Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 291537
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
837 AM MST MON DEC 29 2014

.UPDATE...
ISSUED AT 833 AM MST MON DEC 29 2014

REPORTS FILTERING IN THIS MORNING CONFIRMED AROUND 3-4 INCHES OF
SNOW HAD FALLEN FROM SW OF WHEATLAND EAST TO AROUND GERING.
SO...IN AN EARLIER UPDATE QUICKLY ADDED THEM INTO THE WINTER
WEATHER ADVISORY FOR TODAY. IMPACTS HAVENT BEEN ALL THAT GREAT OUT
THERE THUS FAR...THOUGH ROADWAYS ARE SLICK AND SNOW COVERED IN
SPOTS ACROSS EAST CENTRAL WYOMING AND THE NORTHERN NEBRASKA
PANHANDLE THIS MORNING. SHOULD SEE RATES DECREASE ACROSS THE
ADVISED AREA BY AFTERNOON WITH BETTER DYNAMICS SHIFTING SOUTH.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 345 AM MST MON DEC 29 2014

OBSERVATIONS ACROSS THE AREA SHOW THE ARCTIC FRONT HAS MOVED
ACROSS MOST OF THE FORECAST AREA EARLY THIS MORNING. HAD SOME
LIGHT SNOW ACROSS SOUTHEAST WYOMING LAST NIGHT...WITH SNOW NOW
ONGOING ACROSS MOST OF THE PANHANDLE OF NEBRASKA AND ALONG I80
OVER SOUTHERN WYOMING. ACCUMULATIONS HAVE BEEN LIGHT...SO WILL NOT
EXPAND THE CURRENT WINTER WEATHER ADVISORY. MAY NEED TO CANCEL
THE ADVISORY UP NORTH IF VISIBILITIES DO NOT LOWER SHORTLY. THE
WINTER WEATHER ADVISORY LOOKS GOOD OVER THE MOUNTAINS WHERE 5 TO
10 INCHES HAVE GENERALLY BEEN OBSERVED VIA THE SNOTEL NETWORK. THE
SHORTWAVE RESPONSIBLE FOR THE SNOW EARLIER OVER NIOBRARA AND
CONVERSE COUNTY MOVED A BIT FURTHER NORTH THAN ANTICIPATED. DID
NOT SEE THE HIGH SNOWFALL RATES AS THE FRONT WENT THROUGH THE
AREA...BUT THIS ONLY SEEMED LIKE A SLIGHT POSSIBILITY 24 HOURS
AGO ANYWAYS. LIGHT SNOW AND FLURRIES CURRENTLY NEAR THE I80
CORRIDOR OF EXTREME SOUTHEAST WYOMING...ALTHOUGH LOCALIZED
DOWNSLOPE FLOW AND SUBSIDENCE BEHIND THE FRONT HAS LIMITED
SNOWFALL THUS FAR NEAR CHEYENNE. THIS WILL CHANGE TODAY AS WINDS
SHIFT INTO THE NORTHEAST. SNOWFALL WILL INCREASE FURTHER SOUTH
TODAY AND TAPER TO FLURRIES UP NORTH AS THE SECOND PORTION OF THE
WINTER WEATHER EVENT BEGINS. MODELS INDICATE A STRONG 130+ KNOT
JET STRENGTHENS AND LIFTS NORTHWARD TODAY...WITH BROAD ASCENT AND
UPSLOPE FLOW EXPECTED ACROSS THE SOUTHERN HALF OF THE FORECAST
AREA. MODEL 700-500MB OMEGA IS CONTINUOUSLY BETWEEN 5 TO 10
MB/HOUR DUE TO JET DYNAMICS AND UPSLOPE FLOW THROUGH TUESDAY.
WITHOUT FRONTOGENESIS AND INSTABILITY...THIS IS BASICALLY
CONTINUOUS LIGHT SNOW. THIS APPEARS TO BE A LOW QPF/HIGH POP EVENT
FOR MOST OF THE SOUTHERN PORTION OF THE FORECAST AREA WITH 1 TO 3
INCHES OF SNOW EXPECTED THROUGH EARLY TUESDAY. ALTHOUGH SNOW
ACCUMULATIONS WILL BE CLOSE TO THREE INCHES IN AREAS...BELIEVE THE
SNOW ITSELF WILL BE LOW IMPACT DUE TO VISIBILITIES ABOVE ONE
MILE...RELATIVELY LIGHT WINDS...AND LOW SNOWFALL RATES AS THE
ARCTIC AIRMASS SETTLES OVER THE REGION.

