High Wind in Wyoming, December 13, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
455 AM MST SAT DEC 13 2008

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...
BIG CHANGES ARE IN STORE STARTING LATE TODAY AS A MAJOR PATTERN
SHIFT TAKES PLACE IN THE UPPER FLOW REGIME OVER NORTH AMERICA.
STRONG SOUTHWESTERLY FLOW ALOFT TODAY WILL CONTINUE TONIGHT. A
STRONG SHORTWAVE WILL MOVE ACROSS THE AREA SUN THEN A LOW AMPLITUDE
INDUCED SHORTWAVE RIDGE WILL MOVE ACROSS THE REGION SUN NIGHT.
SURFACE LOW PRESSURE CURRENTLY MOVING OVER NORTHERN WY WILL MOVE
SOUTHEAST AND CONSOLIDATE OVER SOUTHEAST WY TODAY...SETTING THE
STAGE FOR A MAJOR ARCTIC INTRUSION AS WELL AS AN OVERRUNNING
SNOWFALL EVENT. THE SURFACE PRESSURE GRADIENT WILL INCREASE AND
WINDY AREAS WILL EXIST PRIOR TO FRONTAL PASSAGE. WILL EXTEND THE
CURRENT HIGH WIND WARNING IN TIME AS STRONG FLOW AT 700 MB SHOULD BE
ABLE TO CONTINUE MIXING DOWN TO THE SURFACE OVER AND ADJACENT TO THE
MOUNTAINS. WILL UPGRADE THE WINTER STORM WATCH TO A WINTER STORM
WARNING FOR THE MOUNTAINS EFFECTIVE FROM 14/00Z UNTIL 15/00Z. FOR
THE LOWER ELEVATIONS CURRENTLY UNDER A WINTER STORM WATCH...WILL
CHANGE THEIR HIGHLIGHT TO A WINTER WEATHER ADVISORY INSTEAD AS
SNOWFALL AMOUNTS IN LOWER ELEVATIONS ARE EXPECTED TO BE RELATIVELY
LIGHT. HIGH TEMPERATURES THIS AFTERNOON WILL BE ABOVE NORMAL AHEAD
OF THE FRONT. MOISTURE WILL SPREAD EASTWARD TODAY WITH LIGHT SNOW
BECOMING LIKELY IN THE HIGHEST MOUNTAINS. THE ARCTIC FRONT WILL ROAR
THROUGH THE FORECAST AREA THIS EVENING AND WILL BE FOLLOWED BY
GENERALLY LIGHT SNOW AS MOIST MID LEVEL SNOW RIDES OVER THE DENSE
SURFACE BASED COLD AIRMASS. STRONG POSTFRONTAL WINDS WILL PRODUCE
AREAS OF BLOWING SNOW TONIGHT THROUGH SUN MORNING AS THE SNOW SHOULD
BE VERY DRY AND EASILY BLOWN AROUND. SUNDAY WILL BE A NASTY COLD DAY
WITH MAXIMUM TEMPS GENERALLY IN THE SINGLE DIGITS TO MID TEENS WITH
PLENTY OF WIND AND SNOW. COLD AIR ADVECTION WILL CONTINUE IN EARNEST
SUN NIGHT ALTHOUGH SNOWFALL WILL GENERALLY DIMINISH.

.LONG TERM...MONDAY THROUGH FRIDAY...THE ARCTIC AIRMASS WILL
MODERATE VERY LITTLE ON MONDAY THUS TEMPERATURES WILL REMAIN IN THE
TEENS AND SINGLE DIGITS. A CHANCE OF SNOW REMAINS IN THE MOUNTAINS
THROUGHOUT THE DAY WITH CONTINUED OROGRAPHIC ASCENT...WHILE THE
PLAINS WILL REMAIN DRY AS BOUNDARY LAYER MOISTURE DECREASES WITH
SHORTWAVE RIDGE MOVING OVERHEAD. MODELS ARE IN GOOD AGREEMENT WITH
THE NEXT UPPER LEVEL TROUGH APPROACHING THE REGION MONDAY NIGHT.
THUS HAVE AN INCREASED CHANCE FOR LIGHT SNOW OVER THE AREA INTO
TUESDAY MORNING...ESPECIALLY IN THE MOUNTAINS AS THE LOW LEVEL
UPSLOPE INCREASES AHEAD OF TROUGH PASSAGE. DRYING WILL OCCUR IN THE
WAKE OF THE TROUGH LATE TUESDAY AND INTO WEDNESDAY AND TEMPERATURES
WILL SLOWLY BE ON THE RISE AS THICKNESS VALUES INCREASE OVER THE
REGION. MEX GUIDANCE SUGGESTS HOWEVER THAT THE MAJORITY OF LOCATIONS
WILL REMAIN BELOW FREEZING ON WEDNESDAY. 00Z GFS RUN IS WEAKER AND
ABOUT 12 HOURS FASTER THAN ECMWF IN LIFTING OUT REMAINS OF UPPER LOW
THAT IS OVER SOUTHERN CA WED AFTERNOON.  THIS FEATURE WILL BE
TRACKING ACROSS UT AND CO BEFORE DAMPENING OUT OVER NEBRASKA/KS.
LEANED TOWARD THE MORE CONSISTENT AND SLOWER ECMWF ON THE TIMING OF
THIS...SO HAVE KEPT POPS OVER WESTERN CWA THURSDAY AND ADDED A LOW
POP ACROSS EASTERN SECTIONS OF THE CWA AS WELL.  POPS SHOULD BE
CONFINED TO MAINLY MOUNTAIN AREAS THU NIGHT.  MODEL DIFFERENCES
CONTINUE FRIDAY ALTHOUGH BOTH GFS AND ECMWF SHOW INCREASING ZONAL
FLOW ALOFT OVER WY.  GFS HAS A MORE N/S ORIENTED UPPER TROUGH GOING
BY TO OUR NORTH WHILE THE ECMWF HAS THIS TROUGH ORIENTED WSW TO
ENE.  AGAIN...POPS FOR THE BULK OF THE DAY FRIDAY WILL BE LIMITED
NEAR THE MOUNTAINS EXCEPT THAT NEXT SHOT OF COLD AIR WILL BE GETTING
INTO EAST CENTRAL WY WHICH WILL BRING SOME LIGHT SNOW CLOSE TO THERE
LATE IN THE DAY.

