Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241751
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1051 AM MST TUE FEB 24 2015

.UPDATE...
ISSUED AT 1041 AM MST TUE FEB 24 2015

AS ALWAYS...ANOTHER CHALLENGING AND INTERESTING FORECAST SCENARIO
FOR THE NEXT SEVERAL DAYS...THOUGH THIS UPDATE FOCUSES ON THIS
AFTERNOON. OUR MIDNIGHT SHIFT SHORT TERM METEOROLOGIST LEFT THE
FORECAST IN NICE SHAPE. FOR THIS AFTERNOON...HAVE MADE MINOR
MODIFICATIONS TO TEMPERATURES BASED ON TRENDS WITH NEARLY FULL
SUNSHINE AND DOWNSLOPE WARMING AIDING TEMPERATURE RISES...THOUGH
THE CAVEAT IS THE LEFTOVER SNOWFIELD ACROSS THE LARAMIE VALLEY AND
LARAMIE AND FROM CHEYENNE TO KIMBALL...THUS HAVE ACCOUNTED FOR
SNOW ALBEDO IN AFTERNOON TEMPERATURE FORECASTS...WITH WINDS
FLOWING OVER SNOWPACK...THERE WILL BE SOME INTERESTING AND STARK
CONTRASTS IN AFTERNOON TEMPERATURES ACROSS SOUTHEAST WYOMING AND
WESTERN NEBRASKA...MAKING FOR ANOTHER QUITE CHALLENGING AND
INTERESTING TEMPERATURE FORECASTING SCENARIO.  RUBIN

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 501 AM MST TUE FEB 24 2015

CONDITIONS OVERNIGHT HAVE BEEN FAIRLY QUIET WITH MILD TEMPS IN
PLACE AS COMPARED TO LAST NIGHT...EXCEPT FOR KLAR WHICH HAS ONCE
AGAIN DROPPED INTO SUBZERO READINGS WITH SOUTH WINDS IN PLACE. A
SUBTLE SURFACE TROUGH MOVED SOUTH ACROSS THE PLAINS EARLIER ON IN
THE NIGHT WITH WEST-NORTHWEST WINDS GUSTING 20 TO 30 MPH IN ITS
WAKE FOR MANY LOCATIONS. FURTHER WEST...BREEZY CONDITIONS PREVAIL
AS WELL ALONG THE I-80 CORRIDOR WHICH IS LIKELY KEEPING FOG
DEVELOPMENT AT BAY...AT LEAST AT THE OBSERVATION SITES. 11-3.9UM
IMAGERY INDICATES A FEW AREAS OF STRATUS/FOG DEVELOPING IN LOWER
ELEVATIONS OF CARBON AND ALBANY COUNTIES THOUGH...SO LEFT MENTION
OF PATCHY FOG IN THE FORECAST. DOES APPEAR SOME STRATUS IS TRYING
TO DEVELOP ACROSS CONVERSE AND NIOBRARA COUNTIES AS WELL.
OTHERWISE...TODAY WILL REMAIN MOSTLY SUNNY AS AN AREA OF
SUBSIDENCE AND DRY AIR MOVE OVER THE FORECAST AREA. TEMPS ALOFT
WILL WARM A FEW DEGREES AS THE THERMAL RIDGE MOVES OVERHEAD
WHICH...IN COMBINATION WITH INCREASED SOLAR INSOLATION...WILL
BUMP SFC TEMPS UP INTO THE MID-UPPER 30S OUT WEST AND 40S ACROSS
THE PLAINS.

FORECAST IS ON TRACK FOR THE NEXT CLIPPER SYSTEM TO BRING LIGHT-
MODERATE SNOW TO THE CWA TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.
INITIAL PIECE OF VORTICITY ON THE LEADING EDGE OF THE UPPER LEVEL
SHORTWAVE TROUGH WILL MOVE OVERHEAD TUESDAY NIGHT WITH A LEESIDE SFC
LOW DEVELOPING AHEAD OF THIS WAVE. THE COMBINATION OF WEAK PVA AND
SFC CONVERGENCE WITHIN THE DEVELOPING LOW WILL INITIATE LIGHT
SNOW SHOWERS FROM NORTH TO SOUTH OVER THE AREA AFTER MIDNIGHT. A
SECOND SHORTWAVE TROUGH WILL MOVE SOUTHWEST ALONG THE ROCKIES
WEDNESDAY AFTERNOON SHORTLY BEHIND A COLD FRONT MOVING THROUGH THE
CWA IN THE LATE MORNING AND EARLY AFTERNOON. LLVL FRONTOGENESIS
AND INSTABILITY WILL INCREASE AS THE FRONT SLOWS WITHIN THE
MOUNTAINS AND LLVL MOISTURE INCREASES...ALTHOUGH FRONTOGENESIS HAS
BEEN TRENDING WEAKER OVER THE LAST FEW MODEL RUNS. JET FORCING IS
ALSO QUITE WEAK WITH MIDLEVEL ENERGY SOMEWHAT DISORGANIZED...SO
ALL IN ALL ONLY LOOKING AT WIDESPREAD LIGHT SNOW SHOWERS AS THE
SYSTEM MOVES OVERHEAD. MODERATE TO BRIEF HEAVY SNOWFALL COULD
OCCUR WITHIN AREAS OF INSTABILITY AND STRONGEST FRONTOGENESIS
ALONG THE MOUNTAINS AND JUST DOWNWIND OF THE MOUNTAINS. IMPACTS
LOOK TO BE TIED MAINLY TO TRANSPORTATION AS LOW VISIBILITIES AND
QUICK ACCUMULATIONS IN THE MORE VIGOROUS SNOW SHOWERS COULD
IMPACT TRAVEL CONDITIONS. STILL THINKING ACCUMULATIONS OF 1 TO 2
INCHES FOR THE PLAINS WITH PERHAPS SOME TOTALS AROUND 3 INCHES
WHERE SNOW BANDS DEVELOP DOWNWIND OF THE MOUNTAINS IN NW FLOW...1
TO 3 IN THE HIGH VALLEYS...AND 3 TO 7 IN THE MOUNTAINS THROUGH
EARLY THURSDAY MORNING.

