FXUS65 KCYS 241120
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
420 AM MST THU DEC 24 2009

.SHORT TERM...TODAY THROUGH CHRISTMAS DAY...CURRENT IR SATELLITE
LOOP SHOWS PARTLY CLOUDY SKIES ACROSS THE AREA AS THE MAIN BAND OF
SNOW...WHICH IMPACTED MOST OF THE REGION LAST NIGHT...HAS PUSHED
INTO NEBRASKA THIS MORNING. WINDS HAVE ALSO DIMINISHED ACROSS ALL
OF WYOMING...WITH SOME GUSTY WINDS OVER THE WRN NEBRASKA. WITH
DECREASED SNOWFALL AND WINDS...HAVE CANCELLED THE WINTER WEATHER
ADVISORIES THIS MORNING. HOWEVER...EXPECT STRONG WINDS AND SNOW TO
REDEVELOP TONIGHT THROUGH CHRISTMAS MORNING AS THE MAIN UPPER
LEVEL ARCTIC LOW DIGS SOUTHWARD INTO THE HIGH PLAINS BY CHRISTMAS
MORNING. MORE ON THIS LATER. FOR TODAY...MODELS SHOW AN ELONGATED
UPPER LEVEL TROUGH OVER THE AREA...WITH THE ARCTIC COLD FRONT WELL
TO THE EAST OF THE REGION. THIS SOLUTION DIFFERS FROM YESTERDAY
MORNINGS MODEL RUNS WHICH SHOWED THE MAIN ARCTIC LOW DIGGING SOUTH
ACROSS THE AREA TODAY. THEREFORE...CONTINUED TO DECREASE POP OVER
THE AREA TODAY. HAVE ALSO DECREASED WINDS TODAY...AND DO NOT
EXPECT WINDS TO INCREASE AGAIN UNTIL LATER THIS EVENING AS THE LOW
AND A SECONDARY ARCTIC FRONT PUSH INTO THE REGION. TEMPS WILL
REMAIN COLD AND GENERALLY IN THE TEENS...WITH WIND CHILLS BETWEEN 10
BELOW TO 5 ABOVE ZERO.

