Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241742
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1042 AM MST TUE FEB 24 2015

.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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1042 AM MST TUE FEB 24 2015

MAIN IMPACTS TO AVIATION WILL BE FOUND AFTER 09-12Z OF THIS TAF
CYCLE. 17Z SATELLITE IMAGES SHOW A DIMINISHING POCKET OF SCT-
BKN050 CIGS DROPPING SOUTH KDGW-KCDR. ALTHO IT WILL LIKELY LAST
DURING THE FIRST FEW HOURS OF THE TAF...EXPECT DISSIPATION TO
CONTINUE. OTHERWISE...WINDS WILL GENERALLY BE WEST AT AROUND 10
KNOTS THIS AFTERNOON. CONDITIONS WILL DETERIORATE TONIGHT AS A
COLD FRONT SLIDES THROUGH TAF SITES 09-12Z. ALONG WITH A WIND
SHIFT TO NORTHWEST AND EVENTUALLY NORTH...WILL SEE A PERIOD OF
LIGHT SNOW OR SNOW SHOWERS DEVELOP AT TAF SITES. KRWL/KCDR WILL
SEE SNOW EARLIEST AROUND 09Z AND ALL OTHER SITES 12-18Z. FOR NOW
HAVE TRENDED TAFS INTO THE MVFR CATEGORY...THOUGH WILL LIKELY SEE
LOCATIONS DROPPING INTO IFR FOR A TIME ON TUESDAY. ALTHOUGH WILL
AWAIT HIGHER CONFIDENCE IN TIMING/LOCATION TO ADD IFR INTO TAFS.

&&

.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.

&&

$$

SHORT TERM...RJM
LONG TERM...ZF
AVIATION...CAH
FIRE WEATHER...RJM


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