Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 241736
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1036 AM MST WED DEC 24 2014

.UPDATE...
ISSUED AT 605 AM MST WED DEC 24 2014

MOVED UP THE TIME OF THE HIGH WIND WARNING FOR THE SOUTHERN
LARAMIE RANGE AND FOOTHILLS ALONG WITH THE BORDEAUX ZONE AS WINDS
WERE APPROACHING HIGH WIND WARNING TYPE MAGNITUDES. IN FACT
BORDEAUX RECENTLY HAD A GUST TO 59 MPH. WYDOT SENSOR AT BUFORD
EAST GUSTING TO 52 MPH. WILL REISSUE THE NPW HERE SHORTLY TO
MODIFY THE WORDING. AFTER CLOSER INSPECTION OF THE MODLES...HIGH
WINDS COULD CONTINUE LATER INTO TONIGHT BEFORE DROPPING BELOW HIGH
WIND CRITERIA.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)

ISSUED AT 313 AM MST WED DEC 24 2014

STRONG WINDS WILL ONCE AGAIN OCCUR OVER THE WIND PRONE AREA OF
SOUTHEAST WYOMING TODAY. CURRENTLY WINDS IN THE ARLINGTON AREA
ARE SUSTAINED 40 TO 45 MPH WITH GUSTS AROUND 60 MPH. THESE TYPE
WIND SPEEDS MAY SEE A LULL EARLY THIS MORNING...BUT OTHERWISE
CONTINUE THROUGH THIS AFTERNOON. WINDS WILL QUICKLY DROP OFF INTO
THE EVENING HOURS WITH THE LOSS OF DAYTIME MIXING AND WEAKENING
LOW LEVEL PRESSURE GRADIENT. WINDS IN THE SOUTHERN LARAMIE RANGE
AND NEAR BORDEAUX SHOULD HIT HIGH WIND CRITERIA TODAY BUT THERE IS
SOME UNCERTAINLY AS A LOW LEVEL INVERSION WILL HAVE SOME IMPACT
AND COULD KEEP THE STRONGEST WINDS SLIGHTLY ABOVE THE GROUND
LEVEL. ALSO HIGH CLOUDS WILL INCREASE THROUGH THE DAY WHICH COULD
INHIBIT DEEPER BOUNDARY LAYER MIXING. ANOTHER POSSIBLE NEGATIVE IS
THE GREATEST SURFACE PRESSURE FALLS WILL BE OVER SOUTHEAST WYOMING
BY LATER THIS MORNING WHICH IS NOT A FAVORED LOCATION TO SEE WIND
ACCELERATION. REGARDLESS IT WILL BE RATHER WINDY IN THESE AREAS
TODAY SO UPGRADED THE PREVIOUS HIGH WIND WATCH TO A WARNING.

ALL ATTENTION TURNS TO CHRISTMAS DAY AS AN UPPER LEVEL TROUGH
WILL SWING ACROSS THE ROCKIES. A WINTER STORM WATCH HAS BEEN
ISSUED FOR MUCH OF SOUTHEAST WYOMING FOR CHRISTMAS DAY AND NIGHT.
SNOW WILL FIRST DEVELOP ACROSS WESTERN PORTIONS OF THE FORECAST
AREA IN THE MORNING AND THEN SHIFT EAST OF THE LARAMIE RANGE IN
THE AFTERNOON...AND THEN INTO THE NEBRASKA PANHANDLE MAINLY LATE
AFTERNOON AND EVENING.

THE UPPER LEVEL DYNAMICS WITH THIS SYSTEM ARE NOT OVERLY
IMPRESSIVE BUT THAT SAID THERE WILL BE A BROAD AREA OF WEAK TO
MODERATE LIFT THROUGH A DEEP LAYER. ALSO THE MODELS ARE
INDICATING SOME INSTABILITY FOR AREAS ALONG AND WEST OF THE
LARAMIE RANGE WHICH IS THE BIGGEST CONCERN. IN FACT BOUNDARY LAYER
LIFTED INDICES WILL BE NEAR ZERO THURSDAY AFTERNOON AND EVENING.
SHOULD CONVECTIVE ELEMENTS DEVELOP...SEVERAL INCHES OF SNOW COULD
FALL IN A SHORT PERIOD OF TIME. IN ADDITION...NORTH TO NORTHEAST
BOUNDARY LAYER WINDS WILL DEVELOP BEHIND A COLD FRONT LATE
CHRISTMAS DAY. THESE TYPE WINDS ARE FAVORABLE FOR UPSLOPE SNOW
ENHANCEMENT ALONG THE LARAMIE RANGE AND CHEYENNE RIDGE.

