Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 230543
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1043 PM MST SUN FEB 22 2015

.UPDATE...
ISSUED AT 855 PM MST SUN FEB 22 2015

FORECAST RIGHT ON TRACK FOR TONIGHT. CLOUDS WILL SLOWLY DISSIPATE
TONIGHT. COULD SEE SOME FOG NEAR THE SOUTHERN LARAMIE RANGE AND
TOWARDS CHEYENNE SHOULD THE HIGH CLOUDS CLEAR OUT FAST
ENOUGH. CURRENT WIND CHILLS IN THE SOUTHERN LARAMIE RANGE AND
NORTHERN LARAMIE RANGE FOOTHILLS ARE IN THE MINUS 20 TO MINUS 25
DEGREE RANGE WHICH IS COLD ENOUGH FOR A WIND CHILL ADVISORY BUT AS
WINDS BECOME LIGHT OVER THE NEXT SEVERAL HOURS WIND CHILLS SHOULD
IF ANYTHING WARM. SO AT THIS TIME NOT ANTICIPATING THE NEED FOR A
WIND CHILL ADVISORY TONIGHT...BUT WILL KEEP ANY EYE ON IT. THE FEW
LINGERING SNOW FLURRIES NEAR THE COLORADO BORDER WILL END OVER THE
NEXT HOUR OR SO.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 255 PM MST SUN FEB 22 2015

MAIN FORECAST CONCERN OVER THE NEXT 24 HOURS WILL BE SOME
LINGERING SNOW NEAR THE COLORADO BORDER IN ADDITION TO OVERNIGHT
LOWS AND POTENTIAL WIND CHILL VALUES TONIGHT AND INTO EARLY MONDAY
MORNING. STILL GETTING SOME VERY LIGHT SNOW AND OCCASIONAL
FLURRIES NEAR CHEYENNE...LARAMIE...AND OVER THE MOUNTAINS THIS
AFTERNOON. THIS ACTIVITY IS MAINLY DUE TO THE LOCALIZED LLVL
UPSLOPE FLOW. THERE IS SOME ENHANCEMENT IN THE LATEST KCYS RADAR
LOOP ACROSS COLORADO...WHICH IS DUE TO A 120 KNOT JET STREAK
ALOFT. CURRENT MODELS SHOW THIS JET STREAK REMAINING TO OUR
SOUTH...AND ONLY CLIPPING SOUTHEAST WYOMING AND SOUTHERN NEBRASKA.
FOR AREAS SOUTH OF I80...SOME UPPER LEVEL DIVERGENCE ASSOCIATED
WITH THE MARGINAL JET DYNAMICS WILL ENHANCE SNOWFALL RATES A BIT
TONIGHT...MAINLY ALONG AND SOUTH OF I80 FROM LARAMIE OVER TOWARDS
CHEYENNE AND THE NE/WY BORDER. EXPECT SOME LIGHT SNOW ACCUMULATION
BY LATE THIS EVENING...BUT ACCUMULATIONS SHOULD BE BELOW ONE INCH.

EAST WINDS WILL BECOME MORE SOUTHEASTERLY TONIGHT...WITH SPEEDS
AROUND 15 TO 20 MPH LOCALLY WEST OF THE LARAMIE RANGE. CAN NOT
RULE OUT SOME LOCATIONS REACHING WIND CHILL VALUES AROUND -20 BY
EARLY MONDAY MORNING. THE OTHER QUESTION WILL BE PATCHY FOG...BUT
MODEL SOUNDINGS ARE NOT SHOWING ANY CLEAR INDICATION OF FOG
DEVELOPMENT DUE TO LOW TO MIDLEVEL CLOUD COVER. WILL HAVE TO
MONITOR THE CHEYENNE RIDGE WITH A SOUTH TO SOUTHEAST WIND
HOWEVER...SINCE THIS IS A FAVORABLE DIRECTION FOR PERIODS OF FOG
ALONG THE RIDGE. CLOUD COVER WILL LIKELY KEEP MOST OF THE AREA
FROM FALLING TOO FAR BELOW ZERO TONIGHT. STILL...EXPECT READINGS
TONIGHT AND EARLY MONDAY BETWEEN -5 TO 5 ABOVE ZERO ACROSS
SOUTHEAST WYOMING WITH SINGLE DIGITS TO NEAR ZERO ACROSS WESTERN
NEBRASKA. THE COLDEST TEMPS WILL BE FURTHER NORTH IN AREAS WHERE
CLOUD COVER WILL LIKELY DISSIPATE.

FOR MONDAY AND TUESDAY...THE SYSTEM RESPONSIBLE FOR THIS WEEKEND
SNOWFALL WILL PUSH EAST ACROSS THE SOUTHERN ROCKY MOUNTAINS AND
WEAKEN AS IT MOVES INTO THE SOUTHERN PLAINS BY MIDWEEK. A SLIGHT
WARMING TREND IS EXPECTED WITH HIGHS REACHING THE UPPER 30S TO MID
40S ACROSS THE FORECAST AREA...WARMEST IN AREAS WITH LITTLE IF ANY
SNOWPACK NORTHEAST OF I25. THERE IS A SLIGHT CHANCE OF PATCHY FOG
WEST OF THE LARAMIE RANGE BY TUESDAY MORNING...MAINLY ACROSS THE
UPPER NORTH PLATTE RIVER VALLEY FROM SARATOGA TO DOUGLAS DUE TO
WINDS BECOMING LIGHT AND VARIABLE OVERNIGHT.

