973
FXUS63 KUNR 250457
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
957 PM MST WED DEC 24 2025
KEY MESSAGES
- VERY WINDY SOUTH/SOUTHWEST WINDS EXPECTED FOR NORTHEASTERN
WYOMING AND THE BLACK HILLS TONIGHT INTO CHRISTMAS MORNING
- AREAS OF FOG WILL DEVELOP/MOVE INTO FAR NORTHWEST TO SOUTH-
CENTRAL SOUTH DAKOTA OVERNIGHT INTO EARLY CHRISTMAS DAY
- TOASTY CHRISTMAS DAY FOR MANY FOLKS WITH NEAR-RECORD/RECORD
HIGHS EXPECTED
- ARCTIC FRONT BRINGS A QUICK COLD SNAP SATURDAY NIGHT/SUNDAY,
POTENTIALLY WITH STRONG NORTHWEST WINDS AND A BIT OF LIGHT SNOW
UPDATE
ISSUED AT 628 PM MST WED DEC 24 2025
UPGRADED TO A HIGH WIND WARNING FOR EXTREME NORTHEAST CROOK COUNTY
AND THE NORTHERN FOOTHILLS. STRONG FLOW PROGGED JUST OFF THE SFC
WITH OVER 60 KNOTS JUST OVER A 1000 FT LATER TONIGHT THERE.
PRESSURE FALLS WILL SUPPORT TERRAIN INDUCED DOWNSLOPE FLOW VIA
SOUTHWEST WINDS WITH GUSTS OVER 65 MPH POSSIBLE, LOCALLY HIGHER IN
SOME PLACES. FURTHER SE, STARTED THE WIND ADV LATER WITH FLOW NOT
EXPECTED TO INCREASE IN THE EASTERN FOOTHILLS UNTIL LATER IN THE
MORNING. EXTENDED THE TIME OF THE ADV AND WARNING THROUGH EARLY
AFTERNOON GIVEN MODEL TRENDS.
DISCUSSION
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 134 PM MST WED DEC 24 2025
20Z SURFACE ANALYSIS HAD WAVERING FRONTAL BOUNDARY FROM NORTHWEST
MT INTO CENTRAL SD. 30S/40S NORTHEAST OF IT (PLUS SOME
STRATUS/FOG) WITH 50S/60S TO THE SOUTHWEST OF THE BOUNDARY. WATER
VAPOUR LOOP HAD UPPER TROUGH OFF THE WEST COAST WITH ENTRENCHED
SOUTHWEST FLOW ALOFT FROM THE SOUTHWEST CONUS INTO THE NORTHERN
PLAINS. EFFECTS OF THESE FEATURES THE MAIN FORECAST CONCERNS.
TONIGHT/CHRISTMAS DAY, EMBEDDED SHORTWAVE IN SOUTHWEST FLOW ALOFT
WILL ZIP INTO THE NORTHERN PLAINS INDUCING MODEST LOW PRESSURE
OVER MT. AS THE LOW MOVES EAST, IT WILL PROPEL FRONTAL BOUNDARY
NORTHEASTWARD AS A WARM FRONT WITH TIGHT PRESSURE GRADIENT
DEVELOPING. NAM HAS 4MB GRADIENT ACROSS THE BLACK HILLS WITH GFS
AT 6MB BETWEEN 25/06-18Z. BOUNDARY LAYER WINDS AVERAGE 30-50KTS
OVER PARTS OF NORTHEASTERN WY INTO THE BLACK HILLS WITH GFS
STRONGEST. LATEST HREF INDICATES 50KT+ GUST PROBABILITY 50-80%
FROM SPEARFISH TO CUSTER, BUT REST OF PROBABILISTIC GUIDANCE <20%.
GIVEN NAM TYPICALLY HANDLES DOWNSLOPE WINDSTORM POTENTIAL THE
BEST, WILL HOIST A WIND ADVISORY FOR THE BLACK HILLS FOOTHILLS TO
ACCOUNT WITH LATER SHIFTS WATCHING THE TRENDS FOR THE HIGHER BLACK
HILLS/NORTHEASTERN WY. AHEAD OF THE WARM FRONT, SUSTAINED MOIST
NORTHEAST BOUNDARY LAYER FLOW COMBINED WITH DIURNAL COOLING WILL
CREATE STRATUS/FOG FROM FAR NORTHWEST TO SOUTH-CENTRAL SD. SOME
BUFKIT SOUNDINGS HINT AT FREEZING DRIZZLE POTENTIAL, BUT
PROBABILISTIC DATA NOT AS SUPPORTIVE. FINALLY, BEHIND THE WARM
FRONT FOR CHRISTMAS DAY EXPECT NEAR-RECORD/RECORD HIGH
TEMPERATURES GIVEN FORECAST SOUNDINGS WITH A >80% CHANCE OF >65F
MAXT FROM RAPID CITY INTO FAR SOUTHWEST/SOUTH-CENTRAL SD.
ANOTHER WARM DAY FRIDAY, BUT THEN AN UPPER LOW MOVING ACROSS
SOUTHERN CANADA WILL PUSH AN ARCTIC COLD FRONT INTO THE NORTHERN
PLAINS. IT WILL BRING MUCH COLDER TEMPERATURES SATURDAY
NIGHT/SUNDAY WITH THE POTENTIAL FOR STRONG NORTHWEST WINDS GIVEN
FORECAST COLD AIR ADVECTION AND ATTENDANT ISALLOBARIC FORCING.
LIGHT SNOW MAY ALSO OCCUR, ESPECIALLY OVER THE BLACK
HILLS/NORTHEASTERN WY. QUICK WARMUP AGAIN FOR SUNDAY/EARLY NEXT
WEEK, BUT ENSEMBLE SPREADS INCREASE QUITE A BIT WITH LOCATION
DIFFERENCES FOR THE ARCTIC AIR/LOW LEVEL BAROCLINIC ZONE.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 953 PM MST WED DEC 24 2025
GUSTY SOUTHWEST WINDS WILL CONTINUE TO STRENGTHEN ACROSS PARTS OF
NORTHEAST WYOMING AND THE BLACK HILLS AND PERSIST THROUGH
THURSDAY MORNING. GUSTS IN EXCESS OF 45 KNOTS ARE POSSIBLE AT
TIMES.
MVFR/IFR CONDITIONS IN PATCHY DENSE FOG WILL CONTINUE OVER
NORTHWESTERN INTO SOUTH CENTRAL SD. FOG WILL DISSIPATE AFTER 15Z.
UNR WATCHES/WARNINGS/ADVISORIES
SD...DENSE FOG ADVISORY UNTIL 8 AM MST THURSDAY FOR SDZ002-013-014-
032-078.
HIGH WIND WARNING UNTIL 2 PM MST THURSDAY FOR SDZ025.
WIND ADVISORY FROM 5 AM TO 2 PM MST THURSDAY FOR SDZ026-072-074.
WY...HIGH WIND WARNING UNTIL 2 PM MST THURSDAY FOR WYZ060.
UPDATE...JC
DISCUSSION/KEY MESSAGES...HELGESON
AVIATION...WONG
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