Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 201717
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1117 AM MDT SUN APR 20 2014

.UPDATE...
ISSUED AT 1012 AM MDT SUN APR 20 2014

NO BIG CHANGE OR UPDATE TO TODAYS FORECAST AT THIS TIME. TWEAKED
CLOUD COVER AND WARMED TEMPERATURES FASTER THIS MORNING AS DRY AIR
MASS AND SUNNY SKIES HAVE ALLOW SURFACE TEMPERATURES TO RAPIDLY
RISE. TEMPERATURES WILL START TO LEVEL OFF SHORTLY SUCH THAT HIGH
TEMPERATURES SHOULD BE PRETTY CLOSE TO THE GOING FORECAST...MAYBE
A FEW DEGREES WARMER IN SPOTS.

TOUGH TO GUAGE THE CHANCES FOR SHOWERS AND THUNDERSTORMS TODAY.
GUT FEELING IS FOR MAINLY CONVECTION OVER THE MOUNTAINS...
OTHERWISE A FEW ISOLATED SHOWERS AND THUNDERSTORMS...MAINLY FROM
NEAR THE LARAMIE RANGE AND POINTS WEST. IN COMPARISON TO OTHER
MODELS THE NAM IS STILL RATHER BULLISH ON PRECIPITATION DEVELOPING
OVER THE WESTERN CWA THIS AFTERNOON. WILL MONITOR THIS
AFTERNOON...BUT NO CHANGES TO POPS AT THIS TIME. SEVERE STORMS ARE
VERY MUCH UNLIKELY TODAY.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)

ISSUED AT 334 AM MDT SUN APR 20 2014

WATER VAPOR IMAGERY FROM EARLY THIS MORNING SHOWS DRIER AIR AND
SUBSIDENCE MOVING OVER THE REGION WITH JUST SOME SCT MID CLOUDS
MOVING OVER THE FORECAST AREA. A FAIRLY STRONG UPPER LEVEL SHORTWAVE
CURRENTLY OVER THE NORTHERN ROCKIES WILL MOVE ACROSS THE US/CANADIAN
BORDER TODAY. THE ATTENDANT PACIFIC COLD FRONT IS CURRENTLY DRAPED
FROM WESTERN MONTANA DOWN INTO NORTHERN NEVADA...AND WILL MOVE
ACROSS THE PLAINS ROUGHLY BETWEEN 18 AND 00Z AND BACK INTO
THE MOUNTAINS THROUGH 06Z. TEMPS WILL INCREASE BACK INTO THE 60S AND
70S AHEAD OF THE FRONT WHILE A WEAK UPPER LEVEL IMPULSE IN ZONAL
FLOW ALOFT APPROACHES FROM THE WEST. THE COMBINATION OF FEATURES
IS EXPECTED TO BRING A CHANCE FOR SHOWERS AND TSTORMS TO THE HIGH
COUNTRY AND ALONG THE CHEYENNE RIDGE LATE IN THE AFTERNOON. THE NAM
AND ECMWF ARE A BIT MORE BULLISH WITH INSTABILITY THIS AFTERNOON VS
THE GFS...WITH LI`S DROPPING TO BETWEEN MINUS 1 AND MINUS 2. BUT
TIMING OF THE FRONT AND SUBSIDENCE AHEAD OF THE DISTURBANCE LOOKS TO
LIMIT CONVECTION ACROSS THE PLAINS. NOT WHOLLY CONVINCE THERE WONT
BE A STRAY SHOWER OR TWO ALONG THE FRONT AS IT TREKS SOUTH ACROSS
THIS AREA...BUT CHANCES ARE LOW ENOUGH TO WILL KEEP MENTION OUT OF
THE FORECAST.

COOLER TEMPS AND WEAK SOUTHEASTERLY RETURN FLOW WILL KEEP CONDITIONS
DRY FOR THE MOST PART ON MONDAY...WITH ONLY A SLIGHT CHANCE FOR RAIN
SHOWERS WITHIN CONVERGENT SFC FLOW DEVELOPING ALONG THE LARAMIE
RANGE. OTHERWISE...MONDAY LOOKS TO BE A FAIRLY CALM AND PLEASANT
DAY. FLOW ALOFT WILL INCREASE AND BACK TO THE SOUTHWEST AHEAD OF A
RATHER STRONG UPPER TROUGH MOVING ACROSS THE GREAT BASIN MONDAY
NIGHT AND TUESDAY. THE LEESIDE PRESSURE TROUGH WILL STRENGTHEN AHEAD
OF THIS WAVE...WITH INCREASING SOUTHERLY SFC FLOW ADVECTING UPPER
30S TO 40S DEW POINTS INTO THE PANHANDLE ON TUESDAY. A PIECE OF
ENERGY EJECTING OUT AHEAD OF THE TROUGH WILL MOVE OVER THE CWA
TUESDAY AFTERNOON WITH 700MB TEMPS INCREASING TO BETWEEN 7 AND 9C.
SO...EXPECT A BROADER COVERAGE OF CONVECTION TO DEVELOP IN THE
AFTERNOON WITH THE COMBINATION OF ENERGY ALOFT...OROGRAPHICS...AND
SFC CONVERGENCE ALONG THE LEESIDE TROUGH. WILL MAINTAIN ONLY SLIGHT
CHANCE TO CHANCE FOR TSTORMS FOR NOW THO AS WAA ALOFT AND POSSIBLE
MIDLEVEL DRY SLOTTING COULD LIMIT OVERALL EXPANSE AND INTENSITY OF
CONVECTION. BUT...WILL HAVE TO WATCH THIS SYSTEM CLOSELY FOR THE
POTENTIAL A FEW STRONGER STORMS MAY DEVELOP ACROSS THE PANHANDLE
WHERE LLVL MOISTURE AND COOLER TEMPS ALOFT WILL BE IN PLACE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 334 AM MDT SUN APR 20 2014