BITTER COLD TEMPERATURES AND DANGEROUS WIND CHILLS ARE MORE
CONCERNING IN THE SHORT TERM. ALREADY OBSERVING TEMPERATURES IN
MONTANA AND THE DAKOTAS BETWEEN -5 TO -15 THIS HOUR. THIS AIRMASS
WILL PLUNGE SOUTHWARD ACROSS WYOMING TODAY AND ESPECIALLY TONIGHT.
HIGHS TODAY LIKELY HAVE ALREADY OCCURRED IN THE LAST FEW
HOURS...AS TEMPERATURES CONTINUE TO DROP INTO THE SINGLE DIGITS
AND POSSIBLY BELOW ZERO BY THIS EVENING. THE ARCTIC SURFACE HIGH
WILL CONTINUE TO DRIFT SOUTH. THE PRESSURE GRADIENT ASSOCIATED
WITH THE HIGH WILL RESULT IN BRISK EAST TO NORTHEAST WINDS THROUGH
TONIGHT...WITH GUSTS AROUND 20 TO 25 MPH POSSIBLE IN AREAS. LOW
TEMPERATURES TONIGHT ARE EXPECTED TO RANGE BETWEEN 10 BELOW ZERO
TO 20 BELOW ZERO...WITH THE HIGH VALLEYS POSSIBLY AS LOW AS 25
BELOW ZERO IN LOCATIONS SUCH AS LARAMIE AND SARATOGA.
TEMPERATURES AND BRISK WINDS WILL RESULT IN DANGEROUS WIND CHILLS
TONIGHT. FEEL VERY CONFIDENT THAT WIND CHILLS WILL LOWER BETWEEN
25 BELOW TO AS LOW AS 45 BELOW ZERO ACROSS SOUTHEAST WYOMING AND
MOST OF WESTERN NEBRASKA. THEREFORE...ISSUED A WIND CHILL WARNING
ALONG AND WEST OF A LINE FROM THE SOUTHERN LARAMIE RANGE TO
DOUGLAS...AND WENT WITH A WIND CHILL ADVISORY FOR LOCATIONS EAST
OF THE LARAMIE RANGE INCLUDING THE PANHANDLE OF NEBRASKA. EVEN IN
THE WIND CHILL ADVISORY AREAS...BELIEVE WIND CHILLS MAY LOWER TO
35 BELOW FOR SMALL PERIODS OF TIME AS WELL. SAD PART IS...THESE
CONDITIONS MAY NOT BE TOO BAD COMPARED TO TUESDAY NIGHT ACROSS
PORTIONS OF THE FORECAST AREA.

LIGHT SNOW WILL GRADUALLY TAPER TO FLURRIES ON TUESDAY AS THE
STRONG JET PUSHES EASTWARD INTO THE GREAT PLAINS. EXTREMELY COLD
TEMPERATURES ARE EXPECTED TUESDAY AFTERNOON AS THE BULK OF THE
ARCTIC AIR ESTABLISHES ITSELF OVER THE HIGH PLAINS. CURRENT MODEL
TRENDS AND MOS OUTPUT INDICATES HIGH TEMPERATURES REMAINING BELOW
ZERO ACROSS MOST OF SOUTHEAST WYOMING. FORECAST HIGH TEMPERATURES
FOR LARAMIE IS -8...CHEYENNE -3...AND RAWLINS AND DOUGLAS AT -4
DURING THE DAY. WESTERN NEBRASKA WILL NOT BE MUCH WARMER WITH
HIGHS A FEW DEGREES HIGHER THAN ZERO. THE WIND CHILL
WARNING/ADVISORY IS GOOD UNTIL NOON...BUT EXPECT PORTIONS OF THE
AREA TO BE EXTENDED THROUGH THE DAY WITH WIND CHILLS REMAINING
BETWEEN 20 BELOW TO 30 BELOW ZERO.

