506  
FXUS63 KARX 171126  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
526 AM CST SUN DEC 17 2017  
   
UPDATE
 
 
ISSUED AT 525 AM CST SUN DEC 17 2017  
 
DENSE FOG HAS BECOME MORE WIDESPREAD ACROSS PORTIONS OF SOUTHEAST  
MN/NORTHEAST IA. NOT ANTICIPATING MUCH IMPROVEMENT UNTIL LATE  
MORNING. HOISTED A DENSE FOG ADVISORY UNTIL NOON TODAY.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 300 AM CST SUN DEC 17 2017  
 
EARLY THIS MORNING, LOW STRATUS HAS OVERSPREAD THE ENTIRE FORECAST  
AREA ALONG LIGHT EASTERLY FLOW. ALSO SEEING SOME PATCHY DENSE  
FOG, ESPECIALLY ACROSS PORTIONS OF SOUTHEAST MN AND NORTHEAST IA.  
THESE CLOUDS ARE UNLIKELY TO GO ANYWHERE TODAY, TRAPPED UNDER A  
LOW-LEVEL SUBSIDENT INVERSION. FOG WILL DISSIPATE LATER THIS  
MORNING, BUT PERSISTENT CLOUD COVER WILL KEEP TEMPERATURES IN  
CHECK WITH AFTERNOON HIGHS FROM THE UPPER 20S TO MID 30S.  
 
A ROBUST SHORT-WAVE CURRENTLY ROTATING ACROSS CENTRAL KS WILL  
WEAKEN AS IT LIFTS NORTHEASTWARD TODAY, BUT ALL OF ITS QPF IS  
EXPECTED TO REMAIN SOUTH AND EAST OF THE LOCAL AREA. MEANWHILE, A  
SECONDARY NORTHERN STREAM TROUGH WILL MOVE ACROSS THE DAKOTAS AND  
WESTERN MN LATER THIS AFTERNOON. SHORT-TERM HIGH RESOLUTION  
GUIDANCE SHOWS A NARROW BAND OF ENHANCED FRONTOGENESIS OUT AHEAD  
OF THIS WAVE ACROSS CENTRAL MN INTO NORTHERN WI, WHICH MAY PRODUCE  
A BRIEF PERIOD OF LIGHT SNOW THIS AFTERNOON MAINLY IMPACTING  
TAYLOR COUNTY.  
 
CLOUDS AND COOLER TEMPERATURES TODAY SHOULD LIMIT MELTING OF  
CURRENT SNOWPACK, BUT WILL STILL HAVE TO WATCH FOG POTENTIAL  
AGAIN TONIGHT. OTHERWISE, EXPECT LOWS IN THE 20S WITH LIGHT  
SOUTHWEST WIND.  
   
LONG TERM
 
(MONDAY THROUGH SATURDAY)  
ISSUED AT 300 AM CST SUN DEC 17 2017  
 
THE NEXT CANADIAN TROUGH AND ASSOCIATED COLD FRONT WILL MOVE  
ACROSS THE FORECAST AREA MONDAY NIGHT. WITH LITTLE MOISTURE TO  
WORK WITH, NOT EXPECTING ANY PRECIPITATION WITH ITS PASSAGE.  
HOWEVER, STRONG WARM AIR ADVECTION ON MONDAY AHEAD OF THE WAVE  
WILL RESULT IN TEMPERATURES RISING INTO THE UPPER 30S TO LOWER  
40S FOR MOST AREAS. ONLY A SLIGHT DIP IN TEMPERATURES IS EXPECTED  
BEHIND THE FRONT ON TUESDAY WITH HIGHS MAINLY IN THE 30S. BOTH  
DAYS WILL BE BREEZY WITH ROUGHLY 20 TO 30 KTS IN THE SHALLOW MIXED  
BOUNDARY LAYER. SOUTHWEST WINDS MONDAY WILL SHIFT TO THE NORTHWEST  
IN THE POST FRONTAL AIR MASS ON TUESDAY.  
 
A LARGE EASTERN PACIFIC TROUGH IS STILL ON TRACK TO MOVE INTO THE  
INTERMOUNTAIN WEST ON WEDNESDAY. LATEST MODEL TRENDS NOW HAVE THE  
HEAVIEST WARM ADVECTIVE SNOWS ACROSS ND, NORTHERN MN, AND INTO  
NORTHERN WI. COULD STILL SEE SOME OF THIS PRECIPITATION CLIP THE  
NORTHERNMOST FORECAST AREA LATE WEDNESDAY AND WEDNESDAY NIGHT, SO  
POPS IN THE 20-60 PERCENT RANGE SEEM REASONABLE AT THIS TIME.  
 
STILL UNCERTAINTY IN THE SURFACE LOW TRACK THURSDAY INTO FRIDAY.  
HOWEVER, LOOKING AT PAST RUNS OF THE GFS AND EC AT 06Z FRIDAY  
SHOWS A GRADUAL TREND TO THE NORTH AND WEST. IF THIS TREND  
CONTINUES, IT WOULD FAVOR A WARMER AIR MASS ACROSS THE FORECAST  
AREA AND MORE OF A WINTRY MIX THAN PURE SNOW FOR SOME AREAS. THIS  
IS ESPECIALLY TRUE IF THE 17.00Z ECMWF VERIFIES WHICH DEEPENS THE  
SURFACE LOW NEAR THE MN/IA/WI BORDER BY FRIDAY MORNING, KEEPING  
THE PRIMARY DEFORMATION SNOW BAND ACROSS SOUTHERN MN INTO NORTHERN  
WI. 00Z GEFS PLUMES SHOW LA CROSSE SNOW TOTALS RANGING FROM 0 TO  
10 INCHES, SO STILL A LOT OF SPREAD. GIVEN THIS UNCERTAINTY, WILL  
CONTINUE TO FOLLOW A MODEL CONSENSUS, RESULTING IN HIGH END POPS  
FOR MUCH OF THURSDAY, THEN TAPERING OFF FROM WEST TO EAST ON  
FRIDAY. TO MINIMIZE POTENTIAL FLIP-FLOPPING OF THE FORECAST, WILL  
MAINTAIN A MAINLY SNOW P-TYPE, BUT MAY NEED TO EVENTUALLY  
INTRODUCE MORE OF A MIX IF RECENT MODEL TRENDS CONTINUE.  
 
NEXT WEEKEND STILL LOOKS DRY, BUT COLD AS TEMPERATURES PLUMMET  
BEHIND THE DEPARTING WAVE. STILL A QUESTION ON HOW COLD, BUT HIGHS  
BACK INTO THE TEENS TO LOW 20S SEEM REASONABLE AT THIS TIME.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 525 AM CST SUN DEC 17 2017  
 
WIDESPREAD IFR/LIFR STRATUS AND VSBY ACROSS SOUTHEAST MN/SOUTHWEST  
WI AS DAMP AIR IS TRAPPED UNDER A SUBSIDENCE INVERSION WITH VERY  
WEAK LOWER BOUNDARY LAYER WINDS. EXPECT SOME IMPROVEMENT IN THE 1/4SM  
VSBY AT KRST BY NOON TO 1SM.  
 

 
   
ARX WATCHES/WARNINGS/ADVISORIES
 
 
WI...NONE.  
MN...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR MNZ086-087-094-095.  
 
IA...DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR IAZ008>010-018-019.  
 

 
 

 
 
UPDATE...DAS  
SHORT TERM...ROGERS  
LONG TERM...ROGERS  
AVIATION...DAS  
 
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