198
FXUS63 KFSD 181801
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
101 PM CDT MON MAY 18 2026
KEY MESSAGES
- SHOWERS AND ISOLATED THUNDERSTORMS RETURN TO THE AREA THIS
AFTERNOON THIS EVENING INTO TONIGHT.
- A FEW STORMS ALONG AND SOUTHEAST OF A WAYNE TO SHELDON TO
WINDOM LINE MAY BE STRONG TO SEVERE LATE THIS AFTERNOON INTO
THIS EVENING. THE MAIN THREAT WOULD BE HAIL TO HALF DOLLAR
SIZE BUT STORMS THIS STRONG SHOULD REMAIN VERY ISOLATED AND
LIKELY CLOSER TO NEAR AND EAST OF HIGHWAY 60.
- AREAS OF FROST OR FREEZE WILL BE POSSIBLE ON WEDNESDAY
MORNING, WITH THE BETTER CHANCES NORTH OF I-90.
- COOL CONDITIONS PREVAIL THIS WEEK. DRY WEATHER EXPECTED MID
WEEK. ANOTHER ROUND OF STORMS IS POSSIBLE THURSDAY THROUGH
FRIDAY.
DISCUSSION
ISSUED AT 1258 PM CDT MON MAY 18 2026
EARLY THIS AFTERNOON THE SURFACE TO 925 MB FRONT WAS ACROSS SOUTHERN
NE INTO SOUTHERN IA. GIVEN THE MARGINAL STRENGTH OF THE INCOMING
WAVE, THIS BOUNDARY SHOULD NOT LIFT FAR ENOUGH NORTH AND WEST
BY LATE AFTERNOON TO GET INTO THE AREA. THIS SHOULD LIMIT ANY
WIND AND TORNADO THREATS AND KEEP THEM OFF TO THE SOUTHEAST.
HOWEVER, SOME ELEVATED HAILERS WILL REMAIN POSSIBLE ACROSS
MAINLY NORTHWEST IA AS ELEVATED CAPE VALUES RAMP UP TO ABOUT
1000-1500 J/KG AND DEEP LAYER SHEAR IS A FAIRLY STRONG,
UNIDIRECTIONAL 40-50 KNOTS. THIS WOULD BE LIFTING A PARCEL FROM
ABOVE THE STRATUS LAYER, WHICH WOULD LIKELY BE IN ABOUT THE
800-750MB LAYER. THE BETTER CHANCES WILL BE FROM ABOUT 5 PM TO 9
PM.
AFTER THIS WAVE PUSHES THE REMAINING INSTABILITY OUT OF THE AREA
THIS EVENING, DRY AND COOL CONDITIONS ARE EXPECTED FOR TUESDAY AND
WEDNESDAY. THE ONLY CONCERNS ON THESE TWO DAYS WILL BE THE POTENTIAL
FOR FROST AND FREEZE CONDITIONS, MOSTLY NORTH OF I-90, AS SURFACE
HIGH PRESSURE IS IN PLACE. ANOTHER WEAKER WAVE MOVES THROUGH THE
AREA ON WEDNESDAY BUT FOR NOW THIS APPEARS TO BRING MAINLY MID LEVEL
CLOUD COVER.
THE NEXT BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS WILL COME
THURSDAY NIGHT INTO FRIDAY NIGHT. AT THIS TIME SEVERE WEATHER LOOKS
TO REMAIN ISOLATED AS MODEL INSTABILITY FIELDS ARE HINTING AT 1000
J/KG CAPE OR LESS FOR THE MOST PART.
ONCE THIS WAVE PASSES A WARMING TREND SHOULD MOVE IN AS FLAT RIDGING
ALOFT DEVELOPS AHEAD OF A DEEPENING LOW PRESSURE IN THE NORTHERN
ROCKIES. SATURDAY SHOULD BE MILD, LIKELY IN THE 70S, WHILE SUNDAY
SEES THE BETTER CHANCE TO WARM INTO THE 80S.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1243 PM CDT MON MAY 18 2026
WIDESPREAD STRATUS, MAI.NLY IFR BUT OCCASIONALLY MVFR, WILL
PERSIST THROUGH MUCH OF THE NIGHT, BUT GRADUALLY IMPROVE LATER
TONIGHT INTO TUESDAY MORNING. SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL INCREASE IN COVERAGE THROUGH THE AFTERNOON
INTO THE EARLY EVENING, THEN GRADUALLY DIMINISH THROUGH THE
EARLY OVERNIGHT HOURS. THE STRONGEST THUNDERSTORMS WILL BE IN
PARTS OF NORTHWEST IA, WITH THE BETTER CHANCE FROM 5 PM THROUGH
9 PM. A FEW OF THESE STORMS COULD CONTAIN HAIL.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...08
AVIATION...08
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