726  
FXUS63 KFSD 232010  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
310 PM CDT SUN JUL 23 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH MONDAY)  
ISSUED AT 308 PM CDT SUN JUL 23 2017  
 
HIGH PRESSURE AT THE SURFACE WILL MOVE OFF TO THE EAST TONIGHT,  
SHIFTING THE FORECAST AREA'S WINDS AROUND TO AN EAST TO SOUTHEAST  
DIRECTION. USED BIAS CORRECTED GUIDANCE VALUES FOR TONIGHT'S LOWS  
WHICH CAPTURED THE WARMER READINGS IN THE 60S IN OUR EASTERN ZONES  
DUE TO THE RETURN FLOW. CONVERSELY, COOLER READINGS IN THE 50S ARE  
WARRANTED ALONG AND EAST OF THE I 29 CORRIDOR WITH LIGHTER WINDS. IT  
STILL LOOKS LIKE PATCHY OR AREAS OF FOG WILL DEVELOP ACROSS THE  
EASTERN HALF LATE TONIGHT AND VERY EARLY MONDAY DUE TO A LIGHT FLOW  
OF AIR AND SMALL SURFACE DEW POINT DEPRESSIONS. IF THE GROUND WERE  
WET OVER MORE MORE LOCATIONS, THE FOG POTENTIAL WOULD LIKELY BE  
WORSE. BUT AS IT STANDS NOW, IT LOOKS TO MAINLY AFFECT LOW LYING  
AREAS AND LOCATIONS FAVORED BY COOL AIR DRAINAGE AND IT SHOULD BE  
FAIRLY SHALLOW.  
 
MONDAY WILL BE A WARMER DAY, AND FAIRLY BREEZY ALONG AND WEST OF THE  
JAMES RIVER VALLEY AS A SOUTHEAST FLOW OF AIR INCREASES. OUR ZONES  
IN SOUTH CENTRAL SD EASILY MIX TO ABOUT 97 DEGREES. MANUALLY RAISED  
GUIDANCE TEMPERATURES EAST OF I 29 INTO THE LOWER 80S AS 850MB  
TEMPERATURES DO NOT JUSTIFY MID TO UPPER 70S AT THIS TIME. AND IT  
APPEARS AFTER PERUSING OVER THE SOUNDINGS THAT NOT A LOT OF CUMULUS  
WILL DEVELOP IN OUR EAST MONDAY AFTERNOON TO HINDER A RISE IN  
TEMPERATURES. PUT IN A SLIGHT CHANCE OF TSRA LATE MONDAY IN OUR FAR  
WESTERN ZONES DUE TO A SHORT WAVE PASSING ACROSS THIS AREA WHICH IS  
CURRENTLY IN NORTHERN WY. QUITE A NICE VORT MAX IS SHOWING UP ON THE  
WATER VAPOR IMAGERY. IN ADDITION, THE FLOW AT 700MB SHOWS A SECOND  
WAVE MOVING SLOWLY NORTHEASTWARD WHICH IS CURRENTLY IN THE SOUTHERN  
ROCKIES WHICH WILL HELP TO AID IN ASCENT. IT IS DRY BELOW 700MB  
HOWEVER, SO IF ANY ACTIVITY DEVELOPS IT WILL ONLY BE ISOLATED.  
 
   
LONG TERM
 
(MONDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 308 PM CDT SUN JUL 23 2017  
 
POTENTIAL FOR ISOLATED ELEVATED SHOWERS/STORMS BEGINNING IN OUR FAR  
SOUTHWEST LATE MONDAY AFTERNOON WILL CONTINUE THROUGH THE MISSOURI  
VALLEY MONDAY NIGHT. SOUNDINGS REMAIN QUITE DRY BELOW 700MB, BUT  
WITH THE MID-UPPER LEVEL SUPPORT AND ELEVATED INSTABILITY, CANNOT  
RULE OUT SOME VERY LIGHT PRECIPITATION AND/OR CLAP OF THUNDER.  
 