FOR TUESDAY NIGHT...MODELS SHOW THE NEXT UPPER LEVEL SHORTWAVE
RAPIDLY PUSHING SOUTHWARD OUT OF WESTERN CANADA. MODELS ARE ABOUT
6 HOURS OFF ON THE TIMING OF THIS SHORTWAVE...INCLUDING POTENTIAL
PRECIPITATION...BUT BASICALLY SHOW SNOWFALL INCREASING FROM NORTH
TO SOUTH ACROSS EASTERN WYOMING LATE TUESDAY NIGHT AND INTO EARLY
WEDNESDAY MORNING. INCREASED POP WELL NORTH OF I80 LATE TUESDAY
NIGHT FOR DEVELOPING SNOWFALL...ALTHOUGH THE 12Z ECMWF IS LAGGING
BEHIND BY 3 TO 6 HOURS. KEPT POP BELOW 40 PERCENT FOR NOW.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 112 PM MST SUN FEB 22 2015

THE 12Z MEDIUM RANGE NUMERICAL MODELS/ENSEMBLES ARE IN GOOD
AGREEMENT...CONTINUING TO SHOW A PROGRESSION OF THE LONG WAVES
OVER CENTRAL NORTH AMERICA. A SERIES OF SHORTWAVES EMBEDDED
WITHIN THE LARGE SCALE TROUGH WILL TRACK SOUTH AND EAST ACROSS
THE WESTERN AND CENTRAL CONUS DURING THIS FORECAST PERIOD. THE
FIRST WILL MOVE ACROSS THE GREAT BASIN AND SOUTHWEST U.S.
WEDNESDAY AND THURSDAY...WHILE THE SECOND DIVES SOUTHEAST ACROSS
NORTHERN PLAINS AND MIDWEST. THE LATTER WILL USHER IN ANOTHER
SURGE OF ARCTIC AIR PRODUCING WIDESPREAD SNOW AND MUCH COLDER
TEMPERATURES. GIVEN THE MARGINAL UPSLOPE FORCING AND MOISTURE
BEHIND THIS FRONT...ONLY EXPECTING LIGHT SNOW ACCUMULATIONS.
GUSTY NORTHWEST WINDS AND SLOWLY FALLING TEMPERATURES ARE ALSO
EXPECTED BEHIND THE FRONT. LOWS WEDNESDAY NIGHT WILL DROP INTO
THE SINGLE DIGITS AND LOWER TEENS. THE ACTIVE NORTH-NORTHWEST
FLOW ALOFT WILL KEEP SNOW CHANCES GOING MOST AREAS WEDNESDAY
NIGHT AND THURSDAY...AND MAINLY ALONG AND WEST OF THE LARAMIE
RANGE THURSDAY NIGHT THROUGH FRIDAY NIGHT. TEMPERATURES THURSDAY
THROUGH FRIDAY WILL CONTINUE WELL BELOW NORMAL WITH TEENS AND 20S
FOR HIGHS AND SINGLE DIGITS FOR LOWS. SNOW CHANCES INCREASE
FROM WEST TO EAST NEXT WEEKEND AS AN ELONGATED UPPER TROUGH DIGS
SOUTH OVER THE WESTERN CONUS...AND MOISTURE/UPSLOPE FLOW RETURN
FOLLOWING THE PASSAGE OF YET ANOTHER CANADIAN COLD FRONT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1039 PM MST SUN FEB 22 2015

MOSTLY VFR ACROSS SOUTHEAST WYOMING AND THE NEBRASKA PANHANDLE
THROUGH THE TAF PERIOD. SOME ICE FOG IS LIKELY ALONG THE SOUTHERN
LARAMIE RANGE AND EASTWARD TOWARDS CHEYENNE. IFR TO MVFR CIGS AND
VISIBILITIES WILL LIKELY OCCUR THROUGH TONIGHT AND POSSIBLY
THROUGH MONDAY MORNING BEFORE CLEARING. WINDS WILL BE LIGHT
THROUGH THE PERIOD.


&&

.FIRE WEATHER...
ISSUED AT 200 PM MST SUN FEB 22 2015

NO FIRE WEATHER CONCERNS ANTICIPATED THIS WEEK WITH COLDER THAN
NORMAL CONDITIONS AND A CHANCE FOR SNOW FOR THE MIDDLE AND END OF
THE WEEK. THE WARMEST DAY WILL LIKELY BE TUESDAY AS HIGHS MODERATE
INTO THE 30S TO MID 40S WITH RELATIVE HUMIDITIES RANGING BETWEEN
30 TO 50 PERCENT DURING THE DAY. WINDS WILL BE BREEZY AT
TIMES...ESPECIALLY AHEAD OF THE NEXT SURFACE COLD FRONT TUESDAY
NIGHT.

&&

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

&&

$$

UPDATE...SML
SHORT TERM...TJT
LONG TERM...MJ
AVIATION...SML
FIRE WEATHER...TJT


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