000
FXUS63 KARX 032145
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
345 PM CST WED DEC 3 2008
.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT
THE MAIN CONCERN FOR THIS TIME PERIOD CONTINUES TO BE HOW MUCH SNOW
WE MAY GET ON FRIDAY NIGHT.
AT 3 PM...THE POLAR COLD FRONT...WHICH BROUGHT THE SNOW TO THE
AREA THIS MORNING...EXTENDED FROM SAULT STE MARIE MICHIGAN
/EASTERN UPPER MICHIGAN/ TO SOUTHEAST TEXAS. THE SUBSIDENCE IN THE
WAKE OF THIS SYSTEM HAS CAUSED SKIES TO CLEAR THIS AFTERNOON.
HOWEVER LOOKING UPSTREAM THERE ARE ADDITIONAL WEAK EMBEDDED SHORT
WAVE TROUGHS UPSTREAM. ONE OF THESE SYSTEMS WILL LIKELY MOVE TO OUR
SOUTH AND WEST TONIGHT. THIS SYSTEM WILL LIKELY BRING A GRADUAL
INCREASE TO THE CLOUDS TONIGHT. IN ADDITION...IT MAY PRODUCE SOME
SCATTERED FLURRIES FROM TIME TO TIME.
ANOTHER WEAK UPPER LEVEL SYSTEM WILL MOVE SOUTHEAST THROUGH THE
REGION ON THURSDAY AFTERNOON AND EVENING. WITH LIMITED MOISTURE
AND LIFT...IT APPEARS THAT WE WILL ONLY SEE SOME WIDELY SCATTERED
SNOW SHOWERS OR FLURRIES FROM THIS SYSTEM.
WITH VERY GOOD RUN TO RUN MODEL CONSISTENCY THAT A 500 MB SHORT
WAVE TROUGH WILL MOVE SOUTHEAST INTO THE UPPER MISSISSIPPI RIVER
VALLEY ON FRIDAY NIGHT...I RAISED THE SNOW CHANCES UP INTO THE
LIKELY RANGE. WITH THIS SAID...THERE IS STILL SOME TIMING
ISSUES...SO I JUST STAYED WITH THE 12 HOUR POP. LOOKING AT THE
COBB OUTPUT FOR THE LAST SEVERAL DAYS...IT CONTINUES TO LOOK LIKE
THE AREA WILL SEE ANYWHERE FROM 1 TO 3 INCHES OF SNOW. IN
ADDITION...THERE SHOULD BE SOME MODERATE TO STRONG WARM AIR
ADVECTION AHEAD OF THIS SYSTEM...THEREFORE TEMPERATURES SHOULD
CONTINUE TO SLOWLY RISE INTO THE NIGHT. DUE TO THIS...I INTRODUCED
A NON DIURNAL TEMPERATURE CURVE FOR THIS TIME PERIOD.
.LONG TERM...SATURDAY THROUGH WEDNESDAY
SOME LIGHT SNOW WILL CONTINUE IN THE WAKE OF THE 500 MB SHORT WAVE
TROUGH ON SATURDAY MORNING...AND THEN THE COMBINATION OF CYCLONIC
FLOW ALOFT AND INSTABILITY WILL LIKELY CONTINUE A SLIGHT CHANCE OF
SNOW SHOWERS THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL OCCUR
DURING THE MORNING. AS STRONG COLD AIR ADVECTION MOVES INTO THE
AREA DURING THE LATE MORNING AND AFTERNOON...THE TEMPERATURES WILL
EITHER BE STEADY OR SLOWLY FALL. AS A RESULT...I WENT WITH A NON
DIURNAL TEMPERATURE CURVE FOR THE DAY.
