UPPER-LEVEL SUPPORT IS EXPECTED TO STAY OUT
OF OUR NECK OF THE WOODS WITH THE BEST PVA WELL TO THE NORTH...SO
DO NOT EXPECT MUCH MORE THAN ISOLATED TO SCATTERED SNOW SHOWERS
WITH THE FROPA. GFS HAS BEEN TRENDING A BIT TOWARD THE COLDER
ECMWF...SO HAVE MAINTAINED THE PREVIOUS FCST WITH HIGHS ABOUT 15
TO 20 DEGREES COOLER THAN SAT GIVEN H7 TEMPS PLUNGING TOWARD THE
UPPER TEENS BELOW ZERO C. THE MODELS DIFFER IN THE TIMING OF
ANOTHER SHORTWAVE MOVING INTO THE WESTERN US LATE IN THE PERIOD.
IN GENERAL EXPECT PCPN CHANCES TO SLOWLY INCREASE FROM WEST TO
EAST BY LATE TUE OR EARLY WED. UNTIL THEN...DRY WESTERLY H25 FLOW
WITH MODEST 700-300 MILLIBAR MOISTURE PROGS WILL LIMIT RAIN/SNOW
SHOWER POTENTIAL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1017 PM MST WED NOV 26 2014

LATEST HRRR GUIDANCE USED FOR THE 06Z TAF SUITE. HAS IFR/LIFR
PUSHING OFF TO THE EAST INTO CENTRAL NEBRASKA STARTING OFF. HAS
BEEN DOING WELL THIS EVENING...SO DID NOT WANT TO STRAY TO FAR
FROM ITS GUIDANCE. AM CONCERNED THOUGH WITH OUR PANHANDLE AIRPORTS
AS THEY HAVE BEEN UP AND DOWN IN LOW CEILINGS. WENT WITH A SCT002
AT KBFF AND KAIA THROUGH 09Z OR SO BEFORE WINDS BEGIN TO PICK UP
AND SCOUR OUT THE LOW LEVEL MOISTURE. WINDY AGAIN THURSDAY.

&&

.FIRE WEATHER...
ISSUED AT 416 PM MST WED NOV 26 2014

MINIMAL FIRE WEATHER CONCERNS THROUGH THE END OF THE WEEK. MILDER
TEMPERATURES ARE EXPECTED ON THURSDAY THROUGH SATURDAY WITH
MINIMUM AFTERNOON HUMIDITY VALUES DROPPING INTO THE 20-30 PERCENT
RANGE FOR AREAS TO THE EAST OF THE LARAMIE RANGE. WINDY CONDITIONS
WILL PERSIST ACROSS SOUTHEAST WYOMING THROUGH SATURDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL 5 PM MST THURSDAY FOR WYZ106-110-116-117.

NE...NONE.
&&

$$

SHORT TERM...RJM
LONG TERM...CLH
AVIATION...GCC
FIRE WEATHER...RJM


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