489
FXUS63 KFSD 281740
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1240 PM CDT WED MAY 28 2025
KEY MESSAGES
- AREAS OF DENSE FOG, WITH VISIBILITY 1/4 MILE OR LESS, MAY
IMPACT YOUR MORNING COMMUTE. A DENSE FOG ADVISORY HAS BEEN
ISSUED FOR AREAS FROM SOUTH CENTRAL SOUTH DAKOTA (ALONG/WEST OF
THE JAMES RIVER) INTO THE MISSOURI RIVER VALLEY. VISIBILITY IS
EXPECTED TO QUICKLY IMPROVE BY 8-9 AM.
- SCATTERED LIGHT SHOWERS DEVELOP AGAIN TODAY AND THURSDAY,
ESPECIALLY DURING THE AFTERNOON-EARLY EVENING WHEN ISOLATED
THUNDERSTORMS ARE ALSO POSSIBLE. SIMILAR TO TUESDAY AFTERNOON,
CONDITIONS MAY AGAIN FAVOR ISOLATED WEAK FUNNEL CLOUDS, AND
PERHAPS SMALL HAIL/GUSTY WINDS.
- WARMER TEMPERATURES RETURN BY THE WEEKEND WITH MANY LOCATIONS
EXPECTED TO SEE HIGHS IN THE 80S WITH QUIET CONDITIONS.
DISCUSSION
ISSUED AT 400 AM CDT WED MAY 28 2025
MORE EXPANSIVE MID-LEVEL CLOUD COVER EARLY THIS MORNING HAS
LIMITED AREAL EXTENT OF FOG DEVELOPMENT. HOWEVER, SCATTERED HOLES
IN THE MID CLOUD DECK HAVE PROVIDED POCKETS OF OPTIMAL RADIATIONAL
COOLING WITH MORE LOCALIZED AREAS OF DENSE FOG WITH VISIBILITY
1/4 MILE OR LESS. HAVE ISSUED A DENSE FOG ADVISORY FOR A FEW
COUNTIES ALONG THE MISSOURI RIVER VALLEY AS OF 3 AM, BUT WILL
CONTINUE TO CLOSELY MONITOR OTHER AREAS FOR POTENTIAL EXPANSION OF
THE ADVISORY. WITH A RELATIVELY EARLY SUNRISE PRIOR TO 6 AM,
CONCUR WITH MOST GUIDANCE THAT WE SHOULD SEE VISIBILITY QUICKLY
IMPROVE BY THE 8-9 AM HOUR.
THE REMAINDER OF TODAY WILL AGAIN BE DOMINATED BY A STAGNANT
UPPER LOW SPINNING OVERHEAD, WHICH SLOWLY SHIFTS EAST INTO THE
WESTERN GREAT LAKES THURSDAY. WHILE HEATING WILL BE LIMITED
BENEATH THE RELATIVELY COOL UPPER LOW, FORECAST SOUNDINGS SHOW WE
APPROACH CONVECTIVE TEMPS IN THE MID 60S, SO SELF-DESTRUCTIVE
SUNSHINE IS EXPECTED THIS AFTERNOON, WITH SPOTTY SHOWERS EXPANDING
IN COVERAGE BY MID-LATE AFTERNOON. WEAK INSTABILITY WITH MLCAPE ON
THE ORDER OF 100-300 J/KG (SLIGHTLY HIGHER IN SOME SOLUTIONS) WILL
SUPPORT AT LEAST AN ISOLATED THUNDER THREAT INTO THE EARLY EVENING
HOURS. WITH MUCH OF THAT UNSTABLE LAYER ABOVE THE FREEZING LEVEL
(WHICH IS AROUND 6KFT AGL) AND A DRY SUB-CLOUD LAYER, CANNOT RULE
OUT ISOLATED SMALL HAIL AND/OR GUSTY WINDS WITH ANY THUNDERSTORMS.
