314  
FXUS63 KFSD 122332  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
632 PM CDT WED AUG 12 2020  
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY NIGHT)  
ISSUED AT 325 PM CDT WED AUG 12 2020  
 
THE LOW LEVEL JET HAS REMAINED FIRMLY PLANTED ACROSS THE AREA,  
USHERING IN WARM AND MOIST AIR WITH ITS BREEZY WINDS. AREAS ALONG  
AND EAST OF THE I-29 CORRIDOR HAVE HAD A BROKEN STRATUS DECK STICK  
AROUND MOST OF THE DAY, BUT DESPITE THAT TEMPERATURES HAVE CLIMBED  
UP INTO THE MID TO UPPER 80S FOR MOST EXCEPT THOSE ALONG THE BUFFALO  
RIDGE IN SW MN. THE LLJ HAS BEEN TRIGGERING A COUPLE SHOWERS WITHIN  
NW IA AND SW MN, WITH THAT ACTIVITY EXPECTED TO CONTINUE INTO THE  
EVENING HOURS. AS FOR THE THUNDERSTORMS THAT WERE EXPECTED ALONG THE  
MO RIVER VALLEY IN CENTRAL SD, NO STRONG TRIGGERING MECHANISMS HAVE  
PASSED OVERHEAD. BECAUSE OF THIS, THERE HAS ONLY BEEN A COUPLE  
SHOWERS WITH ISOLATED THUNDER FORM AND ARE THUS NO LONGER EXPECTING  
SEVERE WEATHER.  
 
WILL LIKELY SEE THE SHOWERS CONTINUE TO FORM DUE TO THE LLJ  
OVERNIGHT IN SW MN AND NW IA, BUT OTHERWISE WILL BE A RELATIVELY  
QUITE NIGHT WITH LOW TEMPERATURES NEAR 70. THE WINDS INCREASE AFTER  
SUNRISE WITH TEMPERATURES RISING INTO THE MID 80S AGAIN ON THURSDAY.  
WITH THE SYNOPTIC SETUP REMAINING LARGELY UNCHANGED, ANOTHER BROKEN  
STRATUS DECK IS LIKELY TO DEVELOP TOMORROW WHICH WILL KEEP MOST  
AREAS FROM REACHING INTO THE 90S. MORE SHOWERS AND ISOLATED  
THUNDERSTORMS WILL LIKELY FORM ACROSS NW IA AND SW MN DURING THE  
AFTERNOON. WHILE STORMS AREN'T EXPECTED TO DEVELOP IN THE AREA, THEY  
WILL LIKELY FORM IN SOUTHERN ND OR CENTRAL SD DURING THE AFTERNOON  
AND TRAVEL INTO THE AREA OVERNIGHT. THE NAM BASED CAMS ALL SHOW A  
GROUP/LINE OF STORMS FORMING, WITH VARYING SPATIAL AND TEMPORAL  
SOLUTIONS. WITH MLCAPE VALUES IN EXCESS OF 3000 J/KG, SPC'S MARGINAL  
RISK FOR OUR AREA SEEMS WARRANTED ALTHOUGH BULK SHEAR VALUES ARE  
LESS THAN IDEAL FOR SEVERE WEATHER.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 325 PM CDT WED AUG 12 2020  
 
