107  
FXUS63 KFSD 201950  
AFDFSD  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SIOUX FALLS SD  
250 PM CDT TUE MAY 20 2025  
   
KEY MESSAGES  
 
- SHOWER CHANCES OF 20 TO 50 PERCENT CONTINUE TONIGHT THROUGH  
WEDNESDAY WITH THE HIGHEST CHANCES NORTH OF I-90. ADDITIONAL  
RAINFALL AMOUNTS WILL BE LIGHT, RANGING FROM A FEW HUNDREDTHS  
UP TO A TENTH OF AN INCH.  
 
- THURSDAY WILL BE DRY BEFORE SHOWER AND THUNDERSTORM CHANCES  
RETURN FRIDAY INTO THE MEMORIAL DAY WEEKEND. SEVERE WEATHER  
IS NOT EXPECTED AT THIS TIME.  
 
- TEMPERATURES WILL BE SEASONABLY COOL THROUGH MEMORIAL DAY  
WEEKEND WITH HIGHS RANGING FROM THE MID 50S INTO THE 60S AND  
LOWS IN THE UPPER 30S AND 40S. THESE HIGHS ARE 10 TO 15  
DEGREES BELOW LATE MAY NORMALS.  
 
 
   
DISCUSSION  
 
ISSUED AT 250 PM CDT TUE MAY 20 2025  
 
20Z SURFACE ANALYSIS SHOWS LOW PRESSURE ACROSS IOWA WITH AN  
INVERTED TROUGH AXIS FROM ROUGHLY SIOUX CITY TO CHAMBERLAIN.  
ALONG THIS WEAK CONVERGENCE BOUNDARY, DIURNALLY DRIVEN LIGHT  
RAIN SHOWERS HAVE DEVELOPED. THERE HAS YET TO BE ANY LIGHTNING  
ACTIVITY WITH THESE SHOWERS AND BARRING A ROUGE STRIKE OR TWO,  
NOT ANTICIPATING THUNDERSTORMS GIVEN LACK OF INSTABILITY.  
FARTHER NORTH, THE SOUTHERN EDGE OF THE LARGE WARM ADVECTIVE  
RAIN SHIELD IS LIFTING NORTH OUT OF THE FORECAST AREA. TAKEN  
TOGETHER, EXPECT AN OVERALL DRYING TREND INTO THIS EVENING AND  
OVERNIGHT.  
 
ON WEDNESDAY, THE SURFACE LOW AND ASSOCIATED INVERTED TROUGH  
SLIDE EAST AND AWAY FROM THE IMMEDIATE TRI-STATE REGION. 12Z  
GUIDANCE STILL SUGGESTS SOME WRAP AROUND RAIN SHOWERS ESPECIALLY  
ACROSS THE NORTHERN HALF TO THIRD OF THE FORECAST AREA. FOR THIS  
REASON, WILL MAINTAIN 20 TO 50 PERCENT POPS, BUT ANY RAINFALL  
AMOUNTS ARE LIKELY TO BE ONLY A FEW HUNDREDTHS AT BEST. SKIES  
WILL BE MOSTLY CLOUDY, BUT SHOULD BEGIN TO SEE SOME PEAKS OF  
SUN, ESPECIALLY ACROSS THE SOUTH BY LATE AFTERNOON/EVENING.  
TEMPERATURES WILL BE BIT WARMER, PEAKING IN THE LOW TO MID 50S,  
BUT THIS IS 15 TO 20 DEGREES BELOW LATE MAY NORMALS.  
 
500 HPA RIDGING ALOFT AND HIGH PRESSURE AT THE SURFACE BUILDS  
ACROSS THE REGION ON THURSDAY, RESULTING IN MORE SUN THAN  
CLOUDS, DRY CONDITIONS, AND TEMPERATURES IN THE LOW TO MID 60S.  
FRIDAY AND ESPECIALLY INTO SATURDAY, THIS RIDGE BEGINS TO  
BREAK-DOWN GIVEN AN APPROACHING BROAD PACIFIC TROUGH. THE  
EVOLUTION OF THIS TROUGH INTO THE MEMORIAL DAY WEEKEND IS NOT  
HANDLED WELL, BUT CERTAINLY SUGGESTS A MORE UNSETTLED PATTERN.  
FOR THIS REASON, BROAD BRUSHED CHANCE TO LOW-END LIKELY NBM POPS  
SEEMS REASONABLE AT THIS TIME. THAT SAID, A MUCH COOLER AIR  
MASS WITH INSTABILITY BOTTLED UP ACROSS AREAS MAINLY SOUTH OF  
I-80 LOOK TO LIMIT ANY SEVERE POTENTIAL ACROSS FORECAST AREA  
INTO EARLY NEXT WEEK. THIS IS SUPPORTED BY MEDIUM-RANGE SPC  
OUTLOOKS AND CSU-MACHINE LEARNING SEVERE PROBABILITIES OF LESS  
THAN 5 PERCENT.  
 
OF HIGHER CERTAINTY WILL BE TEMPERATURES, WITH DAILY HIGHS INTO  
MEMORIAL DAY WEEKEND IN THE LOW TO MID 60S, WHICH IS ROUGHLY 5  
TO 10 DEGREES BELOW NORMAL.  
 
 
   
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/  
 
ISSUED AT 1228 PM CDT TUE MAY 20 2025  
 
OVERCAST SKIES WITH PERIODS OF LIGHT DRIZZLE WILL BE THE RULE AT  
KHON/KFSD, WHILE KSUX IS LIKELY TO REMAIN DRY. GUIDANCE FAVORS  
HIGH IFR TRANSITIONING TO LOW-MVFR CEILINGS AND 3-5 SM  
VISIBILITY IN DRIZZLE/MIST AT KHON/KFSD AT LEAST INTO THE  
EVENING. THEN, KFSD/KSUX ARE LIKELY TO OSCILLATE AROUND A 1000  
FT AGL CLOUD BASE THIS EVENING AND OVERNIGHT, WHEREAS KHON HAS  
THE BEST CHANCE OF DROPPING BACK TO IFR. A SLOW RISING OF  
CEILINGS IS EXPECTED WEDNESDAY MORNING, BUT STILL LIKELY TO BE  
BELOW 3000 FT AGL BY 21.18Z.  
 
WINDS THROUGH THE PERIOD WILL GENERALLY SHIFT FROM A NORTHEAST  
TO NORTH TO NORTHWEST DIRECTION. KSUX WILL BE THE BREEZIEST WITH  
OCCASIONAL GUSTS UP TO 25 KTS BEGINNING THIS AFTERNOON, WHEREAS  
HIGHER GUSTS UP TO 20 KTS AT KHON/KFSD MAY HOLD OFF UNTIL LATE  
TONIGHT INTO WEDNESDAY MORNING.  
 
 
   
FSD WATCHES/WARNINGS/ADVISORIES  
 
SD...NONE.  
MN...NONE.  
IA...NONE.  
NE...NONE.  
 
 
 
 
 
DISCUSSION...ROGERS  
AVIATION...ROGERS  
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