201
FXUS63 KFSD 191759
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1259 PM CDT WED AUG 19 2026
KEY MESSAGES
- FOG MAY DEVELOP AFTER MIDNIGHT. LOCALLY DENSE FOG COULD BE
POSSIBLE WITH VISIBILITIES LESS THAN 1 MILE.
- ISOLATED TO WIDELY SCATTERED THUNDERSTORMS POSSIBLE LATE
THURSDAY AFTERNOON AND EVENING. GOLF BALL SIZE HAIL AND 60 MPH
WINDS WILL BE THE PRIMARY RISK.
- WARMER TEMPERATURES CONTINUE ON FRIDAY, WITH ANOTHER VERY
CONDITIONAL RISK FOR THUNDERSTORMS IN THE AFTERNOON AND
EVENING.
- SLIGHTLY COOLER WEATHER, WITH MOSTLY DRY CONDITIONS CAN BE
EXPECTED FOR THE UPCOMING WEEKEND, WITH RAIN CHANCES RETURNING
BY MONDAY MORNING.
DISCUSSION
ISSUED AT 1256 PM CDT WED AUG 19 2026
THIS AFTERNOON: RAIN CONTINUES TO MOVE SOUTHEAST THIS AFTERNOON,
WITH GRADUAL SUBSIDENCE SETTING IN BEHIND THE PASSING MID-LVL
VORTICITY. THERE REMAIN A VERY LOW RISKS FOR A FEW ELEVATED
STORMS TO FORM ALONG THE MO RIVER THIS AFTERNOON, AND THEN
FURTHER NORTHWEST INTO CENTRAL SOUTH DAKOTA WHERE A NARROW
TONGUE OF INCREASED BOUNDARY LAYER MOISTURE REMAINS.
TONIGHT: MUCH OF THE EVENING AND OVERNIGHT HOURS IS EXPECTED TO
REMAIN QUIET AND DRY. WHILE A FEW SHOWERS AND THUNDERSTORMS MAY
FORM OVER CENTRAL AND EASTERN ND AND PERHAPS EXTREME NORTHERN
SOUTH DAKOTA. WINDS AT THE SURFACE WILL TURN LIGHT AND VARIABLE,
AND WITH RECENT RAIN AND MOSTLY CLEAR SKIES SOME AREAS OF FOG
MAY DEVELOP BY DAYBREAK. THE LOWEST VISIBILITIES MAY FORM ALONG
THE I-29 CORRIDOR WITH LOCALLY DENSE FOG POSSIBLE AT TIMES.
THURSDAY: ANOTHER EMBEDDED WAVE WITHIN THE NORTHWESTERLY FLOW
PATTERN IS EXPECTED TO DROP THROUGH THE PLAINS AND INTO THE UPPER
MIDWEST ON THURSDAY. THIS WAVE WILL PUSH A SURFACE FRONT INTO THE
TRI-STATE ARE IN THE AFTERNOON WITH BREEZY SOUTHWESTERLY WINDS AHEAD
OF THE FRONT IN THE MORNING. SOUNDINGS AHEAD OF THE BOUNDARY BY
AFTERNOON SHOW MODERATE INSTABILITY UPWARDS OF 2500 J/KG IN A
FEW LOCATIONS. HOWEVER THEY ALSO SHOW AT LEAST 100 J/KG CIN,
WHICH COULD SERVE AS A BIG LIMITING FACTOR FOR CONVECTIVE
DEVELOPMENT IN THE AFTERNOON. THE GREATEST FORCING ALONG THE
BOUNDARY REMAINS FOCUSED FROM NORTHERN MINNESOTA INTO CENTRAL
MINNESOTA, WITH MUCH WEAKER SURFACE CONVERGENCE ALONG THE
BOUNDARY FURTHER SOUTHWEST INTO NORTHERN NEBRASKA. THIS IS
LIKELY WHY, OUTSIDE OF ANY SIGNIFICANT MOISTURE/THERMAL
ADVECTION IN THE BOUNDARY LAYER, CAMS REMAIN VERY ISOLATED IN
CONVECTIVE DEVELOPMENT BY LATE AFTERNOON AND EARLY EVENING. THAT
SAID, GIVEN EFFECTIVE SHEAR OF 35-40 KNOTS, ANY UPDRAFT COULD
ROTATE AND INCREASE THE HAIL SIZE TOWARDS THE 1.5-2" MARK.
FRIDAY: WE MAY SEE A QUICK WARMUP ON FRIDAY INTO THE MIDDLE AND
UPPER 80S AS BRIEF MID-LVL RIDGING MOVES INTO THE TRI-STATE AREA. BY
THE AFTERNOON HOWEVER, MODEL GUIDANCE IS ALL OVER THE PLACE
SUGGESTING PERHAPS ANOTHER WEAK TROUGH PASSES THROUGH THE
PLAINS/MIDWEST LATE IN THE DAY. SHOULD THIS WAVE MATERIALIZE, IT
COULD DRIVE A FRONT AND SOME ASSOCIATED CONVECTION THROUGH THE
EASTERN DAKOTAS FRIDAY AFTERNOON AND EVENING. THIS REMAINS A VERY
LOW-PROBABILITY EVENT, SO WILL KEEP POPS ON THE LOWER END OF
GUIDANCE.
SATURDAY-SUNDAY: MUCH OF THE UPCOMING WEEKEND WILL BE DRY AS
CANADIAN HIGH PRESSURE MOVES THROUGH THE REGION. LIGHT NORTHERLY
WINDS AND WEAK CAA ALOFT WILL PROMOTE A VERY PLEASANT AFTERNOON WITH
NORTHERLY SURFACE WINDS AND LOWER HUMIDITY. SOME MODEST RETURN
FLOW AND WEAK WARM ADVECTION MAY DEVELOP OVER THE WESTERN
DAKOTAS AND NEBRASKA PANHANDLE INTO SUNDAY. MEDIUM RANGE
GUIDANCE HAS SLOWED DOWN THIS EASTWARD PROGRESSION OVER THE PAST
2 DAYS, NOW INDICATING THAT PRECIPITATION CHANCES SHOULD REMAIN
WEST OF THE CWA UNTIL SUNDAY NIGHT INTO MONDAY. HIGH
TEMPERATURES SUNDAY WILL BE VERY SIMILAR TO SATURDAY, IN THE
UPPER 70S TO LOWER 80S.
MONDAY-TUESDAY: PRECIPITATION CHANCES INCREASE EARLY NEXT WEEK AS A
SHORTWAVE CRESTS THE TOP OF THE GROWING MID-LVL RIDGE OVER THE
CENTRAL CONUS. MODEL SPREAD IN BOTH TIMING AND LOCATION OF
PRECIPITATION WILL KEEP THESE POPS ONLY AROUND THE 20-30%
RANGE. TEMPERATURES DO SHOW A WARMING TREND INTO NEXT WEEK, WITH
GROWING PROBABILITIES OF HIGHS REACHING OR EXCEEDING THE 85
MARK AT TIMES INTO MID-WEEK.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1207 PM CDT WED AUG 19 2026
SCATTERED VFR CEILINGS WILL PERSIST INTO THE AFTERNOON AS RAIN
GRADUALLY MOVES SOUTHEAST. A DIURNAL BASED CU FIELD MAY DEVELOP
THIS AFTERNOON, WITH THIS CLOUD BASE DISSIPATING IN THE EVENING.
OVERNIGHT, WINDS TURN LIGHT AND VARIABLE WHICH GIVEN RECENT
RAINFALL COULD LEAD TO SOME AREAS OF FOG.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...DUX
AVIATION...DUX
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