855
FXUS63 KUNR 172339
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
439 PM MST WED DEC 17 2025
KEY MESSAGES
- WIDESPREAD NEAR CRITICAL FIRE WX CONDITIONS ACROSS NORTHEASTERN
WY INTO WESTERN AND SOUTH CENTRAL SOUTH DAKOTA THIS AFTERNOON.
- STRONG SOUTHWEST WINDS WILL CONTINUE THROUGH THE AFTERNOON HOURS
WITH GUSTS ALREADY HITTING 60-70 MPH IN SPOTS.
- THE STRONG WINDS WILL SHIFT TO THE NORTHWEST LATER THIS EVENING
INTO THE OVERNIGHT HOURS AND OVERSPREAD THE REGION WITH GUSTS OF
75- 80+ MPH POSSIBLE ACROSS NORTHWESTERN SD.
- DESPITE MEAGER QPF, POTENTIAL EXISTS FOR FOR SNOW SQUALLS OVER
WESTERN SD LATER TONIGHT INTO EARLY THURSDAY MORNING.
DISCUSSION
(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 119 PM MST WED DEC 17 2025
STRONG SOUTHWESTERLY WINDS HAVE DEVELOPED ACROSS NORTHEASTERN
WYOMING AND WESTERN SOUTH DAKOTA. GUSTY DOWNSLOPE WINDS CONTINUE
ACROSS THE EASTERN BLACK HILLS AND FOOTHILLS WITH PEAK GUSTS OF
55-65 MPH THIS MORNING AND EARLY AFTERNOON.
CONFIDENCE IS INCREASING IN A HIGHER IMPACT HIGH WIND EVENT FOR
NORTHWESTERN SOUTH DAKOTA ACROSS THE I-90 CORRIDOR IN WESTERN
SOUTH DAKOTA OVERNIGHT TONIGHT BEHIND TWO FRONTS IN QUICK
SUCCESSION. FORECAST SOUNDINGS CONTINUE TO SHOW WELL-MIXED
BOUNDARY LAYERS, MIXING DOWN A CORE OF 80-90KT WINDS ATOP THE
MIXED LAYER. HI-RES MODELS PICK UP ON THIS AS WELL, COUPLED WITH
MOS GUIDANCE (OLD SCHOOL!) SHOWING SUSTAINED WINDS OF 40-50+ KNOTS
ACROSS NORTHWESTERN SD OVERNIGHT. THE INGREDIENTS ARE THERE: 3-6
MB PRESSURE RISES BEHIND THE FIRST FRONT THIS EVENING, 6-9+ MB
PRESSURE RISES BEHIND THE SECOND/ARCTIC FRONT LATE TONIGHT, STRONG
CAA/MECHANICAL MIXING OF HIGHER MOMENTUM AIR, AND A CORE OF
70-100 KNOT WINDS AT ~800-700 MB. CONSEQUENTLY, HAVE INCREASED
WINDS IN THIS FORECAST PACKAGE ACROSS THE WESTERN SD PLAINS
TONIGHT WITH MAXIMUM WIND GUSTS ~75-80 MPH, ALTHOUGH POTENTIAL
EXISTS FOR 80+ MPH. LOOKING AT IT PROBABILISTICALLY, THE NBM HAS
PROB OF GUSTS >75 MPH ~65-75%+ FOR MOST OF WESTERN SD; THE 12Z
HREF/REFS HAVE A SIMILARLY HIGH PROBABILITY OF GUSTS >75 MPH
OVERSPREADING NW SD AFTER 11PM MT BEHIND THE SECOND FRONT,
SPREADING SOUTHEASTWARD THROUGH 6AM. THE STRONGEST WINDS (70+ MPH)
ARE EXPECTED TO STRETCH FROM NW SD INTO THE FOOTHILLS AND ALONG
I-90 IN WESTERN SD. WINDS WILL DIMINISH FROM WEST TO EAST LATE
THURSDAY MORNING THROUGH THE AFTERNOON HOURS.
