Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 021147
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
547 AM MDT THU OCT 2 2014

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 407 AM MDT THU OCT 2 2014

RADAR HAS CLEARED OUT OVERNIGHT BUT A FEW AREAS OF MID AND HIGH
LEVEL CLOUDS REMAIN IN PLACE AS THE UPPER LEVEL TROUGH MOVES
OVERHEAD. COULD SEE SOME PATCHY FOG OVER THE FAR WESTERN ZONES IN
WEAK BUT MOIST WESTERLY UPSLOPE FLOW...INCLUDING THE HIGHER
TERRAIN SUCH AS THE SUMMIT. TODAY WILL BE COOL SIMILAR TO
YESTERDAY WITH H7 TEMPS PROGGED TO RANGE FROM -2C TO 2C FROM NORTH
TO SOUTH BY THIS AFTERNOON. WESTERLY WINDS WILL BE QUITE BLUSTERY
ALONG AND WEST OF THE LARAMIE RANGE TODAY IN ADVANCE OF THE NEXT
FAIRLY POTENT CLIPPER SYSTEM THAT WILL BLAST SOUTHEAST INTO THE
HIGH PLAINS FROM CANADA ON THE LEADING EDGE OF A 150KT JET THROUGH
THE AFTERNOON AND EVENING. A STRONG COLD FRONT ASSOCIATED WITH THIS
SYSTEM WILL RACE SOUTH ACROSS THE FORECAST AREA BETWEEN 23 AND 05Z
WITH 10-15MB/6HR PRESSURE RISES IN ITS WAKE. EXPECT NNW WINDS OF
20 TO 30 MPH GUSTING 35 TO 45 MPH FOR A BRIEF PERIOD BEHIND THE
FRONT DUE TO THE STRONG PRESSURE GRADIENT IN PLACE. FORECAST
SOUNDINGS SUGGEST A WELL MIXED LAYER TO ROUGHLY 50MB ABOVE THE
SURFACE IN THE POST FRONTAL ENVIRONMENT WILL ALSO CONTRIBUTE TO
THE GUSTY WINDS. THE HIGHEST WINDS SHOULD OCCUR ACROSS THE EASTERN
PLAINS WHERE THE HIGHER PRESSURE RISES COMBINE WITH STRONGEST
UPPER LEVEL WINDS...ESPECIALLY ALONG RIDGETOPS SUCH AS THE PINE
RIDGE...WILDCAT HILLS...AND CHEYENNE RIDGE. IN ADDITION TO THE
WINDS...GOOD QG AND FRONTAL FORCING WILL PRODUCE SHOWERS IN THE
EVENING MAINLY ALONG AND EAST OF THE LARAMIE RANGE. TEMPS WILL BE
WARM ENOUGH INITIALLY TO KEEP PRECIP LIQUID...BUT STRONG CAA WILL
BRING SNOW LEVELS DOWN TO NEAR 5KFT THRU THE EVENING SO EXPECT TO
SEE A TRANSITION FROM RAIN TO SNOW DURING THIS TIME. STILL LOOKS
LIKE THE BEST JUXTAPOSITION OF COLD AIR AND PRECIP CHANCES WILL
OCCUR FROM THE NORTHERN LARAMIE RANGE/DOUGLAS TO THE PINE RIDGE
AROUND SUNSET...SO WILL MAINTAIN THE FOCUS FOR LIGHT SNOW IN
THIS REGION. EXPECTING ACCUMS OF JUST A DUSTING TO ONE INCH.
CANNOT RULE OUT SNOW MIXING WITH RAIN FURTHER SOUTH IN THE EARLY
OVERNIGHT PERIOD AS WELL...BUT PRECIP AND THUS OVERALL CHANCE FOR
SNOW WILL DIMINISH AS THE FRONT RACES SOUTHEASTWARD AND UPPER
LEVEL FORCING DECOUPLES AND SHIFTS TO THE EAST. TEMPS WILL DROP TO
NEAR OR BELOW FREEZING VALUES OVERNIGHT...BUT WINDS SHOULD REMAIN
ELEVATED ENOUGH TO PREVENT WIDESPREAD FROST FORMATION SO WILL
REFRAIN FROM ISSUING HIGHLIGHTS.

FRIDAY WILL BE MUCH COOLER IN THE POST FRONTAL ENVIRONMENT WITH
BRISK NORTHWEST WINDS PERSISTING AS THE JET REMAINS OVER THE HIGH
PLAINS THRU THE AFTERNOON. DRY CONDITIONS WILL PREVAIL WITH MUCH
DRIER AIR AND SUBSIDENCE MOVING IN FROM THE WEST. THE UPPER JET
WILL STEADILY SHIFT EAST THRU THE EVENING AND OVERNIGHT WITH SKIES
PARTIALLY CLEARING AND SFC WINDS EXPECTED TO BE LIGHT. THIS WILL
INCREASE THE CHANCE FOR A MORE SUBSTANTIAL FROST/FREEZE FRIDAY
NIGHT...SO MAY HAVE TO CONSIDER FROST HIGHLIGHTS FOR THE EASTERN
PANHANDLE DURING THIS TIME.

