FXUS63 KARX 221646
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1046 AM CST TUE DEC 22 2009
.UPDATE...FORCING ASSOCIATED WITH DEPARTING UPPER LEVEL WAVE WAS
ON THE WANE. RADAR IMAGERY AND SURFACE OBSERVATIONS CORROBORATED
THIS AS COVERAGE AND INTENSITY OF SNOW WAS ADVANCING EASTWARD.
REST OF THIS AFTERNOON SHOULD BE A MINIMUM FOR PRECIPITATION...WITH
SMALL CHANCE OF FREEZING DRIZZLE. THIS WAS ALREADY HANDLED WELL IN
CURRENT DATA BASE AND CERTAINLY SEEMS REASONABLE.
ZONE UPDATE FORTHCOMING BY ABOUT 17Z...WITH LATEST SHORT TERM
PRECIPITATION TRENDS INCORPORATED.
THOMPSON
&&
.PREV DISCUSSION... /ISSUED 545 AM CST TUE DEC 22 2009/
UPDATE...THIS MORNING
WITH THE RADAR RETURNS AND SURFACE OBSERVATIONS INDICATING
IMPROVED VISIBILITIES ACROSS SOUTHEAST MINNESOTA AND NORTHEAST
IOWA...WE WILL BE DROPPING THE WINTER WEATHER ADVISORY AROUND
6 AM.
PREV DISCUSSION... /ISSUED 348 AM CST TUE DEC 22 2009/
SHORT TERM...TODAY THROUGH THURSDAY
WINTER STORM IMPACTS CONTINUE TO BE THE MAIN CONCERN FOR MUCH OF
THIS FORECAST PERIOD.
AT 3 AM...A SHORT WAVE TROUGH WAS MOVING EAST ACROSS SOUTHEAST
MINNESOTA...SOUTHERN WISCONSIN...EASTERN IOWA...AND NORTHERN
ILLINOIS. THIS SYSTEM WAS PRODUCING ACCUMULATING SNOW GENERALLY
ALONG AND SOUTH OF INTERSTATE 94. THE 22.00Z MODELS CONTINUE TO
SHOW THAT THIS SYSTEM WILL CONTINUE TO EXIT THE REGION THIS
MORNING. CURRENT PLANS ARE TO LET THE WINTER WEATHER ADVISORY
CONTINUE THROUGH 9 AM THIS MORNING. HOWEVER WITH SAID...IT LOOKS
LIKE THE SNOW MAY BE ALREADY COMING TO END ACROSS THE WESTERN
PORTIONS OF SOUTHEAST MINNESOTA...AND WE WILL RE-EVALUATE TOWARD
6 AM.
ONCE THIS SNOW ENDS THIS MORNING...IT CONTINUES TO LOOK LIKE SOME
WEAK FRONTOGENESIS WILL CONTINUE THROUGH WEDNESDAY MORNING ALONG AND
SOUTH OF A LAKE CITY MINNESOTA TO THE WISCONSIN DELLS LINE. BUFKIT
SOUNDINGS AND THE RELATIVE HUMIDITY VALUES ALONG THE -10C LEVEL AND
COLDER SHOW THAT THERE WILL BE NO ICE CRYSTALS AVAILABLE TO SEED
THE LOW LEVEL MOISTURE. AS A RESULT...IT LOOKS LIKE THE
PRECIPITATION WILL TRANSITION TO FREEZING DRIZZLE EITHER LATE THIS
MORNING OR EARLY AFTERNOON...AND THEN REMAIN IN THE FORM OF
FREEZING DRIZZLE INTO WEDNESDAY MORNING.
FROM WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT..IT LOOKS LIKE A WEAK
SHORT WAVE TROUGH WILL BE MOVING NORTH THROUGH THE REGION. AS THIS
OCCURS...THE MOISTURE TRANSPORT WILL ENHANCE THE MOISTURE ALREADY
LOCATED ACROSS THE AREA...AND IT WILL ALSO ENHANCE THE LIFT ACROSS
THE REGION. THE BUFKIT/MODEL SOUNDINGS SUGGEST THAT THERE WILL BE
AN INCREASE IN THE MOISTURE IN THE TEMPERATURES BELOW -10C. THIS
WILL LIKELY ALLOW THE PRECIPITATION TO TRANSITION MORE OVER TO SNOW.
IT THEN LOOKS LIKE THIS LAYER WILL ONCE AGAIN TRANSITION BACK OVER
TO FREEZING RAIN OR FREEZING DRIZZLE AS WE ONCE AGAIN LOSE THE ICE
CRYSTAL IN THE WAKE OF THIS TROUGH.
ON THURSDAY...IT LOOKS LIKE YET ANOTHER SHORT WAVE TROUGH MAY BE
MOVING NORTHWARD INTO THE REGION. THIS ONCE AGAIN ENHANCE THE
MOISTURE ABOVE -10C...AND THE PRECIPITATION WILL ONCE AGAIN
TRANSITION BACK TO SNOW.
WITH THE TIMING OF THESE SHORT WAVES BEING SO DIFFICULT TO TIME...
