731  
FXUS63 KARX 182303  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
603 PM CDT WED JUL 18 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY)  
ISSUED AT 218 PM CDT WED JUL 18 2018  
 
AFTERNOON WATER VAPOR IMAGERY SHOWED A SHORTWAVE TROUGH CONTINUING  
EASTWARD ALONG THE SD/NE BORDER WITH SURFACE ANALYSIS SHOWING A WARM  
FRONT EXTENDING SOUTHWARD AND A TRAILING COLD FRONT NOT FAR BEHIND.  
THE EVOLUTION OF THIS SYSTEM AND ASSOCIATED SHOWER AND STORM CHANCES  
WILL BE THE MAIN FORECAST CONCERN FOR THIS PERIOD.  
 
MODELS HAVE BEEN CONSISTENT SPINNING UP A SURFACE LOW AS THE TROUGH  
MOVES EASTWARD, WITH SHOWERS AND STORMS MOVING INTO FAR WESTERN  
PORTIONS OF THE FORECAST AREA BY EARLY THURSDAY MORNING. HOWEVER,  
MODEL SOLUTIONS HAVE BEEN ALL OVER THE BOARD ON LOCATION OF THE  
CENTER OF THE SURFACE LOW. THE NAM HAS BEEN THE MOST INCONSISTENT,  
WITH FAIRLY LARGE SHIFTS WITH EACH NEW RUN (E.G. FROM BEING CENTERED  
OVER CENTRAL WISCONSIN BY FRIDAY MORNING IN THE 18.06Z RUN TO  
CENTERED OVER NORTHERN ILLINOIS IN THE 18.12Z RUN). THAT SAID, THE  
18.12Z RUNS OF THE GFS AND ECMWF CAME INTO PRETTY GOOD AGREEMENT  
WITH THE NAM. THE LOCATION OF THIS LOW WILL PLAY A LARGE ROLE IN ANY  
SEVERE WEATHER POTENTIAL ON THURSDAY. THE AMOUNT OF INSTABILITY HAS  
ALWAYS BEEN IN QUESTION, GIVEN INCREASING CLOUDS AND PRECIP ON  
THURSDAY MORNING. THE SOUTHWARD TREND OF THE LOW WOULD FURTHER  
HINDER THE DEVELOPMENT OF ANY INSTABILITY, WITH THE WARM SECTOR  
REMAINING SOUTH OF THE FORECAST AREA. THE STRONGEST DEEP LAYER SHEAR  
ALSO REMAINS SOUTH OF THE SURFACE LOW, THOUGH DECENT 0-3 KM SHEAR OF  
AROUND 25 KTS COULD BE SEEN IN NORTHEAST IOWA INTO FAR SOUTHWEST  
WISCONSIN. SHOULD ANY DESTABILIZATION OCCUR OVER THESE AREAS WITH  
BETTER SHEAR, COULD SEE SOME STRONG TO POSSIBLY SEVERE STORMS, BUT  
GIVEN SOUTHWARD TREND, THINKING OVERALL SEVERE WEATHER THREAT IS  
DIMINISHING FOR MUCH OF THE AREA. THAT SAID, THIS IS ONLY THE FIRST  
TIME MODELS HAVE HAD DECENT AGREEMENT, AND WITH RUN TO RUN  
CONSISTENCY BEING POOR, FORECAST CONFIDENCE IS RATHER LOW.  
 
LOOKING AT RAINFALL POTENTIAL, PRECIPITABLE WATER VALUES OVER 1.5  
INCHES AND WARM CLOUD DEPTHS, THINKING RAIN COULD BE HEAVY AT TIMES,  
BUT SHOULD AFOREMENTIONED SOUTHERN TREND CONTINUE, HEAVY CONVECTIVE  
RAIN WOULD NOT BE A THREAT FOR MUCH OF THE FORECAST AREA. WOULD  
INSTEAD SEE MORE OF A LONG DURATION, STRATIFORM-TYPE RAINFALL WITH  
OCCASIONAL THUNDERSTORMS THROUGH FRIDAY, AS THE LOW CONTINUES TO  
SPIN OFF TO THE EAST/SOUTHEAST. TOTALS LOOK TO BE AROUND AN INCH.  
COULD ALSO SEE SOME LINGERING LIGHT SHOWERS IN WISCONSIN ON  
SATURDAY, BUT THESE ARE NOT EXPECTED TO AMOUNT TO MUCH RAINFALL  
ACCUMULATION.  
 
TEMPERATURES THROUGH THE PERIOD LOOK TO BE COOLER THAN NORMAL GIVEN  
CLOUDS AND PRECIP, WITH HIGHS IN THE 70S THROUGH FRIDAY, THEN  
APPROACHING 80 DEGREES IN A FEW SPOTS ON SATURDAY AS THE RAIN MOVES  
OUT.  
   
LONG TERM
 
(SATURDAY NIGHT THROUGH WEDNESDAY)  
ISSUED AT 218 PM CDT WED JUL 18 2018  
 
SHORT WAVE RIDGING AND SURFACE HIGH PRESSURE WILL BUILD IN FOR  
SUNDAY AND EARLY MONDAY, WITH HIGHS BACK INTO THE 80S FOR MONDAY.  
ANOTHER COLD FRONT WILL MOVE IN FROM THE NORTHEAST MONDAY AFTERNOON,  
BRINGING SHOWER AND STORM CHANCES, BUT THE 18.12Z SUITE OF MODELS  
HAS TRENDED TOWARD LESS QPF, SO IT MAY END UP BEING A DRY FRONTAL  
PASSAGE FOR MANY AREAS. NORTHWESTERLY FLOW WILL THEN SET UP, WITH A  
COOLING TREND INTO MID-WEEK. THE GFS AND ECMWF SUGGEST YET ANOTHER  
COLD FRONTAL PASSAGE ON WEDNESDAY, ALONG WITH SHOWER AND STORM  
CHANCES, BUT PLENTY OF TIME FOR THINGS TO CHANGE BEFORE THEN.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)  
ISSUED AT 603 PM CDT WED JUL 18 2018  
 
THE UPPER LEVEL LOW OVER WESTERN NORTH DAKOTA IS EXPECTED TO MOVE  
SOUTHEAST AND BE OVER SOUTHERN MINNESOTA BY LATE THURSDAY  
AFTERNOON. THE SURFACE LOW WITH THIS SYSTEM SHOULD TRACK FROM  
SOUTH DAKOTA INTO NORTHWEST IOWA. THE FORCING FROM THIS SYSTEM  
WILL BE GRADUALLY INCREASING OVERNIGHT AND THEN BECOME STRONG  
ENOUGH THURSDAY TO PRODUCE SOME RAIN. THE RAIN LOOKS TO START  
MOVING INTO KRST THURSDAY MORNING WITH VFR CONDITIONS INITIALLY  
BUT BY AFTERNOON THE LOWER LEVELS OF THE ATMOSPHERE SHOULD BECOME  
SATURATED ENOUGH TO BRING THE CEILINGS DOWN TO MVFR. KLSE LOOKS TO  
BE MORE ON THE EASTERN FRINGE OF THE RAIN DURING LATE MORNING AND  
AFTERNOON AND WILL ONLY HAVE A VCSH FOR NOW WITH VFR CONDITIONS.  
THUNDER CHANCES LOOK TO BE RATHER LIMITED FOR NOW WITH THE BEST  
INSTABILITY THURSDAY AFTERNOON AHEAD OF THE SURFACE LOW BUT SOUTH  
OF BOTH AIRPORTS.  
 

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

 
 

 
 
SHORT TERM...CA  
LONG TERM...CA  
AVIATION...04  
 
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