DRY NORTHWEST FLOW WILL REMAIN OVERHEAD FOR SATURDAY WITH H7 TEMPS
INCREASING TO BETWEEN 2C AND 6C. THE LEESIDE PRESSURE TROUGH WILL
DEEPEN AS A WEAK PIECE OF ENERGY MOVES OVERHEAD IN THIS FLOW
PATTERN...SO WESTERLY WINDS WILL INCREASE ONCE AGAIN ALONG AND WEST
OF THE LARAMIE RANGE. MAX TEMPS LOOK TO RETURN TO THE 60S AND 70S
FOR MUCH OF THE AREA.

.LONG TERM...(SATURDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 407 AM MDT THU OCT 2 2014

DRY AND MILD CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE EXTENDED
FCST PERIOD. MEDIUM RANGE MODELS REMAIN IN EXCELLENT AGREEMENT WITH
THE OVERALL WEATHER PATTERN. THE CWA SHOULD REMAIN IN THE TRANSITION
ZONE BETWEEN DEEP TROUGHING OVER THE GREAT LAKES REGION AND AN UPPER
RIDGE BUILDING OVER THE WESTERN CONUS. THE UPPER-LEVEL FLOW PATTERN
LOOKS TO BE QUITE ACTIVE...BUT THE MAJORITY OF IMPULSES EMBEDDED IN
THE FLOW ARE EXPECTED TO REMAIN TO THE EAST OF THE CWA. HOWEVER THE
ECMWF STILL SUGGESTS LIGHT QPF OVER EAST CENTRAL WY AND THE NORTHERN
PANHANDLE ON SUN AFTN. THIS IS QUITE POSSIBLE WITH A BACKDOOR COOL
FRONT ENCROACHING ON THOSE ZONES ALONG WITH INCREASING DIFFLUENCE IN
THE EXIT REGION OF AN INTENSE 120+ KT H25 JET...BUT NAM/GFS HAVE
BEEN CONSISTENT WITH A DRY FCST AS BETTER FORCING IS OVER THE
PLAINS. REFRAINED FROM MENTION OF SHOWERS OR TSTMS ATTM. OTHERWISE
CONVECTIVE ACTIVITY WILL BE LACKING AS UPPER RIDGING BECOMES THE
DOMINANT FEATURE ALOFT. MAIN CHANGE TO TEMPERATURE GRIDS WAS TO
INCREASE HIGHS A FEW DEGREES FOR TUE AFTN. THE GFS SHOWS H7 TEMPS
APPROACHING 10C OVER THE PLAINS BY 18Z...AND ANY MIXING WOULD BRING
WESTERLY DOWNSLOPE WINDS DOWN TO THE SFC BY AFTN. TRENDED WARMER
THAN CONSENSUS GUIDANCE AS PATTERN SHOULD FAVOR TEMPS NEAR 80F IN
THE PANHANDLE...ESPECIALLY ALONG THE PLATTE RIVER VALLEY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 535 AM MDT THU OCT 2 2014

PATCHY FOG AND LOCALLY REDUCED VSBYS AS LOW AS 1/4 SM HAVE BEEN
OBSERVED AT KLAR EARLY THIS AM. THIS SHOULD ERODE BY 14Z WITH VFR
CONDITIONS EXPECTED FOR MUCH OF THE DAY. WINDS WILL INCREASE OVER
ALL TERMINALS WIGH GUSTS AROUND 30 KTS COMMON...ESPECIALLY ALONG
AND WEST OF THE LARAMIE RANGE. A STRONG COLD FRONT WILL MOVE SOUTH
ACROSS THE AREA TONIGHT. WINDS WILL SHIFT TO THE NORTH AND REMAIN
GUSTY OVERNIGHT. SHOWERS...POSSIBLY MIXED WITH SNOW...WILL DEVELOP
FROM NORTH TO SOUTH AFTER 00Z. MVFR TO LOCALLY IFR CIGS ARE LIKELY
OVERNIGHT BEHIND THE FRONT. KCDR AND KAIA COULD SEE REDUCED VSBYS
IN SNOW SHOWERS.

&&

.FIRE WEATHER...
ISSUED AT 407 AM MDT THU OCT 2 2014

COOL AND BREEZY CONDITIONS WILL PERSIST OVER THE REGION TODAY AND
FRIDAY. A FAST MOVING CLIPPER SYSTEM WILL BRING A CHANCE FOR LIGHT
PRECIP THIS EVENING MAINLY ALONG AND EAST OF THE LARAMIE RANGE. RAIN
LOOKS TO MIX WITH SNOW POSSIBLY DOWN TO 5000 FEET OR SO...WITH THE
BEST CHANCE FOR SNOW ALONG A LINE FROM THE NORTHERN LARAMIE RANGE TO
THE PINE RIDGE. DRY AND WARMING CONDITIONS ARE ANTICIPATED INTO THE
WEEKEND.

&&

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

$$

SHORT TERM...RJM
LONG TERM...HAMMER
AVIATION...HAMMER
FIRE WEATHER...RJM





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