&&

.AVIATION...VFR CONDITIONS EXPECTED AT TERMINALS TODAY. STRONG AND
GUSTY WINDS OVER THE MOUNTAINS TODAY WILL RESULT IN SOME MOUNTAIN
OBSCURATION DUE TO OROGRAPHIC SNOW.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL NOON SATURDAY FOR WYZ062-WYZ063-WYZ064-
     WYZ066-WYZ067.
     WINTER STORM WARNING FROM 5 PM SATURDAY TO 5 PM SUNDAY FOR
     WYZ063-WYZ064-WYZ066.
     WINTER WEATHER ADVISORY FROM 5 PM SATURDAY TO 5 PM SUNDAY FOR
     WYZ059-WYZ060-WYZ061-WYZ062-WYZ065-WYZ067-WYZ068-WYZ069-
     WYZ070.
NE...WINTER WEATHER ADVISORY FROM 5 PM SATURDAY TO 5 PM SUNDAY FOR
     NEZ001-NEZ002-NEZ003-NEZ019.

&&

SHORT TERM/AVIATION...JR
LONG TERM...RJM/JLH

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
214 PM MST FRI DEC 12 2008

NEZ001>003-019>021-054-055-WYZ059>070-132115-
SIOUX-DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-
CHEYENNE-CONVERSE-NIOBRARA-SOUTHWEST CARBON-NORTH CARBON-
SNOWY RANGE-NORTH LARAMIE RANGE-LARAMIE VALLEY-LARAMIE RANGE-
PLATTE-GOSHEN-CHEYENNE FOOTHILLS-PINE BLUFFS-
214 PM MST FRI DEC 12 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA
PANHANDLE AND SOUTHEAST WYOMING.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A HIGH WIND WARNING IS IN EFFECT FROM 11 PM MST TONIGHT THROUGH 8
AM MST SATURDAY MORNING INCLUDING THE FAVORED AREAS ALONG
INTERSTATE 80 NEAR ARLINGTON...ALONG INTERSTATE 25 NEAR BORDEAUX
AND ACROSS THE SUMMIT OF THE LARAMIE RANGE. STRONG WINDS WILL ALSO BE
PRESENT ACROSS THE HIGHER TERRAIN AREAS OF THE SIERRA MADRE
...SNOWY AND NORTHERN LARAMIE RANGES TONIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

AN ARCTIC COLD FRONT WILL PUSH ACROSS THE REGION SATURDAY NIGHT.
SNOW AND MUCH COLDER TEMPERATURES WILL SPREAD SOUTH BEHIND THE
FRONT...WITH THESE CONDITIONS LINGERING INTO SUNDAY AFTERNOON. NEW
SNOW ACCUMULATIONS OF 3 TO 6 INCHES WILL BE POSSIBLE BY SUNDAY
EVENING. ALSO...WITH VERY COLD TEMPERATURES MOVING INTO THE AREA WITH
BRISK NORTH WINDS OF 20 TO 30 MPH...WIND CHILL VALUES OF 15 TO 25
BELOW ZERO WILL BE POSSIBLE BY LATE SUNDAY AFTERNOON AND CONTINUING
THROUGH MONDAY. A WINTER STORM WATCH IS IN EFFECT FOR MUCH OF THE
AREA SATURDAY EVENING THROUGH SUNDAY AFTERNOON. ALTHOUGH THE
SOUTHERN PORTION OF THE NEBRASKA PANHANDLE IS NOT INCLUDED IN THE
WINTER STORM WATCH AT THIS TIME...LIGHT SNOW ACCUMULATIONS CAN
ALSO BE EXPECTED THERE ALONG WITH THE GUSTY NORTH WINDS AND VERY
COLD TEMPERATURES.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO REPORT ANY SNOWFALL ACCUMULATIONS OR
SIGNIFICANT REDUCTION OF VISIBILITY DUE TO BLOWING SNOW OVER THE
WEEKEND.

&&

THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND
CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT...
HTTP://WEATHER.GOV/CHEYENNE