830
FXUS63 KFSD 171141
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
641 AM CDT THU APR 17 2025
KEY MESSAGES
- ISOLATED SHOWERS AND THUNDERSTORMS THROUGH LATE THIS MORNING;
STRONG TO SEVERE STORMS UNLIKELY.
- GREATEST STORM CHANCES THIS AFTERNOON AND EVENING ALONG AND
SOUTHEAST OF A VERMILLION TO SLAYTON LINE. STRONG TO SEVERE
STORMS ARE POSSIBLE, MAINLY BETWEEN 4 PM AND 10 PM. LARGE HAIL
TO THE SIZE OF PING-PONG BALL SIZED (ISOLATED LARGER) IS THE
MAIN THREAT, WITH DAMAGING WIND GUSTS TO 60 MPH A SECONDARY
HAZARD.
- SHOWERS CONTINUE TONIGHT THROUGH FRIDAY AFTERNOON WITH COOLER
AND BREEZY CONDITIONS.
- PERIODIC LOW RAIN CHANCES AND NEAR NORMAL TEMPERATURES RETURN
FOR THE WEEKEND THROUGH MID NEXT WEEK. CONFIDENCE IN
PRECIPITATION CHANCES AND TIMING IS LOW (LESS THAN 30%).
DISCUSSION
ISSUED AT 345 AM CDT THU APR 17 2025
NOW-TONIGHT: A FEW RETURNS ON RADAR THIS MORNING ACROSS SOUTHWESTERN
MN AND NORTHERN IA WITH THE FIRST WEAK SHORT WAVE, BUT HAVE NOT SEEN
ANY PRECIPITATION REACH THE GROUND THROUGH 3 AM CDT/08Z. IT'S A MILD
BUT BREEZY START TO THE DAY, WITH CURRENT TEMPS IN THE 50S. LOOKING
BACK TO THE WEST, INCREASED CIRRUS EXISTS OVER NORTHERN NE WITH THE
NEXT WAVE, WHICH WE'LL BE WATCHING AS IT MOVES NORTHEAST THROUGH
DAYBREAK FOR POTENTIAL SHOWER/STORM DEVELOPMENT. ALTHOUGH THIS AREA
IS COINCIDENT WITH WAA, NOSE OF THE UPPER JET, AND THE DEVELOPING
SURFACE LOW PRESSURE, ANY SHOWER/STORM DEVELOPMENT LOOKS TO BE
HIGHLY ISOLATED. STRONG CAP REMAINS IN PLACE, SO WE'D EITHER NEED TO
BREAK THE CAP OR HAVE STORMS DEVELOP OFF OF ROUGHLY 700 MB. THE
ISSUE IS THAT DESPITE ELEVATED INSTABILITY AT THIS LEVEL, WE'RE
LACKING MOISTURE THROUGH AND BELOW THIS LEVEL. THEREFORE, LIMITED
MENTION TO SPRINKLES AND POPS TO LESS THAN 15% THROUGH LATE MORNING.
CONCERN SHIFTS TO THE AFTERNOON AND EVENING HOURS AS SURFACE LOW
PRESSURE, ATTENDANT FRONTS, AND ELEVATED COLD FRONT MOVE EAST
THROUGH THE FORECAST AREA. GUIDANCE THIS MORNING IS BEGINNING TO MIX
MORE EFFICIENTLY ALONG AND SOUTHEAST OF A VERMILLION TO SLAYTON
LINE, ERODING THE CAP MORE QUICKLY (AS EARLY AS 2-3 PM CDT/19-20Z)
NEAR AND JUST AHEAD OF THE COLD FRONT. THIS AREA IS AT THE GREATEST
RISK OF STRONG TO SEVERE STORMS THROUGH THE AFTERNOON AND EVENING,
THOUGH THERE REMAINS SOME QUESTION IN MOISTURE RETURN IN THE LOWER
MID LEVELS - ESPECIALLY GIVEN THE CONVECTION ON-GOING AT THE TIME OF
THIS DISCUSSION ACROSS KS AND WESTERN MO. TIMING COULD BE AS EARLY
AS 2 PM FOR A ROGUE STORM BUT THINK THE GREATEST RISK IS 4 PM
CDT/21Z CONTINUING THROUGH 10 PM CDT/18.03Z. MUCAPE 1200-1500+ J/KG
ALONG WITH STEEP MID LEVEL LAPSE RATES OVER 7.5 DEG C/KM AND 0-6
BULK SHEAR VALUES INCREASING TO OVER 40 KNOTS SUPPORT A LARGE HAIL
THREAT OF PING-PONG BALL SIZE (1.5") HAIL. CAN'T ENTIRELY RULE OUT
LARGER HAIL FOR MORE ISOLATED, SUPERCELLULAR STORMS AHEAD OF ANY
LINEAR (TIED TO THE FRONT) STORMS. WIND GUSTS TO 60 MPH ARE POSSIBLE
WITH DCAPE VALUES PROGGED OVER 800 J/KG OVER NORTHWESTERN IA.
COULD SEE LOCALLY HEAVIER RAINFALL RATES WITH PWAT VALUES 1-1.5";
HOWEVER, CONVECTION SHOULD BE PROGRESSIVE ENOUGH TO LIMIT CONCERNS
TO LOCALIZED PONDING OF WATER THIS AFTERNOON THROUGH TONIGHT.
