FXUS65 KCYS 081120
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
420 AM MST TUE DEC 8 2009
.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT...
BROAD UPPER TROUGH CONTINUES TO BE PRESENT ACROSS THE UNITED
STATES WITH VERY COLD AIR IN PLACE ACROSS THE WESTERN UNITED
STATES. UPPER LEVEL HEIGHTS CONTINUE TO BE AROUND 3 TO 4 STANDARD
DEVIATIONS AWAY FROM NORMAL FOR EARLY DECEMBER...AND HIGH TEMPERATURES
TODAY WILL AGAIN BE AROUND 35 DEGREES COOLER THAN NORMAL. TODAY
WILL BE THE COLDEST DAY OF THE PERIOD AS THE BULK OF THE JET
STREAM ENERGY IS NOW IN THE BASE OF THE TROUGH AND WILL START TO
ADVECT THIS STORM SYSTEM EASTWARD.
THE WINTER WEATHER ADVISORY ALREADY IN EFFECT ACROSS MUCH OF THE
AREA CONTINUES TO LOOK REASONABLE AS SNOWFALL WILL INCREASE
THROUGH THE TODAY PERIOD. THE REGIONAL MM5 FROM UCAR IS SHOWING A
CONSIDERABLE INCREASE IN PRECIPITATION ACROSS THE AREA BETWEEN 12Z
AND 15Z WITH THE GREATEST AMOUNTS EXPECTED ACROSS THE SOUTHEAST
WYOMING PORTION OF THE ADVISORY DURING THIS PERIOD. BUFKIT
SOUNDING DATA FROM THE MODELS SUPPORTS THE BEST ACCUMULATIONS AS THE
LIFT IS IN THE BEST TEMPERATURE RANGE FOR SNOWFLAKE GROWTH. AS ALL
MODELS INDICATE THE 700 MB LOW SHIFTS EAST OF COLORADO...THE BEST
PRECIPITATION AMOUNTS FROM THE MM5 SHIFT INTO THE NEBRASKA
PANHANDLE AFTER 15Z AND CONTINUING THROUGH AROUND 21Z. LIGHT
ACCUMULATIONS OF AROUND AN INCH CAN BE EXPECTED AFTER 21Z...BEFORE
LOW LEVEL FLOW BACKS TO A NORTHWEST DIRECTION AND SNOWFALL WILL
DIMINISH BY AROUND MIDNIGHT EXCEPT FOR ALL BUT OROGRAPHIC SNOW
SHOWERS IN THE HIGHER TERRAIN AREAS. BITTERLY COLD TEMPERATURES
CAN BE EXPECTED TONIGHT...WITH SOME AREAS IN THE NEBRASKA
PANHANDLE EXPERIENCING NEAR RECORD LOWS.
WEDNESDAY...NORTHWEST FLOW WILL CONTINUE AND LEAD TO CONTINUED
CHANCES FOR OROGRAPHIC SNOW SHOWERS INTO THE HIGHER TERRAIN AREAS
OF SOUTHEAST WYOMING. ELSEWHERE...CONDITIONS SHOULD BE DRY. WITH
THE SURFACE LOW CONTINUING TO EVOLVE ACROSS THE GREAT LAKES AND
IMPROVED MIXING...THE AREA WILL SEE A START TO A WARMING TREND
WITH WINDS INCREASING THE POTENTIAL FOR SIGNIFICANT BLOWING SNOW
AND REDUCED VISIBILITIES CREATING TRAVEL PROBLEMS. WITH THE
EXISTING ADVISORY...WILL ONLY INCREASE MENTION OF BLOWING SNOW
ACROSS THE AREA IN THE FORECAST. FUTURE SHIFTS WILL NEED TO
MONITOR THE NEED FOR A HIGHLIGHT FOR THE BLOWING SNOW WEDNESDAY.
EVEN THOUGH THE WARMING TREND WILL BEGIN WEDNESDAY...HIGH
TEMPERATURES ARE STILL EXPECTED TO BE AROUND 20 TO 25 DEGREES
BELOW NORMAL. VERY COLD CONDITIONS WILL PERSIST WEDNESDAY
NIGHT...BUT THE WINDY CONDITIONS ALONG AND WEST OF THE LARAMIE
RANGE ARE EXPECTED TO KEEP OVERNIGHT LOWS AROUND 10 DEGREES WARMER
THAN TONIGHT.
