421
FXUS63 KUNR 191731
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1031 AM MST THU DEC 19 2024
KEY MESSAGES
- HIGH WINDS WILL CONTINUE OVER MUCH OF THE AREA THROUGH THIS
AFTERNOON, WITH GUSTS BECOMING STRONGER IN MANY AREAS AFTER
DAYBREAK.
- AFTER A COLD DAY TOMORROW ACROSS NORTHWESTERN AND SOUTH CENTRAL
SOUTH DAKOTA, MILD AND MOSTLY DRY CONDITIONS ARE EXPECTED FOR
THE NEXT SEVERAL DAYS.
- THE BEST CHANCE FOR MEASURABLE PRECIPITATION THROUGH CHRISTMAS
EVE LOOKS TO BE WITH A QUICK-MOVING DISTURBANCE ON SUNDAY THAT
COULD BRING A FEW RAIN AND SNOW SHOWERS TO THE AREA.
DISCUSSION
(TODAY THROUGH WEDNESDAY)
ISSUED AT 230 AM MST THU DEC 19 2024
WATER VAPOR IMAGERY THIS MORNING SHOWS A CLIPPER RAPIDLY MOVING EAST-
SOUTHEASTWARD ACROSS THE CENTRAL DAKOTAS, WITH A BLOSSOMING AREA OF
DEEP MOISTURE IMMEDIATELY DOWNSTREAM. A DISTINCT AREA OF SUBSIDENCE
AND ASSOCIATED DRYING IS EVIDENT TO THE SOUTH AND WEST OF THIS
FEATURE FROM NORTHERN NE ACROSS MUCH OF OUR AREA AND EXTENDING
NORTHWESTWARD INTO EASTERN MT. AT THE SURFACE, RECENT ANALYSES SHOW
PRESSURE RISES OF 5-8 MB/3 HR OVER MUCH OF EASTERN MT AND SOUTHERN
SK COINCIDENT WITH REASONABLY STRONG COLD AIR ADVECTION BEHIND AN
ATTENDANT COLD FRONT. COMBINED WITH A TIGHT SURFACE PRESSURE
GRADIENT ON THE WESTERN SIDE OF THE CLIPPER SYSTEM, THESE FEATURES
ARE CONTRIBUTING TO A BROAD CORRIDOR OF 50+ MPH WIND GUSTS FROM
NORTHWESTERN/WEST CENTRAL SD THROUGH NORTHEASTERN MT, WITH SOME
GUSTS OF 60-70 MPH OBSERVED IN RECENT HOURS, EVEN AHEAD OF THE MAIN
FRONT FOLLOWING THE PASSAGE OF A PREFRONTAL TROUGH.
AS THIS MAIN COLD FRONT CROSSES THE REGION THIS MORNING, PRESSURE
RISES OF 3-6 MB/3 HR ARE ANTICIPATED IN ITS WAKE. BETWEEN NOW AND
12Z, STRONG COLD AIR ADVECTION WILL OVERSPREAD NORTHWESTERN SD
BEFORE EXPANDING ACROSS SOUTH CENTRAL SD THROUGH 18Z. THESE FACTORS
WILL LEAD TO INCREASING WIND GUSTS OVER THE NEXT SEVERAL HOURS AND
AN EXPANSION OF WARNING-LEVEL GUSTS TO ENCOMPASS MANY OF OUR SD
ZONES. LATEST HREF SUGGESTS THAT WIND GUSTS NEAR OR EXCEEDING
WARNING CRITERIA ARE PROBABLE TO LIKELY (60-90% PROBABILITIES OF 55+
MPH WIND GUSTS) FROM JACKSON COUNTY SOUTH AND EASTWARD, WHICH
EFFECTIVELY REPRESENTS THE AREAS ON THE PLAINS THAT HAVE YET TO
REACH WARNING-CRITERIA GUSTS DURING THIS EVENT. AS IN PAST EVENTS,
THE HREF ALSO SUGGESTS VERY HIGH PROBABILITIES OF WARNING-LEVEL
GUSTS ACROSS HIGHER TERRAIN OF THE BLACK HILLS, BUT THIS HAS YET TO
MATERIALIZE IN MOST LOCATIONS. GIVEN THE POTENTIAL FOR FROUDE
NUMBERS TO INCREASE ABOVE 2 AFTER 09Z, WHICH MAY PROVE MORE
CONDUCIVE TO HIGH WINDS OVER THE BLACK HILLS, WILL MAINTAIN THE HIGH
WIND WARNING THERE FOR NOW DESPITE DECREASING CONFIDENCE. FARTHER
WEST, THE STRONGEST PRESSURE RISES AND COLD AIR ADVECTION ONLY SKIRT
NORTHEASTERN WY EARLY THIS MORNING, SUGGESTING THAT WARNING-CRITERIA
WIND GUSTS WILL LARGELY REMAIN EAST OF THOSE ZONES; HOWEVER, A FEW
GUSTS AROUND 60 MPH REMAIN POSSIBLE THROUGH AROUND 12Z. COLD AIR
ADVECTION AND PRESSURE RISES QUICKLY SHIFT SOUTHEASTWARD WITH THE
PARENT LOW TOMORROW AFTERNOON, WHICH SHOULD ALLOW FOR GUSTS TO
DIMINISH BY 21-00Z.
