FXUS65 KCYS 250405
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
905 PM MST THU DEC 24 2009
.UPDATE...FORECAST LOOKS ON TRACK FOR THE REST OF TONIGHT AND
CHRISTMAS DAY BASED ON TRENDS...SATELLITE IMAGERY...UPPER AIR PLOTS
AND THIS EVENINGS NAM RUN. MADE MINOR MODIFICATIONS TO
TEMPERATURES...DEWPOINTS...WINDS...CLOUD COVER...SNOW COVERAGE
FOR THE REST OF TONIGHT. RUBIN
&&
.PREV DISCUSSION... /ISSUED 252 PM MST THU DEC 24 2009/
SHORT TERM...TONIGHT THROUGH SATURDAY...
VERY COMPLICATED FORECAST PACKAGE WITH A WIDE VARIETY OF
HIGHLIGHTS ALREADY ISSUED DUE TO VARYING SNOW AMOUNTS ALREADY
RECEIVED...EXPECTED WINDS AND WIND CHILLS...AND ADDITIONAL
SNOWFALL EXPECTED THROUGH SATURDAY. STORM SYSTEM HAS CONTINUED TO
CHALLENGE THE MODELS WITH A CHANGING SCENARIO AS THE SOUTHERN
UPPER LOW ABSORBS THE UPPER LEVEL DISTURBANCE IN THE NORTHWEST
FLOW OVER THE FORECAST AREA. HOW THIS INTERACTION BETWEEN THE TWO
STORM SYSTEMS ACTUALLY OCCURS WILL PLAY A BIG ROLE IN THE NEXT 48
HOURS OF SENSIBLE WEATHER HERE IN SOUTHEAST WYOMING AND THE
NEBRASKA PANHANDLE.
IT NOW APPEARS LIKELY THAT THE LONG AWAITED VERY STRONG NORTHWEST
WINDS WILL FINALLY DEVELOP LATE THIS EVENING ACROSS THE AREA.
THESE WINDS WILL RESULT FROM THE DISTURBANCE IN THE NORTHWEST FLOW
ALOFT STRENGTHENING THE PLAINS SYSTEM AND ENHANCING THE STRENGTH
OF THE SURFACE LOW AS IT MOVES TO THE UPPER MISSISSIPPI VALLEY
TONIGHT. THE STRENGTHENING PRESSURE GRADIENT AT THE SURFACE AND
700 MB WILL CREATE WIDESPREAD VERY STRONG WINDS EARLY CHRISTMAS
MORNING THROUGH AT LEAST SATURDAY MORNING. AREAS ALREADY HAVING
RECEIVED ACCUMULATING SNOWFALL OF A FEW INCHES OR MORE OVER THE
PAST FEW DAYS WILL IMMEDIATELY SEE INCREASED BLOWING SNOW AND
HAZARDOUS CONDITIONS DEVELOPING. ONE OF THESE AREAS IS THE SUMMIT
ACROSS INTERSTATE 80 WHERE TRAVEL CONDITIONS ARE AGAIN EXPECTED TO
DETERIORATE WITH THE INCREASING WINDS LATE TONIGHT...AND THE
ADDITION OF NEW SNOW ACCUMULATIONS DURING THE DAY FRIDAY. AREAS OF
THE SOUTHERN NEBRASKA PANHANDLE WHERE LITTLE SNOW FELL OVER THE
PAST FEW DAYS WILL HAVE THE STRONG WINDS AS THE MAIN CONCERN
INITIALLY...AND HAVE KEPT THIS AREA UNDER A WIND ADVISORY.
TWO THINGS ARE THEN EXPECTED TO INCREASE PRECIPITATION ACROSS MOST
OF THE AREA AGAIN CHRISTMAS DAY. FIRST IS THE STRENGTHENING
STACKED STORM SYSTEM OVER THE UPPER MISSISSIPPI VALLEY WILL
WOBBLE...OR RETROGRADE...WEST A BIT. THIS MOVEMENT IS IMPORTANT
SINCE IT WILL WRAP AROUND MORE MOISTURE OVER THE FORECAST AREA. AS
THE UPPER DISTURBANCE MOVES SOUTHEAST ACROSS THE AREA
TONIGHT...THERE WILL DEVELOP AN AREA OF STRONG MID-LEVEL
ISENTROPIC LIFT WHICH WILL FEED OFF THE WRAP AROUND MOISTURE TO
ENHANCE SNOWFALL. GREATEST ACCUMULATIONS ARE MOST LIKELY ACROSS
THE PINE RIDGE AREA IN THE NORTHERN PANHANDLE EARLY CHRISTMAS DAY
THROUGH EARLY SATURDAY...AND WEST ACROSS CONVERSE AND NIOBRARA
COUNTIES. WITH THE CONSISTENT SLOWING OF THIS STORM SYSTEM FROM
RUN TO RUN IN THE MODELS...HAVE DECIDED TO JUST GO WITH A WINTER
STORM WATCH FOR THESE AREAS BEGINNING CHRISTMAS MORNING AND
CONTINUING THROUGH FRIDAY NIGHT. THE COMBINATION OF WINDS AND
ACCUMULATING SNOW WILL LIKELY CREATE VERY HAZARDOUS
CONDITIONS...BUT WANTED TO GIVE THE NEXT SHIFT A LOOK AT ANOTHER
MODEL RUN TO PINPOINT THE SOLUTION. STRONG NORTHWEST WINDS SHOULD
KEEP ONLY LIGHT ACCUMULATIONS AROUND CHEYENNE...BUT THE STRONG
WINDS AND BLOWING SNOW WILL CREATE TRAVEL HAZARDS DUE TO AREAS OF
LIMITED VISIBILITY...AND THE WINTER WEATHER ADVISORY SHOULD BE
ENOUGH TO RAISE AWARENESS FOR THE SNOW AND BLOWING SNOW. THE
SOUTHERN PANHANDLE AREAS SHOULD ALSO SEE ACCUMULATING SNOWS AND
DEVELOPING BLOWING SNOW...BUT THE WINDS SHOULD BE THE MAIN CONCERN
SINCE ACCUMULATIONS SHOULD BE JUST 1 TO 3 INCHES.
