831
FXUS63 KUNR 182311
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
411 PM MST WED DEC 18 2024
KEY MESSAGES
- A CLIPPER SYSTEM WILL BRING CHANCES FOR LIGHT RAIN/FREEZING RAIN
ACROSS NORTHWESTERN SD THIS EVENING AND STRONG NORTHWEST WINDS
ACROSS THE SD PLAINS LATE TONIGHT INTO THURSDAY
- MOSTLY DRY CONDITIONS ARE EXPECTED LATE WEEK INTO AT LEAST EARLY
NEXT WEEK WITH TEMPERATURES NEAR TO ABOVE AVERAGE ACROSS MOST
OF THE AREA.
DISCUSSION
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 201 PM MST WED DEC 18 2024
CURRENT SFC OBS DEPICT NORTHWEST-SOUTHEAST ORIENTED WARM FRONT
DRAPED ACROSS WESTERN SD AND PUSHING NORTHWARD. A DEVELOPING SFC
LOW IS CENTERED OVER SOUTHERN AB/NORTHWESTERN MT ASSOCIATED WITH A
SHORTWAVE TROF CROSSING THE NORTHERN ROCKIES. VISIBLE SATELLITE
IMAGERY DEPICTS ERODING BAND OF LOW CLOUDS OVER CENTRAL SD WITH
MID LEVEL WV IMAGERY SHOWING PUSH OF MOISTURE ASSOCIATED WITH THE
INCOMING SYSTEM ENTERING THE NORTHERN PLAINS.
THE UPPER LEVEL SHORTWAVE AND ATTENDANT SFC LOW/CLIPPER SYSTEM
WILL SWING SOUTHEAST THROUGH THIS AFTERNOON AND EVENING, MAKING IT
TO THE NORTHERN PLAINS BY LATE TONIGHT. THE CENTER OF THE LOW
(ALONG WITH THE STRONGEST FORCING) WILL PASS TO OUR NORTH WHICH
WILL KEEP MOST OF THE AREA DRY WITH THIS SYSTEM. HOWEVER
NORTHWESTERN INTO SOUTH CENTRAL SD MAY SEE SLIGHT CHANCES FOR
PRECIP LATER THIS EVENING AS A COLD FRONT PUSHES THROUGH. THERMAL
PROFILES FAVOR FREEZING RAIN DEVELOPING OVER NORTHWESTERN SD AS
SFC TEMPERATURES WILL DIP BELOW FREEZING WITH WARMER AIR ALOFT.
ANY ICE ACCUMULATIONS ARE EXPECTED TO BE LIGHT, GENERALLY A TRACE
TO PERHAPS A HUNDREDTH OF AN INCH.
3 HR PRESSURE RISES OF 4 TO 5 MB AND CAA BEHIND THE FRONT WILL
SUPPORT THE DEVELOPMENT OF STRONG NORTHWEST WINDS EARLY THURSDAY
MORNING. THESE PRESSURE RISES ALONG WITH A CORRIDOR OF 60-70KT
WINDS AT ~850-725 MB WILL BE SUPPORTIVE OF WIND GUSTS OF 55-65MPH
AT THE SURFACE. HREF PROBABILITIES HAVE 60-70% FOR WIND GUSTS OF
60 MPH OR GREATER ACROSS NORTHWESTERN SD THROUGH EARLY THIS
MORNING. THEREFORE HAVE OPTED TO UPGRADE THE HIGH WIND WATCH TO A
HIGH WIND WARNING. AS FOR SOUTH CENTRAL SD, THE MOST RECENT MODEL
RUNS HAVE POINTED TO MORE FAVORABLE CONDITIONS FOR STRONG WINDS TO
DEVELOP. THE 12Z RUN OF THE HREF DEPICTS 60-80% PROBABILITIES FOR
WIND GUSTS EXCEEDING 55 MPH, THOUGH THE CHANCES DROP OFF TO 10%
FOR GUSTS EXCEEDING 60 MPH. HOWEVER, WITH MODEST PRESSURE RISES OF
4 TO 5 MB/3HR AND 50-60KT WINDS JUST OFF THE SURFACE, THERE IS
THE POTENTIAL FOR HIGH WIND WARNING CRITERIA GUSTS. THEREFORE HAVE
EXPANDED THE HIGH WIND WARNING TO COVER SOUTH CENTRAL SD. WINDS
WILL DIE DOWN LATE THURSDAY AFTERNOON AS THE CLIPPER SLIDES TO THE
SOUTHEAST WITH HIGH PRESSURE BUILDING IN ITS WAKE.