LOW TEMPERATURES ON TUESDAY NIGHT WILL BE TRICKY...AS THE 1050MB
ARCTIC SURFACE HIGH DRIFTS SOUTHWARD INTO COLORADO AND KANSAS.
WINDS WILL BECOME VERY LIGHT OR CALM. CALM WINDS WITH A SURFACE
SNOW PACK AND CLEARING SKIES DURING THIS TIME OF THE YEAR
TYPICALLY RESULTS IN RAPIDLY FALLING TEMPERATURES AFTER SUNSET.
THERE IS STILL UNCERTAINTY AS TO HOW LOW OUR TEMPS WILL FALL SINCE
WINDS MAY SHIFT INTO THE WEST EARLY WEDNESDAY MORNING. FOR
NOW...WENT A FEW DEGREES BELOW MOS WITH LOWS GENERALLY 20 BELOW TO
30 BELOW ZERO OVER MOST OF THE FORECAST AREA INCLUDING WESTERN
NEBRASKA. THE COLDEST TEMPERATURES WILL LIKELY BE IN THE NORTH
PLATTE RIVER VALLEY AND LARAMIE VALLEY. WOULD NOT BE SURPRISED
TO SEE A FEW READINGS APPROACHING 40 BELOW ZERO IN ISOLATED PARTS
OF WYOMING. EVEN WITH LIGHT WINDS...WILL LIKELY NEED A WIND CHILL
WARNING ACROSS THE WHOLE FORECAST AREA TUESDAY NIGHT WITH WIND
CHILLS BETWEEN 30 BELOW TO 50 BELOW ZERO. BY EARLY WEDNESDAY
MORNING...TEMPERATURES ALONG AND EAST OF THE LARAMIE RANGE WILL
QUICKLY WARM TO NEAR ZERO BY SUNRISE DUE TO INCREASING WESTERLY
WINDS...EVEN THOUGH WIND CHILL VALUES WILL STILL REMAIN
DANGEROUSLY COLD THROUGH THE MORNING.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 330 AM MST MON DEC 29 2014

CONTINUED COLD IN THE EXTENDED WITH SNOW PACK AND 700MB
TEMPERATURES -8 TO -10C ACROSS THE CWFA. UNDERCUT GUIDANCE ON
TEMPERATURES BY SEVERAL DEGREES. WINDS WILL BE LIGHT AS WELL...SO
NO DOWNSLOPING TO HELP RAISE TEMPERATURES EAST OF THE LARAMIE
RANGE EXPECTED FOR MUCH OF THE WEEK. LOOKS FAIRLY DRY AS WELL AS A
CLOSED LOW TRACKS ACROSS NEW MEXICO.

WINDS FINALLY BEGIN INCREASING SATURDAY EVENING AS ANOTHER ARCTIC
BOUNDARY BEGINS TO SAG INTO THE AREA FROM THE NORTH. GFS AND ECMWF
DIFFER SIGNIFICANTLY ON THIS FEATURE. GFS DRIVES THE FRONT TO THE
EAST SLOPES OF THE LARAMIE RANGE WHILE CURRENT ECMWF KEEPS THE
FRONT NORTHEAST OF OUR AREA. HOPEFULLY...WE GET A LITTLE MORE
CONSISTENCY IN MODELS AS WE GET CLOSER TO THE WEEKEND.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 512 AM MST MON DEC 29 2014

WIDESPREAD LIGHT SNOW TO CONTINUE THROUGH THE DAY WITH IFR/LIFR
VISIBILITIES IN THE HEAVIER SNOW. DO THINK THESE LOW CONDITIONS
WILL CONTINUE INTO THE AFTERNOON HOURS BEFORE CONDITIONS IMPROVE.


&&

.FIRE WEATHER...
ISSUED AT 300 AM MST MON DEC 29 2014

NO FIRE WEATHER CONCERNS THIS WEEK DUE TO BITTER COLD TEMPERATURES
AND PERIODS OF SNOW. TEMPERATURES WILL REMAIN BELOW NORMAL WITH A
DECENT SNOWPACK THROUGH THE WEEK. TEMPERATURES MAY INCREASE TO
NEAR NORMAL LATER IN THE WEEK...BUT HUMIDITIES WILL REMAIN ABOVE
50 PERCENT DURING THE DAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
     WYZ101>114.

     WIND CHILL ADVISORY FROM 6 PM THIS EVENING TO NOON MST TUESDAY
     FOR WYZ102-107-108-117>119.

     WIND CHILL WARNING FROM 6 PM THIS EVENING TO NOON MST TUESDAY
     FOR WYZ101-103>106-109>116.

NE...WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR NEZ019-
     095-096.

     WIND CHILL ADVISORY FROM 6 PM THIS EVENING TO NOON MST TUESDAY
     FOR NEZ002-003-019>021-054-055-095-096.

&&

$$

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



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