Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 270521
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1021 PM MST FRI DEC 26 2014

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 302 PM MST FRI DEC 26 2014

TONIGHT...PRIMARY CHALLENGES TONIGHT WILL BE MINIMUM TEMPERATURES
AND AREAL FOG DEVELOPMENT.

UPPER TROUGH AXIS MOVES FROM EASTERN WYOMING AND EASTERN COLORADO
AROUND SUPPERTIME...TO EASTERN SOUTH DAKOTA AND EASTERN NEBRASKA BY
DAWN WITH NORTHWEST FLOW ALOFT OVER OUR COUNTIES. WITH FRESHLY
FALLEN SNOW COVER...RELATIVELY MINIMAL MIXING AND LIGHT WINDS AND
MID AFTERNOON TEMPERATURES ONLY IN THE SINGLE DIGITS AND
TEENS...HAVE UNDERCUT MOST GUIDANCE LOW TEMPERATURES.

FOG OCCURRING AT MID AFTERNOON AT TORRINGTON AND SCOTTSBLUFF WITH
TEMPERATURE AND DEWPOINT SPREADS AROUND 4 DEGREES...SO HAVE ADDED
EARLY EVENING FOG THERE. WITH CLEARING SKIES...RESIDUAL SNOW COVER
AND LIGHT WINDS...HAVE ADDED AREAS OF FOG LATE THIS EVENING ACROSS
ALL LOCALES ESPECIALLY IN LIGHT OF CURRENT TEMPERATURE AND DEWPOINT
SPREADS. AFTER MIDNIGHT...BOUNDARY LAYER WINDS FROM THE NORTHWEST
EXPECTED TO INCREASE...ESPECIALLY EAST OF INTERSTATE 25...LIMITING
AREAL FOG COVERAGE...WHILE WEST OF INTERSTATE 25...BOUNDARY LAYER
PROGS AND MINIMAL MIXING AND INVERSIONS EXPECTED TO SET UP OVER THE
SNOW FIELD...THUS EXPECT GREATER AREAL COVERAGE OF FOG WEST OF I-25
AFTER MIDNIGHT...VERSUS EAST OF I-25.

SATURDAY...PRIMARY CHALLENGES WILL BE TEMPERATURES AND WINDS. AS FOR
TEMPERATURES...RESIDUAL SNOW COVER AND SCATTERED TO BROKEN MIDDLE
AND HIGH CLOUDS WILL LIMIT WARMING DOWNWIND OF APPROACHING SHORTWAVE
TROUGH ALOFT OVER WESTERN MONTANA. OUR MIDNIGHT SHIFT TEAM SET THE
TABLE WELL WITH A HIGH WIND WATCH FOR ARLINGTON IN THE
AFTERNOON...AND WE HAVE ENOUGH CONFIDENCE TO UPGRADE TO A HIGH WIND
WARNING FOR ARLINGTON AND ELK MOUNTAIN IN THE AFTERNOON BASED ON THE
700 MB GRADIENTS FROM CRAIG TO CASPER OF 55 TO 60 METERS...USUALLY
ENOUGH TO PRODUCE HIGH WINDS AT ARLINGTON ESPECIALLY WITH PROGGED
DOWNWARD VERTICAL MOTION.

SATURDAY NIGHT...PRIMARY CHALLENGE WILL BE WINDS. CRAIG TO CASPER
700 MB HEIGHT GRADIENTS PEAKS NEAR 60 METERS...AND WITH PROGGED
DOWNWARD VERTICAL MOTION...WE FEEL CONFIDENT IN UPGRADING OUR
INHERITED HIGH WIND WATCH TO A HIGH WIND WARNING FOR OUR
BORDEAUX...INTERSTATE 80 SUMMIT...VEDAUWOO AND BUFORD LOCATIONS...
ESPECIALLY THE CLIMATOLOGICALLY FAVORED TIME OF THE NIGHT FOR
STRONGER WINDS TO MATERIALIZE. THANK YOU TO OUR MID SHIFT TEAM FOR
THE EARLY HEADS UP ON THE WINDS.

AS FOR MINIMUM TEMPERATURES...DECENT MIXING...WINDS TO THE LEE OF
THE LARAMIE RANGE WILL PRODUCE LOCALLY WARMER TEMPERATURES FROM
BORDEAUX TO CHEYENNE AND THE COLORADO STATE LINE...WITH CONSIDERABLY
COLDER TEMPERATURES IN THE LOWER ELEVATIONS WHERE WINDS WILL NOT
MATERIALIZE AS MUCH LIKE ALONG THE NORTH PLATTE RIVER VALLEY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 302 PM MST FRI DEC 26 2014

