371 
FXUS65 KCYS 211714
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1014 AM MST THU FEB 21 2013

.AVIATION...18Z TAFS

CONTINUING TO BE IMPACTED BY BANDS OF SNOW MOVING FROM SOUTHEAST
TO NORTHWEST FROM WESTERN NEBRASKA/NORTHWESTERN KANSAS INTO THE
PANHANDLE AND HERE TO CHEYENNE. AM EXPECTING THESE BANDS TO
CONTINUE THROUGH THE AFTERNOON BEFORE THE UPPER LOW FINALLY MOVES
EAST INTO CENTRAL NEBRASKA THIS EVENING. WHAT THAT MEANS FOR OUR
AIRPORTS ARE PERIODS OF MVFR OUTSIDE THE BANDS AND THEN AS THE
BANDS MOVE IN...IFR TO LIFR CONDITIONS IN HEAVIER SNOW. DO EXPECT
IMPROVING CONDITIONS AFTER 00Z FOR OUR SOUTHEAST WYOMING
AIRPORTS...PARTICULARLY KCYS WITH GRADUALLY IMPROVING CONDITIONS
IN THE PANHANDLE AROUND 03Z. FOR KRWL AND KLAR...WOULD EXPECT
CONDITIONS TO STEADILY IMPROVE THIS AFTERNOON.

CLAYCOMB


&&

.PREV DISCUSSION... /ISSUED 836 AM MST THU FEB 21 2013/ 

DISCUSSION...
LIGHT SNOW WILL CONTINUE OVER MUCH OF THE CWA THROUGH MIDDAY.  THE
STORM SYSTEM WILL CONTINUE TO MOVE EAST AND AS IT DOES...THE
WRAPAROUND SNOW SHOULD TAPER OFF FROM WEST TO EAST OVER THE CWA
THIS AFTERNOON.  LESS THAN AN INCH OF SNOW IN MOST AREAS...WITH
SLIGHTLY LARGER ADDITIONAL ACCUMULATIONS OVER PARTS OF THE 
PANHANDLE.  IN A RECENT UPDATE MADE MINOR ADJUSTMENTS TO THE FIRST
PERIOD OF THE FORECAST. 

PREV DISCUSSION... /ISSUED 344 AM MST THU FEB 21 2013/

SHORT TERM...TODAY THROUGH SATURDAY...
WATER VAPOR IMAGERY LOOP INDICATED THAT THE POTENT UPPER LOW
PRESSURE SYSTEM HAD MOVED FROM ARIZONA TO NEW MEXICO. UPPER
DIFFLUENT FLOW DOWNSTREAM RESULTED IN A LINE OF STRONG CONVECTION
FROM SOUTH CENTRAL KANSAS TO WEST CENTRAL TEXAS. TO THE NORTH AND
NORTHEAST OF THE BROAD SURFACE LOW OVER THE SOUTHERN ROCKIES...
WIDESPREAD SNOW WAS OCCURRING WITH MODERATE TO HEAVY AMOUNTS FROM
NORTH/CENTRAL KANSAS INTO NEBRASKA. LIGHT SNOW WAS OBSERVED ACROSS
MUCH OF THE CWA. ACCUMULATIONS OVERNIGHT RANGED FROM LESS THAN A
QUARTER INCH TO AS MUCH AS TWO TO THREE INCHES OVER THE SNOWY/SIERRA
MADRE RANGES. EASTERLY SURFACE WINDS OF 5 TO 15 MPH PREVAILED.
VISIBILITIES IN FALLING SNOW AND FOG WERE REDUCED TO LESS THAN A
MILE AT TIMES. TEMPERATURES AT 3 AM WERE IN THE TEENS.