ON THE OTHER SIDE OF THEN EQUATION...THE MAIN AREA OF STRONGER
LIFT WILL MOVE ACROSS THE AREA RATHER QUICKLY SO THE MAIN TIME
FRAME FOR ANY HEAVIER DYNAMIC DRIVEN SNOW MAY BE SHORT LIVED. ALSO
THERE WILL BE VERY MINIMAL OROGRAPHIC ENHANCEMENT OVER THE SNOWY
AND SIERRA MADRE RANGES...WHICH COULD MEAN SNOW TOTALS OVER THESE
MOUNTAINS MAY NOT BE MUCH MORE THAN IN THE SURROUNDING LOWER
ELEVATIONS. IN OTHER WORDS THE MOUNTAINS MAY HAVE A TOUGH TIME
PICKING UP 12 INCHES OF SNOW NEED TO VERIFY A WINTER STORM
WARNING. ALSO AS WINDS WILL BE RELATIVELY LIGHT IN THE
MOUNTAINS...THE IMPACTS WILL BE MINIMAL ON A RELATIVE BASIS. AT
ANY RATE...THIS IS A MARGINAL SNOW EVENT TO REACH WINTER STORM
CRITERIA AND THE IMPACTS EVEN WITH 6 OR 7 INCHES OF SNOW MAY BE
MORE LIKE AN ADVISORY... ESPECIALLY WEST OF THE LARAMIE RANGE
WHERE WINDS WILL BE RELATIVELY LIGHT. EAST OF THE LARAMIE RANGE
EXPECTING SOME GUSTS TO 30 MPH WHICH WHEN COMBINED WITH SNOW WILL
PRODUCE REDUCED VISIBILITIES. INTO THE NEBRAKSA PANHANDLE WINDS
WILL BE NORTHERLY AT 15 TO 20 MPH WITH GUSTS AROUND 30 MPH
CHRISTMAS NIGHT BUT SNOW AMOUNTS SHOULD ONLY BE IN THE 2 TO 4 INCH
RANGE.

SNOW WILL TAPER OFF TO FLURRIES LATE CHRISTMAS NIGHT THROUGH
FRIDAY MORNING. BY FRIDAY AFTERNOON ONLY EXPECTING A FEW SNOW
FLURRIES OVER THE AREA WHILE WINDS WILL BECOME LIGHT. OTHER THAN
SOME SNOW COVERED ROADS...TRAVEL CONDITIONS SHOULD BE DECENT BY
FRIDAY AFTERNOON.

.LONG TERM...(FRIDAY NIGHT THROUGH NEXT TUESDAY)
ISSUED AT 400 AM MST WED DEC 24 2014

LONG RANGE MODELS IN EXCELLENT AGREEMENT THROUGH NEXT WEEKEND AND
INTO THE FINAL WEEK OF 2014...SHOWING THE POTENTIAL OF ANOTHER
SNOW EVENT LATE ON SUNDAY AS AN ARCTIC FRONT MOVES INTO THE
REGION. ALL MODELS SHOW THE WINTER STORM...WHICH WILL POTENTIALLY
IMPACT THE FORECAST AREA ON CHRISTMAS DAY...WEAKENING AS IT MOVES
EAST OF THE ROCKY MOUNTAINS FRIDAY NIGHT. THIS SYSTEM WILL
EVENTUALLY REFORM IN THE SOUTH LATER IN THE WEEKEND...BUT WILL
RESULT IN NORTHERLY FLOW AND COLD TEMPERATURES ACROSS SOUTHEAST
WYOMING AND WESTERN NEBRASKA. HIGH TEMPS ON SATURDAY WILL LIKELY
STRUGGLE TO REACH THE MID 20S ACROSS THE FORECAST AREA...WITH LOWS
POTENTIALLY BELOW ZERO IN SOME LOCATIONS DUE TO SOME SURFACE
SNOWPACK.