ARCTIC AIR MASS WILL PUSH INTO THE NORTHERN PLAINS THURSDAY AND
FRIDAY AS THE CLIPPER MOVES OUT OF THE REGION. THE COLDEST TEMPS
SHOULD REMAIN TO OUR NORTH/NORTHEAST WITH HIGHS IN NORTHWESTERN SD
IN THE 20S AND HIGHS ACROSS NORTHWESTERN WY AND SOUTHWESTERN SD
IN THE 40S. RIDGE BUILDS OVER THE WESTERN US BY THIS WEEKEND WITH
TEMPERATURES ACROSS THE CWA WARMING INTO THE 40S TO 50S BY
SATURDAY AND SUNDAY. WEAK SHORTWAVE CROSSES THE REGION LATE FRIDAY
INTO SATURDAY. MOISTURE WITH THIS SYSTEM WILL BE LIMITED AND IT
LOOKS LIKE THE ONLY SENSIBLE WEATHER IMPACTS WILL BE BREEZY
SOUTHERLY WINDS FRIDAY AFTERNOON FOLLOWED BY A WIND SHIFT TO THE
NORTHEAST AS THE WAVE PASSES THROUGH. A SLIGHTLY STRONGER
SHORTWAVE CROSSES THE REGION SUNDAY WHICH COULD BRING CHANCES FOR
LIGHT RAIN/SNOW ACROSS PARTS OF NORTHEASTERN WY AND FAR WESTERN
SD. NEAR ZONAL FLOW WILL FACILITATE MILD CONDITIONS THROUGH
CHRISTMAS WEEK. DETERMINISTIC GUIDANCE IS STILL SHOWING A SYSTEM
DEVELOPING OVER THE CENTRAL PLAINS AND SWINGING UP NORTH BY
CHRISTMAS DAY, WHICH COULD GIVE US ANOTHER SHOT AT LIGHT RAIN
AND/OR SNOW ACROSS NORTHEASTERN WY INTO WESTERN SD.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 409 PM MST WED DEC 18 2024
A STRONG CLIPPER SYSTEM WILL APPROACH THE REGION THIS EVENING
WITH INCREASING FLOW OFF THE SURFACE. THIS WILL SUPPORT LOW LEVEL
WIND SHEAR (40-60KT AT 2000FT) BEFORE THE SURFACE FRONT MOVES
THROUGH LATER TONIGHT. EXPECT WINDS OF 30 TO 40 KNOTS WITH GUSTS
OVER 50 KNOTS BEHIND THE FRONT. IN ADDITION, LIGHT MIXED
PRECIPITATION IS POSSIBLE ACROSS NORTHWESTERN SD THIS EVENING.
WINDS WILL BEGIN TO TAPER OFF THUR AFTERNOON WEST TO EAST.
UNR WATCHES/WARNINGS/ADVISORIES
SD...HIGH WIND WARNING FROM 11 PM THIS EVENING TO 2 PM MST THURSDAY
FOR SDZ001-002-078.
HIGH WIND WARNING FROM 2 AM TO 2 PM MST THURSDAY FOR SDZ012>014-
031-032-043-072-073.
WIND ADVISORY FROM 8 AM TO 3 PM MST THURSDAY FOR SDZ025-026.
HIGH WIND WARNING FROM 8 AM MST /9 AM CST/ TO 3 PM MST /4 PM
CST/ THURSDAY FOR SDZ044-046-047-049-077.
WY...NONE.
DISCUSSION/KEY MESSAGES...WONG
AVIATION...JC
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