544
FXUS63 KFSD 170447
AFDFSD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1047 PM CST MON DEC 16 2024
KEY MESSAGES
- A CLIPPER SYSTEM WILL MOVE THROUGH THE AREA ON TUESDAY,
BRINGING ACCUMULATING SNOW WITH IT. THIS SYSTEM WILL BRING A
BAND OF LIGHT TO MODERATE SNOW TO LOCATIONS ALONG AND NORTH OF
I-90. THE HIGHEST SNOWFALL TOTALS WILL OCCUR ALONG AND NORTH
OF HIGHWAY-14 WHERE AMOUNTS UP TO 2 INCHES OR MORE IS
EXPECTED.
- CONFIDENCE IS BEGINNING TO BUILD IN THE POTENTIAL FOR ANOTHER ROUND
OF SNOW ON THURSDAY. HOWEVER, THE HIGHEST PROBABILITIES FOR
SNOW LIE ACROSS CENTRAL MINNESOTA.
- DRY CONDITIONS RETURN FOR THE END OF THE WEEK AND WEEKEND WITH
TEMPERATURES MODERATING BACK TO NEAR SEASONABLE.
DISCUSSION
ISSUED AT 247 PM CST MON DEC 16 2024
MAINLY CLEAR SKIES PERSIST ACROSS THE FORECAST AREA THIS AFTERNOON.
THIS HAS ALLOWED FOR TEMPERATURES TO WARM TO THE MID 30S TO UP TO
THE UPPER 40S, WARMEST ALONG THE MISSOURI RIVER VALLEY. WHILE GUSTY
WESTERLY WINDS PERSIST, WINDS HAVE BEEN ON A WANING TREND. THUS THE
WIND ADVISORY WILL BE ALLOWED TO EXPIRE AT 3 PM. WINDS WILL FURTHER
WANE THROUGH THE REST OF THE AFTERNOON AND EVENING HOURS. HOWEVER,
CLOUDS WILL BEGIN TO INCREASE ALOFT AHEAD OF AN INCOMING CLIPPER
SYSTEM. THIS SYSTEM WILL BE RESPONSIBLE FOR OUR NEXT CHANCE OF SNOW
ON TUESDAY. BUT FOR THE OVERNIGHT HOURS, LOW TEMPERATURES WILL
REMAIN COLD, FALLING DOWN TO THE 20S ACROSS THE AREA.
WITH THE PREVIOUSLY MENTIONED WAVE ENCROACHING ON THE REGION TUESDAY
MORNING, SNOW WILL BREAK OUT AROUND THE HIGHWAY-14 CORRIDOR, WEST OF
BROOKINGS, SOUTH DAKOTA BEFORE SPREADING EAST/SOUTHEASTWARDS. THE
FRONT END OF THIS SYSTEM WILL BE DRIVEN BY MID LEVEL FRONTOGENESIS
(FGEN) ALONG WITH QUASI-GEOSTROPHIC (QG) SYNOPTIC LIFT VIA WARM AIR
ADVECTION (WAA) AND POSITIVE VORTICITY ADVECTION (PVA). THIS WILL
RESULT IN SNOW FALLING ALONG THE NARROW BAND OF FGEN ITSELF GIVEN
WEAK INSTABILITY CHARACTERIZED BY EQUIVALENT POTENTIAL VORTICITY
(EPV) VALUE NEAR ZERO ARE PRESENT ABOVE THE ELEVATED FRONT. AS THE
MORNING PROGRESSES, STRONGER OMEGA (UPWARD MOTION) WILL DEVELOP
WITHIN THE DENDRITIC GROWTH ZONE (DGZ). THIS WILL RESULT IN SNOW
COVERAGE EXPANDING ACROSS PART OF THE AREA. LATEST 12Z GUIDANCE HAS
COME IN FURTHER NORTH WITH THE HEAVIEST SNOWFALL AMOUNTS, COINCIDENT
WITH THE STRONGEST FORCING FOR ASCENT. THIS LOOKS TO MAINLY BE ALONG
AND NORTH OF HIGHWAY-14 BUT LIGHTER SNOWFALL IS STILL POSSIBLE DOWN
TOWARDS I-90. FORCING FOR ASCENT WILL WEAKEN A BIT DURING THE
AFTERNOON HOURS. THAT SAID, STRONGER FGEN AROUND 925 MB LOOKS TO
TAKE OVER DURING THE LATE AFTERNOON AND EVENING HOURS WITHIN THE
NORTHERN PART OF THE 925 TROUGH. THIS WILL SLIDE THROUGH PORTIONS
FROM EAST CENTRAL SOUTH DAKOTA, SOUTHWEST MINNESOTA, AND NORTHWEST
IOWA THROUGH THE EVENING HOURS BEFORE EXITING THE AREA AFTER
MIDNIGHT. TOTAL SNOWFALL AMOUNTS UP TO 1-3 INCHES IS EXPECTED,
HIGHEST ALONG HIGHWAY-14. LIGHTER SNOWFALL AMOUNTS BELOW AND
INCH IS EXPECTED SOUTH OF I-90. CONSIDERATION WAS GIVEN TO
ISSUING A WINTER WEATHER ADVISORY BUT HAVE HELD OFF AT THIS
TIME. WILL CONTINUE TO ASSESS THIS POTENTIAL.