FOR TONIGHT AND CHRISTMAS DAY...COMPLICATED WEATHER SITUATION
POSSIBLE WITH STRONG WINDS...BLOWING SNOW...AND EVEN MORE SNOW
POSSIBLE. MODELS IN GOOD AGREEMENT SHOWING THE ARCTIC UPPER LOW
AND ASSOCIATED FRONTAL BOUNDARY DIGGING SOUTH THIS EVENING INTO NE
COLORADO AND INTO CNTRL NEBRASKA AND KANSAS BY CHRISTMAS DAY. THE
UPPER LEVEL LOW ACROSS TEXAS IS EXPECTED TO EJECT NORTHEAST...AND
THEN RETROGRADE WESTWARD AS IT IS GRADUALLY ABSORBED INTO THE
ARCTIC LOW...WITH A STRONG 988 SURFACE LOW ACROSS THE MISSISSIPPI
RIVER VALLEY RETROGRADING WESTWARD AS WELL TOWARDS ERN NEBRASKA AS
THE UPPER LEVEL LOW AND THE SURFACE LOW BECOME VERTICALLY STACKED. 
THIS WILL RESULT IN LOW TO MIDLEVEL NORTH TO NORTHEAST FLOW AND
MIDLEVEL ISENTROPIC LIFT OVER MOST OF SOUTHEAST WYOMING AND
NEBRASKA PANHANDLE. EXPECT SNOW TO REDEVELOP BY LATE THIS EVENING
AND GRADUALLY PUSH SOUTHWARD INTO CHRISTMAS DAY WITH ADDITIONAL
SNOW ACCUMULATIONS LIKELY...ESPECIALLY ALONG AND EAST OF THE
LARAMIE RANGE. ALSO...AS THE PRESSURE GRADIENT INCREASE OVER THE
AREA...EXPECT WINDS TO INCREASE AND BECOME STRONG EARLY CHRISTMAS
MORNING THROUGH CHRISTMAS DAY. MOS AND MODEL SOUNDINGS HINT AT
BORDERLINE HIGH WIND WARNING CRITERIA OVER THE HIGH PLAINS WITH
700MB WINDS OVER 60 KTS AND 850MB WINDS NEAR 40KTS. INCREASED POP
THROUGH CHRISTMAS EVENING ACROSS THE WHOLE FORECAST AREA WITH THE
HIGHEST POP OVER THE HIGH PLAINS NRN NEBRASKA...AND LOWER VALUES
WEST OF THE LARAMIE RANGE. WIND ADVISORY CONDITIONS ARE EXPECTED
ACROSS THE NEBRASKA PANHANDLE WITH A FEW LOCATIONS SUCH AS SIDNEY
AND KIMBALL NEAR HIGH WIND WARNING CRITERIA CHRISTMAS AFTERNOON.
ALSO...WITH ACCUMULATING SNOW EXPECTED ACROSS THE HIGH PLAINS WITH
MODELS HINTING AT 2 TO 6 INCHES OF SNOW AROUND THE PINE RIDGE...A
WINTER WEATHER ADV IS POSSIBLE FOR SNOW AND BLOWING SNOW ACROSS
THE NEBRASKA PANHANDLE AND PORTIONS OF ERN WYOMING FOR CHRISTMAS.
AT THIS TIME...NOT VERY CONFIDENT ABOUT ACCUMULATING SNOW OVER 3
INCHES SINCE MODELS HAVE BEEN A BIT WET LATELY. BUT MORE CONFIDENT
ABOUT THE STRONG WINDS AND BLOWING SNOW DURING CHRISTMAS DAY.
SINCE THE WINTER WEATHER ADV WAS CANCELLED THIS MORNING...WILL
HOLD OFF ON ISSUING THE SAME PRODUCT FOR NOW...BUT WILL REWORD
THE HAZARDOUS WEATHER OUTLOOK. IN SUMMARY...EXPECT HAZARDOUS
TRAVEL CONDITIONS CHRISTMAS DAY ACROSS MOST OF THE FORECAST AREA
EXCEPT MAYBE CARBON COUNTY WITH PERIODS OF LIGHT SNOW...BLOWING
SNOW...AND GUSTY WINDS UP TO 50 MPH WITH SUSTAINED WINDS AROUND 35
MPH. SNOW ACCUMULATIONS OF 1 TO 3 INCHES ARE POSSIBLE EAST OF THE
LARAMIE RANGE THROUGH CHRISTMAS EVENING WITH SLIGHTLY HIGHER
AMOUNTS OVER THE NRN NEBRASKA PANHANDLE.

