RSS FeedsIssued by NWS La Crosse, WI
000 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