LIGHT RAIN WILL QUICKLY TRANSITION TO SNOW AS THE ARCTIC FRONT
PUSHES INTO THE NW SD LATER THIS EVENING. WHILE THE BEST MOISTURE
WILL REMAIN DISPLACED EAST, STRONG LOW-LEVEL LAPSE RATES COUPLED
WITH VERY STRONG WINDS WILL SUPPORT SNOW SQUALL POTENTIAL IN ANY
HEAVIER BANDS OF SNOW OVERNIGHT. THE BEST SNOW SQUALL POTENTIAL
WILL EXIST AFTER 10PM ACROSS NW SD INTO THE WESTERN SD PLAINS
THROUGH THE OVERNIGHT HOURS, ALTHOUGH MEAGER QPF/MOISTURE WILL
YIELD ONLY TRANSIENT VISIBILITY REDUCTIONS.
UPPER LEVEL FLOW WILL BECOME ZONAL FRIDAY WITH HIGHS WARMING BACK
INTO THE 50S AND 60S AHEAD OF ANOTHER CLIPPER SYSTEM FRIDAY NIGHT
INTO SATURDAY MORNING WITH LIGHT SNOW ACROSS NE WY INTO THE BLACK
HILLS. COOLER SATURDAY BEHIND ANOTHER COLD FRONT BEFORE DRY,
ZONAL/SOUTHWESTERLY FLOW RETURNS FOR NEXT WEEK - LOOKING MILD FOR
CHRISTMAS.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 425 PM MST WED DEC 17 2025
FIRST COLD FRONT IS MOVING THROUGH THE AREA EARLY THIS EVENING
WITH STRONG WEST/SOUTHWESTERLY WIND GUSTS FROM 30-50KTS AHEAD OF
IT AND STRONG WEST/NORTHWEST WIND GUSTS FROM 30-55KTS BEHIND IT. A
SECOND COLD FRONT WILL BRING STRONGER WIND GUSTS FROM THE
NORTHWEST REACHING 40-60KTS+ AT TIMES OVERNIGHT INTO THURSDAY
MORNING. A BAND OF RAIN WILL CROSS THE AREA EARLY THIS EVENING
WITH LOCAL MVFR/IFR CONDITIONS. THE SECOND FRONT WILL HAVE
ISOLATED SNOW SHOWERS, ESPECIALLY OVER THE NORTHERN BLACK HILLS
WITH LOCAL MVFR/IFR CONDITIONS. WINDS WILL QUICKLY DIE DOWN
THURSDAY AFTERNOON WITH VFR CONDITIONS PREVAILING.
FIRE WEATHER
ISSUED AT 119 PM MST WED DEC 17 2025
STRONG WEST-SOUTHWESTERLY WINDS AND LOW RELATIVE HUMIDITY WILL
SUPPORT NEAR-CRITICAL FIRE WEATHER CONDITIONS. WINDS CONTINUE TO
GUST 40-60+ MPH ACROSS PORTIONS OF NW WY INTO SOUTHWESTERN AND SOUTH-
CENTRAL SD THIS AFTERNOON. WHILE RELATIVE HUMIDITY WON'T MEET THE
TRADITIONAL CRITICAL VALUE (<15%), RH ~25-30% THIS AFTERNOON COUPLED
WITH THE STRONG WINDS WILL SUPPORT NEAR-CRITICAL CONDITIONS.
UNR WATCHES/WARNINGS/ADVISORIES
SD...HIGH WIND WARNING UNTIL 11 AM MST THURSDAY FOR SDZ001-002-012-
013-025-041-072-073-078.
HIGH WIND WARNING FROM 10 PM MST /11 PM CST/ THIS EVENING TO 1
PM MST /2 PM CST/ THURSDAY FOR SDZ014-026-030>032-042>044-
046-047-049-074>077.
HIGH WIND WARNING UNTIL 8 AM MST THURSDAY FOR SDZ024-027>029.
WY...HIGH WIND WARNING UNTIL 11 AM MST THURSDAY FOR WYZ059-060.
HIGH WIND WARNING UNTIL 8 AM MST THURSDAY FOR WYZ057.
HIGH WIND WARNING UNTIL 5 AM MST THURSDAY FOR WYZ054>056-058.
DISCUSSION/KEY MESSAGES...SE
AVIATION...HELGESON
FIRE WEATHER...SE
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