RAINFALL AMOUNTS LARGELY LESS THAN HALF AN INCH, WITH THE HIGHEST
CHANCES (40-50%) FOR MORE THAN HALF AN INCH OF RAIN ACROSS
SOUTHWESTERN MN.
FOR TEMPERATURES, THIS WILL BE TIMING DEPENDENT. EXPECT AREAS WEST
OF WAGNER TO DE SMET TO WARM INTO THE 60S, WITH 70S TO NEAR 80
FURTHER EAST WHERE WE'LL REMAIN IN THE WARM SECTOR THE LONGEST. IF
MOISTURE RETURN IS EFFICIENT, WE COULD SEE DEW POINTS TODAY IN THE
EAST IN THE 50S. LOWS TONIGHT FALL INTO THE MID 30S (WEST) TO MID
40S (EAST) BEHIND THE COLD FRONT. BREEZY CONDITIONS PREVAIL TODAY
AND TONIGHT, ESPECIALLY BEHIND THE FROPA.
FRIDAY: ELONGATED MID AND UPPER LEVEL TROUGH CONTINUES TO SLIDE TO
THE EAST FRIDAY. SOUTHWESTERLY FLOW ALOFT AND A FEW MID LEVEL SHORT
WAVES WILL ALLOW FOR LIGHT PRECIPITATION TO CONTINUE THROUGH AT
LEAST THE FIRST HALF OF THE DAY FRIDAY. COOLER AND BREEZY CONDITIONS
PREVAIL WITH LOWER LEVEL NORTHERLY FLOW. HIGHS IN THE UPPER 40S TO
LOWER 50S WITH WIND GUSTS TO 30 MPH. CHILLIER CONDITIONS FRIDAY
NIGHT WITH LOWS FALLING INTO THE UPPER 20S TO LOWER 30S.
SATURDAY-MONDAY: CLOSED MID/UPPER LOW DEVELOPS IN THE FOUR CORNERS
REGION OUT OF THE AFOREMENTIONED TROUGH. THIS FEATURE MOVES TO THE
NORTHEAST THROUGH THE WEEKEND; HOWEVER, GUIDANCE HAS BEEN
CONTINUALLY TRENDING FURTHER TO THE SOUTH WITH THE TRACK OF THIS LOW
AND THE ATTENDANT SURFACE LOW. WILL MAINTAIN THE NBM POPS, WITH
MODERATE CHANCES (40-55%) OF MEASURABLE (0.01" OR MORE) RAINFALL
ALONG/EAST OF I-29 SUNDAY INTO MONDAY. DETERMINISTIC GUIDANCE IS
QUITE VARIED ON THE TRACK OF THE SURFACE LOW. AT 21.06Z, THE GFS HAS
THE CENTER OF THE LOW IN WESTERN IL, THE ECMWF IS IN CENTRAL IA, AND
THE CANADIAN IS STILL CENTERED IN FAR NORTHWESTERN MO. SO LOW
CONFIDENCE IN PRECIP CHANCES. TEMPERATURES START OFF THE WEEKEND
COOLER THAN AVERAGE WITH HIGHS IN THE 50S SATURDAY, WARMING TO THE
60S AND 70S MONDAY. LOWS IN THE LOWER TO MID 30S.
TUESDAY-THURSDAY: QUASI-ZONAL TO ZONAL FLOW REGIME SETS UP FOR MID
NEXT WEEK. NEAR TO ABOVE AVERAGE TEMPERATURES EXPECTED. A FEW SHORT
WAVES COULD BRING PERIODIC PRECIPITATION CHANCES SO WILL MAINTAIN
THE LOW (~30% OR LESS) CHANCES POPULATED FROM THE NBM.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 634 AM CDT THU APR 17 2025
VFR CONDITIONS THIS MORNING INTO THE EARLY PART OF THE
AFTERNOON, WITH INCREASING MID AND HIGH CLOUDS. CAN'T RULE OUT A
SHOWER OR ISOLATED THUNDERSTORM THROUGH AROUND 18Z.
LLJ IS LEADING TO SOME LLWS AT KSUX INTO NORTHWESTERN IA THIS
MORNING. LLWS CONDITIONS REMAIN JUST BELOW CRITERIA AT KFSD, SO
HAVE OMITTED WITH THIS PACKAGE. COLD FRONT IS EXPECTED TO MOVE
THROUGH THE AREA TODAY AND TONIGHT. AHEAD OF THE FRONT, BREEZY
SOUTHERLY WINDS WILL GUSTS TO AROUND 20 TO 25 KNOTS. WINDS SHIFT
BEHIND THE FRONT TO NORTHERLY AND REMAIN STRONG THROUGH THE END
OF THE PERIOD WITH GUSTS AROUND 30 KNOTS.
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON
AND EVENING, MAINLY ALONG AND SOUTHEAST OF A VERMILLION (KVMR)
TO SLAYTON (KDVP) LINE. SOME OF THESE STORMS COULD BE STRONG TO
SEVERE WITH LARGE HAIL THE MAIN THREAT. SHOWERS AND VERY
ISOLATED STORMS CONTINUE INTO THE MORNING HOURS FRIDAY. MVFR AND
LOWER STRATUS WILL BUILD IN BEHIND THE FRONT, AND EXPECT MVFR
AND LOWER CONDITIONS WITH ANY CONVECTION.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...SG
AVIATION...SG
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