018
FXUS63 KFSD 111954
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
254 PM CDT THU SEP 11 2025
KEY MESSAGES
- TEMPERATURES WARM TO WELL ABOVE MID-SEPTEMBER NORMALS HEADING
INTO THE WEEKEND AND INTO EARLY NEXT WEEK.
- RAIN/STORM CHANCES INCREASE THIS WEEKEND, WITH A 20-40% CHANCE
MAIN WEST OF THE JAMES RIVER SATURDAY NIGHT AND A 40-70%
CHANCE AREA- WIDE SUNDAY INTO SUNDAY NIGHT.
- AN ISOLATED SEVERE STORM CAN'T BE ENTIRELY RULED OUT WITH THE
ACTIVITY SUNDAY INTO SUNDAY NIGHT, BUT A LOT OF UNCERTAINTY
AND LIMITING FACTORS EXIST SO KEEP UP TO DATE WITH THE LATEST
FORECAST.
DISCUSSION
ISSUED AT 250 PM CDT THU SEP 11 2025
IT'S A MAINLY SUNNY AND WARM LATE SUMMER DAY ACROSS THE
AREA, WITH SMOKE ALOFT CREATING A BIT OF A HAZY APPEARANCE TO THE
SKIES. THE GOOD NEWS IS THAT THIS SMOKE SHOULD STAY ALOFT. HIGHS ARE
GOING TO CLIMB INTO THE 80S ACROSS THE AREA AS RIDGING ALOFT
DOMINATES OUR AREA. A WEAK UPPER-LEVEL WAVE WILL RIDE THE WESTERN
EDGE OF THE RIDGE TONIGHT, TRIGGERING SHOWERS AND STORMS TO OUR
WEST. WITH THE BETTER UPPER-LEVEL SUPPORT TO OUR WEST, THUNDERSTORMS
ARE NOT EXPECTED TO IMPACT OUR AREA. HOWEVER, THE CAMS ARE GOING
BACK AND FORTH ON THE POTENTIAL FOR SOME LIGHT SHOWERS TONIGHT WEST
OF THE JAMES RIVER AS A LLJ AROUND 30-35 KTS PULLS IN SOME MOISTURE
FROM THE SOUTH. CURRENT THINKING IS THAT THE CAP WILL BE STRONG
ENOUGH OVER THE AREA TO EVEN PREVENT THESE LIGHT SHOWERS FROM
DEVELOPING, SO KEEPING THE FORECAST DRY FOR TONIGHT. TEMPERATURES
LOOK TO DROP INTO THE 60S TONIGHT, AND WITH HIGHER WINDS EXPECTED
OVERNIGHT (8-15 MPH), FOG IS UNLIKELY TO DEVELOP.
RIDGING ALOFT CONTINUES INTO THE DAY TOMORROW, ALLOWING HIGH
TEMPERATURES TO GET EVEN WARMER THAN TODAY WITH HIGHS EXPECTED TO BE
IN THE MID-80S TO LOW-90S TOMORROW AFTERNOON. THE ONE THING THAT
COULD LIMIT SOME HEATING TOMORROW AFTERNOON WILL BE IF THE HRRR/RAP
COME TRUE AND SCATTERED SHOWERS/STORMS DEVELOP DURING THE DAY. WAA
WILL CONTINUE TO BE STRONG AT 850 MB, AND AT THE SURFACE WE'LL HAVE
A LOW PRESSURE SYSTEM WANDERING AROUND TO OUR WEST. MODEL SOUNDINGS
SHOW A CAPPED ENVIRONMENT DURING THE DAY ALONG AND EAST OF THE JAMES
RIVER, SO RAIN MAY END UP BEING HARD TO COME BY THERE. WEST OF THE
JAMES, DAYTIME HEATING MAY BE ENOUGH TO BREAK THE CAP, SO CAN'T RULE
OUT STORMS DEVELOPING IN MAINLY SOUTH-CENTRAL SOUTH DAKOTA DURING
THE LATE-AFTERNOON TO EVENING HOURS. THE BEST UPPER-LEVEL SUPPORT
WILL ONCE AGAIN BE TO OUR WEST, SO WIDESPREAD ACTIVITY IS NOT
EXPECTED. SEVERE WEATHER LOOKS UNLIKELY AS BULK SHEAR WILL BE QUITE
WEAK.
