FXUS63 KARX 250954
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
354 AM CST WED NOV 25 2009

.SHORT TERM...TODAY THROUGH FRIDAY

AT 3 AM...A SURFACE LOW WAS LOCATED NEAR MILWAUKEE. THIS SYSTEM
WAS PRODUCING RAIN EAST OF A LINE FROM NEILLSVILLE TO SPARTA TO 
LANCASTER IN WESTERN WISCONSIN. FURTHER WEST...ANOTHER LINE OF
RAIN WAS LOCATED FROM MASON CITY IOWA NORTHEAST TO THE WESTERN TIP
OF LAKE SUPERIOR. THIS IS ASSOCIATED WITH SOME WEAK TO MODERATE 
FRONTOGENETIC FORCING LOCATED BETWEEN 800 AND 700 MB. THERE IS
ALSO SOME 700 MB MOISTURE CONVERGENCE IN THIS AREA. WHILE THE
25.00Z MODELS ARE DRY...THE FRONTOGENESIS CAN BE FOLLOWED IN THE 
NAM/WRF THROUGH 25.15Z...AND THEN IT RAPIDLY WEAKENS ACROSS
WESTERN WISCONSIN. DUE TO THIS BAND AND YET ANOTHER BAND OF
PRECIPITATION ASSOCIATED WITH A SHORT WAVE TROUGH OVER WESTERN
MINNESOTA AND NORTHWEST IOWA...THE PRECIPITATION CHANCES WERE LEFT
IN THE LIKELY RANGE /60 TO 70 PERCENT/ THIS MORNING.

FROM THIS AFTERNOON THROUGH TONIGHT...THE SHORT WAVE TROUGH WILL
MOVE SOUTHEAST ACROSS IOWA AND CENTRAL ILLINOIS. THIS SYSTEM WILL
PRODUCE WEAK FRONTOGENESIS AND MODERATE ISENTROPIC LIFT ACROSS THE
FORECAST AREA THROUGH THIS EVENING...AND THEN IT QUICKLY WEAKENS
AND MOVES SOUTHEAST OVERNIGHT. AS A RESULT...THERE CONTINUES TO BE A
STRONG SIGNAL OF PRECIPITATION. BUFKIT AND AWIPS SOUNDINGS SUGGEST
THAT THIS PRECIPITATION WILL BE MAINLY IN THE FORM OF RAIN.
HOWEVER AS COLD AIR ADVECTION MOVES INTO THE AREA THIS AFTERNOON
AND EVENING...IT WILL GRADUALLY TRANSITION TO EITHER A RAIN AND 
SNOW MIX...OR ALL SNOW. THIS SHOULD START TO HAPPEN IN SOUTHEAST
MINNESOTA AND NORTHEAST IOWA THIS AFTERNOON...AND ACROSS THE
REMAINDER OF THE AREA TONIGHT. VALLEY LOCATIONS MAY JUST SEE RAIN
FROM THIS SYSTEM. UNLIKE THE PAST COUPLE OF DAYS...IT LOOKS LIKE
THE SNOW AMOUNTS SHOULD RANGE FROM JUST A TRACE TO A COUPLE TENTHS
OF AN INCH. THE GFS INDICATES THAT AS THE PRECIPITATION IS ABOUT
TO END...WE START TO LOSE OUR ICE CRYSTAL SEEDING AND THERE MAY BE
JUST ENOUGH ISENTROPIC LIFT TO PRODUCE A BRIEF PERIOD OF DRIZZLE.

WITH THE SUBSIDENCE LOCATED ACROSS REGION ON THANKSGIVING...THE
PRECIPITATION CHANCES WERE REMOVED FROM THE FORECAST.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

FROM SATURDAY NIGHT THROUGH SUNDAY...IT CONTINUES TO LOOK LIKE A
LONG WAVE TROUGH WILL PRODUCE SOME PRECIPITATION ACROSS MUCH OF
THE AREA. THE ECMWF IS THE MOST PROGRESSIVE WITH THIS SYSTEM AND
IT CONFINES ITS PRECIPITATION CHANCES TO MAINLY SATURDAY NIGHT. 
MEANWHILE WILL GFS HAS PRECIPITATION FROM SATURDAY NIGHT THROUGH
MONDAY. WITH SUCH DIFFERENCES IN THE MODELS...I WILL DEFER ANY
CHANGES TO DAY SHIFT.

&&

.AVIATION...TODAY THROUGH THURSDAY NIGHT

COMPLEX AVIATION SCENARIO FOR THE NEXT 24 HOURS. CURRENTLY...A LOW 
PRESSURE SYSTEM WAS MOVING NORTHEAST OUT OF NORTHERN ILL...WRAPPING 
RAIN AROUND IT AND AFFECTING KLSE. MEANWHILE AT KRST...A BAND OF -RA 
WAS APPROACHING FROM THE WEST...DUE TO LOW LEVEL FRONTOGENETIC 
FORCING. CONDITIONS WERE MOSTLY IFR...WITH CEILINGS AT OR BELOW 1 
KFT AND VSBYS LESS THAN 3 MILES. HOWEVER...SOME IMPROVEMENT INTO VFR 
CATEGORY VSBYS/CEILINGS WERE FOUND WITH THAT BAND OF PCPN 
APPROACHING KRST...AND JUST WEST OF THERE. 

A DISTURBANCE A LOFT WILL QUICKLY REPLACE THE DEPARTING 
LOW...BRINGING MORE PCPN...MOSTLY FROM LATE AFTERNOON THROUGH ABOUT 
06Z TONIGHT. COLDER AIR IN THE WAKE OF THE LOW WILL LEAD TO -RA 
MIXING WITH SNOW...THEN CHANGING OVER TO ALL SNOW. AS THE SYSTEM 
EXITS...THERE COULD BE A COUPLE HOURS OF -DL OR -FZDL AS SOME 
ISENTROPIC LIFT COULD LINGER THROUGH A RELATIVELY SHALLOW CLOUD 
LAYER DEVOID OF ICE CRYSTALS. CONFIDENCE NOT HIGH IN THIS...BUT IT 
IS A POSSIBILITY. 

CEILINGS PRESENT MORE OF A PROBLEM FOR THE TAF SITES. LATEST 
FOG/STRATUS SATELLITE IMAGERY...COUPLED WITH SFC OBS...SHOW A BREAK 
FROM THE IFR CONDITIONS BETWEEN THE DEPARTING LOW AND APPROACHING 
SHORTWAVE TROUGH. MODEL RH FIELDS DO PICK THIS UP...BUT QUICKLY 
SATURATE THIS RELATIVELY DRY LAYER BY LATE MORNING. OVERALL...IFR 
CONDITIONS SHOULD DOMINATE THE NEXT 24 HOURS...BUT BELIEVE THERE 
COULD BE A FEW HOURS THIS MORNING WHERE CONDITIONS IMPROVE. 
WEST-EAST RUNNING TIME/HEIGHT X-SECTIONS THEN POINT TO DECREASING 
SATURATION BY THANKSGIVING AFTERNOON...AS A RIDGE OF HIGH PRESSURE 
BUILDS IN. EXPECT CLEARING SKIES AS A RESULT...WITH A MOSTLY CLEAR 
THU NIGHT.   

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT/LONG TERM...BOYNE
AVIATION...RIECK