623
FXUS63 KFSD 181148
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
648 AM CDT THU SEP 18 2025
KEY MESSAGES
- PATCHY DENSE FOG HAS DEVELOPED ACROSS THE AREA, ESPECIALLY
OVER NORTHWEST IOWA. VISIBILITIES COULD DROP TO A QUARTER MILE
OR LOWER AT TIMES, SO USE EXTRA CAUTION ON THE ROADS.
- SCATTERED SHOWERS AND ISOLATED STORMS WILL CONTINUE TO BE
POSSIBLE INTO THE WEEKEND, WITH THE BEST CHANCES (30-60%)
AREA-WIDE ON THURSDAY AND THEN EAST OF I-29 FRIDAY.
- NEAR-TO-SLIGHTLY BELOW NORMAL TEMPERATURES ARE EXPECTED INTO
THE WEEKEND, WITH A SLIGHT WARM-UP POSSIBLE EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 354 AM CDT THU SEP 18 2025
SKIES HAVE CLEARED OVER A LARGE PART OF THE AREA THIS
MORNING WHICH HAS ALLOWED FOR SOME FOG TO DEVELOP AS THERE IS STILL
PLENTY OF MOISTURE OUT THERE. THE FOG MAY REDUCE VISIBILITIES DOWN
TO 1 TO 2 MILES AT TIMES, SO BE SURE TO USE EXTRA CAUTION ON THE
ROADS AS YOU HEAD OUT TO WORK AND SCHOOL. FOG SHOULD LIFT BY 9-10
AM. OTHERWISE, MOST OF US ARE DRY TO START TODAY AS ANY INSTABILITY
WANED OVERNIGHT AND DECREASED THE SHOWER COVERAGE ALONG THE
CONFLUENCE BANDS THAT HAVE BEEN ROTATING THROUGH THE AREA SINCE
YESTERDAY. ALL THIS IS ASSOCIATED WITH A NEARLY STACKED LOW PRESSURE
SYSTEM THAT WILL BE SLOWLY LIFTING NORTH/NORTHEAST ACROSS THE
REGION. THE CENTER OF THE LOW PRESSURE SYSTEM IS OVER CENTRAL SOUTH
DAKOTA, PLACING US ON THE WARM SECTOR OF THE SYSTEM. LOW STRATUS
WILL WRAP AROUND THE CIRCULATION, KEEPING CLOUDY SKIES IN THE
FORECAST FOR THIS MORNING. THESE CLOUDS MAY HAVE SOME DRIZZLE
ASSOCIATED WITH IT AS SOUNDINGS ARE SHOWING A LITTLE BIT OF
INSTABILITY IN THIS LOW CLOUD LAYER MAINLY WEST OF I-29. WE'LL SEE A
FEW BREAKS IN THE CLOUD COVER THIS AFTERNOON, AND THIS WILL HELP
LEAD TO SCATTERED SHOWERS WITH ISOLATED LIGHTNING STRIKES TO DEVELOP
AND PIVOT AROUND THE AREA FROM SOUTHWEST TO NORTHEAST THIS AFTERNOON
AS DAYTIME HEATING ALLOWS FOR AROUND 250-500 J/KG OF MLCAPE TO
DEVELOP. CAPE PROFILES WILL BE SKINNY ONCE AGAIN, THOUGH NOT AS TALL
AS IT WAS YESTERDAY. SO THE RAIN WON'T LIKELY BE AS HEAVY AS
YESTERDAY, BUT ON TOP OF THE RAIN FROM YESTERDAY, CAN'T RULE OUT
SOME SMALL STREAM OR MINOR RIVER FLOODING PARTICULARLY IF AREAS THAT
SAW STORMS YESTERDAY SEE THEM ONCE AGAIN TODAY.
ANOTHER SHORTWAVE/UPPER-LOW LOOKS TO PIVOT AROUND THE MAIN LOW
PRESSURE SYSTEM TO IT'S SOUTH LATE TODAY INTO TONIGHT, WHICH SHOULD
HELP WITH FORCING MORE WIDESPREAD SHOWER/STORM DEVELOPMENT OVER THE
FAR EASTERN CWA IN NORTHWEST IOWA AND SOUTHWEST MINNESOTA TONIGHT.
THIS WILL LIKELY JUST INCREASE COVERAGE FOR RAIN AS OPPOSED TO
INCREASING THE SEVERITY OF THE RAIN, BUT DO HAVE 50-60% POPS THAT
LIFT NORTH THROUGH TONIGHT ALONG AND EAST OF A STORM LAKE TO WINDOM
LINE WHILE THE REST OF THE AREA GENERALLY HAS 20-40% POPS. FOR
DAYTIME TEMPERATURES TODAY, DID BLEND IN SOME NBM 25TH PERCENTILE
BASED ON YESTERDAY'S TRENDS AND WITH THE CLOUD COVER WE'LL SEE
TODAY. HIGHS WILL BE IN THE LOW-60S WEST TO MID-70S EAST AND TONIGHT
WE'LL SEE LOWS MAINLY IN THE 50S ACROSS THE AREA.