VERY COLD TEMPERATURES WILL COMBINE WITH THE INCREASING WINDS
OVERNIGHT IN NIOBRARA...GOSHEN...SIOUX...DAWES AND BOX BUTTE
COUNTIES TO CREATE WIND CHILLS AROUND 20 TO 25 BELOW ZERO
OVERNIGHT TONIGHT...AND HAVE ISSUED A WIND CHILL ADVISORY FOR
THOSE AREAS.
FINALLY...THE MOISTURE AND LIFT WRAPPING AROUND INTO THE HIGHER
TERRAIN OF SOUTHEAST WYOMING WILL ALSO CREATE ADVISORY SNOWFALL
AMOUNTS IN THE MOUNTAINS OF THE SNOWY AND SIERRA MADRE RANGES
CHRISTMAS DAY AND FRIDAY NIGHT. HAVE ALSO ISSUED A WINTER WEATHER
ADVISORY IN THOSE LOCATIONS THROUGH EARLY SATURDAY MORNING. AS IS
OFTEN THE CASE IN THE HIGHEST TERRAIN...STRONG WINDS WILL BE
PRESENT ACROSS EXPOSED AREAS SO BLOWING AND DRIFTING SNOW WILL
CREATE A HAZARD TO THOSE RECREATING IN THE HIGHER TERRAIN.
CONDITIONS WILL GENERALLY IMPROVE SATURDAY...ASSUMING THE STORM
SYSTEM DOES NOT SLOW DOWN MORE. MODELS ARE HINTING AT THE STORM
MOVING TO THE GREAT LAKES BY LATE IN THE DAY SATURDAY.
LONG TERM...SATURDAY NIGHT THROUGH THURSDAY...
EFFECTS FROM SFC/UPPER LOWS OVER THE MIDWEST SHOULD FINALLY MOVE OUT
OF THE CWA SATURDAY NIGHT AS SYSTEM BEGINS TO ACCELERATE EASTWARD.
STILL A LITTLE WRAP AROUND SNOW SHOWERS POSSIBLE OVER THE FAR
NORTHEAST PART OF THE CWA SAT NIGHT THUS HAVE SHADED IN SOME LOW
POPS THERE. MILDER AND MAINLY DRY WEATHER SHOULD THEN RESIDE OVER
THE CWA FOR THE EARLY PART OF NEXT WEEK AS AREA WILL BE IN BETWEEN
MAIN FLOW STREAMS WITH SEASONAL TEMPERATURES. TWO STREAMS TRY TO
PHASE BY MIDWEEK WITH A DISTURBANCE DROPPING ACROSS THE REGION BY
THURSDAY POSSIBLY BRINGING A MINOR SHOT OF COOLER AIR AND SOME LIGHT
PCPN TO CLOSE OUT THE YEAR.
AVIATION...
VFR CONDITIONS AREA WIDE THROUGH THIS EVENING THEN CIGS
LOWERING TO MVFR/LCL IFR CONDITIONS OVER MAINLY THE PLAINS LATER
TONIGHT AND CHRISTMAS DAY AS UPPER LOW OVER THE NRN HIGH PLAINS
MOVES SE AND SOME MOISTURE WRAPS AROUND. STRONG SFC WINDS WILL ALSO
DEVELOP EAST OF THE MTNS LATER TONIGHT AND CONTINUE CHRISTMAS DAY.
FIRE WEATHER...
NO SIGNIFICANT FIRE CONCERNS AS WINTER STORM CONTINUES TO IMPACT
THE AREA EVEN THOUGH IT IS CENTERED OVER THE CENTRAL UNITED
STATES. VERY STRONG NORTHWEST WINDS WILL DEVELOP AND CREATE
HAZARDOUS TRAVEL CONDITIONS THROUGH CHRISTMAS DAY AND INTO
SATURDAY. ADDITIONAL SNOWFALL ACCUMULATIONS ARE ALSO
EXPECTED...AND VARIOUS WINTER WEATHER HIGHLIGHTS HAVE BEEN ISSUED
THROUGH EARLY SATURDAY.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WIND CHILL ADVISORY UNTIL 5 AM FRIDAY FOR WYZ102-WYZ108.
WINTER STORM WATCH FROM 5 AM FRIDAY TO 5 AM SATURDAY FOR WYZ102-
WYZ108.
WINTER WEATHER ADVISORY UNTIL 5 AM SATURDAY FOR WYZ101-WYZ103-
WYZ106-WYZ107-WYZ116-WYZ117-WYZ118-WYZ119.
WINTER WEATHER ADVISORY FROM 5 AM FRIDAY TO 5 AM SATURDAY FOR
WYZ112-WYZ114.
NE...WIND CHILL ADVISORY UNTIL 5 AM FRIDAY FOR NEZ002-NEZ003-NEZ095-
NEZ096.
WINTER STORM WATCH FROM 5 AM FRIDAY TO 5 AM SATURDAY FOR NEZ002-
NEZ003-NEZ095-NEZ096.
WIND ADVISORY FROM 5 AM FRIDAY TO 11 AM SATURDAY FOR NEZ019-
NEZ020-NEZ021-NEZ054-NEZ055.
&&
$$
SHORT TERM/AVIATION...CARPENTER
LONG TERM...RE
