FXUS63 KARX 212140
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
338 PM CST MON DEC 21 2009
.SHORT TERM...TONIGHT THROUGH THURSDAY
PLENTIFUL CONCERNS FOR THIS FORECAST. FIRST CONCERN WILL BE WITH
SNOW ACROSS HE SOUTHWEST TONIGHT THROUGH TUESDAY MORNING...THEN
MAJOR WINTER STORM AFFECTING THE AREA MAINLY WEDNESDAY AFTERNOON
THROUGH FRIDAY NIGHT.
MAIN FEATURE OF INTEREST THIS AFTERNOON WAS A VIGOROUS MID-LEVEL
SHORTWAVE TROUGH ROTATING SOUTHEAST ACROSS THE WESTERN DAKOTAS PER
THE WATER VAPOR IMAGERY. STRONG ISENTROPIC LIFT AHEAD OF THE WAVE
WAS SPREADING -SN ACROSS MUCH OF SD/SOUTHERN MN/INTO NORTHEAST IA.
OTHERWISE...ACROSS THE REMAINDER OF THE LOCAL AREA...STRATUS
OVERCAST PREVAILED WITH TEMPERATURES RIGHT AROUND NORMAL SEASONAL
VALUES FOR THIS FIRST DAY OF WINTER.
21.12Z NAM/GFS AS WELL AS THE 21.15Z SREF ALL IN GOOD AGREEMENT WITH
MID-LEVEL WAVE MOVING FROM THE NORTHERN PLAINS THROUGH IA/IL TONIGHT
THROUGH TUESDAY MORNING. BEYOND THIS...MODELS STARTING TO COME INTO
BETTER AGREEMENT REGARDING WINTER STORM AFFECTING THE AREA FROM
WEDNESDAY THROUGH FRIDAY NIGHT.
FOR TONIGHT...WILL BE WATCHING SNOW INCREASING ACROSS SOUTHWEST
SECTIONS OF THE FORECAST AREA AS MODERATE 925-700MB
FRONTOGENESIS/285K SURFACE ISENTROPIC LIFT ARRIVE IN ADVANCE OF THE
MID-LEVEL WAVE. NAM NORTHEAST-SOUTHWEST CROSS SECTION ACROSS THE
AREA SHOWS RATHER STRONG OMEGA// 10MICROBARS // THROUGH THE MINUS
15C ISOTHERM FOR POSSIBLE DEEP DENDRITIC GROWTH ACROSS PORTIONS OF
NORTHEAST IA AROUND 06Z TONIGHT. 21.09Z SREF BACKS THIS UP WITH A
30-50 PERCENT PROBABILITY OF 100MB MEAN DEPTH DENDRITE GROWTH ACROSS
THAT AREA. AS SUCH...WILL HOIST A WINTER WEATHER ADVISORY FOR SNOW
FOR AREAS ALONG AND SOUTH OF A LINE FROM DODGE
CENTER/ROCHESTER/CALEDONIA MN...THROUGH VIROQUA/RICHLAND CENTER FROM
7 PM TONIGHT THROUGH 9 AM TUESDAY WHERE 2 TO LOCALLY 5 INCHES IS
POSSIBLE. SNOW SHOULD TAPER TO FLURRIES BY LATE MORNING AS BEST
FORCING PUSHES SOUTHEAST OF THE AREA.
ATTENTION THEN TURNS TO DEVELOPING/MASSIVE WINTER STORM ON THE
LEESIDE OF THE ROCKIES/SOUTHERN PLAINS TUESDAY NIGHT INTO WEDNESDAY.
