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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