323  
FXUS63 KARX 252329  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
629 PM CDT TUE SEP 25 2018  
   
SHORT TERM
 
(TONIGHT AND WEDNESDAY)  
ISSUED AT 244 PM CDT TUE SEP 25 2018  
 
MAIN SHORT-TERM FCST CONCERNS ARE EXITING SHRA THIS EVENING AND  
COOLER TEMPERATURES AGAIN.  
 
DATA ANALYSIS AT 18Z HAD THE COLD FRONT SLIPPING SE ACROSS THE  
REGION, NEAR A KGRB-KPDC-KMCI LINE. MOIST, UNSTABLE AIRMASS AHEAD OF  
THE THE FRONT. RISK OF A FEW SEVERE STORMS FROM FAR SOUTHERN WI TO  
NORTHERN MO THIS AFTERNOON AS A VIGOROUS MID LEVEL SHORTWAVE SEEN IN  
WV IMAGERY AIDS LIFT AND AN AREA OF SHRA/TSRA MOVING EAST-NE ACROSS  
SW WI TO THE EAST 1/3 OF IA. AHEAD OF THE FRONT THIS AFTERNOON,  
STILL KIND OF SUMMERY WITH TEMPS IN THE 70S-LOW 80S AND DEW  
POINTS IN THE LOW-MID 60S. BEHIND THE FRONT IS AUTUMN WITH TEMPS  
MOSTLY IN THE UPPER 40S TO LOWER 60S AND SOME NW WINDS.  
 
MODEL RUNS OF 25.12Z INITIALIZED WELL. SOLUTIONS QUITE SIMILAR AS  
THE MID LEVEL TROUGH AXIS ROTATES ACROSS AND EAST OF THE AREA  
TONIGHT/WED. SHORT-TERM FCST CONFIDENCE IS GOOD THIS CYCLE.  
 
FOR THE SHORT-TERM, PRESENT TIMING HAS THE SFC FRONT WELL EAST OF  
THE FCST AREA BY 00Z, WITH THE FORCING/LIFT FROM THE SHORTWAVE  
EXITING EAST AROUND 00Z. SOME LINGERING SHRA CHANCES ACROSS THE EAST  
SIDE OF THE FCST AREA 00-03Z REASONABLE. THE FCST THEN TRENDS DRY  
FOR THE REST OF TONIGHT/WED AS COOLER/DRY CAN HIGH PRESSURE BUILDS  
IN BEHIND THE FRONT. CLOUDS DECREASE/CLEAR LATER THIS EVENING/  
OVERNIGHT IN THE DEEPER SUBSIDENCE BEHIND THE MID LEVEL TROUGH AXIS  
AND LOWER LEVEL ANTI-CYCLONIC FLOW SPREADING INTO THE AREA. WED  
WOULD TREND AS A MOSTLY SUNNY DAY AS CAN HIGH PRESSURE SLIDES ACROSS  
THE REGION, HOWEVER RATHER CONSISTENT MODEL SIGNAL FOR THE WEAK  
SHORTWAVE IN WESTERN ND TO SPREAD A BATCH OF 925-850MB MOISTURE/  
STRATO-CU CLOUDS SE ACROSS MUCH OF THE FCST AREA WED MORNING. ALL  
MODELS KEEP THIS PROGRESSIVE, WITH A PARTLY SUNNY/MOSTLY CLOUDY  
MORNING BECOMING A MOSTLY SUNNY AFTERNOON. COOLER AIR ALOFT WITH  
SOME DIURNAL WARMING RESULTS IN DEEPER MIXING WED, FOR SOME  
BRISK/GUSTY W TO NW WINDS FOR THE LATER MORNING/AFTERNOON HOURS.  
BLEND OF GUIDANCE LOWS FROM THE UPPER 30S-MID 40S TONIGHT AND IN THE  
MID 50S-LOWER 60S WED LOOK GOOD FOR NOW.  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH TUESDAY)  
ISSUED AT 244 PM CDT TUE SEP 25 2018  
 