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
DEEP UPPER LOW WILL BEGIN THE PERIOD NR THE MID-MISSISSIPPI RIVER 
VALLEY...WITH ITS AFFECTS STILL BEING FELT ACROSS THE ERN HALF OF 
THE CWA. WRAPAROUND MOISTURE AND ASSOCIATED LIGHT SNOW CHANCES WILL 
CONTINUE TO BACK WESTWARD INTO THE AREA FRIDAY NIGHT AS THE UPPER 
LOW WOBBLES WEST OF THE GREAT LAKES. BROAD ASCENT WILL BE GREATEST 
ACROSS THE NEBRASKA PANHANDLE FRIDAY NIGHT. AS A RESULT...HAVE 
BUMPED UP SNOW CHANCES ACROSS ERN ZONES...AND SPREAD THEM WEST BACK 
INTO THE MOUNTAINS OF SOUTHEAST WYOMING AS WELL. ADDITIONALLY...THE 
SFC PRESSURE GRADIENT WILL REMAIN TIGHT ON FRIDAY NT...WHICH WILL 
KEEP WINDS UP AND AREAS OF BLOWING SNOW ACROSS THE REGION. ALTHOUGH 
THE UPPER LOW WILL REMAIN ANCHORED IN NR THE GREAT LAKES FOR 
SATURDAY...A STRENGTHENING UPPER RIDGE OVER ALBERTA WILL ADVECT 
DRIER AIR INTO THE NRN ROCKIES... EFFECTIVELY BRINGING SNOW CHANCES 
TO AN END AND RELAXING THE SFC PRESSURE GRADIENT AND SFC WINDS. 
LARGE SCALE SUBSIDENCE BENEATH THE UPPER LEVEL RIDGE WILL KEEP 
CONDITIONS FOR THE MOST PART THROUGH EARLY NEXT WEEK...OUTSIDE WEAK 
OROGRAPHIC SNOW SHOWERS IN THE HIGHEST MOUNTAINS ON MONDAY THROUGH 
WEDNESDAY. THE NEXT SHORTWAVE WAS DELAYED UNTIL WEDNESDAY NT AND 
THURSDAY PER 00Z DETERMINISTIC MODELS...WHICH WILL KEEP CONDITIONS 
DRY IN THE LOWER ELEVATIONS UNTIL THAT TIME. HAVE REDUCED POPS 
EARLIER IN THE WEEK...AND INTRODUCED CLIMO POPS FOR WED NT AND 
THURSDAY. HIGH TEMPERATURES WILL BE 10 TO 15 DEGREES BELOW NORMAL 
FOR SATURDAY...WITH HIGHS IN THE TEENS WEST AND 20S EAST. AS CLOUDS 
DECREASE ON SUNDAY...TEMPERATURES WILL MODERATE ABOUT 5 
DEGREES...WITH LOW 20S WEST...AND UPPER 20S EAST. ALTHOUGH GUIDANCE 
IS TRYING TO WARM TEMPERATURES BACK TO NEAR NORMAL BY MIDDLE OF NEXT 
WEEK...IT IS LIKELY BEING INFLUENCED TO STRONGLY BY CLIMO... 
ESPECIALLY IN NORTHWEST FLOW. SO...KEPT HIGH TEMPERATURES SEVERAL 
DEGREES BELOW GUIDANCE...WHICH WILL YIELD FAIRLY PERSISTENT HIGHS 
GENERALLY IN THE 20S.

&&

.AVIATION...SNOW CAME TO AN END AT AREA TERMINALS THIS MORNING...GIVING WAY TO 
VFR CONDITIONS. THESE CONDITIONS WILL CONTINUE THROUGH THE DAY 
TODAY. WEST/NORTHWEST WINDS WILL BE PRESENT AT AREA TERMINALS TODAY 
WITH WIND SPEEDS OF AROUND 15 KTS GUSTING TO 25 KTS AT TIMES. WIND 
SPEEDS WILL INCREASE SUBSTANTIALLY THIS EVENING...WITH SUSTAINED 
WINDS OF 25 TO 30 KTS AND GUSTS TO 40 KTS ON CHRISTMAS DAY. THE KRWL 
AND KLAR TERMINALS CAN EXPECT SLIGHTLY LIGHTER WINDS DURING THIS 
PERIOD. OBVIOUSLY THESE STRONG WINDS WILL CREATE SIGNIFICANT AREAS 
OF BLOWING AND DRIFTING SNOW ON FRIDAY...AND REDUCE VISBS TO 
IFR/MVFR CONDITIONS ACCORDINGLY. ALSO...SNOW WILL SPREAD BACK INTO 
THE NEBRASKA TERMINALS TONIGHT AND FRIDAY...WITH PERHAPS AN INCH OR 
TWO OF ADDITIONAL ACCUMULATIONS POSSIBLE.
&&

.FIRE WEATHER...A STRONG WINTER STORM OVER THE PLAINS WILL
CONTINUE TO IMPACT THE AREA THROUGH CHRISTMAS DAY AND POSSIBLY
INTO THE WEEK WITH STRONG WINDS...SNOW AND BLOWING SNOW. NO FIRE
WEATHER CONCERNS AT THIS TIME.
&&

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

&&

$$

SHORT TERM...TJT 
LONG TERM/AVIATION...HAHN