384
FXUS63 KFSD 172300
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
600 PM CDT THU APR 17 2025
KEY MESSAGES
- SHOWERS AND THUNDERSTORMS ARE EXPECTED TO FORM ALONG A COLD
FRONT THIS AFTERNOON THROUGH THIS EVENING. SOME OF THESE
STORMS COULD BE STRONG TO SEVERE, ESPECIALLY FOR AREAS
SOUTHEAST OF A LINE FROM VERMILLION, SOUTH DAKOTA TO SLAYTON,
MINNESOTA.
- THE GREATEST THREAT WITH THESE STORMS IS LARGE HAIL UP TO 2
INCHES IN DIAMETER. SECONDARY TO THESE ARE WIND GUSTS 60-65
MPH. THOUGH THE RISK IS LOW, A TORNADO OR TWO CANNOT BE RULED
OUT.
- SHOWERS CONTINUE 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 248 PM CDT THU APR 17 2025
THIS AFTERNOON-FRIDAY: THIS AFTERNOON WE ARE AT RISK FOR STRONG TO
SEVERE THUNDERSTORMS. THE AREA MOST LIKELY TO SEE STORMS IS
SOUTHEAST OF A LINE FROM VERMILLION, SOUTH DAKOTA TO SLAYTON,
MINNESOTA. THE LLJ BEGINS TO INCREASE THIS AFTERNOON, INCREASING
SHEAR. THIS ALSO WORKS TO BRING NORTHWARD MOISTURE WITH
DEWPOINTS EXPECTED TO REACH THE UPPER 50S IN NORTHWESTERN IOWA,
AND SOUTHWESTERN MINNESOTA. WITH THE MOISTURE COMES INCREASING
INSTABILITY. MUCAPE OF 1500-2000 J/KG COUPLED WITH 0-6 BULK
SHEAR OF 40-50 KTS, AND 0-3 STORM RELATIVE HELICITY OF 100-200
M2/S2 ALL INDICATE STRONGER ROTATING STORMS ARE POSSIBLE.
SOUNDINGS INDICATE THAT THE STRONG CAP FROM EARLIER IN THE DAY
HAS MOSTLY ERODED OUT, INCREASING CHANCES FOR SURFACE BASED
CONVECTION. ELONGATED CLOCKWISE CURVED HODOGRAPHS FURTHER
SUPPORT THIS ANALYSIS. MIDLEVEL LAPSE RATES ARE EXPECTED TO BE
7.5 C/KM OR GREATER. CONSIDERING ALL THESE FACTORS, THE GREATEST
THREAT WITH THESE STORMS IS MOST LIKELY LARGE HAIL OF 2 INCHES
IN DIAMETER. IN ADDITION, AS RAIN FALLS THROUGH A LAYER OF
MIDLEVEL DRY AIR, EVAPORATIONAL COOLING COULD ENHANCE
THUNDERSTORM DOWN DRAFTS. MODEL SOUNDINGS SUPPORT THIS WITH
DCAPE OF AROUND 800 J/KG. DOWNDRAFTS AND OUTFLOW GUSTS OF 60-65
MPH ARE AN ADDITIONAL THREAT. THOUGH STORM BASES WILL BE
RELATIVELY HIGH, (ABOVE 5000 FT AGL) AND THE RISK IS LOW, A
TORNADO OR TWO CANNOT BE RULED OUT. BULK SHEAR IN THE 0-1 KM
LAYER IS BORDERLINE, BETWEEN 15- 30 KTS. BUT AREAS ALONG THE
WARM FRONT HAVE INCREASED RISK AS THE WARM, MOIST AIR BEGINS TO
OVERRUN THE COOLER, DRY AIR MOVING SOUTHEAST. AREA AT GREATEST
RISK FOR TORNADO DEVELOPMENT IS ALONG AND SOUTH OF HIGHWAY 20.
THUNDERSTORMS ARE EXPECTED TO CONTINUE FORMING ALONG THE COLD
FRONT THROUGH THE THIS EVENING, CLEARING TO THE EAST AFTER 11
PM. RAINFALL TOTALS LOOK TO BE HIGHEST EAST OF I- 29 AT AROUND A
QUARTER OF AN INCH TO A HALF AN INCH. HOWEVER, LOCALLY HIGHER
AMOUNTS ARE POSSIBLE UNDER STRONGER THUNDERSTORMS.