ALSO, SIMILAR TO YESTERDAY AFTERNOON, THE RAP CONTINUES TO SHOW
AREAS OF ENHANCED STRETCHING POTENTIAL (ESP), WHICH COULD SUPPORT
OF WEAK FUNNELS WITH UPDRAFTS DEVELOPING ALONG SUBTLE BOUNDARIES
WHICH MAY BE TRAVERSING THE REGION. THOUGH IT IS DIFFICULT TO
PINPOINT ANY SPECIFIC LOCATIONS JUST YET, THE LATEST RAP DOES
SEEM TO FAVOR AREAS ALONG/EAST OF HWY 81.
OUR SHOWER/STORM ACTIVITY WILL DIMINISH WITH LOSS OF DAYTIME
HEATING EARLY THIS EVENING, BUT A LINGERING TROUGH EXTENDING INTO
THE AREA FROM THE DEPARTING UPPER LOW ON THURSDAY WILL BRING A
RENEWED CHANCE OF SHOWERS AND A FEW STORMS TO MAINLY SOUTHEAST
PARTS OF THE FORECAST AREA THURSDAY.
THIS UPPER LOW FINALLY LOSES ITS GRIP ON THE NORTHERN PLAINS BY
THURSDAY NIGHT-FRIDAY, ALLOWING UPPER RIDGING AND WARMER AIR TO
BUILD INTO THE REGION FOR THE UPCOMING WEEKEND AND INTO EARLY NEXT
WEEK. BY LATE SUNDAY AND MONDAY, NAEFS AND ECMWF ENSEMBLES SHOW
850MB TEMPERATURES NEARING THE 90TH PERCENTILE OF CLIMATOLOGY AND
WIDESPREAD HIGHS IN THE 80S SEEMS REASONABLE, THOUGH NBM 50TH TO
75TH PERCENTILE SHOWS SOME POTENTIAL FOR SOME AREAS REACHING THE
LOWER 90S.
SOUTHWEST FLOW ALOFT DEVELOPS INTO THE AREA BY LATE MONDAY AS THE
UPPER RIDGE SHIFTS EAST, AND WILL SEE MODERATE (40-60%) CHANCES
FOR SHOWERS AND STORMS RETURN TO THE REGION TOWARD THE END OF THIS
FORECAST PERIOD MONDAY NIGHT INTO TUESDAY. POCKETS OF STRONGER
INSTABILITY AND/OR SHEAR MAY RESULT IN SOME STRONGER STORMS MONDAY
NIGHT-TUESDAY, THOUGH DIFFERENCES IN TIMING AND STRENGTH OF ANY
EMBEDDED WAVES AMONG VARIOUS MODELS RESULT IN LOWER CONFIDENCE IN
DETAILS AT THIS RANGE.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1239 PM CDT WED MAY 28 2025
MOSTLY VFR CONDITIONS WILL PREVAIL FOR THIS PERIOD. ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEGUN TO FORM ACROSS
THE REGION AS THE UPPER CLOSED LOW CONTINUES TO ROTATE ABOVE US.
WHILE THESE SHOWERS ARE NOT EXPECTED TO BECOME SEVERE, SOME
COULD PRODUCE LIGHTNING, SMALL HAIL, AND WIND GUSTS 30-40 MPH.
IN ADDITION, WE'VE RECEIVED SEVERAL REPORTS OF WEAK COLD AIR
FUNNELS AROUND THE REGION. THESE FUNNELS ARE EXPECTED TO BE
BRIEF, AND NOT TOUCH DOWN, BUT COULD CONTINUE INTO THE EARLY
EVENING HOURS.
SHOWERS ARE EXPECTED TO TAPER OFF THIS EVENING, AND OVERNIGHT WINDS
WILL BE LIGHT AND VARIABLE. THERE IS RISK FOR SOME PATCHY DENSE FOG
DEVELOPMENT, ESPECIALLY FOR AREAS THAT RECEIVED ADDITIONAL
RAIN, AND AREAS ALONG AND WEST OF THE JAMES RIVER. FOG IS
EXPECTED TO QUICKLY DISSIPATE AFTER SUNRISE.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...JH
AVIATION...AJP
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