743
FXUS63 KUNR 162124
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
224 PM MST MON DEC 16 2024
KEY MESSAGES
- QUICK MOVING SYSTEM WITH NARROW BAND OF FRONTOGENESIS WILL BRING
LIGHT SNOW TO THE AREA TONIGHT INTO TUESDAY MORNING, PRIMARILY
NORTH OF I-90. EXPECTED SNOW AMOUNTS AROUND AN INCH WITH LOCALLY
HIGHER AMOUNTS POSSIBLE. SOME UNCERTAINTY REMAINS ON EXACT
PLACEMENT OF STRONGEST FRONTOGENESIS AND SUBSEQUENT IMPACT ON
LOCALLY ENHANCED SNOW POTENTIAL.
- ANOTHER QUICK MOVING CLIPPER WILL BRING RAIN/SNOW CHANCES ACROSS
FAR NORTHERN FORECAST AREA LATE WEDNESDAY INTO THURSDAY. SNOW
AMOUNTS WILL BE MINIMAL; GUSTY NW WINDS BEHIND A COLD FRONT
THURSDAY (GUSTS 35-50 MPH).
- GENERALLY DRY WITH SLOWLY WARMING TEMPERATURES FOR THE LATTER
HALF OF THE WEEK INTO THE WEEKEND.
DISCUSSION
(THIS EVENING THROUGH MONDAY)
ISSUED AT 220 PM MST MON DEC 16 2024
UPPER LEVEL ANALYSIS SHOWS BRISK NORTHWESTERLY FLOW ACROSS THE
NORTHERN PLAINS. INFRARED IMAGERY (WV/IR) SHOWS WEAK SHORTWAVE
TROUGH PUSHING THROUGH THE FORECAST AREA WITH A BROAD AREA OF
MOISTURE AND LIFT OVERSPREADING THE NORTHERN ROCKIES AHEAD OF A
STRONGER/DEEPER UPPER TROUGH OFF THE PACIFIC NW COAST. A SURFACE
COLD FRONT IS SLOWLY SAGGING SOUTHWARD AND STRETCHES FROM WESTERN MN
ACROSS NORTHWESTERN SD INTO CENTRAL MT.
UPPER TROUGH AXIS WILL PIVOT THROUGH THE NORTHERN ROCKIES THROUGH
THE EVENING, WITH QUICK MOVING SHORTWAVE TROUGH PUSHING INTO THE
FORECAST AREA AFTER 06Z TONIGHT. PACIFIC MOISTURE CONTINUES TO
STREAM INTO THE REGION AHEAD OF THE TROUGH (PRECIPITABLE WATER
VALUES FORECAST TO BE ~150-175% OF NORMAL). BROAD UPPER LEVEL ASCENT
COUPLED WITH INCREASED MOISTURE AND MID-LEVEL FRONTOGENESIS WILL
SUPPORT A BAND OF LIGHT SNOW ACROSS NORTHWESTERN SD INTO CENTRAL SD
LATE TONIGHT. PRECIPITATION CHANCES WILL TAPER OFF FROM WEST TO EAST
AFTER 16-18Z TUESDAY.
UNCERTAINTY REMAINS ON EXACT PLACEMENT OF SNOW + POTENTIAL FOR
LOCALLY ENHANCED SNOW TONIGHT, ALL TIED TO THE EXACT PLACEMENT OF
THE MOST FOCUSED LOW-TO-MID-LEVEL FRONTOGENESIS. THE 12Z HREF SUITE
HAS THE HIGHEST QPF NORTH OF I-90, WITH FOCUSED AREAS IN THE BLACK
HILLS AND ALONG ND/SD BORDER (>40-50% OF QPF >0.05") WITH LESSER
AMOUNTS SOUTH OF I-90 (PROB OF QPF >0.05" AROUND 15-20% OR LESS).
RECENT DETERMINISTIC RUNS (NAM, ECMWF, AND GFS, SPECIFICALLY)
HINT AT ACCUMULATING SNOW POTENTIAL FROM I-90 SOUTHWARD TOWARD THE
NE/SD BORDER (ALONG THE NORTHERN PERIPHERY OF THE DEVELOPING MID-
LEVEL LOW CENTER WHERE MORE FOCUSED LOW-LEVEL FGEN IS FORECAST).
THE CURRENT FORECAST KEEPS WITH THE MORE NORTHERN SOLUTION WHERE
AN INCH OR TWO OF SNOW IS POSSIBLE FROM CENTRAL HAAKON COUNTY
THROUGH NORTHWESTERN SD AND THE HIGHER ELEVATIONS OF THE BLACK
HILLS, WITH LESSER AMOUNTS SOUTH OF I-90 (< 1" SNOW). WILL
CONTINUE TO MONITOR FOR THE SOUTHERN SOLUTION AND ANY HEAVIER
BANDS OF SNOW WITH LOCALLY HIGHER AMOUNTS, ESPECIALLY ALONG I-90.
SUBSIDENCE AND DRYING WILL OVERSPREAD THE FORECAST AREA TUESDAY
AFTERNOON WITH PRECIPITATION QUICKLY SHIFTING EAST. MILD
TEMPERATURES AND BREEZY SOUTHEASTERLY WINDS ARE FORECAST WEDNESDAY
AHEAD OF ANOTHER QUICK MOVING SYSTEM AND COLD FRONT. THE
STRONGEST LIFT AND MOISTURE WILL REMAIN DISPLACED TO THE NORTH
WITH LIGHT QPF FOR FAR NORTHWESTERN SD LATE WEDNESDAY INTO
THURSDAY. BARRING ANY SHIFTS SOUTHWARD WITH THE BEST LIFT, OUR
MAIN WEATHER CONCERN WILL BE STRONG NORTHWEST WINDS THURSDAY
BEHIND THE FRONT. WHILE THE STRONGEST COLD AIR ADVECTION AND
PRESSURE RISES (2-5 MB/3 HR) WILL REMAIN DISPLACED EAST, 40-45+
KNOT WINDS ARE FORECAST ~850-750 MB THURSDAY AFTERNOON, WHICH
WOULD SUPPORT GUSTS TO 50 MPH (AND POSSIBLY HIGHER).
UPPER LEVEL RIDGING AND DRIER WESTERLY FLOW RETURN BY FRIDAY INTO
THE WEEKEND WITH MILD TEMPERATURES FOR THE WEEKEND INTO NEXT WEEK.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)
ISSUED AT 1017 AM MST MON DEC 16 2024
GUSTY NORTHWEST WINDS CAN BE EXPECTED ACROSS SOUTH DAKOTA PLAINS
THROUGH THIS MORNING WITH WINDS DECREASING THIS AFTERNOON. SOME
LOW STRATUS/LIGHT SNOW WITH MVFR/IFR CONDITIONS WILL SLIP INTO
NORTHWESTERN SOUTH DAKOTA LATE TONIGHT. OTHERWISE, VFR CONDITIONS
ARE EXPECTED THROUGH THE TAF PERIOD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...SE
AVIATION...13
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