WINDS CONTINUE TO BE THE MAIN FORECAST CHALLENGE IN THE LONG
TERM...FOLLOWED BY THUNDERSTORM CHANCES.

STARTING OFF TUESDAY NIGHT...LOOKS LIKE WE SHOULD SEE ONGOING
CONVECTION MOVING OUT INTO THE PANHANDLE TUESDAY EVENING. NAM
SHOWING 40 TO LOW 50 DEWPOINTS IN THE PANHANDLE TUESDAY NIGHT. GFS
AND NAM SHOWING FAIRLY WIDESPREAD QPF ENDING AROUND 06Z. WENT
AHEAD WITH CHANCE POPS AS IT REMAINS UNSTABLE OUT THERE THROUGH
THE EVENING HOURS. NAM FORECASTING LIFTED INDICES OF -3 TO -4C. TO
THE WEST...A STRONG SHORTWAVE TRACKS THROUGH WESTERN WYOMING WITH
A COLD FRONT FORECAST TO MOVE JUST WEST OF CARBON COUNTY TUESDAY
EVENING. FAIRLY UNSTABLE CONDITIONS OUT THAT WAY TOO...SO A
COMBINATION OF UNSTABLE AIR AND UPSLOPING CONDITIONS SHOULD GIVE
US FAIRLY GOOD CHANCES FOR SHOWERS AND THUNDERSTORMS.

SHORTWAVE TRACKS INTO EASTERN MONTANA BY 12Z WEDNESDAY. COLD FRONT
LOOKS TO MOVE THROUGH SOUTHEAST WYOMING THROUGH THE DAY WEDNESDAY
WITH 700MB WINDS REALLY RAMPING UP BEHIND THE FRONT. BOTH THE GFS
AND ECMWF SHOWING 700MB WINDS INCREASING TO 45 TO 50KTS BEHIND
THIS FRONT. GUIDANCE HAS BEEN SHOWING THIS HAPPENING FOR SEVERAL
MODEL RUNS NOW...SO CONFIDENCE IS GROWING THAT WE WILL AT LEAST
SEE OUR WIND PRONE AREAS HITTING WARNING CRITERIA WEDNESDAY
AFTERNOON AND MAYBE AS EARLY AS WEDNESDAY MORNING IF THE ECMWF
SOLUTION COMES TRUE.

WINDS REMAIN ELEVATED THURSDAY INTO FRIDAY AS THE GFS AND TO A
LESSER EXTENT THE ECMWF KEEP 700MB WINDS OF 40KTS OR HIGHER. BY
FRIDAY MORNING...A SURFACE LOW MOVES INTO NORTH CENTRAL
WYOMING...EASING THE GRADIENT AND WINDS THROUGH FRIDAY AFTERNOON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY MORNING)
ISSUED AT 1117 AM MDT SUN APR 20 2014

VFR EXPECTED OVER ALL AERODROMES THROUGH MONDAY UNDER A GENERALLY
WESTERLY WIND FLOW ALOFT. A FEW SHOWERS ARE POSSIBLE MAINLY NEAR THE
COLORADO BORDER THIS AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 334 AM MDT SUN APR 20 2014

THIS AFTERNOON WILL SEE A CHANCE FOR SHOWERS AND TSTORMS MAINLY
ALONG AND WEST OF INTERSTATE 25...WITH WETTING RAINS LIKELY FROM
THIS ACTIVITY. HUMIDITY VALUES WILL GENERALLY STAY ABOVE 20 PERCENT
DURING THE AFTERNOON HOURS TODAY THROUGH MIDWEEK...ALTHOUGH
HUMIDITIES MAY DROP TO 15 PERCENT ACROSS FAR WESTERN PORTIONS OF
CARBON COUNTY ON MONDAY. GOOD RECOVERIES ARE EXPECTED AT NIGHT.
ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS IS POSSIBLE ON
TUESDAY...WITH GUSTY WINDS LIKELY TUESDAY AND WEDNESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

UPDATE...SML
SHORT TERM...RJM
LONG TERM...CLAYCOMB
AVIATION...RE
FIRE WEATHER...RJM









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