746
FXUS63 KUNR 250422
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1022 PM MDT THU SEP 24 2020
UPDATE
ISSUED AT 658 PM MDT THU SEP 24 2020
BASED ON UPSTREAM OBS AND THE EXPECTATION OF ENHANCED PRESSURE
RISES BEHIND AN APPROACHING COLD FRONT, CONFIDENCE IS INCREASING
IN A STRONG WIND EVENT TONIGHT FOR MUCH OF THE WRN SD PLAINS. MAIN
POINT OF CONSIDERATION THIS EVENING HAS BEEN THE POTENTIAL FOR
NOCTURNAL STABILIZATION TO LIMIT ABILITY FOR WINDS TO MAKE IT TO
THE SFC, PARTICULARLY GIVEN A LACK OF APPRECIABLE CAA BEHIND THE
FRONT. NEVERTHELESS, BASED ON FCST SOUNDINGS AND OBSERVED POST-
FRONTAL PRESSURE RISE OF 5 MB/2 HR AT KMLS, THINK CAA WILL BE
JUST ENOUGH TO PROMOTE STEEP LAPSE RATES IN THE LOWEST 1-2 KFT
ABOVE GROUND LAYER, FACILITATING THE TRANSFER OF SOME GUSTS 40+
KT TO THE SFC. THUS, HAVE INTRODUCED A WIND ADVISORY FOR MUCH OF
THE AREA THROUGH 10Z, WITH THE EXPECTATION THAT THE WINDS WILL
DEVELOP FROM NW TO SE ACROSS THE ADVISORY AREA BEGINNING SHORTLY.
SUSPECT HIGHEST GUSTS WILL BE IN THE "SQUEEZE" ZONE EAST OF THE
BLACK HILLS, LIKELY BEGINNING CLOSER TO 04-06Z.
EXPIRATION TIME OF 02Z FOR RED FLAG WARNING OVER NERN WY STILL
LOOKS TO BE ON TRACK. PREFRONTAL SW WINDS ARE GRADUALLY
DIMINISHING AND SHOULD MOSTLY GIVE WAY TO NOCTURNAL STABILIZATION
IN THE NEXT HOUR OR SO. AS THE FRONT CROSSES THE AREA LATER THIS
EVENING, WINDS WILL INCREASE OUT OF THE NW, BUT RH WILL ALSO RISE.
DISCUSSION
(THIS EVENING THROUGH THURSDAY)
ISSUED AT 146 PM MDT THU SEP 24 2020
WATER VAPOR SHOWS UPPER RIDGE EXTENDING FROM THE DESERT SW INTO
THE NORTHERN PLAINS, WITH UPPER TROF OVER THE PAC NW INTO THE
NORTHERN ROCKIES. AT THE SURFACE, LOW IS CENTERED OVER
NORTHEASTERN MT WITH DRYLINE EXTENDING SOUTHWARD INTO NORTHEASTERN
WY, AND COLD FRONT THROUGH SOUTH CENTRAL MT. DRY/GUSTY SOUTHWEST
WINDS ACROSS NORTHEASTERN WY EARLY THIS AFTERNOON WITH EXPANDING RED
FLAG CONDITIONS.
DRY COLD FRONT ASSOCIATED WITH TROF MOVING THROUGH THE NORTHERN
ROCKIES WILL CREATE A PERIOD OF GUSTY NORTHWEST WINDS THIS
EVENING AND OVERNIGHT, WITH WINDS DECREASING ON FRIDAY. HIGHS
FRIDAY WILL BE A BIT COOLER THAN TODAY.
MEAN UPPER TROF SHIFTS THROUGH THE NORTHERN ROCKIES INTO THE
NORTHERN PLAINS LATE FRIDAY INTO SATURDAY. STRONG COLD FRONT MOVES
THROUGH EARLY SATURDAY PRODUCING GUSTY NORTHWEST WINDS AND COOLER
TEMPS. NOT MUCH MOISTURE TO WORK WITH, BUT THERE COULD BE A FEW
SHOWERS. GIVEN THE STRENGTH OF WINDS AND COLD ADVECTION, SOME
WIND HIGHLIGHTS MAY BE NECESSARY ESPECIALLY FOR NORTHWEST SD.