ON SUNDAY...ALL MODELS SHOW A POTENT SHORT WAVE TROUGH DIGGING
SOUTH AND WEST TOWARDS THE GREAT BASIN REGION. AT THE SURFACE...AN
ARCTIC AIRMASS WILL QUICKLY MOVE SOUTHWARD WITH THE ARCTIC COLD
FRONT MOVING TOWARDS SOUTHERN WYOMING BY LATE SUNDAY EVENING. THE
SHORTWAVE TROUGH WILL EVENTUALLY STALL BEFORE IT TRANSITIONS
WESTWARD...RESULTING IN A BROAD TROUGH AXIS SETTLING OVER MOST OF
THE NORTHERN UNITED STATES. THE POLAR JET STREAM WILL BECOME
ACTIVE AS THE ARCTIC FRONT MOVES SOUTH...RESULTING IN A PERIOD OF
LIGHT SNOW SUNDAY NIGHT THROUGH MONDAY. SNOW ACCUMULATIONS APPEAR
TO BE LIGHT TO MODERATE...WITH THE GFS SHOWING THE GREATEST
POTENTIAL FOR MODERATE SNOW ACCUMULATIONS AS THE FRONT AND JET
AXIS STALL JUST SOUTH OF THE FORECAST AREA. THE GEM IS THE MOST
PROGRESSIVE...SHOWING THE ARCTIC AIRMASS REMAINING TO THE
NORTHEAST. THE ECMWF IS MORE SIMILAR TO THE GFS...BUT NOT SHOWING
THE SHORTWAVE TROUGH DIGGING AS FAR TO THE WEST...RESULTING IN
LESS PRECIPITATION. INCREASED POP ACROSS MOST OF SOUTHEAST WYOMING
BETWEEN 35 TO 50 PERCENT. BOTH THE GFS AND ECMWF SHOWING THE BULK
OF THE ARCTIC AIRMASS IMPACTING THE REGION THROUGH EARLY NEXT
WEEK REGARDLESS OF SNOW AMOUNTS. FOR NOW...LOWERED MIN AND MAX
TEMPERATURES ANOTHER 5 TO 10 DEGREES COMPARED TO THE PREVIOUS
FORECAST...WITH HIGHS IN THE SINGLE DIGITS AND TEENS BY TUESDAY
AFTERNOON AND LOWS BELOW ZERO. HOWEVER IF CURRENT MODEL RUNS
VERIFY...THIS FORECAST MAY BE 10 TO 15 DEGREES TOO WARM WITH
MODEL SOUNDINGS INDICATING HIGHS REMAINING BELOW ZERO THROUGH
TUESDAY AFTERNOON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 1036 AM MST WED DEC 24 2014

A PATCH OF MVFR CIGS AROUND KRWL EARLY THIS AFTERNOON OTHERWISE VFR
CONDITIONS EXPECTED THROUGH THIS EVENING OVER THE AREA.  MVFR CIGS
SHOULD RETURN TO KRWL LATER TONIGHT WITH DETERIORATING CONDITIONS
BEGINNING FROM THE NW BY 18Z THURSDAY.  GUSTY WINDS THIS AFTERNOON
AROUND THE SE WY MTNS.

&&

.FIRE WEATHER...
ISSUED AT 313 AM MST WED DEC 24 2014

STRONG WINDS WILL BE FOUND OVER WIND PRONE AREAS OF SOUTHEAST WYOMING
TODAY. ELSEWHERE WINDS WILL BE LIGHT TO BREEZY. A WINTER STORM
SYSTEM WILL MOVE ACROSS THE AREA CHRISTMAS DAY AND NIGHT WITH SEVERAL
INCHES OF SNOW EXPECTED. LINGERING SNOW SHOWERS AND FLURRIES FRIDAY
THEN DRY SATURDAY. ANOTHER WEATHER SYSTEM TO IMPACT THE ARE
EARLY NEXT WEEK.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM THURSDAY MORNING THROUGH LATE THURSDAY
     NIGHT FOR WYZ104-105-109>114.

     WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH LATE THURSDAY
     NIGHT FOR WYZ106-107-115>118.

     HIGH WIND WARNING UNTIL 5 AM MST THURSDAY FOR WYZ106-110-116-117.

NE...NONE.
&&

$$

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



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