Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 170006
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
506 PM MST TUE DEC 16 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 243 PM MST TUE DEC 16 2014

TONIGHT...MOST WIDESPREAD CHALLENGE WILL BE FOG
DEVELOPMENT...INCLUDING AREAL COVERAGE AND VISIBILITIES. WHERE FOG
WAS SLOWEST TO ERODE...FROM TORRINGTON...TO SCOTTSBLUFF AND TO
ALLIANCE...INCLUDING OVER THE SNOWFIELD...3 PM TEMPERATURE AND
DEWPOINT SPREADS ARE ONLY 2 TO 5 DEGREES WITH CLEARING MID LEVEL
SKIES NOTED ON VISIBLE SATELLITE IMAGERY...THUS EXPECT FOG TO
DEVELOP RATHER QUICKLY AND SPREAD OVER AFOREMENTIONED LOCALES IN
THE LATE AFTERNOON AND EARLY EVENING HOURS.

LOW LEVELS AND BOUNDARY LAYER SATURATE UP DECENTLY
OVERNIGHT...ESPECIALLY OVER OUR WESTERN COUNTIES OF CARBON AND
ALBANY...AND MID AFTERNOON TEMPERATURE DEWPOINT SPREADS ARE ONLY
AROUND 7 DEGREES AT RAWLINS AND LARAMIE...ALONG WITH MID LEVEL
CLEARING PROGGED...THUS EXPECT RATHER EXTENSIVE FOG TO DEVELOP LATE
THIS EVENING AND OVERNIGHT ACROSS OUR WESTERN COUNTIES.

NEGATIVELY TILTED SHORTWAVE TROUGH ALOFT MOVES FROM WESTERN WYOMING
THIS AFTERNOON...TO NORTHWEST WYOMING BY MIDNIGHT AND TO CENTRAL
MONTANA BY DAYBREAK...BASED ON SATELLITE AND RADAR TRENDS...EXPECT
INCREASING AREAL COVERAGE OF SNOW SHOWERS THIS EVENING ACROSS OUR
WYOMING COUNTIES...ESPECIALLY OVER AND NEAR THE SNOWY AND SIERRA
MADRE RANGES...WITH A SLOW CESSATION AND DECREASE IN AREAL SNOW
COVERAGE LATE THIS EVENING AND OVERNIGHT. MAY EVEN SEE A FEW
FLAKES ALONG AND EAST OF INTERSTATE 25...THOUGH COVERAGE LOOKS
QUITE MINIMAL.

WEDNESDAY...SPLIT TROUGHS ALOFT MOVE ACROSS OUR REGION WITH THE
BULK OF SNOW AND DEEPER MOISTURE LOCATED OVER COLORADO...THOUGH
OUR SNOWY AND SIERRA MADRE RANGES WILL SEE SCATTERED OROGRAPHIC
SNOW SHOWERS...MOSTLY DRY ELSEWHERE.

WEDNESDAY NIGHT...NORTHERN STREAM SHORTWAVE TROUGH ALOFT MOVES OVER
THE WESTERN DAKOTAS...WITH THE SOUTHERN STREAM SHORTWAVE TROUGH
ALOFT MOVING OVER WESTERN KANSAS...THUS MINIMAL COVERAGE OF SNOW
SHOWERS OVER OUR COUNTIES...MAINLY OVER THE SNOWY AND SIERRA MADRE
RANGES...DRY ELSEWHERE.

THURSDAY...PSEUDO CYCLONIC FLOW ALOFT CONTINUES OVER OUR COUNTIES
WITH ONE SHORTWAVE ALOFT OVER THE FOUR CORNERS WITH MOST OF THAT
SHORTWAVE TROUGH SNOW OVER WESTERN COLORADO...THOUGH WILL SEE SOME
OROGRAPHIC SNOW SHOWERS OVER OUR SNOWY AND SIERRA MADRE RANGES...
DRY ELSEWHERE.

