476
FXUS63 KARX 262117
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
317 PM CST THU NOV 26 2009
SHORT TERM
TONIGHT THROUGH SUNDAY NIGHT
MAIN FORECAST CONCERNS THROUGH THIS PERIOD DEAL WITH CLOUDS
TONIGHT...TEMPERATURES...AS WELL AS PRECIPITATION CHANCES FOR SUNDAY/SUNDAY
NIGHT.
AT 20Z...VISIBLE SATELLITE SHOWED VAST AMOUNT OF CLOUD COVER IN
THE WAKE OF A LOW PRESSURE SYSTEM OVER THE GREAT LAKES COVERING
MUCH OF THE REGION. TAMDAR SOUNDING FROM KMSP AT 1730Z SHOWED A
STRONG INVERSION ABOVE 900MB KEEPING THE CLOUDS TRAPPED UNDER...THEREFORE
LITTLE SUBSIDENCE ABLE TO HELP SCOUR OUT CLOUD COVER. HAVE TO GO
WEST TO THE SURFACE RIDGE AXIS OVER THE WESTERN PARTS OF
MINNESOTA/IOWA TO SEE CLEARING. IN THE UPPER LEVELS...LARGE RIDGE
SEEN OVER THE WESTERN HALF OF THE CONUS...WITH TROUGH TO THE EAST
OF THE FORECAST AREA INTO THE SOUTHEASTERN US. THIS PUTS THE
FORECAST AREA IN NORTHWEST FLOW...WITH COOLER AND NEAR NORMAL
AFTERNOON TEMPERATURES OBSERVED.
CLOUD COVER TODAY HAS NOT BEEN HANDLED PARTICULARLY WELL TODAY...AS
CLEARING TREND HAS BASICALLY BEEN NON-EXISTENT. SURFACE RIDGE AXIS
SHOULD MOVE EAST INTO THE AREA TONIGHT THOUGH...THEREFORE STILL
EXPECTING CLOUDS TO DECREASE OVERNIGHT. AT THE SAME TIME...CIRRUS
SPILLING OVER THE UPPER LEVEL RIDGE WILL MOVE IN. LOOKING UPSTREAM
THOUGH...THESE CIRRUS ARE PRETTY SCATTERED IN NATURE...THUS HAVE
DECREASED SKY COVER FOR TONIGHT. ALTHOUGH THE CLEARING SKIES AND
LIGHT WINDS WOULD HAVE AN ARGUMENT FOR SOME RADIATIONAL COOLING
AND POSSIBLY LOWER TEMPERATURES...THERE WILL BE WARM AIR ADVECTION
INTO THE AREA WITH THE THE RIDGE BUILDING IN AND FLOW IN THE MID
AND UPPER LEVELS TURNING MORE WESTERLY TO OFFSET THAT COOLING SO
THOSE REASONINGS...ALONG WITH SLOWER CLEARING TREND...WILL STAY WITH LOWS
ABOVE NORMAL TONIGHT.
WARMER/ABOVE NORMAL AIR WILL BE PLACED ACROSS THE AREA INTO THE
WEEKEND WITH 925MB TEMPERATURES INCREASING TO AROUND 5C BY SATURDAY
AFTERNOON. A WEAK AND DRY COLD FRONT WILL PASS ACROSS THE FORECAST
AREA ON SATURDAY WITH MID-LEVEL SHORTWAVE TROUGH FOLLOWING AND
MOVING THROUGH ON SUNDAY/SUNDAY NIGHT. MOISTURE IS LACKING WITH
THE PASSAGES OF THESE FEATURES...AND UPWARD MOTION/LIFT IS VERY
WEAK SO DROPPED THE ACCUMULATING PRECIPITATION CHANCES AND JUST
KEPT FLURRIES IN FOR SUNDAY. COOLER AIR WILL MOVE IN BEHIND THESE
FEATURES...BRINGING TEMPERATURES BACK TO NEAR NORMAL FOR SUNDAY.