CHAOS CONTINUES AT THE 500 MB LEVEL AS YET ANOTHER SHORT-WAVE ROUNDS
THE BASE OF THE UPPER-LOW ON FRIDAY, SETTING OFF MORE SCATTERED
SHOWERS AND STORMS ESPECIALLY EAST OF I-29 WHEN THE SHORTWAVE
PASSAGE LINES UP WITH DAYTIME HEATING. INSTABILITY WILL BE EVEN
LOWER ON FRIDAY THOUGH, SO STRONG/HEAVY STORMS ARE NOT EXPECTED.
JUST ANOTHER CLOUDY AND DREARY DAY WITH OCCASIONAL SHOWERS EXPECTED,
THOUGH CLOUDS WILL START TO BREAK AWAY WEST OF THE JAMES ALLOWING
FOR SOME SUNSHINE BEFORE THE SUN SETS. TEMPERATURES WILL ONCE AGAIN
BE NEAR TO JUST BELOW SEASONAL NORMALS. GUIDANCE SHOWS ANOTHER
SHORTWAVE MOVING INTO THE AREA DURING THE DAY ON SATURDAY, WITH A
STRONGER WAVE JUST TO OUR SOUTH SATURDAY MORNING. THIS WILL ALL HELP
KEEP RAIN CHANCES IN THE FORECAST MAINLY SOUTH OF I-90 SATURDAY
MORNING AND THEN MAINLY EAST OF I-29 SATURDAY AFTERNOON. FROM THERE,
GUIDANCE INDICATES ANOTHER UPPER-LOW DIVING QUICKLY FROM SOUTHERN
CANADA INTO THE GREAT PLAINS, BUT THERE IS SOME UNCERTAINTY IN ITS
OVERALL DEVELOPMENT AND PLACEMENT. FOR THAT REASON, WILL MAINTAIN
THE LOW (30% OR LESS) NBM POPS FOR SUNDAY, MONDAY, AND TUESDAY. FROM
THERE, MODELS DIVERGE SIGNIFICANTLY. TEMPERATURE-WISE, LOOK FOR NEAR
SEASONAL TEMPERATURES TO CONTINUE INTO MUCH OF NEXT WEEK AS THERE
ARE NO SIGNS OF ANY MAJOR PUSHES OF COLD AIR ADVECTION ANYTIME IN
THE NEAR FUTURE.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 645 AM CDT THU SEP 18 2025
WE'RE STARTING THE PERIOD WITH PATCHY FOG AND LOW STRATUS ACROSS THE
AREA. THE FOG MAY BE DENSE AT TIMES WITH VISIBILITIES A QUARTER MILE
OR LESS IN NORTHWEST IOWA, BUT FOR THE MOST PART THE LOWEST
VISIBILITIES WILL RANGE FROM 1-2SM THROUGH ROUGHLY 14Z. IFR TO MVFR
STRATUS WILL LINGER THROUGH THE MORNING HOURS BEFORE LIFTING TO VFR
AT KFSD HEADING INTO THE AFTERNOON. KHON IS LIKELY TO STAY AROUND 2-
3 KFT FOR ITS CIGS INTO THE AFTERNOON HOURS. SCATTERED SHOWERS AND
ISOLATED STORMS WILL DEVELOP THROUGHOUT THE AFTERNOON AND EVENING,
BUT LOW CONFIDENCE IS LOCATION OF DEVELOPMENT. GUIDANCE INDICATES
THE BEST CHANCE OF RAIN IS EAST OF I-29 THROUGH TONIGHT. ENOUGH
CONFIDENCE TO INCLUDE THUNDER IN THE PROB30 FOR KSUX, BUT OVERALL
THUNDER IS EXPECTED TO BE ISOLATED. ADDITIONAL LOW STRATUS LOOKS TO
DEVELOP LATE TONIGHT ACROSS MOST OF THE AREA.
A LOW PRESSURE SYSTEM WILL DRIFT NORTHEAST THROUGH THE AREA THIS
AFTERNOON AND WILL HAVE THE MOST IMPACT ON WIND DIRECTION THROUGH
THE PERIOD. WINDS WILL BE MAINLY OUT OF THE SOUTH-SOUTHWEST THROUGH
TODAY INTO TONIGHT, WITH WINDS GRADUALLY TURNING TO THE WEST-
NORTHWEST WITH TIME. WINDS WILL BE FAIRLY LIGHT THROUGH THE PERIOD,
AROUND 5-10 KTS.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...SAMET
AVIATION...SAMET
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