190
FXUS63 KFSD 132329
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
629 PM CDT SAT SEP 13 2025
KEY MESSAGES
- TEMPERATURES REMAIN WELL ABOVE NORMAL THROUGH THE WEEKEND AND
INTO EARLY NEXT WEEK.
- CONVECTION CHANCES REMAIN LOW INTO SUNDAY MORNING, HOWEVER
CHANCES DO INCREASE SUNDAY AFTERNOON INTO SUNDAY NIGHT. A FEW
STORMS WILL BE POSSIBLE IN CENTRAL SD TONIGHT.
- CONDITIONAL RISKS FOR ISOLATED SEVERE STORMS DEVELOP SUNDAY
AFTERNOON INTO THE EVENING. MARGINAL HAIL AND BRIEF STRONG
WIND GUSTS ARE THE PRIMARY RISKS.
- NEXT REASONABLE RISK FOR RAIN ARRIVES TUESDAY AND CONTINUES
THROUGH WEDNESDAY, WITH COOLER TEMPERATURES THE SECOND HALF OF
NEXT WEEK.
DISCUSSION
ISSUED AT 152 PM CDT SAT SEP 13 2025
THIS AFTERNOON: SURFACE LOW CONTINUES TO LINGER WEST OF THE JAMES
RIVER THIS AFTERNOON, WITH COOLER AND MORE STABLE AIR PULLING INTO
FAR SOUTH CENTRAL SOUTH DAKOTA. FURTHER EAST, TEMPERATURES CONTINUE
TO SOAR THROUGH THE 80S AND INTO THE 90S AS A SECONDARY WARM
FRONT ACCELERATES NORTH TOWARDS HIGHWAY 14. DEEPER MIXING
THROUGHOUT THE TRI-STATE AREA, AND IMPACTS OF DRYING VEGETATION
AND RECENT LACK OF RAIN, IS DROPPING DEW POINTS INTO THE LOWER
60S, THIS DEW POINT DROP OFFSET WITH HIGHER TEMPERATURES IS
RESULTING IN HEAT INDEX VALUES NEAR THE MIDDLE TO UPPER 90S.
TONIGHT: CONVECTION RISKS BEGIN TO INCREASE OVER WESTERN SOUTH
DAKOTA AND NEBRASKA THIS EVENING AS AN UPPER WAVE PIVOTS NORTHWARD
THROUGH THE PLAINS. GENERALLY MOST OF THE CONVECTION RISKS ARE
LIKELY TO STAY WEST OF THE CWA, WITH AN OUTSIDE RISK OF AN ELEVATED
THUNDERSTORM LIFTING NORTHWARD THROUGH SOUTH CENTRAL SOUTH DAKOTA
TOWARDS OR AFTER MIDNIGHT. FURTHER EAST, WINDS MAY BRIEFLY TURN
LIGHT AND VARIABLE AT TIMES, POTENTIALLY LEADING TO MINOR
FOG/STRATUS IN THE HIGHER ELEVATIONS OF THE RIDGE.
SUNDAY-SUNDAY NIGHT: MODELS REMAIN MOSTLY IN AGREEMENT THROUGH
SUNDAY, WITH MINOR TIMING DIFFERENCES REMAINING IN ARRIVAL OF
VORTICITY LIFTING NORTHWARD THROUGH THE PLAINS AT MID-DAY. OUTSIDE
OF LINGERING MORNING SHOWERS WEST OF THE JAMES RIVER, VARIABLE
MID- UPPER CLOUD COVER IS ANTICIPATED FURTHER EAST INTO THE
EARLY AFTERNOON HOURS. THIS CLOUD COVER BRINGS SOME UNCERTAINTY
ON JUST HOW UNSTABLE WE'LL GROW ACROSS THE CWA IN THE AFTERNOON.