LONG TERM
MONDAY THROUGH THURSDAY
THE PERIOD BEGINS WITH AN UPPER LEVEL SHORTWAVE TROUGH MOVING OUT
OF THE UPPER MISSISSIPPI RIVER VALLEY REGION WITH A STRONG UPPER
LOW OVER MEXICO. RIDGING THEN BUILDS IN FOR MONDAY NIGHT AND
TUESDAY. 26.00Z MEDIUM RANGE MODELS IN DECENT AGREEMENT THROUGH
THIS TIME...KEEPING A DRY FORECAST WITH WARMING TEMPERATURES FOR
TUESDAY AND WEDNESDAY. THE UPPER LOW WILL PROGRESS ACROSS THE SOUTHERN
STATES WHILE TROUGHING BEGINS TO DIG DOWN INTO THE CONUS. ALTHOUGH
THE SOLUTIONS ARE ALL INDICATING THIS TROUGHING...THE ECMWF/GEM
PLACES IT FURTHER WEST ACROSS THE ROCKIES WHILE THE GFS/GFS
ENSEMBLES DIG IT SOUTH INTO THE PLAINS. SENSIBLE WEATHER
DIFFERENCES BETWEEN THE LOCATION OF THESE UPPER TROUGHS WOULD BE A
CHANCE FOR SOME PRECIPITATION TUESDAY NIGHT/WEDNESDAY WITH THE
FURTHER EAST SOLUTION...WHILE THE WESTERN SOLUTIONS WOULD KEEP THE
AREA DRY. GFS SHOWING BROAD QG FORCING AHEAD OF SHORTWAVE ENERGY
MOVING INTO THE REGION THROUGH THIS TIME WITH ISENTROPIC LIFT IN
THE 285-300K LAYER. THIS LIFT ISN/T REAL FOCUSED EITHER...BEING
PRETTY BROAD. PW/S LESS THAN HALF INCH BUT AMPLE ENOUGH FOR
PRECIPITATION PRODUCTION. ALSO...GFS ENSEMBLE PLUMES INDICATING UP TO TWO
TENTHS OF AN INCH OF PRECIPITATION. SIGNAL IS WEAK AT THIS
POINT...WITH MAJORITY OF THE PRECIPITATION LOOKING TO BE NORTH OF
THE AREA. AND AS IT IS ONLY BEING SEEN THROUGH THE GFS
SOLUTIONS...WILL KEEP WITH CONTINUITY AND THE DRY FORECAST FOR
NOW.
00Z MODELS ARE IN FAIR AGREEMENT...THAT WITH THE TROUGHING IN
PLACE...THE UPPER LOW ACROSS THE SOUTH WILL GET PULLED BACK INTO
THE MAIN FLOW...AND PUSH NORTHWARD TOWARDS THE GREAT LAKES. THIS
WILL BRING PRECIPITATION CHANCES BACK TO THE FORECAST AREA FOR THE
END OF THE PERIOD...MAINLY ACROSS THE SOUTH AND EASTERN PARTS OF
THE FORECAST AREA. HOWEVER...IF THERE IS A CHANGE AND AS THIS LOW
STAYS FURTHER EAST...OUTCOME WILL BE QUITE DIFFERENT.
ADDITIONALLY...ANOTHER SHORTWAVE TROUGH LOOKS TO MOVE DOWN INTO
THE NORTHERN PART OF THE COUNTRY...BRINGING MORE COLD AIR BACK
INTO THE REGION FOR THURSDAY. THUS WILL GO WITH A COOLING TREND GOING
TOWARDS THE BACK PART OF THE WEEK.
AVIATION
TONIGHT AND FRIDAY
MFVR CLOUD DECK REMAINS PROBLEMATIC THIS AFTERNOON INTO EARLY THIS
EVENING...WITH SLOWER DECREASE/CLEARING THAN EARLIER EXPECTED.
CLEARING/DECREASE IS PROGRESSING SOUTHEAST ACROSS MN...AND WILL
SPREAD ACROSS THE TAF SITES MAINLY IN THE 26.20Z TO 27.01Z TIME
FRAME. ONCE THE MVFR STRATUS DECK IS GONE...CLOUDS AFTER ABOUT 01Z
TONIGHT AND FRI APPEAR LIMITED TO SCT-BKN CIRRUS...WITH GOOD VFR
CONDITIONS MUCH OF TONIGHT/FRI AS HIGH PRESSURE AND A DRIER AIRMASS
SLIDE ACROSS THE REGION. WINDS DO SWITCH FROM NORTHWEST TO SOUTH/
SOUTHEAST OVERNIGHT AS THE SFC RIDGE AXIS MOVES EAST AND LOW
PRESSURE DEVELOPS IN THE NORTHERN PLAINS.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
SHORT/LONG TERM...BROOKS
AVIATION...RRS
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