LOOKING AT THE BIG PICTURE FOR THE WEEKEND, SATURDAY WILL SEE AN
UPPER-LEVEL LOW OVER THE NORTHERN ROCKIES AND A TROUGH DIGGING OUT
OF THE DESERT SOUTHWEST AND LIFTING NORTHEASTWARD TOWARDS OUR AREA
WHILE TAKING ON A NEGATIVE TILT INTO THE DAY ON SUNDAY. THIS WILL BE
THE FOCUS ON OUR NEXT AND MORE WIDESPREAD RAIN CHANCES FOR SUNDAY
INTO AT LEAST THE START OF SUNDAY NIGHT. FIRST FOR SATURDAY, THE
BEST UPPER-LEVEL SUPPORT WILL STILL BE WEST OF THE AREA SO THE BEST
CHANCE OF RAIN WILL BE WEST OF US. STILL, SOME SHOWERS AND STORMS
WILL MOVE INTO THE AREA WEST OF THE JAMES RIVER THROUGH SATURDAY
NIGHT, WITH RAIN CHANCES AROUND 20-40% IN THOSE AREAS. AS PREVIOUSLY
MENTIONED, BETTER RAIN CHANCES (40-70% CHANCE) WILL ARRIVE BY SUNDAY
AS THE TROUGH EJECTS TO THE NORTHEAST ACROSS THE AREA. IN TERMS OF A
SEVERE WEATHER THREAT, DETERMINISTIC GUIDANCE IS SPLIT ON THE AMOUNT
OF INSTABILITY FOR SATURDAY, WITH THE 12Z GFS HAVING LITTLE TO NO
INSTABILITY, WHILE THE ECMWF SHOWS 1000-2000 J/KG OF MUCAPE. LOOKING
OVER AT LREF JOINT PROBABILITIES OF MUCAPE > 500 J/KG, CIN > -25
J/KG, AND BULK SHEAR > 30 KTS, IT'S MORE IN LINE WITH THE GFS WITH
LESS THAN A 10% CHANCE OF THESE PARAMETERS BEING MET SATURDAY NIGHT.
WITH ALL THAT SAID, SEVERE WEATHER LOOKS UNLIKELY AT THIS TIME FOR
SATURDAY/SATURDAY NIGHT, BUT SHOULD GET A BETTER IDEA ONCE CAM RUNS
GO OUT THAT FAR. FOR SUNDAY, GUIDANCE SHOWS A DISCONNECT BETWEEN THE
AREAS WITH GREATEST SHEAR AND THE AREAS WITH HIGHEST INSTABILITY, SO
THERE IS STILL A LOT OF UNCERTAINTY IN SEVERE WEATHER CHANCES. THE
ECMWF HAS BETTER OVERLAP THAN COMPARED TO THE GFS, AND THE JOINT
PROBABILITIES OF THE SAME PARAMETERS MENTIONED ABOVE ARE BETWEEN 10
AND 20%. SO AT THIS POINT, CERTAINLY CAN'T RULE OUT AN ISOLATED
SEVERE STORM ON SUNDAY, BUT THE PARAMETERS AREN'T TOO GREAT OVERALL
AT THIS TIME. WILL STILL NEED TO RESPECT THE NEGATIVELY TILTED
TROUGH, SO CONTINUE TO KEEP UP TO DATE WITH THE LATEST FORECAST. IN
TERMS OF RAINFALL TOTALS SUNDAY INTO SUNDAY NIGHT, ENSEMBLES SHOW A
ROUGHLY 20-60% CHANCE OF AT LEAST 0.1" OF RAIN, BUT LESS THAN A 20%
CHANCE OF RAINFALL TOTALS GREATER THAN A HALF AN INCH.
HEADING INTO THE NEXT WORK WEEK, GUIDANCE LARGELY AGREES ON AN UPPER-
LEVEL LOW COMING OUT OF THE PACIFIC NORTHWEST AND MOVING EASTWARD,
THOUGH MODELS BEGIN TO QUICKLY DIVERGE ON THE PATH AND LOCATION OF
THE UPPER-LOW. STILL, AN APPROACHING TROUGH WILL LIKELY KEEP RAIN
CHANCES IN THE FORECAST THROUGH PORTIONS OF NEXT WEEK, WITH RAIN
CHANCES PEAKING AGAIN TUESDAY NIGHT INTO WEDNESDAY. WITH NO MAJOR
COLD FRONTS NOR ANY SIGNS OF COLD AIR ADVECTION INTRUSIONS, EXPECT
TEMPERATURES TO STAY NEAR TO ABOVE NORMAL HEADING THROUGH MUCH OF
NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1213 PM CDT THU SEP 11 2025
VFR CONDITIONS EXPECTED THROUGH THE PERIOD. BREEZY CONDITIONS ARE
EXPECTED THIS AFTERNOON AND EVENING, WITH SOUTHEASTERLY GUSTS AROUND
20 KTS EXPECTED ALONG AND WEST OF I-29 TO THE JAMES RIVER,
INCREASING TO GUSTS OF 25-30 KTS ALONG AND WEST OF THE JAMES. WINDS
WILL GRADUALLY LESSEN TONIGHT, BUT THE LLJ WILL KICK UP AND CAUSE
LLWS CONCERNS AT TIMES OVERNIGHT AND INTO EARLY TOMORROW MORNING.
FOG IS NOT EXPECTED TO DEVELOP DUE TO ELEVATED WINDS (SOUTHEAST
AROUND 10 KTS) OVERNIGHT. SOUTHEASTERLY GUSTS OF 15-20 KTS WILL
RETURN ACROSS THE AREA THROUGH TOMORROW MORNING.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...SAMET
AVIATION...SAMET
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