795
FXUS63 KUNR 211117
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
417 AM MST SUN DEC 21 2025
KEY MESSAGES
- MILD AND WINDY CONDITIONS FOR MOST OF THE UPCOMING WEEK.
- MAINLY DRY, A FEW SPRINKLES/FLURRIES POSSIBLE THIS
AFTERNOON/EVENING.
- NEAR RECORD HIGH TEMPERATURES MONDAY AND WEDNESDAY.
DISCUSSION
(TODAY THROUGH SATURDAY)
ISSUED AT 203 AM MST SUN DEC 21 2025
LATEST UPPER LEVEL ANALYSIS SHOWS QUASI-ZONAL FLOW OVER THE
FORECAST AREA WITH WEAK RIDGING BUILDING OVER THE WESTERN CONUS
AND A DEEPENING LOW OVER THE GULF OF ALASKA/PACIFIC OCEAN. AT THE
SURFACE, HIGH PRESSURE IS IN PLACE WITH A STATIONARY BOUNDARY
EXTENDING THROUGH EASTERN MONTANA AND CENTRAL SOUTH DAKOTA.
TEMPERATURES AT 08Z ARE MAINLY IN THE 20S.
THE UPPER RIDGE SHIFTS SLOWLY EAST TODAY AND TONIGHT AS THE
PACIFIC UPPER LOW DEEPENS. WARM AIR ADVECTION AHEAD OF THE NEXT
IMPULSE WILL SUPPORT HIGHS IN THE LOW 40S TO LOW 50S. MID AND HIGH
LEVEL MOISTURE INCREASES, RESULTING IN INCREASED CLOUD COVER
ACROSS THE FORECAST AREA. WEAK FRONTOGENESIS MAY RESULT IN A FEW
SPRINKLES AND FLURRIES THIS AFTERNOON AND EVENING.
SOUTHWESTERLY WINDS WILL INCREASE TONIGHT ACROSS NORTHEAST WY,
THE BLACK HILLS, AND EASTERN FOOTHILLS WITH INCREASED FLOW ALOFT
AND A TIGHTENING PRESSURE GRADIENT. THIS COULD SUPPORT ADVISORY
LEVEL WINDS IN THE FOOTHILLS AFTER MIDNIGHT TONIGHT AND DURING THE
DAY ON MONDAY WHEN THE STRONGEST PRESSURE GRADIENT WILL BE IN
PLACE ACROSS THE HILLS. DOWNSLOPE WINDS AND PREFRONTAL CONDITIONS
WILL RESULT IN WARM TEMPERATURES ON MONDAY WHICH WILL APPROACH
NEAR RECORD HIGHS AS MOST RECORDS ARE IN THE MID-60S.
A DRY COLD FRONT MOVES THROUGH THE AREA LATE MONDAY/MONDAY
EVENING, SWITCHING THE WINDS AROUND TO THE NORTHWEST AND BRINGING
IN A LITTLE BIT OF COLDER AIR. WARM AIR ADVECTION QUICKLY BEGINS
EARLY TUESDAY, ALLOWING HIGHS OVER THE SOUTHWESTERN PORTION OF THE
FORECAST AREA TO BE SIMILAR TO MONDAY. HOWEVER, HIGHS ON THE
SOUTH DAKOTA PLAINS WILL BE 5F TO 10F COOLER ON TUESDAY.
CONDITIONS TUESDAY NIGHT AND WEDNESDAY WILL BE SIMILAR TO TONIGHT
AND MONDAY, AS INCREASING WARM AIR ADVECTION, WESTERLY FLOW, AND
DOWNSLOPE WINDS WILL ALLOW FOR NEAR RECORD HIGHS ON CHRISTMAS EVE.
MODEL CONSISTENCY LESSENS BEGINNING ON CHRISTMAS, DUE TO THE
TIMING OF THE NEXT COLD FRONT/UPPER TROUGH AS THE STRONG UPPER LOW
OFF BRITISH COLUMBIA WEAKENS AND DIVES SOUTHWARD DOWN THE
CALIFORNIA COAST. THE TIMING AND STRENGTH OF THE NEXT COLD
FRONT/UPPER TROUGH EJECTING OVER THE ROCKIES WILL GREATLY
INFLUENCE CONDITIONS ON CHRISTMAS. MOST DETERMINISTIC MODELS AND
THE THE MEAN ENSEMBLES DELAY THE ARRIVAL, ALLOWING FOR WARMER
CONDITIONS TO CONTINUE. AS THIS SYSTEM MOVES ACROSS THE FORECAST
AREA, THERE COULD BE A CHANCE OF LIGHT PRECIPITATION DUE TO COLD
AIR OVER RUNNING THE WARM AIR.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 416 AM MST SUN DEC 21 2025
VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. SOUTHWEST
WINDS WILL INCREASE EARLY THIS EVENING ACROSS PORTIONS OF
NORTHEASTERN WYOMING AND THE BLACK HILLS.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...SMITH
AVIATION...SMITH
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