AFTER ANY LINGERING SHOWERS AND THUNDERSTORMS EXIT OFF TO OUR EAST,  
THE LLJ WILL CONTINUE TO BRING IN ABOVE NORMAL TEMPERATURES WITH  
BREEZY CONDITIONS. THIS WILL LIKELY BE OUR LAST DAY WITH DEWPOINTS  
IN THE 70S, AS A COLD FRONT IS GOING TO BE PUSHED ACROSS THE AREA BY  
A SURFACE HIGH PRESSURE IN SOUTHERN SASKATCHEWAN. THIS COLD FRONT  
WILL BE ACTING AS THE FOCUS MECHANISM FOR CONVECTION LATER IN THE  
AFTERNOON, LARGELY EAST OF THE JAMES RIVER VALLEY. LOOK FOR AROUND  
3000 J/KG OF MLCAPE, WITH ROUGHLY 40 KNOTS OF BULK SHEAR TO BE  
AVAILABLE FOR THE STORMS TO TAP INTO. BEST SOUNDING PROFILES LOOK TO  
BE ACROSS SW MN ALONG AND NORTHEAST OF THE BUFFALO RIDGE, WHERE THE  
THICKEST CAPE PROFILES ARE ALONG WITH DECENT VEERING WINDS. SEVERE  
THUNDERSTORMS WILL BE POSSIBLE PRIMARILY ALONG AND EAST OF THE I-29  
CORRIDOR, WITH BEST CHANCES ALONG THE BUFFALO RIDGE WHICH MATCHES  
WELL WITH SPCS DAY 3 MARGINAL AND SLIGHT RISK.  
 
MODELS DISAGREE ON HOW QUICKLY THE AFOREMENTIONED COLD FRONT WILL  
BE PUSHED THROUGH THE AREA, BUT THERE IS DECENT AGREEMENT THAT  
TEMPERATURES WILL BECOME MORE SEASONABLE WITH HIGHS IN THE LOWER 80S  
AND DEWPOINTS DROPPING BACK DOWN INTO THE 60S. A COUPLE MODELS HINT  
AT SOME STORMS FORMING ALONG THE NORTHERN INSTABILITY GRADIENT LATE  
SATURDAY AFTERNOON INTO SUNDAY MORNING, SO HAVE LEFT A SLIGHT CHANCE  
OF THAT OCCURRING IN THE GRIDS BUT CONFIDENCE IS NOT HIGH ON THAT  
OCCURRING. THE REST OF THE EXTENDED FORECAST WILL FEATURE BELOW TO  
AVERAGE TEMPERATURES, WITH SLIGHTLY BREEZY DAYTIME CONDITIONS. DON'T  
SEE ANY STRONG SIGNALS FOR RAIN CHANCES INTO THE MIDDLE OF THE WEEK,  
LARGELY THANKS TO UPPER LEVEL RIDGING AND NORTHWESTERLY FLOW  
ALOFT.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)  
ISSUED AT 632 PM CDT WED AUG 12 2020  
 
WHILE NOT ZERO, CHANCES FOR PRECIPITATION OVER THE NEXT 24 HOURS  
ARE RATHER REMOTE, WITH LOW CHANCES PRIMARILY CONFINED TO PORTIONS  
OF SOUTHWEST MN/NORTHWEST IA, EAST OF OUR TAF SITES. COULD SEE  
MVFR STRATUS AND/OR FOG IMPACT AREAS EAST OF I-29 IN THE 09Z-15Z  
WINDOWS AS WELL. AGAIN THIS CURRENTLY EXPECTED TO REMAIN EAST OF  
TAF SITES, BUT WILL CARRY SCT015-025 AT KFSD/KSUX TO INDICATE  
PROXIMITY OF THE POTENTIAL CLOUD BANK TO OUR EAST.  
 
SOUTHERLY LOW LEVEL JET THROUGH CENTRAL SD WILL BRING A PERIOD OF  
NON-CONVECTIVE LOW LEVEL WIND SHEAR TO KHON DURING THE PRE-DAWN  
HOURS, WITH THESE STRONGER WINDS ALOFT TRANSLATING TO OCCASIONAL  
GUSTS 20-30KT DURING THE LATE MORNING-AFTERNOON HOURS THURSDAY.  
 

 
   
FSD WATCHES/WARNINGS/ADVISORIES
 
 
SD...NONE.  
MN...NONE.  
IA...NONE.  
NE...NONE.  

 
 

 
 
SHORT TERM...APT  
LONG TERM...APT  
AVIATION...JH  
 
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