A STRONG JET STREAK WILL DEEPEN THE TROF OVER THE NORTHERN PLAINS
ON SUNDAY, DRIVING ANOTHER COLD FRONT THROUGH THE AREA. ANOTHER
PERIOD OF GUSTY NORTHWEST WINDS AND POTENTIAL WIND HIGHLIGHTS CAN
BE EXPECTED WITH HIGHS IN THE 50S/60S. AGAIN, NOT MUCH MOISTURE
TO WORK WITH BUT A FEW -SHOWERS EXPECTED, POSSIBLY MIXING WITH
SNOW AT TIMES IN THE HIGHER ELEVATIONS.
UPPER TROF SETS UP OVER THE UPPER MIDWEST/GREAT LAKES THROUGH THE
END OF NEXT WEEK, WITH PERIODIC DRY COLD FRONTS AND BOUTS OF GUSTY
NORTHWEST WINDS AND ELEVATED FIRE WEATHER CONDITIONS. TEMPS LIKELY
TO BE NEAR AND BELOW CLIMO FOR MOST OF THE PERIOD.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1022 PM MDT THU SEP 24 2020
VFR CONDS SHOULD CONTINUE THROUGH THE TAF PERIOD. LOCALIZED
REDUCTIONS TO VSBYS DUE TO SMOKE AND HAZE CANNOT BE RULED OUT.
BREEZY N/NW WINDS BEHIND A COLD FRONT WILL CONTINUE TO OVERSPREAD
THE AREA FROM NW TO SE THROUGH THE NIGHT. OCCASIONAL GUSTS OVER 40
KT WILL BE POSSIBLE, ESPECIALLY OVER THE WRN SD PLAINS IMMEDIATELY
EAST OF THE BLACK HILLS. WINDS AND GUSTS WILL DIMINISH LATE
TONIGHT INTO THE MORNING.
FIRE WEATHER
ISSUED AT 146 PM MDT THU SEP 24 2020
DRY/GUSTY SOUTHWEST WINDS BEHIND A DRY LINE HAVE CREATED RED FLAG
CONDITIONS OVER NORTHEAST WY THIS AFTERNOON. RED FLAG CONDITIONS
ARE EXPECTED TO CONTINUE INTO THE EVENING, BEFORE A COLD FRONT
BRINGS SLIGHTLY HIGHER RELATIVE HUMIDITY BACK INTO THE REGION
TONIGHT. THERE WILL BE A PERIOD OF GUSTY NORTHWEST WINDS BEHIND
THE COLD FRONT.
GUSTY NORTHWEST WINDS WILL DEVELOP BOTH SATURDAY AND SUNDAY ACROSS
THE REGION AS A SERIES OF COLD FRONT MOVES THROUGH. ALTHOUGH A FEW
SHOWERS WILL BE POSSIBLE, MOISTURE WILL BE LIMITED AND MOST AREAS
WILL REMAIN DRY. MINIMUM RELATIVE HUMIDITY OF 20-35 PERCENT BOTH
DAYS COMBINED WITH THE GUSTY WINDS WILL CREATE ELEVATED FIRE
WEATHER CONDITIONS THROUGH THE WEEKEND.
MUCH OF NEXT WILL BE NEAR OR A BIT COOLER THAN AVERAGE. A SERIES
OF DRY COLD FRONTS WILL BRING GUSTY NORTHWEST WINDS AND LOW
RELATIVE HUMIDITY AT TIMES ALONG WITH ELEVATED FIRE WEATHER
CONDITIONS.
UNR WATCHES/WARNINGS/ADVISORIES
SD...WIND ADVISORY UNTIL 4 AM MDT FRIDAY FOR SDZ001-002-012>014-025-
026-031-032-043-072-073.
WY...NONE.
UPDATE...SHERBURN
DISCUSSION...JOHNSON
AVIATION...SHERBURN
FIRE WEATHER...JOHNSON
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