LOOKING BEYOND THIS PERIOD...THE UNCERTAINTY PROGRESSIVELY
INCREASES WITH EACH SUCCESSIVE DAY. MUCH OF THIS HAS TO DEAL WITH
A RAPIDLY WEAKENING MADDEN JULIAN OSCILLATION /MJO/ FORCING...STRONG
FORCING DEVELOPING ACROSS THE WESTERN INDIAN OCEAN...AND YET
ADDITIONAL STRONG FORCING OVER THE ATLANTIC NEAR 40 DEGREES WEST
LONGITUDE. CPC/S 30-DAY 150 MB WIND ANALYSIS SHOW THAT THERE IS A
STRONG 150 MB LOW EMBEDDED /NEAR THE INTERNATIONAL DATELINE/ IN
THE WAVE TRAIN ASSOCIATED WITH THE MJO. AS THE OSCILLATION
CONTINUE TO APPROACH 160 DEGREES EAST LONGITUDE...THIS LOW WILL
LIKELY MOVE INTO THE EAST PACIFIC. THIS MAY RESULT IN A QUICK
TRANSITION TO A SPLIT 500 MB FLOW PATTERN ACROSS NORTH AMERICA BY
EARLY NEXT WEEK. IF THIS DOES INDEED OCCUR...IT WOULD EVOLVE FROM THE
CLOSED LOW OFF THE WEST COAST MOVING EAST INTO THE SOUTHWEST UNITED
STATES AND THEN OPENING UP INTO A LONG WAVE PATTERN. AS THIS
OCCURS...THE SOUTHERN STREAM SHOULD MOVE NORTHWARD ACROSS THE
CENTRAL AND EASTERN UNITED STATES. THE MAIN QUESTION IN THIS
SCENARIO IS HOW FAR NORTH WOULD THIS STREAM GETS. AT THE THE SAME
TIME...A NORTHERN STREAM WOULD BE LOCATED FROM BRITISH COLUMBIA
SOUTHEAST TO THE GREAT LAKES. THERE ARE SEVERAL GFS AND GEM
ENSEMBLE MEMBERS WHICH DO SHOW THIS SCENARIO. IN EACH OF
THEM...THEY SHOW THAT THE TWO STREAMS PHASE ACROSS THE EASTERN
GREAT LAKES AND OHIO VALLEY. AS THE CONVECTION ASSOCIATED WITH THE
MJO WEAKENS...STRONG CONVECTION WILL LIKELY DEVELOP ACROSS THE
ABNORMALLY WARM WESTERN INDIAN OCEAN. THE COMBINATION OF THIS
FORCING AND THE ATLANTIC FORCING WOULD RESULT IN A VERY RAPID
RETURN TO A FAIRLY AMPLIFIED 500 MB TROUGH ACROSS THE EASTERN HALF
OF THE UNITED STATES. THIS COULD RESULT IN SOME VERY COLD AIR
PLUNGING SOUTHWARD INTO THE REGION. 3 OF THE 11 MREF MEMBERS IN
THE PLUME DIAGRAM SHOW 2 METER TEMPERATURES IN THE -15C TO -20C
RANGE BY MID WEEK.
MEANWHILE THE OPERATIONAL GFS AND ECMWF SHOW THAT THERE WILL BE
JUST ONE 500 MB LONG WAVE TROUGH ACROSS THE EASTERN HALF OF THE
COUNTRY. THIS WOULD BE RATHER SIMILAR TO THE 500 MB PATTERN THAT
CURRENTLY EXISTS ACROSS THE CONTINENT. THERE ARE SEVERAL ENSEMBLE
MEMBERS WHICH SUPPORT THESE SOLUTIONS. WITH TWO DISTINCT MODELS
CAMPS...IT IS NOT TOO SURPRISING TO SEE THE VARYING RUN TO RUN
DISCONTINUITIES.
WHILE THERE IS UNCERTAINTY...MOST OF THE ENSEMBLE MEMBERS DO
SUPPORT THAT A 500 MB SHORT WAVE TROUGH WILL BRING A GOOD CHANCE
OF SNOW TO THE AREA FROM SUNDAY NIGHT INTO MONDAY NIGHT. DUE TO
THIS...I DID RAISE THE SNOW CHANCES A BIT MORE.
&&
.AVIATION...THIS AFTERNOON THROUGH THURSDAY MORNING
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT BOTH TAF SITES THROUGH
MUCH OF THE PERIOD...AS A RIDGE OF HIGH PRESSURE BUILDS IN.
OCCASIONAL MVFR CEILINGS ARE POSSIBLE THIS AFTERNOON AND AGAIN
TONIGHT INTO THURSDAY MORNING.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&
$$
SHORT/LONG TERM...BOYNE
AVIATION...THOMPSON
