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000
FXUS65 KCYS 091720
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1015 AM MST MON DEC 9 2013

.UPDATE...
ISSUED AT 954 AM MST MON DEC 9 2013

WIND GUSTS TO 60 MPH HAVE BEEN PRODUCING SIGNIFICANT REDUCTIONS IN
VISIBILITY IN THE ARLINGTON AREA THIS MORNING. WEB CAMS SHOWING
VISIBILITIES ONLY A FEW HUNDRED FEET IN PLACES. ELECTED TO GO WITH
A BLIZZARD WARNING AS VISIBILITIES WILL STAY BELOW 1/4 FOR SEVERAL
HOURS TODAY AND LIKELY THROUGH TONIGHT. THE STRONG WINDS WILL
CONTINUE THROUGH TUESDAY AFTERNOON BUT MOST LIKELY THE SNOW WILL
BECOME COMPACTED AND/OR WILL BE LOFTED OUT OF THE AREA. FOR NOW
HAVE THE BLIZZARD WARNING FOR THE ARLINGTON ZONE GOING THROUGH
TUESDAY AFTERNOON...BUT CHANCES ARE IT WILL BE CONVERTED BACK TO A
HIGH WIND WARNING THE BULK OF THE SNOW HAS BECOME COMPACTED OR
BLOW AWAY...JUST NOT SURE HOW FAST THAT WILL OCCUR.

INTO THE SOUTHERN LARAMIE RANGE WHERE THERE IS SLIGHTLY LESS SNOW
ON THE GROUND AND NOT QUIET AS MUCH BLOWING AS SHOWN ON THE WEB
CAMS...KEPT THE HIGH WIND WARNING GOING WITH THE MENTION OF
BLOWING SNOW AND ALSO ISSUED A SPS. MAY EVENTUALLY NEED A
BLIZZARD WARNING FOR THIS AREA...BUT FOR NOW IT APPEARS GROUND
BLIZZARD CONDITIONS ARE LOCALIZED AND GENERALLY SHORT LIVED AS
VISIBILITY BOUNCES UP AND DOWN.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY NIGHT)
ISSUED AT 330 AM MST MON DEC 9 2013

MAIN STORY IN THE SHORT TERM WILL BE THE STRONG WINDS ACROSS
SOUTHEAST WYOMING...ESPECIALLY THE WIND PRONE AREAS. SHORTWAVE IN
THE NORTHWESTERLY FLOW ALOFT SHOWS UP NICELY ON WATER VAPOR
IMAGERY ACROSS WYOMING INTO CENTRAL COLORADO. THIS SHORTWAVE IS
BRINGING DOWN ANOTHER REINFORCING SHOT OF VERY COLD AIR WITH 700MB
TEMPS AROUND -22C. THE WIND CHILL ADVISORY HAS BEEN WORKING OUT
WELL IN THE PANHANDLE WITH VALUES CURRENTLY IN THE -20 TO -30
RANGE. ANOTHER SHORTWAVE DROPS SOUTHEASTWARD ACROSS THE DAKOTAS BY
THIS AFTN. PRESSURE FALLS OVER THE NORTHERN PLAINS WILL BEGIN TO
INCREASE THE LLVL GRADIENT ACROSS OUR REGION BY MIDDAY. THE 700MB
CAG-CPR GRADIENT RISES QUICKLY TO 68 METERS BY 18Z AND REMAINS
AROUND 70 METERS THROUGH 18Z TUES. THE 850MB GRADIENT IS EVEN
HIGHER...AT 75-80 METERS OVER THE SAME PERIOD. TAKING A LOOK AT
CROSS SECTIONS AND SOUNDINGS ACROSS SOUTHEAST WYOMING...THIS IS AN
CASE WHERE THE STRONGEST WINDS ARE IN THE SFC-700MB LAYER WITH A
BIT WEAKER AND MORE NORTHWESTERLY ORIENTATION IN THE 700-500MB
LAYER. ALTHOUGH LLVL MIXING DOES NOT LOOK PARTICULARLY GREAT
ESPECIALLY TONIGHT...THE STRONG SFC WINDS IN THIS EVENT WILL BE
PRIMARILY DRIVEN BY THE VERY STRONG LLVL GRADIENT AND LESS BY
MIXING OF WINDS ALOFT. CONFIDENCE WAS HIGH ENOUGH TO UPGRADE THE
HIGH WIND WATCHES TO A WARNING. MOVED THE START TIME FOR THE
SOUTHERN LARAMIE RANGE UP TO 06Z TUES AS THE GFS SHOWS 700MB WINDS
INCREASING TO 55 KTS AT THAT POINT.