A STRONG SFC HIGH WILL PLOW INTO THE CENTRAL AND HIGH PLAINS
WEDNESDAY NIGHT AND THURSDAY...BRINGING A RETURN OF VERY COLD
ARCTIC AIR TO THE REGION. WINDS WILL VEER TO AN EAST-SOUTHEAST
COMPONENT WITH VERY LIGHT SNOW SHOWERS LIKELY TO OCCUR IN THE
MOUNTAINS AND ALONG THE CHEYENNE RIDGE IN THIS FAVORABLE UPSLOPE
REGIME THROUGH MUCH OF THURSDAY. HIGH TEMPS FOR THURSDAY WILL
RETURN TO THE TEENS AND 20S.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 501 AM MST TUE FEB 24 2015

MODELS CONTINUE TO ADVERTISE A COLD AND SLIGHTLY UNSETTLED PATTERN
THROUGH THE WEEKEND. WITH A SFC HIGH ACROSS NEBRASKA ON THURS
NIGHT...SFC WINDS WILL BE SOUTH TO SOUTHEASTERLY ACROSS THE
PLAINS. LOW CLOUDS WILL BE ENTRENCHED ACROSS THE SOUTHERN LARAMIE
RANGE AND ALONG THE CHEYENNE RIDGE WITH LIGHT SNOW/FLURRIES
POSSIBLE INTO FRI MORNING. LOWS WILL BE QUITE COLD ON THURS
NIGHT...ESPECIALLY WHERE SKIES CLEAR. WEAK FLOW ALOFT AND WELL
BELOW NORMAL TEMPS WILL DOMINATE FOR FRI AND SAT AS THE NEXT UPPER
LEVEL TROUGH DIGS INTO THE GREAT BASIN. BOTH THE GFS AND ECMWF
SHOW LLVL OVERRUNNING/ISENTROPIC LIFT INCREASING BY SAT EVENING WITH
THE BEST CHANCE OF WIDESPREAD QPF FROM 21-09Z SUN. EVEN WITH THE
BEST QG ASCENT OVER NORTHEAST COLORADO (THE MODELS HAVE BEEN
CONSISTENT AT DEPICTING THIS)...A FEW INCHES OF SNOW WOULD FALL IN
AREAS ALONG THE COLORADO BORDER. BUMPED UP POPS TO AROUND 40
PERCENT FROM CHEYENNE TO SIDNEY. SNOW WILL QUICKLY COME TO AN END
BY SUN MORNING. WITHOUT ANY SFC TROUGHING AND DOWNSLOPE
WINDS...TEMPS WILL STRUGGLE TO GET ABOVE FREEZING THROUGH EARLY
NEXT WEEK...ESPECIALLY WITH SOME SNOWPACK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 501 AM MST TUE FEB 24 2015

VFR CONDITIONS THROUGH LATE TUESDAY NIGHT. VFR CIGS WITH BASES
5-10 THOUSAND FEET WILL BE POSSIBLE OVER THE NEBRASKA PANHANDLE
THIS AFTERNOON. NORTHWEST WINDS OF 15-20 KTS ARE ALSO EXPECTED
OVER THE PANHANDLE THROUGH 18Z. WEST TO SOUTHWEST WINDS WILL
OCCASIONALLY GUST TO 25 KTS AT THE WY SITES BY TONIGHT. A COLD
FRONT WILL BEGIN TO MOVE OVER THE REGION AFTER AROUND 09Z WED WITH
INCREASING CLOUD COVER AND SNOW SHOWERS.


&&

.FIRE WEATHER...
ISSUED AT 501 AM MST TUE FEB 24 2015

NO FIRE WEATHER CONCERNS ARE EXPECTED THIS WEEK DUE TO PERIODS OF
SNOWFALL AND GENERALLY COLD TEMPERATURES IN PLACE. SLIGHTLY
WARMER TEMPERATURES WILL OCCUR TODAY BEFORE ANOTHER ARCTIC SYSTEM
INVADES THE AREA ON WEDNESDAY. VERY COLD TEMPERATURES AND A GOOD
CHANCE FOR LIGHT TO MODERATE SNOW WILL OCCUR WEDNESDAY INTO
THURSDAY WITH BELOW NORMAL TEMPERATURES EXPECTED TO PERSIST
THROUGH THE WEEKEND.

&&

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

$$

UPDATE...RUBIN
SHORT TERM...RJM
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...RJM



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