THE WEATHER GRIDS JUST HAVE SNOW AND FREEZING RAIN IN THEM FROM
WEDNESDAY AFTERNOON THROUGH THURSDAY. AS IMPLIED EARLIER...THE
PRECIPITATION TYPE ASSOCIATED WITH THIS SYSTEM WILL BE HIGHLY
DEPENDENT UPON WHETHER THERE WILL ANY ICE CRYSTAL AROUND TO SEED
THE LOW LEVEL MOISTURE OR NOT. WHEN THERE ARE PERIODS OF ENHANCED
LIFT /ASSOCIATED WITH THESE WAVE/...THE PRECIPITATION WILL LIKELY
BE IN THE FORM OF SNOW. MEANWHILE IN THE WAKE OF THESE
SYSTEMS...THE MID AND UPPER LEVEL MOISTURE WILL DRY AND THE
PRECIPITATION WILL TREND TOWARD FREEZING RAIN.
IT IS THE TRANSITION OF THE PRECIPITATION FROM BACK AND FORTH
BETWEEN SNOW AND FREEZING RAIN WHICH WILL MAKE SNOW AND ICING
FORECASTS REALLY COMPLICATED WITH THIS WINTER STORM. WITH THE
COBB DATA KEEPING THE PRECIPITATION MAINLY AS SNOW...IT REALLY IS
NO HELP OTHER THAN TRYING TO ASSIGN SNOW TO LIQUID RATIOS WHEN IT
DOES LOOK LIKE THE PRECIPITATION WILL BE MAINLY SNOW. HOWEVER
WITH SAID...THERE WILL BE LIKELY ENOUGH SNOW AND ICE ACCUMULATIONS
TO WARRANT KEEPING THE WINTER STORM WATCH GOING.
LONG TERM...THURSDAY NIGHT THROUGH MONDAY
ON THURSDAY NIGHT...IT LOOKS LIKE THE BEST FORCING WILL BE LOCATED
ACROSS THE REGION AS THE NEARLY VERTICALLY STACKED LOW PRESSURE
SYSTEM APPROACHES THE AREA. THIS LOOKS LIKE WHEN THE BEST SNOW
ACCUMULATIONS WILL LIKELY OCCUR ACROSS MUCH OF THE FORECAST AREA.
THERE MAY BE EVEN ENOUGH WARM AIR ALOFT IN SOUTHWEST AND CENTRAL
WISCONSIN FOR THE PRECIPITATION TO CHANGE OVER TO EITHER RAIN OR
FREEZING RAIN. AT THIS TIME...JUST THE FREEZING RAIN IS COVERED IN
THE FORECAST GRIDS.
ON FRIDAY...THE MAIN FORECAST QUESTIONS ARE WHERE THE DRY SLOT
WILL END UP AND THE DEFORMATION PRECIPITATION. AT THIS TIME...IT
LOOKS LIKE THE DRY SLOT WILL BE JUST SOUTHEAST OF THE FORECAST
AREA AND THIS WOULD LIKELY RESULT IN DEFORMATION SNOW FALLING
ACROSS MUCH OF THE FORECAST AREA.
WITH THE POTENTIAL ADDITIONAL SNOW ACCUMULATIONS RUNNING BETWEEN
4 AND 8 INCHES AND MAYBE SOME ICE ACCUMULATIONS OF A TENTH OR
TWO TENTHS ACROSS SOUTHWEST AND CENTRAL WISCONSIN FROM THURSDAY
NIGHT INTO FRIDAY...THE WINTER STORM WATCH STILL LOOKS VERY
WARRANTED.
FROM FRIDAY NIGHT INTO SATURDAY...IT CONTINUES TO LOOK LIKE THE
COLDER AND DRIER AIR WILL BE SLOWER AT MOVING INTO THE FORECAST
AREA. AS A RESULT...THE TEMPERATURE AND DEW POINTS GRIDS WERE
RAISING DURING THIS TIME PERIOD.
&&
AVIATION...TODAY AND TONIGHT
IFR TO MVFR CONDITIONS ARE EXPECTED TO PERSIST THROUGHOUT THE
FORECAST PERIOD AS A MID LEVEL TROF MOVES EAST OF THE REGION EARLY
THIS MORNING. LIGHT TO MODERATE SNOW WILL TAPER OFF QUICKLY THIS
MORNING BEFORE SUNRISE WITH VIS IMPROVING BUT CIGS REMAINING LOW
WITH A SIGNIFICANT AMOUNT OF LOW LEVEL MOISTURE REMAINING IN PLACE
THROUGHOUT THE REGION. WITH DRIER AIR MOVING IN AT THE MID TO UPPER
LEVELS...FORECAST SOUNDINGS ARE INDICATING THAT SOME FREEZING
DRIZZLE WILL BE POSSIBLE TODAY INTO TONIGHT. WINDS WILL REMAIN OUT
OF THE EAST THROUGH TODAY WITH THE NEXT SURFACE LOW DEVELOPING IN
THE SOUTHERN PLAINS.
THIS NEXT STORM SYSTEM DEVELOPING IN THE PLAINS IS EXPECTED TO BRING
A SIGNIFICANT AMOUNT OF PRECIPITATION INTO THE TAF REGION WHICH WILL
LIKELY INCLUDE SNOW AND FREEZING RAIN. AN EXTENDED PERIOD OF MVFR
OR LOWER CONDITIONS IS EXPECTED THROUGH THE END OF THE WEEK.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...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 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 STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR IAZ008-IAZ009-IAZ010-IAZ011-IAZ018-IAZ019-
IAZ029-IAZ030.
&&
$$
SHORT/LONG TERM...RRS
AVIATION..........THOMPSON
