791  
FXUS63 KARX 212322  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
622 PM CDT MON AUG 21 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH TONIGHT)  
ISSUED AT 240 PM CDT MON AUG 21 2017  
 
HIGH IMPACT WEATHER POTENTIAL: ALL EYES ON THUNDERSTORM POTENTIAL,  
WITH SOME RISK FOR SEVERE STORMS, PARTICULARLY DURING THE 4-8PM  
TIME FRAME AND ESPECIALLY ACROSS NORTHEAST IOWA.  
 
AS OF 18Z, NOT ONLY IS IT DARKER THAN NORMAL ACROSS THE AREA (THANKS  
ECLIPSE), BUT A WARM FRONT REMAINS DRAPED ACROSS CENTRAL IOWA, WHILE  
A COLD FRONT IS TAKING SHAPE ACROSS NEBRASKA AND THROUGH THE  
NORTHERN PLAINS, AHEAD OF A STRONGER SHORTWAVE DROPPING THROUGH  
NORTH DAKOTA. AIRMASS DESTABILIZATION CONTINUES SOUTH OF THE WARM  
FRONT/COLD FRONT INTERFACE INTO MUCH OF NORTHERN AND CENTRAL IOWA,  
WHILE MUCH LESS INSTABILITY IS IN PLACE FARTHER NORTH. ON THE RADAR  
FRONT, ONE COMPLEX OF STORMS CONTINUES TO WORK EAST OUT OF SOUTH  
DAKOTA, WHILE ADDITIONAL STORMS CONTINUE TO BUBBLE ACROSS NORTHERN  
IOWA, WITH SOME ADDITIONAL DEVELOPMENT NORTHWARD INTO PARTS OF  
SOUTH-CENTRAL MINNESOTA.  
 
HEADING THROUGH THE AFTERNOON AND EVENING HOURS, WILL BE WATCHING  
THAT SOUTH DAKOTA COMPLEX, WHICH CONTINUES TO GRADUALLY GROW  
UPSCALE AS IT ENCOUNTERS BETTER INSTABILITY WITH TIME INTO  
NORTHWEST IOWA. MEANWHILE, ADDITIONAL CONVECTION SHOULD TEND TO  
BUBBLE ALONG THE NORTHWARD ADVANCING WARM FRONT INTO NORTHERN OR  
CENTRAL IOWA. HOW FAR NORTH SAID WARM FRONT ADVANCES REMAINS VERY  
LOW CONFIDENCE, PARTICULARLY WITH STILL-ONGOING CONVECTION RIGHT  
ALONG IT, BUT ITS PLACEMENT WILL STRONGLY DICTATE SEVERE POTENTIAL  
UP THIS WAY. PRETTY DECENT LAPSE RATES IN COMBINATION WITH MLCAPE  
PUSHING 3000 J/KG (OR MAYBE EVEN SLIGHTLY HIGHER) DOES SUGGEST A  
HAIL THREAT, WITH ENHANCED 0-1KM SHEAR RIGHT ALONG THE WARM FRONT  
SUGGESTIVE OF A LOW END TORNADO THREAT. THAT THREAT LOOKS TO JUST  
CLIP NORTHEAST IOWA PER CURRENT TRENDS, WHILE BETTER 0-3KM SHEAR  
SUGGESTS MORE OF A LINEAR SYSTEM WITH THE POTENTIAL FOR SOME  
STRONGER WIND GUSTS. AT THE MOMENT, THE HIGHEST SEVERE RISK LOOKS  
TO BE ACROSS NORTHEAST IOWA INTO MAYBE FAR SOUTHWEST WISCONSIN.  
 