FOLLOWING THE DRY DAY ON WEDNESDAY, ANOTHER COLD FRONT WILL SLIDE  
THROUGH ON THURSDAY, PROVIDING ANOTHER SHOT OF COLD AIR AND RAIN  
CHANCES. THE QUESTION WILL BECOME HOW FAR SOUTH INTO THE FORECAST  
AREA THE RAIN EXTENDS. THE 25.12Z GFS AND NAM HAVE RAIN EXTENDING  
ACROSS THE ENTIRE FORECAST AREA, WHILE THE 25.00Z ECMWF KEEPS THE  
RAIN CONTAINED IN ONLY NORTHERN PORTIONS OF THE FORECAST AREA. ONE  
THING MODELS ARE CONSISTENT ON IS ONLY A FEW HUNDRED J/KG AT MOST OF  
MUCAPE IN THE AREA, SO NOT THINKING THERE WILL BE THUNDER.  
 
SOME SHORTWAVE ENERGY WILL THEN MOVE ALONG THE FRONT AND LEAD TO A  
BAND OF RAIN, BUT STILL QUESTIONS AS TO EXACTLY WHERE THIS WILL SET  
UP. THE 25.12Z GFS KEEPS EVERYTHING SOUTH OF THE FORECAST AREA,  
WHILE THE 25.00Z ECMWF IS FARTHER NORTH, GIVING NEARLY THE ENTIRE  
AREA SOME LIGHT RAIN. THE GFS THEN BRINGS IN MORE RAIN CHANCES  
SATURDAY AFTERNOON/EVENING AND SUNDAY WHILE THE ECMWF KEEPS THE AREA  
DRY UNTIL MONDAY. BOTTOM LINE, GIVEN RECENT RUN TO RUN INCONSISTENCY  
FOR ALL MODELS, FORECAST CONFIDENCE FOR FRIDAY THROUGH SUNDAY IS  
RATHER LOW, BUT GENERALLY LOOKING COOL WITH OFF AND ON LIGHT RAIN  
CHANCES. FRIDAY NIGHT DOES LOOK TO BE THE COLDEST NIGHT IN THE  
PERIOD, WITH HIGH PRESSURE NEARLY OVERHEAD. AT THIS POINT, LOOKING  
AT LOWS IN THE LOWER TO MID 30S, WITH SOME SPOTS DIPPING INTO THE  
20S.  
 
MODELS ARE ACTUALLY IN BETTER AGREEMENT THEN FOR THE BEGINNING OF  
NEXT WEEK, BRINGING A WARM FRONT NORTHWARD THROUGH THE AREA, LEADING  
TO MORE RAIN CHANCES. ALSO LOOKING AT A SLIGHT WARMUP GIVEN THE  
STRONGER SOUTHERLY FLOW, WITH HIGHS GETTING BACK INTO THE LOWER TO  
MID 60S.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)  
ISSUED AT 629 PM CDT TUE SEP 25 2018  
 
WITH THE SHOWERS NOW WELL EAST OF BOTH AIRPORTS, LOOKING AT WHEN  
THE MVFR CLOUDS WILL MOVE OUT. OBSERVATIONS INDICATE THESE EXTEND  
BACK INTO CENTRAL MINNESOTA, SO EXPECTING IT WILL BE THE MIDDLE OF  
THE EVENING BEFORE SOLID VFR CONDITIONS MOVE IN. ANOTHER PERIOD OF  
MVFR CEILINGS SHOULD OCCUR WEDNESDAY MORNING AS A SHORT WAVE  
TROUGH, CURRENTLY OVER THE DAKOTAS, SWEEPS ACROSS THE REGION.  
THESE SHOULD NOT LAST LONG WITH VFR CONDITIONS EXPECTED FOR THE  
AFTERNOON.  
 

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

 
 

 
 
SHORT TERM...RRS  
LONG TERM....CJA  
AVIATION...04  
 
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