THE 00Z DETERMINISTIC MODEL GUIDANCE ARE IN GOOD AGREEMENT LIFTING
THE UPPER LOW AND ITS BROAD SURFACE REFLECTION NORTHEAST FROM THE
SOUTHERN ROCKIES THROUGH THE CENTRAL PLAINS AND UPPER MIDWEST
DURING THE NEXT 24 TO 48 HOURS. PERIODS OF MOSTLY LIGHT SNOW WILL
CONTINUE THROUGH MIDDAY...WITH A GRADUAL DECREASE IN COVERAGE
BEGINNING THIS AFTERNOON ACROSS THE PLAINS AS THE STORM/S INFLUENCE
MOVES FURTHER AWAY FROM THE REGION. WRAP-AROUND MOISTURE LOOKS TO
LINGER THROUGH FRIDAY MORNING FOR MUCH OF THE PANHANDLE...WHILE 
OROGRAPHIC SNOW SHOWERS CONTINUE FOR THE MOUNTAINS UNDER CYCLONIC
NORTHWEST FLOW. A SHORTWAVE RIDGE ALOFT TRANSLATES EAST ACROSS
THE REGION ON SATURDAY...WITH SOUTHWEST FLOW ALOFT ADVECTING
PACIFIC MOISTURE INTO EASTERN AND SOUTHERN WYOMING. THE MODELS
ARE NOT AS ROBUST WITH THIS SYSTEM AS COMPARED TO THIS WEEK/S
STORM. THE ECMWF REMAINS THE DEEPER/SLOWER SOLUTION VERSUS THE
GFS.

WINDS WITH TODAY/S LOW PRESSURE SYSTEM WILL NOT BE AS GUSTY
WITH SPEEDS OF 15 TO 25 MPH. STILL THESE WINDS WILL CREATE
AREAS OF BLOWING AND DRIFTING SNOW FOR MAINLY SOUTHERN PORTIONS
OF THE PANHANDLE THROUGH MIDDAY. THE WINTER WEATHER ADVISORY
REMAINS IN EFFECT UNTIL 3 PM THIS AFTERNOON. ADDITIONAL SNOW
TODAY WILL RANGE FROM 2 TO 4 INCHES FOR THE SOUTHERN MOUNTAINS
TO 1 TO 3 INCHES FOR THE EASTERN PLAINS AND WESTERN PANHANDLE.
WEST WINDS RAMP UP BEGINNING FRIDAY AFTERNOON AND POTENTIALLY
BECOME STRONG AND GUSTY FOR MUCH OF SOUTHEAST WYOMING FRIDAY 
NIGHT AND SATURDAY. THE 00Z MESO-ETA 850 AND 700MB HEIGHT 
GRADIENTS INCREASE TO NEAR 70M AND 60M RESPECTIVELY BETWEEN 00Z
AND 12Z SATURDAY. LIKEWISE...THE NAM12 700MB WIND PROGS SHOW
50 TO 55 KT SHORTLY AFTER MIDNIGHT FRIDAY AND LAST UNTIL MIDDAY
SATURDAY. THE MAIN AREAS OF CONCERN FOR HIGH WINDS WOULD BE
THE SOUTHERN LARAMIE RANGE/FOOTHILLS AND NORTH SNOWY RANGE
FOOTHILLS...INCLUDING ARLINGTON...I-80 SUMMIT AND VEDAUWOO.

TEMPERATURES TODAY WILL BE COOLER THAN AVERAGE WITH 700MB VALUES
BETWEEN -12 AND -14C. AS A RESULT...HIGHS WILL BE IN THE TEENS AND
20S. SLIGHT TEMPERATURE MODERATION IS EXPECTED FRIDAY BUT STILL
BELOW NORMAL. EVEN MILDER TEMPERATURES ARE IN STORE FOR SATURDAY
ACROSS THE EASTERN PLAINS AND PANHANDLE WITH INCREASING DOWNSLOPE
FLOW. 700MB TEMPERATURES REBOUND TO -8C...YIELDING HIGHS IN THE
40S.