CAMS HAVE BACKED OFF ON OVERALL MLCAPE VALUES, ONLY APPROACHING
800-1200 J/KG OF THIN CAPE IN MOST AREAS BY 2-4PM. HOWEVER THE
INCREASING SYNOPTIC LIFT, SLIGHT SURGE IN 850MB WINDS, AND
BOUNDARY LAYER CONFLUENCE (EAST OF THE JAMES RIVER) MAY LEAD TO
THE DEVELOPMENT OF ISOLATED TO SCATTERED STORMS BY MID-LATE
AFTERNOON. GREATER FOCUS IS LIKELY TO TAKE PLACE ALONG AND WEST
OF THE JAMES RIVER, WHERE INSTABILITY MAY ACTUALLY BE LOWER, BUT
CONVERGENCE HIGHER. WITH FREEZING LEVELS AOA 13-14K FEET AND
MID-LVL LAPSE RATES ONLY NEAR 6 C/KM, FEEL THAT HAIL SIZE SHOULD
BE LIMITED. HOWEVER MODEST EFFECTIVE SHEAR OF 35 TO 45 KNOTS,
WITH INCREASING 925:850MB FLOW, AND SLIGHT DRY LAYER AT 700 MB
COULD PROMOTE A FEW STRONGER WIND GUSTS IN MULTI-CELL TO BRIEFLY
SUPERCELLULAR STORMS. AGAIN THOUGH, INSTABILITY REMAINS VERY
QUESTIONABLE. SHOULD A BIT MORE 0-5KM CAPE FORM, GIVEN THE
INCREASE IN LVL HELICITY NEAR THE WESTERN BOUNDARY, A BRIEF TOR
COULD NOT BE RULED OUT. THE LOSS OF DAYTIME HEATING SHOULD LEAD
TO A CONTINUE DOWNTREND IN CONVECTION BY AND AFTER SUNSET, WITH
DRY CONDITIONS MOVING INTO THE REGION OVERNIGHT.
MONDAY: THE UPPER TROUGH PIVOT OVER NORTH DAKOTA ON MONDAY, WITH
BROAD SOUTHWESTERLY SURFACE FLOW LINGERING OVER THE TRI-STATE AREA
ON MONDAY. TEMPERATURES AGAIN RISE INTO THE 80S AND FOR MOST AREAS
NO CONVECTION IS ANTICIPATED OUTSIDE OF LINGERING EARLY DAY SHOWERS.
TUESDAY-FRIDAY: LONGWAVE TROUGHING REMAINS CENTERED FROM CENTRAL
CANADA INTO THE ROCKIES THROUGH THE MIDDLE OF THE WEEK. BY TUESDAY
AN EXTENDED SURFACE FRONT FROM EASTERN NORTH DAKOTA THROUGH CENTRAL
SOUTH DAKOTA AND INTO WESTERN NEBRASKA. THE BUILDUP OF
INSTABILITY TUESDAY AFTERNOON COULD LEAD TO A FEW THUNDERSTORMS
ALONG THIS FRONT IN THE WESTERN CWA, THROUGH THE LACK OF SHEAR
SHOULD PRECLUDE WIDESPREAD SEVERE WEATHER. THIS ALIGNS WITH THE
VERY LOW PROBABILITIES OF SEVERE WEATHER DEPICTED BY MACHINE
LEARNING SEVERE WEATHER GUIDANCE.
THE TRACK AND ORIENTATION OF THE UPPER TROUGH BY WEDNESDAY WILL
DETERMINE THE LINGERING RISKS FOR CONVECTION INTO THE
WEDNESDAY/THURSDAY TIMEFRAME. THERE REMAINS QUITE A BIT OF
DIFFERENCE BETWEEN THE ECMWF/GFS/CMC MOSTLY CENTERED AROUND THE
TIMING OF THE TROUGH AND ANY EMBEDDED WAVES WITHIN IT. PRECIPITATION
CHANCES REMAIN SPREAD THROUGH THE END OF THE WEEK, BUT IT
CERTAINLY DOESN'T LOOK LIKE THE ENTIRE 2ND HALF OF THE WEEK
WILL BE FILLED WITH RAIN, BUT MORE SPORADIC RAIN CHANCES.
CONFIDENCE IS MUCH HIGHER THAT WE'LL SEE A DROP IN TEMPERATURES
WEDNESDAY ONWARD WITH HIGHS NEAR TO SLIGHTLY BELOW NORMAL IN THE
70S.
AVIATION /00Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 625 PM CDT SAT SEP 13 2025
LARGELY VFR CONDITIONS PREVAIL THROUGH THE PERIOD. MAY SEE SOME
SHOWERS ACROSS SOUTH CENTRAL SD TONIGHT INTO SUNDAY MORNING,
WITH MORE WIDESPREAD SHOWER AND STORM CHANCES EXPANDING EAST
LATER IN THE PERIOD TOWARD SUNDAY NIGHT. HAVE INCLUDED PROB30
GROUP AT KHON WHERE THERE IS A BIT MORE AGREEMENT IN
TIMING/COVERAGE, BUT HAVE OMITTED FROM KFSD AND KSUX FOR NOW.
LLJ STRENGTHENS AGAIN TONIGHT FOR AREAS SOUTH AND EAST OF KFSD,
LEADING TO LLWS. SOUTHERLY WIND GUSTS AROUND 20 TO 25 KNOTS
RETURN AGAIN DURING THE DAY AND INTO THE EVENING SUNDAY.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...DUX
AVIATION...SG
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