ACTIVE WINTERTIME PATTERN HAS SETTLED IN ACROSS NOAM WITH WEATHER
SYSTEMS PINWHEELING AROUND A PERSISTENT HUDSON BAY LOW. THE
PRIMARY FORECAST CONCERN FOR NEXT WEEK WILL BE AN ARCTIC FRONT
THAT WILL BRING ANOTHER BRIEF SHOT OF ACCUMULATING SNOW FOR
SUNDAY NIGHT AND MONDAY FOLLOWED BY BITTERLY COLD AIR FOR
MONDAY... TUESDAY AND WEDNESDAY. 12Z MODELS ARE GOOD AGREEMENT IN
THE OVERALL PATTERN PROGRESSION...BUT DETAILS DIFFER WHICH ISNT
UNUSUAL 2-3 DAYS OUT. THE HIGH WIND EVENT WILL BE WINDING
DOWN...BUT MAY STILL BE LINGERING SUNDAY MORNING AS THE NEXT
SHORTWAVE DIVES INTO THE PACNW. MODELS ARE CONSISTENT IN DROPPING
THE ARCTIC COLD FRONT SOUTH SUNDAY NIGHT. AS LLVLS WINDS TURN
NORTH/NORTHEAST AND UPSLOPE ENSUES...WILL SEE SNOW GET GOING
ACROSS ALL OF SE WY AND THE W NE PANHANDLE. SNOW WILL LIKELY
CONTINUE INTO THE DAY ON MONDAY AS WELL BEFORE COMING TO AN AT
SOME POINT MONDAY NIGHT. HAVE CONTINUED EARLIER TRENDS OF BOOSTING
SNOW CHANCES ON SUNDAY NIGHT AND MONDAY. NOW WITH THE NOT SO
CONSISTENT PART...SNOW AMOUNTS. MODEL SOLUTIONS STILL VARY
SIGNIFICANTLY. THE ECMWF/NAM/CANADIAN MODELS CONTINUE TO BE THE
LIGHTEST WITH GENERALLY 1-3 INCHES OVER LOWER ELEVATIONS AND MAYBE
2- 5 INCHES OVER THE MOUNTAINS. MEANWHILE THE GFS IS SIGNIFICANTLY
MORE BULLISH IN THE SOUTHERN LARAMIE RANGE AND ADJACENT HIGH
PLAINS AND VALLEYS...WHERE SHOULD IT VERIFY...AMOUNTS WOULD REACH
ADVISORY/WARNING CRITERIA. MODELS ARE NOTORIOUSLY POOR FOR THEIR
HANDLING OF ARCTIC BOUNDARIES...SO DONT HAVE STRONG CONFIDENCE IN
EITHER DIRECTION. FOR NOW HAVE STEERED TOWARDS A MIDDLE GROUND AND
WILL TREND ACCORDINGLY. THOSE WITH TRAVEL PLANS SUNDAY NT AND
MONDAY WILL DEFINITELY WANT TO CHECK BACK FOR LATER FORECASTS.

AND NOW FOR THE BITTER COLD...H7 TEMPERATURES FALL TO AROUND -24C BY
TUESDAY. HIGH TEMPERATURES MONDAY WILL ONLY REACH THE SINGLE DIGITS
AND WILL LIKELY NOT REACH ABOVE ZERO FOR AREAS ON TUESDAY. OVERNIGHT
LOWS WILL FALL TO -15 TO -25F ON BOTH MONDAY NIGHT AND TUESDAY
NIGHT. HAVE UNDERCUT GUIDANCE DURING THIS PERIOD AND STILL MAY NOT
BE COLD ENOUGH.

FLOW SPLITS AFTER TUESDAY AS UPPER LOW CLOSES ACROSS THE SW CONUS
DETACHING FROM NRN STREAM. THIS WILL RESULT IN A DRY PERIOD ACROSS
THE AREA WITH TEMPERATURES SLOWLY MODERATING BACK TOWARDS SEASONAL
LEVELS FOR THE SECOND HALF OF NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1018 PM MST FRI DEC 26 2014

WESTERLY WINDS ARE BEGINNING TO DEVELOP THIS EVENING...SO SHOULD
SEE SNOW AND LOWER CEILINGS BEGIN TO DISSIPATE THROUGH THE EARLY
MORNING. ONE SITE OF CONCERN IS KLAR...WHICH COULD CONTINUE TOS EE
IFR CONDITIONS IN UPSLOPING WESTERLY WINDS AGAINST THE WEST SLOPES
OF THE LARAMIE RANGE. SINCE VISIBILITIES ARE IMPROVING...WENT
AHEAD AND USED A TEMPO GROUP FOR KLAR. BY 09Z THOUGH...LATEST HRRR
FORECAST SHOWING IMPROVING CONDITIONS JUST ABOUT EVERYWHERE. COULD
SEE REDUCED VISIBILITIES IN BLSN FOR AIRPORTS WEST OF THE LARAMIE
RANGE TOMORROW LATE MORNING AND AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 237 AM MST FRI DEC 26 2014

SNOW WILL TAPER OFF FROM NORTH TO SOUTH TODAY AS A STORM SYSTEM
SHIFTS FROM THE ROCKIES INTO THE PLAINS. ADDITIONAL SNOW
ACCUMULATIONS WILL BE MINIMAL WITH NEW SNOW AMOUNTS GENERALLY LESS
THAN ONE INCH. COLD AND DRY SATURDAY WITH MOSTLY CLEAR SKIES...AND
WINDY TO VERY WINDY ALONG AND WEST OF THE LARAMIE RANGE. STRONG WINDS
WILL CONTINUE INTO SUNDAY MORNING BEFORE DECREASING. ANOTHER SHOT
OF SNOW POSSIBLE SUNDAY INTO MONDAY. VERY COLD MONDAY AND TUESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING FROM 11 AM SATURDAY TO 11 AM MST SUNDAY FOR
     WYZ110.

     HIGH WIND WARNING FROM 5 PM SATURDAY TO 11 AM MST SUNDAY FOR
     WYZ106-116-117.

NE...NONE.
&&

$$

SHORT TERM...RUBIN
LONG TERM...CAH
AVIATION...GCC
FIRE WEATHER...TJT


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