MAIN FOCUS FOR PRECIPITATION WILL BE LATE TUESDAY THROUGH WEDNESDAY.  
100+ KT UPPER JET HAS TRENDED A LITTLE FARTHER NORTH, TRACKING NEAR  
THE CANADIAN BORDER IN THE LATEST MODELS, BUT WILL STILL BE LOOKING  
AT ASSOCIATED MID-UPPER WAVE DRAGGING A COOL FRONT TO NEAR OUR FAR  
NORTHWEST CORNER AROUND HURON BY LATE IN THE DAY. FORECAST SOUNDINGS  
(ASIDE FROM OVERLY MIXED GFS) REMAIN CAPPED AHEAD OF THE BOUNDARY,  
BUT THIS FRONT SHOULD BECOME A FOCUS FOR STORM DEVELOPMENT BY LATE  
TUESDAY/TUESDAY NIGHT AS IT PUSHES ACROSS THE FORECAST AREA. BETTER  
FORCING/SHEAR FOCUSED NORTH OF THE FORECAST AREA, BUT POCKETS OF  
MODERATE SHEAR COMBINED WITH CAPE VALUES EXCEEDING 2000 J/KG SHOULD  
SUPPORT ISOLATED STRONG-SEVERE STORMS ACROSS OUR NORTHERN FORECAST  
AREA. AHEAD OF THE FRONT, STRONG THERMAL RIDGE IN SOUTH-SOUTHWEST  
LOW LEVEL FLOW SHOULD RESULT IN THE LAST DAY OF HOT TEMPERATURES WE  
WILL SEE IN THE NEAR FUTURE. TEMPERED THE WARMING/MIXING POTENTIAL  
ACROSS FAR NORTHERN AREAS/HIGHWAY 14 CORRIDOR, WHERE WE HAVE SEEN A  
FAIRLY WIDESPREAD 2-4 INCHES OF RAIN OVER THE PAST WEEK. HOWEVER,  
EVEN THERE LOW LEVEL TEMPERATURES SUGGEST HIGHS SHOULD TOP 90 AGAIN  
FOR THE FIRST TIME SINCE THIS RAINY STRETCH BEGAN. IN CONTRAST, OUR  
PERSISTENT DRY LOCATIONS IN THE SOUTHWEST CWA SHOULD MORE EASILY  
CLIMB INTO THE UPPER 90S TO AROUND 100.  
 
COLD FRONT PUSHES SLOWLY SOUTHWARD LATE TUESDAY NIGHT/WEDNESDAY,  
WITH MODELS SHOWING A MORE POTENT SHORTWAVE LIFTING OUT OF THE  
CENTRAL ROCKIES AND INTERACTING WITH THE BOUNDARY THROUGH THE DAY  
WEDNESDAY AND INTO WEDNESDAY EVENING. DEPENDING ON TIMING OF THE  
BOUNDARY, AND EVEN MORE, THE EXTENT OF ANY RAIN ON WEDNESDAY, COULD  
AGAIN SEE AN ISOLATED STRONG-SEVERE STORM IN OUR FAR SOUTHEAST LATE  
WEDNESDAY. WITH MOST OF THE AREA NORTH OF THE FRONT, AND POTENTIAL  
FOR QUITE A BIT OF CLOUD COVER/RAIN ACROSS THE AREA, TEMPERATURES ON  
WEDNESDAY WILL BE QUITE A BIT COOLER WITH HIGHS IN THE UPPER 70S TO  
MID 80S.  
 
LATE NEXT WEEK, SURFACE HIGH BEGINS TO DOMINATE ACROSS THE UPPER  
MISSISSIPPI VALLEY, WITH ANY SIGNIFICANT LOW LEVEL MOISTURE CUTOFF  
BY A BOUNDARY PUSHING THROUGH THE CENTRAL/SOUTHERN PLAINS. THIS  
SHOULD LEAD TO A FAIRLY DRY PERIOD THURSDAY-SUNDAY, WITH DAYTIME  
TEMPERATURES NEAR TO A FEW DEGREES BELOW NORMAL.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)  
ISSUED AT 1229 PM CDT SUN JUL 23 2017  
 
CUMULUS CLOUDS WILL BE ABUNDANT IN SOUTHWEST MINNESOTA THROUGH MID  
AFTERNOON. HOWEVER ANY UPPER END MVFR CEILINGS WILL MIX OUT TO A  
HIGHER LEVEL, PRODUCING VFR CONDITIONS BY MID AFTERNOON. THE OTHER  
ITEM TO WATCH FOR IS FOG DEVELOPMENT LATE TONIGHT AND VERY EARLY  
MONDAY. AS HIGH PRESSURE MOVES OFF TO THE EAST, FOG COULD BE FOUND  
AT KFSD, BUT MORE PROMINENTLY IN NORTHWEST IOWA AFFECTING THE  
KSUX TAF SITE. AT THIS TIME, CERTAINLY WOULD NOT RULE OUT IFR FOG  
FOR KSUX FOR A BRIEF TIME SHORTLY AFTER SUNRISE.  
 

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

 
 

 
 
SHORT TERM...MJ  
LONG TERM...JH  
AVIATION...MJ  
 
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