MOISTURE SURGING NORTHWARD AHEAD OF OF THE CYCLOGENESIS COULD BRING
A MIX OF LIGHT SNOW/POSSIBLY SOME FREEZING DRIZZLE INTO THE AREA
TUESDAY NIGHT THROUGH WEDNESDAY MORNING AS SOUNDINGS SHOW BORDERLINE
ICE AND SURGE OF LOWER LEVEL MOISTURE. BY WEDNESDAY
AFTERNOON...DEEPER COLUMN MOISTURE ARRIVES FOR INDUCTION OF
ICE...CHANGING ANY MIX TO ALL SNOW. WITH DRY EAST/NORTHEAST FLOW
THANKS TO HUDSONS BAY HIGH...WILL LIKELY BE A RATHER SHARP
DELINEATION WHERE THE PRECIPITATION WILL SET UP. RIGHT NOW...1-2
INCHES LOOK LIKELY ALREADY THROUGH WEDNESDAY AFTERNOON ACROSS
NORTHEAST IA INTO SOUTHEAST MN/FAR SOUTHWEST WI.
AS MENTIONED IN THE MODEL DISCUSSION ABOVE...SHORT/MEDIUM RANGE
MODELS STARTING TO COME INTO AGREEMENT THAT THE LOW WILL RAPIDLY
DEEPEN/OCCLUDE AS IT MOVES SLOWLY NORTHWARD FROM OK INTO CENTRAL MO
WEDNESDAY NIGHT THROUGH THURSDAY. THIS WILL SET UP STRONG
TROWAL/850MB MOISTURE TRANSPORT INTO THE AREA FOR A RAPID EXPANSION
OF PRECIPITATION INTO THE AREA. WILL LIKELY HAVE TO CONTEND WITH
HYDROMETEOR TYPES AS WARMER AIR GETS WRAPPED INTO THE AREA AHEAD OF
THE LOW. MODELS SOUNDING SHOW A WINTRY MIX SCENARIO INCLUDING ICING
POSSIBILITIES BASICALLY ALONG/SOUTH OF I-90 WEDNESDAY NIGHT THROUGH
THURSDAY. FURTHER NORTH/WEST...THE COLUMN SHOULD STAY COLD ENOUGH
FOR ALL SNOW.
WITH THE POTENTIAL FOR DANGEROUS CONDITIONS FOR THE UPCOMING
CHRISTMAS TRAVEL...DECIDED TO HOIST A WINTER STORM WATCH VALID
WEDNESDAY AFTERNOON THROUGH FRIDAY. SEE OUR WEATHER.GOV/ARX HOMEPAGE
FOR LATEST INFORMATION PERTAINING TO THIS WINTER STORM.
.LONG TERM...THURSDAY NIGHT THROUGH MONDAY
MAIN CONCERN DEALS WITH THE WINTER STORM TRAVERSING NORTHEAST ACROSS
THE AREA CHRISTMAS EVE THROUGH CHRISTMAS NIGHT. THE 21.00Z ECMWF AS
WELL AS THE 21.12Z GFS/GEM IN GOOD AGREEMENT IN TAKING THE
VERTICALLY STACKED LOW FROM NORTHERN MO FRIDAY MORNING...INTO UPPER
MICHIGAN BY SATURDAY MORNING. WITH THIS TRACK...IT APPEARS NORTHWEST
HALF OF THE FORECAST AREA MAY BE ON THE EASTERN PERIPHERY OF HEAVIEST
DEFORMATION SNOW. VERY HEAVY SNOW POTENTIAL ALONG WITH WINDY
CONDITIONS FOR SOME BLOWING/DRIFTING SNOW WILL LIKELY CONTINUE THE
NEED FOR HEADLINES. MEANWHILE...FURTHER SOUTH/EAST ACROSS THE
AREA...THERE IS STILL THE LIKELIHOOD OF A WINTRY MIX THROUGH
CHRISTMAS EVE BEFORE CHANGING TO ALL SNOW BY CHRISTMAS MORNING AS
THE COLUMN DYNAMICALLY COOLS. WILL CONTINUE TO MONITOR THIS
SITUATION CLOSELY. BEYOND THIS...COLDER NORTHWEST FLOW ALOFT
DOMINATES THE AREA THROUGH THE WEEKEND AND MONDAY. CONTINUED SMALL
SNOW CHANCE THROUGH SATURDAY WITH CYCLONIC FLOW STILL PREVAILING
ACROSS THE AREA. COLDER ARCTIC-TYPE AIR APPEARS IT WILL SLOWLY SEEP
INTO THE UPPER MIDWEST ON MONDAY WITH HIGHS EXPECTED TO ONLY TOP OFF
IN THE LOWER/MIDDLE TEENS.