THURSDAY NIGHT...FAST MOVING...MOISTURE STARVED SHORTWAVE TROUGH
ALOFT MOVES ACROSS OUR COUNTIES...THOUGH WITH MINIMAL LOW AND MID
LEVEL MOISTURE...ONLY SOME ISOLATED MOUNTAIN SNOW SHOWERS ON TAP.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 243 PM MST TUE DEC 16 2014

SHORTWAVE TROUGH WILL MOVE OVERHEAD ON FRIDAY UNDER WEAK NORTHWEST
FLOW. MODELS KEEP THE HIGHEST LLVL MOISTURE OVER THE MOUNTAINS THRU
THE DAY WHICH IS REASONABLE IN THIS FLOW PATTERN...SO KEPT SNOW
CHANCES CONFINED TO THE SNOWY AND SIERRA MADRES MOUNTAINS. ANOTHER
WEAK SHORTWAVE TROUGH WILL MOVE THROUGH ON SATURDAY/SATURDAY NIGHT
WITH A SLIGHTLY MORE NORTHERLY TRACK...SO COULD SEE LIGHT SNOW
SHOWERS RETURNING TO THE MOUNTAINS INCLUDING THE NORTHERN LARAMIE
RANGE THROUGH THIS TIME. WINDS ALOFT WILL BEGIN TO INCREASE SUNDAY
AND MONDAY AS A STRONG EASTERN PAC HIGH BUILDS IN FROM THE WEST. THE
STORM TRACK WILL THUS SHIFT OVER THE NORTHERN ROCKIES AND HIGH
PLAINS THROUGH THE EARLY PART OF THE WEEK...WITH WINDY CONDITIONS
AND INCREASING COVERAGE OF SNOW SHOWERS EXPECTED. THE NOSE OF A 150+
KT JET WILL MOVE OVERHEAD MONDAY...WITH A RATHER VIGOROUS VORT MAX
MOVING FROM THE NORTHERN ROCKIES INTO THE CENTRAL PLAINS IN THE LFQ
REGION OF THE JET. STILL LOOKS FAVORABLE FOR MORE WIDESPREAD SNOW
SHOWERS OVER THE CWA ON MONDAY...ESPECIALLY OVER THE MOUNTAINS AND
NORTHERN PLAINS FROM DOUGLAS TO ALLIANCE IN BETTER PROXIMITY TO THE
JET DIFLUENCE AND LIFT FROM THE VORT MAX. THE LLVL GRADIENT WILL
INCREASE IN ADVANCE OF THE WAVE AS THE LEESIDE TROUGH DEEPENS AS
WELL...SO SHOULD ALSO SEE WINDS BECOME MODERATE TO STRONG LATE
SUNDAY THROUGH MONDAY. THE ASSOCIATED COLD FRONT WILL MOVE ACROSS
THE EASTERN PLAINS SOMETIME LATE MONDAY...AND SHOULD STALL HERE
THROUGH TUESDAY. WINDY CONDITIONS WITH CHANCES FOR LIGHT SNOW WILL
CONTINUE OVER THE MOUNTAINS WITH RAIN/SNOW MIX OVER THE PLAINS AS A
RESULT. TEMPS THROUGH THE PERIOD WILL REMAIN AROUND NORMAL FOR THIS
TIME OF YEAR...WITH A SLIGHT BUMP UPWARDS AS DOWNSLOPE WINDS KICK IN
FOR MONDAY AND TUESDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 501 PM MST TUE DEC 16 2014

FOG WILL BE THE MAIN AVIATION CONCERN FOR MOST TERMINALS ACROSS
SOUTHEAST WY AND THE WESTERN NE PANHANDLE. LINGERING LIGHT SNOW
SHOWERS SHOULD HAVE LITTLE IMPACT. EXPECT IFR/LIFR CIGS AND VSBYS
TO DEVELOP BETWEEN 03Z AND 06Z AND PERSIST THROUGH THE NIGHT. THE
MOST LIKELY AREA TO SEE LOCALLY DENSE FOG WITH VSBYS LESS THAN ONE
QUARTER OF A MILE WILL BE THE PLATTE RIVER VALLEY WITH LIGHT
UPVALLEY WINDS...INCLUDING BFF. THE PANHANDLE SITES COULD SEE IFR
CONDITIONS WELL INTO THE AFTERNOON ON WED.

&&

.FIRE WEATHER...
ISSUED AT 243 PM MST TUE DEC 16 2014

MINIMAL ISSUES DUE TO PROJECTED HUMIDITIES AND WINDS.

&&

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

$$

SHORT TERM...RUBIN
LONG TERM...RJM
AVIATION...CLH
FIRE WEATHER...RUBIN



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