Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 210339
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
839 PM MST THU NOV 20 2014

.UPDATE...
ISSUED AT 830 PM MST THU NOV 20 2014

EVENING WATER VAPOR IMAGERY/00Z REGIONAL UPPER AIR ANALYSIS
REVEALED A SHORTWAVE TROUGH AXIS FROM WESTERN MT TO NORTHERN
NM. THIS TROUGH WAS DELINEATED BY A LARGE BAND OF MID/UPPER
LEVEL MOISTURE. REGIONAL RADARS DETECTED WEAK RETURNS OVER THE
SOUTH CENTRAL WY MOUNTAIN ZONES WHERE OROGRAPHIC LIFT WAS
TRIGGERING SOME LIGHT SNOW SHOWERS. THESE SHOWERS WILL COME
TO AN END TONIGHT...WITH CLOUDS GRADUALLY DECREASING FROM
WEST TO EAST WITH THE PASSAGE OF THE TROUGH BY FRIDAY MORNING.
NO SIGNIFICANT CHANGES PLANNED TO THE AFTERNOON FORECAST.

&&

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 230 PM MST THU NOV 20 2014

BATCH OF MOISTURE EVIDENT ACROSS MUCH OF WESTERN WYOMING WILL
SHIFT EAST ACROSS THE CWA OVERNIGHT ALONG WITH A WEAK UPPER
IMPULSE. NOT MUCH EFFECT FROM THIS OTHER THAN SOME MTN SNOW
SHOWERS MAINLY THIS EVENING.

FRIDAY WILL BE ANOTHER FAIRLY MILD AND DRY DAY ACROSS THE CWA
UNDER A GENERALLY WESTERLY FLOW ALOFT. WINDS COULD GET A LITTLE
GUSTY AROUND THE MTNS IN THE AFTERNOON AS SOME 40KT WINDS AT 700MB
PASS ACROSS BUT NOT LOOKING TOO SIGNIFICANT. MUCH MORE SIGNIFICANT
WINDS LOOK TO DEVELOP LATE FRIDAY NIGHT AND SATURDAY AS THE
STRONGER WESTERLIES ALOFT SAG SOUTH OVER THE AREA AND AN
APPROACHING SHORTWAVE INDUCES PRESSURE FALLS OVER THE HIGH PLAINS
INCREASING THE PRESSURE GRADIENT. LOW LEVEL INVERSION SHOULD KEEP
THE STRONGER WINDS OFF THE SFC THROUGH EARLY SATURDAY THEN THE
WINDS SHOULD INCREASE DURING THE DAY AS THE INVERSION IS LOST.
EARLIER FORECAST REASONING LOOKS ON TRACK WITH THE ARLINGTON/BORDEAUX
AREAS LIKELY SEEING THE INITIAL STRONG WINDS AS 700MB WINDS
INCREASE TO OVER 60KTS...WITH OTHER AREAS LIKELY HOLDING OFF UNTIL
A PACIFIC FRONT PASSES ACROSS IN THE LATE AFTERNOON. GIVEN LATER
PERIODS AND TIMING UNCERTAINTIES WILL HOLD OFF ON A WATCH FOR NOW
THOUGH SOME HIGHLIGHTS WILL VERY LIKELY BE NEEDED EVENTUALLY.
OTHERWISE NEXT SLUG OF MOISTURE SHOULD REACH WESTERN PARTS OF THE
CWA SATURDAY AFTERNOON WITH SNOW SHOWERS INCREASING OVER THAT AREA
THROUGH SATURDAY EVENING.

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 230 PM MST THU NOV 20 2014

MEDIUM RANGE MODEL GUIDANCE IS IN GOOD AGREEMENT WITH BROAD SCALE
TROUGHING OVER THE CENTRAL US INTO EARLY NEXT WEEK. THIS RESULTS IN
FAST NORTHWEST FLOW ALOFT ANCHORED OVER THE WESTERN STATES FOR MUCH
OF THE EXTENDED PERIOD. A VERY ACTIVE WEATHER PATTERN SHOULD PREVAIL
THROUGH THE PERIOD. NUMEROUS SHOTS OF MID LEVEL MOISTURE WILL
OCCUR WITH SMALLER SCALE DISTURBANCES EMBEDDED WITHIN THE
FLOW...EVIDENCED BY MODELED 700-300 MILLIBAR RH FIELDS. FAVORABLE
OROGRAPHICS LIKELY FOR THE SNOWIES AND SIERRA MADRES THROUGH AT
LEAST TUE WITHIN MOIST NORTHWEST FLOW REGIME...SO MOUNTAIN SNOW
AMOUNTS COULD ACTUALLY GET QUITE HIGH OVER THE COURSE OF SEVERAL
DAYS. WINTER HEADLINES COULD BE NECESSARY IN THE FUTURE. A WINDY
PATTERN TOO WITH MULTIPLE HIGH WIND EPISODES POSSIBLE. GFS AND
ECMWF DIVERGE CONSIDERABLY INTO THE MIDDLE PART OF NEXT WEEK. GFS
SHOWS THE CWA ON THE EASTERN FRINGE OF AN AMPLIFYING UPPER RIDGE
ALONG THE WEST COAST. THE ECMWF SHOWS THE H25 JET CORE DIRECTLY
OVERHEAD. REGARDLESS...THE STRENGTH OF THIS JET IS PROGGED TO BE
IMPRESSIVE WITH 155+ KT AT H25 SOMEWHERE TO THE NORTHEAST. BOTH
SOLUTIONS PLACE THE CWA UNDER INTENSE SUBSIDENCE IN THE RIGHT EXIT
REGION ON TUE NIGHT AND WED. THIS WOULD BE THE MOST LIKELY TIME
FOR A WIDESPREAD WIND EVENT WITH GFS H85 CAG-CPR GRADIENTS AROUND
60 METERS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY EVENING)
ISSUED AT 830 PM MST THU NOV 20 2014

VFR CONDITIONS WILL PREVAIL THROUGH FRIDAY. ABUNDANT MID/UPPER
LEVEL CLOUDINESS ASSOCIATED WITH A PASSING PACIFIC DISTURBANCE
WILL GRADUALLY CLEAR FROM WEST TO EAST FRIDAY MORNING. LOWEST
CELINGS TONIGHT WILL RANGE BETWEEN 8000 AND 10000 FT AGL...WITH
THE MOUNTAIN TOPS OBSCURED. WINDS OUTSIDE THE MOUNTAIN ZONES WILL
BE LIGHT OVERNIGHT. BREEZY WEST WINDS WILL THEN SPREAD ACROSS
MUCH OF SOUTHEAST WY FRIDAY MORNING AND CONTINUE THROUGH THE
AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 230 PM MST THU NOV 20 2014

NO CONCERNS ANTICIPATED THROUGH SATURDAY AS WEATHER FACTORS WILL
BE NON-CRITICAL. AFTER THAT PERIODS OF STRONG WINDS SHOULD OCCUR
AROUND THE MOUNTAINS SUNDAY INTO NEXT WEEK BUT NO OTHER FACTORS
ARE EXPECTED TO RAISE CONCERNS.

&&

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

$$

UPDATE...MJ
SHORT TERM...RAE
LONG TERM...CLH
AVIATION...MJ
FIRE WEATHER...RAE


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