WITH REGARD TO TEMPS...TODAY WILL BE ANOTHER COLD DAY WITH 700MB
TEMPS ONLY RISING TO -14C BY THE AFTN. ALTHOUGH LOW TEMPS WILL
INCREASE AROUND 15 DEGREES TONIGHT DUE TO THE INCREASE IN
WINDS...WIND CHILL VALUES WILL STILL BE VERY COLD ESPECIALLY IN
THE WIND PRONE AREAS OF SOUTHEAST WY. TEMPS ON TUES WILL FINALLY
WARM TO AROUND FREEZING AS THE LEE TROUGH AND THERMAL RIDGE ARE
WELL DEVELOPED TO THE EAST OF THE LARAMIE RANGE. SHORTWAVE MOVES
ACROSS THE AREA BY TUES AFTN AND EVENING. WEAK FORCING OVER THE
PLAINS WITH RESULT IN A SLIGHT CHANCE OF SNOW SHOWERS MAINLY
ACROSS THE PANHANDLE DURING THE EVENING. PRESSURE RISES BEHIND THE
SHORTWAVE WILL BRING AN ABRUPT END TO THE HIGH WINDS BY TUES
EVENING.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 330 AM MST MON DEC 9 2013

COLD AIR TO REMAIN IN PLACE WEDNESDAY AS 700MB TEMPERATURES STILL
-8 TO -10C OVER THE CWFA. GOING TO BE TRICKY WITH
GUSTY...DOWNSLOPING WEST WINDS THOUGH. DO THINK WE WILL PROBABLY
SEE OUR TEMPERATURES CLIMB TO THE UPPER 20S AND MAYBE LOW 30S
WEDNESDAY WITH THESE DOWNSLOPING WINDS.

TEMPERATURES DO START TO WARM THURSDAY THOUGH AS GFS SHOWING
700MB TEMPERATURES CLIMBING TO +2C THURSDAY AFTERNOON. COULD BE
OUR FIRST HIGHS ABOVE FREEZING FOR OVER A WEEK. DID NOT GO QUITE
AS HIGH AS MOS GUIDANCE FOR HIGHS THURSDAY. MEX GUIDANCE SHOWING
UPPER 40S FOR HIGHS HERE AT CHEYENNE AND SIDNEY. STILL HAVE A
PRETTY GOOD SNOW PACK ACROSS THE CWFA...SO KNOCKED THESE
TEMPERATURES DOWN INTO THE LOW 40S.

SHORTWAVE MOVES THROUGH THE AREA ON FRIDAY. LOOKS LIKE FRIDAY
AFTERNOON COULD BE BREEZY AS 700MB WINDS CLIMB TO 45KTS. 700MB
TEMPERATURES DROP BACK DOWN TO AROUND -8C...BUT QUICKLY CLIMB BACK
TO NEAR FREEZING FOR SATURDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 1015 AM MST MON DEC 9 2013

VFR OVER ALL TERMINALS THROUGH EARLY TUESDAY WITH SOME VFR GIGS THIS
AFTERNOON AND EVENING MAINLY OVER THE NEB PANHANDLE AS HIGH CLOUDS
MOVE SSE.  GUSTY SFC WINDS MAY CAUSE LOWERED VISIBILITIES IN BLOWING
SNOW IN AREAS MAINLY FROM KRWL TO KCYS THROUGH THIS EVENING.

&&

.FIRE WEATHER...
ISSUED AT 217 AM MST MON DEC 9 2013

MINIMAL FIRE WEATHER CONCERNS ACROSS THE REGION. TEMPERATURES WILL
CONTINUE TO BE BELOW NORMAL THROUGH MIDWEEK. WINDS WILL REALLY
BEGIN TO INCREASE ACROSS SOUTHEAST WYOMING BY MONDAY AFTERNOON.
GUSTS TO 60 MPH WILL BE POSSIBLE IN THE WIND PRONE AREAS THROUGH
TUESDAY AFTERNOON DUE TO A STRONG PRESSURE GRADIENT. MINIMUM
AFTERNOON HUMIDITY VALUES WILL BE ABOVE 50 PERCENT THROUGH
WEDNESDAY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...BLIZZARD WARNING UNTIL 6 PM MST TUESDAY FOR WYZ110.

     HIGH WIND WARNING UNTIL 6 PM MST TUESDAY FOR WYZ106-116-117.

NE...NONE.
&&

$$

UPDATE...LIEBL
SHORT TERM...FINCH
LONG TERM...CLAYCOMB
AVIATION...RE
FIRE WEATHER...FINCH