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY NIGHT...
MEDIUM RANGE MODELS IN POOR AGREEMENT WITH THE NEXT COLD FRONT
AND ASSOCIATED PACIFIC STORM SYSTEM PUSHING ACROSS THE NORTHERN
AND CENTRAL ROCKIES SATURDAY AND SATURDAY NIGHT. THE 00Z GFS IS 
A FULL 12 HOURS FASTER COMPARED TO THE ECMWF WITH THIS SYSTEM AND
SHOWS IT PUSHING ACROSS SOUTHEAST WYOMING AS AN OPEN WAVE. GFS
ENSEMBLES ARE IN POOR AGREEMENT...WITH HALF THE ENSEMBLE
PERTURBATIONS MORE IN LINE WITH THE ECMWF. THE 00Z ECMWF SHOWS THE
UPPER LEVEL TROUGH DIGGING SOUTHWARD INTO THE FOUR CORNERS REGION
AND LESS PROGRESSIVE. THE GEM AND NEW 06Z NAM SHOW THIS LESS
PROGRESSIVE SOLUTION AS WELL...SO TRENDED FORECAST TOWARDS THE
ECMWF. INCREASED POP BETWEEN 40 TO 80 PERCENT...HIGHEST IN THE
MOUNTAINS...FOR LIGHT TO MODERATE SNOW ACCUMULATIONS. THE GFS ON
THE OTHER HAND NOW SHOWS MAINLY DOWNSLOPE WINDS AND HARDLY ANY
PRECIPITATION AT ALL. REGARDLESS OF WHICH SOLUTION
VERIFIES...COLDER TEMPERATURES AND WINDY CONDITIONS ARE EXPECTED
AS A SURFACE LOW DEVELOPS ACROSS THE CENTRAL PLAINS ON SUNDAY.
BLOWING SNOW MAY BECOME AN ISSUE ON SUNDAY DEPENDING ON SNOW
ACCUMULATIONS.

MODELS SHOW ANOTHER WEAKER UPPER LEVEL TROUGH PUSHING ACROSS THE
NORTHERN ROCKIES AND CLIPPING THE FORECAST AREA ON TUESDAY. THIS
FEATURE WILL BE QUICK MOVING AND EAST OF THE FORECAST AREA BY
TUESDAY NIGHT. NOT MUCH PRECIPITATION WITH THIS SYSTEM...SO KEPT
POPS ON THE LOW SIDE. OTHERWISE...COOL TEMPERATURES WILL CONTINUE
WITH WINDY CONDITIONS THROUGH THE MIDDLE OF NEXT WEEK.

&&

FIRE WEATHER...
A VIGOROUS LOW PRESSURE SYSTEM OVER THE SOUTHERN ROCKIES WILL MOVE
NORTHEAST INTO THE UPPER MIDWEST DURING THE NEXT 24 TO 48 HOURS.
SNOW WILL BE WIDESPREAD OVER THE DISTRICTS TODAY...TAPERING OFF
TONIGHT AND FRIDAY. ACCUMULATIONS THROUGH FRIDAY WILL RANGE FROM
ONE TO THREE INCHES FOR THE PLAINS...TO SIX TO EIGHT INCHES OVER
THE SNOWY AND SIERRA MADRE RANGES. IT WILL BE MILDER AND WINDY FOR
MUCH OF SOUTHEAST WYOMING FRIDAY NIGHT AND SATURDAY. WEST WINDS
MAY GUST AS HIGH AS 55 MPH FOR WIND PRONE AREAS. MINIMUM HUMIDITIES
BOTH FRIDAY AND SATURDAY WILL BE 30 TO 40 PERCENT. ACCUMULATING
SNOW RETURNS TO THE DISTRICTS THIS WEEKEND AS ANOTHER LOW PRESSURE
SYSTEM MOVES THROUGH THE CENTRAL ROCKIES.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 3 PM THURSDAY FOR WYZ119.
NE...WINTER WEATHER ADVISORY UNTIL 3 PM THURSDAY FOR NEZ003-NEZ019-
     NEZ020-NEZ021-NEZ054-NEZ055.

&&

$$

SHORT TERM/FIRE WEATHER...JAMSKI
LONG TERM/AVIATION...TJT