.LONG TERM...THURSDAY THROUGH MONDAY NIGHT...THE MEAN 500MB PATTERN
THROUGH THE PERIOD WILL BE DOMINATED BY A CONTINUED STRONG POLAR
VORTEX OVER CANADA. A VERY STRONG UPPER SHORTWAVE WILL DIG SOUTH
ALONG THE WEST SIDE OF THE POLAR VORTEX AND WILL BECOME ELONGATED
ACROSS SOUTHERN CANADA BY SATURDAY MORNING. AS THIS OCCURS...HEIGHTS
OVER WYOMING AND THE NEBRASKA PANHANDLE WILL INCREASE BACK TO NEAR
550 DAM. THIS WILL MEAN AN OVERALL INCREASE OF TEMPERATURES BACK TO
NEAR NORMAL FOR THIS TIME OF YEAR. FLOW ALOFT WILL BECOME MORE ZONAL
AS WELL WITH A NUMBER OF WEAK SHORTWAVES MOVING ACROSS THE SOUTHERN
US THROUGH THE PERIOD. SO FOR THE MOST PART...THE CWA WILL BE MOSTLY
DRY AND WINDY WITH MAINLY OROGRAPHIC SHOWERS OCCURRING IN FAST ZONAL
FLOW ALOFT. AT THE SURFACE...HIGH PRESSURE WILL PERSIST OVER THE
ROCKIES WITH LEE TROUGH DEEPENING ON THURSDAY AND FRIDAY. THUS CAN
EXPECT STRONG AND GUSTY WINDS TO AFFECT THE WIND PRONE REGIONS OF
SOUTHEAST WYOMING THROUGH EARLY SATURDAY. A COLD FRONT ASSOCIATED
WITH THE STRONG LOW OVER CANADA WILL SLIDE FROM EAST TO WEST ACROSS
THE NEBRASKA PANHANDLE AND THE PLAINS OF WYOMING SATURDAY EVENING
AND NIGHT. WINDS WILL BEGIN TO EASE AS THE FRONT MOVES IN AND
TEMPERATURES WILL COOL BEHIND THE FRONT. LOOKS AS IF COLD AIR WILL BE
SHALLOW ENOUGH TO REALLY ONLY AFFECT THE NEBRASKA PANHANDLE AND THE
LOWER ELEVATIONS OF THE WYOMING PLAINS. UPSLOPE FLOW WILL DEVELOP
ALONG THE FRONT AS IT STALLS ALONG THE LARAMIE RANGE WHILE A
SHORTWAVE ALOFT MOVES ACROSS THE ROCKIES. COULD SEE LIGHT SNOW
DEVELOP SATURDAY NIGHT INTO SUNDAY ACROSS MUCH OF THE CWA WITH THE
COMBINATION OF UPSLOPE FLOW AND SYNOPTIC LIFT FROM THE SHORTWAVE.
THE FRONT WILL QUICKLY RETREAT EAST WITH HELP FROM THE UPPER LEVEL
SHORTWAVE AND SFC HIGH PRESSURE WILL BUILD INTO THE ROCKIES ONCE
AGAIN SUNDAY AND SUNDAY NIGHT. EXPECT STRONG AND GUSTY WESTERLY
WINDS WITH MAINLY OROGRAPHIC SNOW SHOWERS OVER THE SIERRA MADRE AND
SNOW MOUNTAINS TO RETURN FOR MONDAY. MODELS HINT AT ANOTHER BACKDOOR
TYPE COLD FRONT TO MOVE FROM EAST TO WEST ACROSS AREAS EAST OF THE
LARAMIE RANGE ON MONDAY NIGHT.
&&
.AVIATION...
WIDESPREAD MVFR CONDITIONS EARLY THIS MORNING WILL BY SUNRISE BECOME
WIDESPREAD IFR AND AREAS OF LIFR THROUGH THE REST OF THE MORNING
DURING THE PERIOD OF HEAVIEST SNOWFALL. CONDITIONS WILL GRADUALLY
IMPROVE FROM WEST TO EAST THROUGH THE AFTERNOON AND INTO THIS
EVENING. SNOWFALL WILL PERSIST LONGEST INTO THE EVENING HOURS IN
THE NEBRASKA PANHANDLE. AREAS OF BLOWING SNOW WILL BEGIN TO
DEVELOP BY EARLY WEDNESDAY MORNING CREATING LIMITED VISIBILITY AT
THE TERMINALS WEST OF A LINE FROM NEAR DOUGLAS TO NEAR CHEYENNE.
&&
.FIRE WEATHER...
NO FIRE WEATHER CONCERNS TODAY AS ACCUMULATING SNOWFALL WILL
CONTINUE ALONG WITH BITTERLY COLD TEMPERATURES. TEMPERATURES ARE
EXPECTED TO MODERATE BACK TO NEAR NORMAL VALUES BY NEXT WEEKEND.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER WEATHER ADVISORY UNTIL 3 PM TUESDAY FOR WYZ106-WYZ107-
WYZ108-WYZ110-WYZ112-WYZ113-WYZ114-WYZ115-WYZ116-WYZ117-
WYZ118-WYZ119.
WINTER WEATHER ADVISORY UNTIL 11 AM TUESDAY FOR WYZ109-WYZ111.
NE...WINTER WEATHER ADVISORY UNTIL 3 PM TUESDAY FOR NEZ002-NEZ003-
NEZ019-NEZ020-NEZ021-NEZ054-NEZ055-NEZ095-NEZ096.
&&
$$
SHORT TERM/AVIATION...CARPENTER
LONG TERM...RJM