&&
.AVIATION...TONIGHT AND TUESDAY
MVFR/IFR STRATUS CLOUDS WILL PERSIST ACROSS THE THE TAF SITES
TONIGHT/TUE...WITH LOW LEVEL MOISTURE UNDER AN INVERSION NORTH OF A
WARM FRONT. VSBYS MAINLY IN THE MVFR RANGE WILL PERSIST AS WELL.
HOLE IN THE LOWER CLOUDS...WITH SOME VFR CIGS...HAD OPENED UP OVER
PARTS OF SOUTH-CENTRAL/SOUTHEAST MN EARLY THIS AFTERNOON...BUT THIS
TO BE SHORT-LIVED WITH DEEPER MOISTURE/LIFT TO SPREAD INTO/ACROSS
THE AREA FROM LATE THIS AFTERNOON INTO TUE MORNING. A SHORTWAVE
COULD BE SEEN MOVING EAST ALONG SD/NEB BORDER IN IR/WV IMAGERY.
INCREASING 275-295K ISENTROPIC LIFT/MOISTURE TRANSPORT/CONVERGENCE
NORTH OF THE WARM FRONT AND LIFT/DIVERGENCE ALOFT AHEAD OF THE
SHORTWAVE ALREADY SPREADING SNOW/LOWERING VSBYS SOUTHEAST ACROSS SD.
THIS EXPECTED TO ARRIVE IN KRST AREA AROUND 23Z THEN KLSE AROUND
04Z...WITH VSBYS/CIGS QUICKLY BECOMING IFR AS THE STRONGER/DEEPER
LIFT AND SNOW BAND TRANSLATE ACROSS THE TAF SITES WITH THE SHORTWAVE
TONIGHT INTO TUE MORNING.
SNOW ADVISORY POSTED FOR KRST AREA TONIGHT INTO TUE MORNING...KLSE
AREA JUST NORTHEAST OF THE STRONGER/DEEPER MOISTURE/LIFT. 3-4 INCHES
OF SNOW EXPECTED AT KRST...2-3 INCHES AT KLSE. SNOW TO TAPER TO
FLURRIES BY LATE MORNING...BUT MVFR VSBYS/IFR CIGS EXPECTED TO
CONTINUE THRU TUE INTO TUE NIGHT. CONDITIONS DO NOT LOOK TO IMPROVE
MUCH THROUGH THE CHRISTMAS HOLIDAY AS A STRONGER SYSTEM LIFTS INTO
THE REGION...WITH A MIX OF WINTRY PRECIP TYPES OR MDT-HEAVY SNOW
LOOKING LIKELY STARTING WED AND CONTINUING INTO FRI NIGHT.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY UNTIL 9 AM CST TUESDAY FOR WIZ053-WIZ054-
WIZ055-WIZ061.
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR WIZ053-WIZ054-WIZ055-WIZ061.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY
AFTERNOON FOR WIZ017-WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-
WIZ042-WIZ043-WIZ044.
MN...WINTER WEATHER ADVISORY UNTIL 9 AM CST TUESDAY FOR MNZ086-MNZ087-
MNZ094-MNZ095-MNZ096.
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.
WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY
AFTERNOON FOR MNZ079.
IA...WINTER WEATHER ADVISORY UNTIL 9 AM CST TUESDAY FOR IAZ008-IAZ009-
IAZ010-IAZ011-IAZ018-IAZ019-IAZ029-IAZ030.
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR IAZ008-IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-
IAZ029-IAZ030.
&&
$$
SHORT/LONG TERM...DAS
AVIATION...RRS