LIGHT SHOWERS CONTINUE AS MOISTURE WRAPS AROUND THE SURFACE LOW AS
IT MOVES OFF TO THE EAST FRIDAY MORNING. SHOWERS WILL BE LIGHT AND
VERY SPOTTY IN NATURE. DREARY CONDITIONS WILL BE THE STORY OF THE
DAY BEFORE THINGS FINALLY DRY OUT IN THE LATE AFTERNOON FROM WEST TO
EAST. HIGHS WILL BE SOMEWHAT LIMITED FRIDAY THANKS TO THE NORTHERLY
WINDS AND CLOUDS, IN THE UPPER 40S TO LOW 50S. LOWS FRIDAY NIGHT
WILL FALL TO THE UPPER 20S TO LOW 30S.
THE WEEKEND: A POSITIVELY TILTED DEEP UPPER TROUGH CONTINUES TO MAKE
ITS WAY EAST SATURDAY. AS IT DOES SO, IT WILL CLOSE OFF OVER THE
FOUR CORNERS AREA AND A SURFACE LOW WILL DEVELOP. FOR OUR
REGION, CLOUDS WILL DECREASE SATURDAY MORNING BECOMING MOSTLY
SUNNY. HIGHS WILL CLIMB INTO THE MID TO UPPER 50S. LOWS SATURDAY
NIGHT WILL FALL TO THE 30S. LATE SATURDAY NIGHT TO EARLY SUNDAY
MORNING THE SURFACE LOW WILL EJECT OUT INTO THE CENTRAL PLAINS
AND ACCELERATE TO THE NORTHEAST. AS IT DOES SO, AN AREA OF
SHOWERS AND THUNDERSTORMS WILL DEVELOP, MOSTLY ALONG AND EAST OF
I-29. THERE REMAINS DIFFERENCE IN MODEL GUIDANCE ON TRACK, WITH
THE NAM AND THE GFS KEEPING THE STORM FARTHER EAST, WHILE THE
EC AND CAN BRING IT FARTHER WEST. THIS STORM QUICKLY MOVES
NORTHEAST OVERNIGHT SUNDAY.
MONDAY-THURSDAY: ALOFT FLOW BECOMES QUASI-ZONAL. MONDAY LOOKS TO BE
DRY, BUT BY TUESDAY A MIDLEVEL SHORTWAVE BRINGS ANOTHER ROUND OF
PRECIPITATION. A SERIES OF SHORTWAVES FOLLOWS WITH CHANCES FOR RAIN
ABOUT EVERY OTHER DAY FROM WEDNESDAY ONWARD. HIGH VARIANCE IN
GUIDANCE KEEPS CONFIDENCE IN STORM TRACKS AND TIMING LOW. AS SUCH,
HAVE LEFT NBM POPS AS THEY ARE THROUGH THE EXTENDED FORECAST.
AVIATION /00Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 559 PM CDT THU APR 17 2025
A FEW SHOWERS AND THUNDERSTORMS ACROSS THE REGION THIS EVENING. ONE
LINE FROM WAGNER, SOUTH DAKOTA NORTHEAST TO CANBY MINNESOTA. THIS
LINE WILL CONTINUE TO MOVE NORTH-NORTHEAST. WHILE SEVERE IS NOT
EXPECTED, SOME LIGHTNING IS BEING PRODUCED. ANOTHER LINE OF SHOWERS
AND THUNDERSTORMS STRETCHES FROM SLOAN, IOWA NORTHEAST TO SPENCER,
IOWA. THIS LINE DOES STILL CONTAIN THE POTENTIAL FOR STRONG TO
SEVERE THUNDERSTORMS WITH THE GREATEST THREAT BEING HAIL TO 2 INCHES
IN DIAMETER AND WIND GUSTS 60-65 MPH. THE SEVERE THREAT IS EXPECTED
TO BE THROUGH THE AREA BY 10-11PM TONIGHT.
WINDS TONIGHT WILL BE NORTHERLY AND BREEZY, WITH GUSTS 20-30 KTS,
WITH THE STRONGEST GUSTS EAST OF THE JAMES RIVER VALLEY. GUSTS TO 25
KTS EVENTUALLY SPREADS EASTWARD INTO NORTHWESTERN IOWA AND
SOUTHWESTERN MINNESOTA. BREEZY WINDS CONTINUE THROUGH FRIDAY MID
AFTERNOON BEFORE THEY BEGIN TO TAPER OFF FRIDAY EVENING.
LIGHT, SPOTTY RAIN SHOWERS WILL CONTINUE OVERNIGHT AND THROUGH THE
DAY FRIDAY. AS THE STORM SYSTEM CONTINUES TO MOVE EAST SHOWERS
EVENTUALLY TAPER OFF FRIDAY EVENING. CEILINGS DURING THIS PERIOD
WILL BE VFR TO LOW VFR, WITH POTENTIAL FOR BRIEF PERIODS OF MVFR.
THIS IS ESPECIALLY TRUE UNDER ANY RAIN SHOWERS.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...AJP
AVIATION...AJP
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page