THANKFULLY THIS WHILE SETUP APPEARS PROGRESSIVE, AND WHILE PWAT  
VALUES DO CLIMB TOWARD 2 INCHES, THE OVERALL RISK FOR WIDESPREAD  
HEAVY RAIN APPEARS LOW. WITH THAT SAID, WILL HAVE TO WATCH THE  
INTERFACE WHERE CONVECTION DEVELOPS ALONG THE WARM FRONT FOLLOWED BY  
ADDITIONAL STORMS ON THE COLD FRONT, AS A LOCALIZED AXIS OVER  
NORTHERN OR CENTRAL IOWA COULD RECEIVE SOME HEAVY RAINS. HOWEVER, AS  
MENTIONED IN THIS SPACE YESTERDAY, OUR RISK FOR STORMS APPEARS IT  
WILL REALLY DROP OFF BY 06Z AS THE UPPER WAVE AND COLD FRONT QUICKLY  
DROP THROUGH THE REGION.  
   
LONG TERM
 
(TUESDAY THROUGH MONDAY)  
ISSUED AT 240 PM CDT MON AUG 21 2017  
 
ANOTHER GREAT STRETCH OF WEATHER IS ON THE WAY TUESDAY THROUGH  
FRIDAY AS UPPER TROUGHING DOMINATES WHILE CANADIAN HIGH PRESSURE  
DROPS THROUGH THE REGION. THAT SETUP SHOULD DELIVER VERY COMFORTABLE  
AND MAINLY DRY CONDITIONS, WITH THE POSSIBLE EXCEPTION OF A FEW  
SHOWERS WEDNESDAY NIGHT WITH HINTS OF A STRONGER WAVE CROSSING THE  
AREA. NOT MUCH IN THE WAY OF MOISTURE WITH THAT FEATURE BUT  
SOMETHING TO WATCH. BIGGER STORY IS BELOW NORMAL TEMPERATURES ONCE  
AGAIN, WITH LOWS BACK IN THE 40S AND LOWER 50S FOR EVERYONE. GREAT  
SLEEPING WEATHER!  
 
OTHERWISE, LOOKING LIKE PRECIPITATION CHANCES WILL GRADUALLY RETURN  
TO THE AREA TOWARD SATURDAY OR SUNDAY AS BROAD RETURN FLOW GETS  
UNDERWAY AHEAD OF OUR NEXT COLD FRONT SLATED CURRENTLY TO ARRIVE  
TOWARD MONDAY. STILL PLENTY OF QUESTIONS ABOUT SPECIFIC TIMING THAT  
FAR OUT, BUT EVEN THAT FAR OUT, THERE REMAIN PRETTY STRONG SIGNALS  
THAT TEMPS WILL REMAIN NEAR TO BELOW NORMAL.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 622 PM CDT MON AUG 21 2017  
 
WATCHING AN EXPANSIVE AREA OF LIGHT RAIN SHOWERS MOVE ACROSS THE  
AREA THIS EVENING. REMOVED THUNDER FROM BOTH KRST/KLSE AS THE  
MAJORITY OF STORMS HAVE BEEN WELL SOUTH OF TAF AIRFIELDS OVER THE  
PAST COUPLE HOURS. WITH THE EXCEPTION OF A BRIEF DIP INTO THE  
MVFR RANGE, CEILINGS HAVE GENERALLY REMAINED WELL ABOVE 3000 FT  
AGL. HOWEVER, RAIN HAS BEEN STEADY ENOUGH TO RESULT IN SOME  
REDUCTIONS IN VISIBILITY BETWEEN 3 AND 5 SM. BASED ON LATEST  
RADAR TRENDS, RAIN SHOULD END AT KRST BY 22.02Z AND AT KLSE BY  
22.03Z. CLOUDS WILL TAKE MORE TIME TO CLEAR WITH SOME GUIDANCE  
STILL SUGGESTING THE CHANCE FOR SOME MVFR CEILINGS OVERNIGHT.  
EXPECT MORE PERMANENT CLEARING LATE TONIGHT INTO EARLY TUESDAY  
MORNING WITH VFR CONDITIONS THEREAFTER. LIGHT SOUTHWEST WIND WILL  
GRADUALLY TURN TO THE WEST-NORTHWEST THROUGH THE PERIOD.  
 

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

 
 

 
 
SHORT TERM...LAWRENCE  
LONG TERM...LAWRENCE  
AVIATION...ROGERS  
 
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