WEDNESDAY WILL BE A QUIET DAY AS SURFACE RIDGING MOVES THROUGH THE
NORTHERN PLAINS. WITH 850 MB TEMPERATURES REMAINING BELOW 0C ALONG
WITH LIGHT NORTHWEST FLOW, HIGH TEMPERATURES WILL BE BELOW AVERAGE,
ONLY WARMING TO THE 20S ACROSS THE MAJORITY OF THE AREA. LOCATIONS
ALONG THE MISSOURI RIVER WILL BE THE WARMEST WITH HIGH TEMPERATURES
WARMING TO AROUND FREEZING. WITH HIGH PRESSURE IN PLACE, WEDNESDAY
WILL BE A COLD BUT DRY DAY. LOW TEMPERATURES WILL FALL TO
LOW TEENS TO MID 20S OVERNIGHT.
THE BREAK FROM SNOW CHANCES WILL BE SHORT THOUGH AS ANOTHER UPPER
LEVEL SHORTWAVE TROUGH PUSHES THROUGH PARTS OF THE NORTHERN PLAINS
AND UPPER MIDWEST ON THURSDAY. AS OF NOW, THE BEST FORCING FOR
ASCENT ALONG WITH THE BEST MOISTURE LOOKS TO RESIDE MAINLY ACROSS
CENTRAL MINNESOTA. THIS IS SUPPORTED BY THE ENSEMBLES AS THEY SHOW
THEIR HIGHEST PROBABILITIES FOR EXCEEDING A TENTH OF AN INCH OF QPF
ACROSS THIS SAME AREA. LOCATIONS ALONG AND NORTHEAST OF A LINE FROM
HURON, SD TO SIOUX FALLS, SD TO STORM LAKE, IA HAVE THE HIGHEST
PROBABILITIES, UP TO A 30-50% CHANCE, FOR SEEING LIGHT SNOW (BELOW 1
INCH) THOUGH THIS CAN CHANGE OVER THE COMING DAYS. ASIDE FROM SNOW
CHANCES, THURSDAY WILL BE A RELATIVELY WARMER DAY AS HIGH
TEMPERATURES WARM TO THE LOW 30S TO MID 40S. HOWEVER, A STRONG COLD
FRONT WILL SWEEP THROUGH THE AREA, DROPPING LOW TEMPERATURES DOWN TO
THE SINGLE DIGITS BOTH ABOVE AND BELOW 0F DURING THE OVERNIGHT
HOURS.
FRIDAY WILL BE ANOTHER COLD DAY WITH HIGH TEMPERATURES REMAINING IN
THE TEENS TO MID 20S. THE GOOD NEWS IS THAT UPPER LEVEL RIDGING WILL
BUILD OVER THE CENTRAL CONUS FOR THE WEEKEND, WARMING HIGH
TEMPERATURES BACK TO NEAR SEASONABLE BY SUNDAY. MONDAY WILL CONTINUE
THE TREND OF NEAR SEASONABLE TO POSSIBLE ABOVE AVERAGE TEMPERATURES.
THERE COULD BE ADDITIONAL CHANCES FOR PRECIPITATION EARLY NEXT WEEK
BUT MEDIUM RANGE GUIDANCE VARIES IN THESE POSSIBILITIES. HAVE STUCK
WITH A DRY FORECAST FOR NOW BUT TRENDS WILL BE MONITORED.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1046 PM CST MON DEC 16 2024
QUIET CONDITIONS CONTINUE TO PREVAIL ACROSS THE REGION, WITH LATEST
SATELLITE IMAGERY SHOWING A NARROW CORRIDOR OF STRATUS DRIFTING
ALONG AND SOUTH OF US HIGHWAY 14. WHILE KHON HAS DROPPED TO MVFR
LEVEL, NOT SURE IF THIS DECK WILL MAKE IT TO KFSD. FOR NOW, HAVE
KEPT CIGS AT VFR LEVELS. WILL CONTINUE TO MONITOR TRENDS AND AMEND
AS NECESSARY. AS ALLUDED TO IN THE PREVIOUS DISCUSSION, WILL SEE
SNOW CHANCES RETURN NEAR DAYBREAK FOR AREAS ALONG AND NORTH OF I-90.
SHOULD SEE CIGS/VSBYS GRADUALLY DECREASE WITH THE ONSET OF
PRECIPITATION, WITH AREAS NEAR US HIGHWAY 14 LIKELY TO SEE THE MOST
IMPACTS. WINDS DURING THIS TIME LOOK TO BECOME MORE EASTERLY, WITH
SUSTAINED SPEEDS BETWEEN 5 TO 10 MPH POSSIBLE THROUGH THE AFTERNOON.
OTHERWISE, LOOK FOR PRECIPITATION TO GRADUALLY DIMINISH TUESDAY
EVENING, WITH LINGERING LIGHT SNOW STILL POSSIBLE IN AREAS EAST OF I-
29 BY THE END OF THE PERIOD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
DISCUSSION...MEYERS
AVIATION...SST
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