583  
FXUS63 KARX 172305  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
605 PM CDT TUE JUL 17 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH WEDNESDAY)  
ISSUED AT 313 PM CDT TUE JUL 17 2018  
 
MAIN FORECAST CONCERNS IN THE SHORT-TERM ARE ON THE POTENTIAL FOR  
PATCHY FOG TONIGHT IN SOME RIVER VALLEY LOCATIONS.  
 
SURFACE HIGH PRESSURE EDGES EAST OF THE REGION LATE TONIGHT THROUGH  
WEDNESDAY AS A TROUGH APPROACHES FROM THE HIGH PLAINS. THE HIGH  
WILL PROVIDE MAINLY DRY AND QUIET WEATHER ACROSS THE AREA AT LEAST  
THROUGH WEDNESDAY. MOSTLY CLEAR SKIES AND LIGHT WINDS WILL SET  
THE STAGE FOR PATCHY VALLEY FOG, MAINLY IN RIVER VALLEYS. WINDS  
INCREASE JUST ABOVE THE SURFACE THROUGH AROUND 1500 FEET TONIGHT  
WHICH SHOULD LIMIT ANY FOG IN THE MAIN CHANNEL OF THE MISSISSIPPI  
RIVER. THE MAIN FOG CONCERNS WILL BE ALONG TRIBUTARY RIVER VALLEYS  
TO THE MISSISSIPPI RIVER. CLOUDS WILL GRADUALLY INCREASE ACROSS  
THE REGION FROM WEST TO EAST LATE IN THE DAY ON WEDNESDAY AS THE  
TROUGH EDGES INTO EASTERN SOUTH DAKOTA/NEBRASKA.  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH TUESDAY)  
ISSUED AT 313 PM CDT TUE JUL 17 2018  
 
MAIN FORECAST CONCERNS ARE ON THE POTENTIAL FOR HEAVY RAINFALL  
WEDNESDAY NIGHT THROUGH THURSDAY.  
 
THE TROUGH IS EXPECTED TO PUSH INTO THE UPPER MISSISSIPPI RIVER  
VALLEY ON THURSDAY WITH SURFACE LOW PRESSURE DEEPENING. MOISTURE  
WILL BE PUMPED NORTHWARD INTO THE AREA AHEAD OF THIS LOW WITH  
PRECIPITABLE WATER VALUES INCREASING TO AROUND 1.8 INCHES WITH  
WARM CLOUD DEPTH OF 3.5 KM. MOST OF THE CAPE WILL BE CONFINED TO  
AREAS SOUTH OF INTERSTATE 90, POTENTIALLY ONLY PORTIONS OF  
NORTHEAST IOWA AND FAR SOUTHWEST WISCONSIN. THIS WILL LIMIT THE  
POTENTIAL FOR ANY STRONGER STORMS AS FAR AS WIND AND HAIL GO, WITH  
THE PRIMARY THREAT BEING HEAVIER RAINS. THE BULK OF THE RAIN  
SHOULD SPREAD FROM WEST TO EAST ACROSS THE AREA AFTER 12Z THURSDAY  
WITH RAIN THEN PERSISTING THROUGH MUCH OF THE DAY, WITH SCATTERED  
EMBEDDED THUNDERSTORMS. ANY STORMS COULD PRODUCE LOCALLY HEAVY  
RAINFALL IN ADDITION TO THE ONGOING RAINS. SOME DIFFERENCES NOTED  
IN THE FORECAST MODELS ON THE LOW TRACK, ESPECIALLY WITH RESPECT  
TO THE 12Z NAM, WHICH TAKES THE LOW SOUTHEAST INTO NORTHERN  
ILLINOIS. THIS IS THE ONLY MODEL DOING THIS AT THIS TIME SO  
TREATING IT AS AN OUTLIER. THE ECMWF, GFS, AND CANADIAN TAKE THE  
LOW INTO EASTERN/NORTHEAST WISCONSIN THURSDAY NIGHT INTO FRIDAY  
THEN STALLS. THE LOW THEN SITS OVER THIS AREA INTO SATURDAY, AND  
THEN THE BIG QUESTION IS HOW FAR WEST WILL RAIN SHOWERS OCCUR. THE  
SHOWERS COULD CONTINUE INTO SATURDAY FOR AREAS ALONG AND EAST OF  
THE MISSISSIPPI RIVER. HIGH PRESSURE SHOULD THEN FINALLY BUILD IN  
SATURDAY NIGHT INTO SUNDAY, BUT WITH THE CUTOFF LOW IN THE AREA,  
THERE IS THE POTENTIAL FOR RAIN SHOWERS TO LINGER, ESPECIALLY OVER  
CENTRAL WISCONSIN. BY THE TIME THE RAIN ENDS, TOTALS OF 1.5 TO 2  
INCHES ARE EXPECTED. THE WIDESPREAD CLOUD COVER AND RAIN OVER THE  
REGION ON THURSDAY WILL RESULT IN COOLER HIGH TEMPERATURES IN THE  
UPPER 60S TO LOWER 70S.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)  
ISSUED AT 605 PM CDT TUE JUL 17 2018  
 
QUIET VFR CONDITIONS EXPECTED THROUGH WEDNESDAY AFTERNOON. AN  
AREA OF HIGH PRESSURE CENTERED OVER LAKE SUPERIOR WILL REMAIN  
NEARLY STATIONARY AND KEEP SKIES CLEAR WITH LIGHT EAST TO  
SOUTHEAST WINDS. SOME CONCERN FOR VALLEY FOG OVERNIGHT WITH THE  
LIGHT WINDS. FORECAST SOUNDINGS FROM THE 17.21Z RAP WOULD SUGGEST  
IT WILL BE TOO DRY TONIGHT FOR FOG TO FORM AS IT DOES NOT SHOW  
SATURATION OCCURRING AT THE SURFACE. HOWEVER THE 17.18Z NAM  
FORECAST SOUNDINGS WOULD BE SUPPORTIVE OF VALLEY FOG WITH A  
VISIBILITY REDUCTION AT KLSE. FOR NOW, WILL MAINTAIN CONTINUITY  
WITH THE PREVIOUS FORECAST AND NOT INCLUDE ANY FOG AT KLSE BUT  
WILL MONITOR TRENDS THROUGH THE EVENING FOR POSSIBLE INCLUSION  
WITH LATER FORECASTS.  
 

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

 
 

 
 
SHORT TERM...WETENKAMP  
LONG TERM...WETENKAMP  
AVIATION...04  
 
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