BY TOMORROW NIGHT, MODEL CONSENSUS SUGGESTS THAT LOW-LEVEL THERMAL
RIDGING WILL ALREADY BEGIN TO NOSE BACK INTO THE REGION AS ANOTHER
LEE TROUGH TAKES SHAPE FROM AB SOUTHEASTWARD TO EASTERN CO. 850 MB
TEMPERATURES APPROACHING 10C ACROSS NORTHEASTERN WY WITH SUBZERO 850
MB TEMPERATURES OVER OUR EASTERN ZONES WILL LEAD TO A NOTABLE
SURFACE TEMPERATURE GRADIENT BY FRIDAY AFTERNOON. HIGHS MAY STRUGGLE
TO CLIMB OUT OF THE TEENS OVER OUR NORTHEAST, WHEREAS PORTIONS OF
CAMPBELL COUNTY COULD END UP IN THE MID 50S. THE AFOREMENTIONED
TROUGH AXIS MOVES EAST OF THE AREA LATE FRIDAY INTO EARLY SATURDAY,
WITH FEW SENSIBLE WEATHER IMPACTS ANTICIPATED. BY 06-12Z SUNDAY,
LREF SHOWS THAT 850 MB TEMPERATURES OF AT LEAST 10C, WHICH WOULD BE
ABOVE THE 90TH PERCENTILE FOR RAPID CITY BASED ON THE SPC'S SOUNDING
CLIMATOLOGY, ARE POSSIBLE TO LIKELY (55-85%) OVER MUCH OF WESTERN
AND SOUTH CENTRAL SD.
A STRONGER TROUGH AND ASSOCIATED UPPER-LEVEL DISTURBANCE CROSSES THE
REGION LATE SATURDAY NIGHT THROUGH SUNDAY. INCREASED DEEP Q-VECTOR
CONVERGENCE AND IMPROVED MOISTURE TRANSPORT WHEN COMPARED TO THE
LATE FRIDAY/EARLY SATURDAY SYSTEM SUGGEST THIS COULD BE OUR NEXT
POTENTIAL FOR WIDESPREAD--ALBEIT LIKELY LIGHT--PRECIPITATION. FOR
NOW, THE LREF KEEPS THE BEST CHANCES FOR EVEN MEASURABLE
PRECIPITATION MOSTLY ALONG AND NORTH OF I-90, WITH PROBABILITIES OF
0.01" OF QPF INCREASING FROM ~0% AROUND THE NE/SD BORDER TO ~50% AT
THE ND/SD BORDER. ALTHOUGH PRECIPITATION CHANCES ARE SLIGHT,
CONFIDENCE IS HIGH IN A PROLONGED PERIOD OF ABOVE NORMAL
TEMPERATURES, WITH THE EPS, GEFS, AND GEPS ALL SHOWING VERY HIGH
PROBABILITIES (90%+) OF SURFACE TEMPERATURE ANOMALIES OF 5F OR
GREATER OVER MOST OF THE AREA FROM SUNDAY AFTERNOON THROUGH
CHRISTMAS DAY.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1028 AM MST THU DEC 19 2024
STRONG, GUSTY NORTHWEST WINDS WILL CONTINUE THROUGH 22Z OVER MOST
OF WESTERN SD. GUSTS TO 40-55KTS WILL BE COMMON THIS MORNING FROM
K2WX-KRAP/KPHP-KICR. WINDS WILL QUICKLY DIMINISH LATE THIS
AFTERNOON AND EVENING. VFR CONDITIONS ARE EXPECTED THROUGH THE
PERIOD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...HIGH WIND WARNING UNTIL 2 PM MST THIS AFTERNOON FOR SDZ001-002-
012>014-025-026-030>032-043-072>074-078.
WIND ADVISORY UNTIL 2 PM MST THIS AFTERNOON FOR SDZ027-041-042-
075-076.
HIGH WIND WARNING UNTIL 3 PM MST /4 PM CST/ THIS AFTERNOON FOR
SDZ044-046-047-049-077.
WY...HIGH WIND WARNING UNTIL 2 PM MST THIS AFTERNOON FOR WYZ060.
DISCUSSION/KEY MESSAGES...SHERBURN
AVIATION...10/SCHULTZ
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