746
FXUS63 KUNR 182311
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
411 PM MST TUE FEB 18 2025
KEY MESSAGES
- BITTERLY COLD TEMPERATURES CONTINUE. DESPITE LIGHT WINDS, EXPECT
WIND CHILLS AS LOW AS 20 TO 40 BELOW ZERO THROUGH THURSDAY
MORNING.
- LIGHT SNOW WILL LINGER THROUGH THE AFTERNOON AND EVENING HOURS.
ADDITIONAL SNOW AMOUNTS LESS THAN AN INCH EXPECTED.
- WARMING TREND THURSDAY THROUGH THE WEEKEND. WARMEST TEMPERATURES
SUNDAY INTO EARLY NEXT WEEK WITH 50S LIKELY (PROBABILITY > 50%
FOR MUCH OF THE WYOMING AND SOUTH DAKOTA PLAINS FOR SATURDAY;
HIGHER SUNDAY ONWARD).
DISCUSSION
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 137 PM MST TUE FEB 18 2025
WATER VAPOR IMAGERY SHOWS SHORTWAVE TROUGH STREAMING THROUGH THE
FORECAST AREA EARLY THIS AFTERNOON WITH DRIER AIR/SUBSIDENCE FURTHER
UPSTREAM. AT THE SURFACE, A 1048 MB HIGH CONTINUES TO SLOWLY SLIDE
INTO CENTRAL NORTH DAKOTA WHILE THE SURFACE STATIONARY FRONT REMAINS
ENTRENCHED ACROSS WESTERN MONTANA THROUGH CENTRAL WYOMING INTO
EASTERN COLORADO. LIGHT SNOW WILL LINGER THROUGH THE AFTERNOON
INTO THE EVENING HOURS, BEFORE UPPER LEVEL ASCENT SHIFTS EASTWARD.
ANY ADDITIONAL ACCUMULATION EXPECTED TO BE LESS THAN AN INCH.
WIND CHILLS RANGE FROM 15 TO 40 BELOW ZERO, COLDEST ACROSS
NORTHWESTERN SOUTH DAKOTA.
THE SURFACE HIGH PRESSURE WILL CONTINUE TO SAG SOUTHWARD INTO
EASTERN NORTH DAKOTA/SOUTH DAKOTA OVER THE NEXT 24-36 HOURS WITH
LARGE-SCALE SUBSIDENCE OVERSPREADING THE NORTHERN PLAINS THROUGH
WEDNESDAY. EXPECT GRADUALLY CLEARING SKIES LATER TONIGHT THROUGH
THURSDAY MORNING. WHILE WINDS ARE FORECAST TO BE LIGHT TONIGHT,
CLEAR SKIES + FRESH SNOW PACK + ENTRENCHED ARCTIC AIR WILL RESULT
IN ANOTHER NIGHT OF WIND CHILLS 25 TO 40 BELOW ZERO. THE EXTREME
COLD WARNING CONTINUES FOR NORTHWESTERN SOUTH DAKOTA THROUGH 18Z
WEDNESDAY, WITH A COLD WEATHER ADVISORY FOR THE REST OF THE
FORECAST AREA. WILL NEED ADDITIONAL HEADLINES/EXTENSION OF
HEADLINES FOR WEDNESDAY NIGHT INTO THURSDAY WITH STRONGER WINDS
FORECAST, ALTHOUGH TEMPERATURES WILL BE MODESTLY "WARMER" (AIR
TEMPERATURES OF 0F TO -20F WED NIGHT VS. -15F TO -35F TONIGHT).
DESPITE THE SLIGHTLY WARMER TEMPERATURES, STRONGER WINDS WILL
RESULT IN MORE WIDESPREAD 35 TO 40 BELOW ZERO WIND CHILLS
OVERNIGHT WEDNESDAY INTO THURSDAY MORNING, ESPECIALLY ACROSS
WESTERN SD PLAINS.
HIGH PRESSURE WILL FINALLY SHIFT INTO THE MIDWEST AND MISSISSIPPI
VALLEY FRIDAY INTO THE WEEKEND WITH UPPER LEVEL RIDGING BUILDING
OVER THE WESTERN HALF OF THE US. WARMER WESTER-SOUTHWESTERLY FLOW
WILL RESULT IN AMPLE WARM AIR ADVECTION THURSDAY INTO THE
WEEKEND. RECENT SNOW COVER WILL MODERATE WARMING THURSDAY INTO
FRIDAY, ALTHOUGH CONTINUED WARM WESTERLY FLOW WILL HELP MELT SNOW
INTO THE WEEKEND. ENSEMBLE GUIDANCE CONTINUES TO SHOW A HIGH
LIKELIHOOD OF WIDESPREAD 50S BY SATURDAY, BUT ESPECIALLY SUNDAY
INTO EARLY NEXT WEEK: NBM PROBABILITY OF >50F IS AROUND 40-65%+
FOR MUCH OF THE WESTERN SD PLAINS AND FOOTHILLS SATURDAY, WITH
EXPANDING AREA OF PROBABILITY ~85%+ BY SUNDAY FOR NORTHEASTERN WY
AND WESTERN SD PLAINS.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 411 PM MST TUE FEB 18 2025
WIDESPREAD MVFR/AREAS IFR CONDITIONS DUE TO LIGHT SNOW/LOW STRATUS
WILL VERY SLOWLY IMPROVE FROM NORTHWEST TO SOUTHEAST TONIGHT.
SIGNIFICANT IMPROVEMENT IS LIKELY WEDNESDAY, ESPECIALLY FOR
NORTHEASTERN WY/NORTHWESTERN SD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...EXTREME COLD WARNING UNTIL 11 AM MST WEDNESDAY FOR SDZ001-002-
012>014-078.
COLD WEATHER ADVISORY UNTIL 11 AM MST /NOON CST/ WEDNESDAY FOR
SDZ024>032-041>044-046-047-049-072>077.
WY...COLD WEATHER ADVISORY UNTIL 11 AM MST WEDNESDAY FOR WYZ054>060.
DISCUSSION/KEY MESSAGES...SE
AVIATION...10
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