359
FXUS63 KUNR 250441
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1041 PM MDT THU OCT 24 2024
KEY MESSAGES
- WARM AND DRY WEATHER IS EXPECTED THIS WEEKEND, WITH ELEVATED TO
CRITICAL FIRE WEATHER CONDITIONS LIKELY.
- A SIGNIFICANT CHANGE IN THE WEATHER PATTERN IS BECOMING
INCREASINGLY PROBABLE EARLY NEXT WEEK, WHICH COULD BRING MUCH
COOLER TEMPERATURES AND WIDESPREAD PRECIPITATION CHANCES.
DISCUSSION
(THIS EVENING THROUGH THURSDAY)
ISSUED AT 212 PM MDT THU OCT 24 2024
WATER VAPOR IMAGERY THIS AFTERNOON SHOWS A SHORTWAVE TROUGH SHIFTING
FROM WEST TO EAST OVER THE NORTHERN PLAINS, WITH THE BULK OF
ENHANCED DEEP MOISTURE NOW TO OUR EAST. A PAIR OF UPPER-LEVEL LOWS
ARE EVIDENT FROM NEAR THE GULF OF AK SOUTHWARD TO THE EASTERN
PACIFIC, OFF THE COAST OF CA/OR. LINGERING SHOWERS OVER CENTRAL SD,
WHICH ARE LARGELY VIRGA AT THIS POINT, SHOULD DEPART OUR EASTERN
ZONES OVER THE NEXT COUPLE OF HOURS. DAY CLOUD PHASE DISTINCTION RGB
IMAGERY INDICATES SOME LOW STRATUS/STRATOCUMULUS IN THE WAKE OF THIS
SHOWER ACTIVITY AS HIGH PRESSURE EXPANDS INTO THE REGION. BREEZY
NORTH TO NORTHWEST WINDS PERSIST BEHIND A SURFACE FRONT, WHICH IS
NOW ANALYZED FROM CENTRAL NE NORTHEASTWARD THROUGH EASTERN SD.
TEMPERATURES ARE SEASONABLE, RANGING FROM THE MID 40S IN THE BLACK
HILLS TO LOWER 60S OVER SOUTHWESTERN AND SOUTH CENTRAL SD.
SURFACE RIDGE SLIDES EASTWARD TONIGHT INTO TOMORROW MORNING,
BRINGING CLEAR, CALM, AND COOL CONDITIONS TO MOST. SOUTHERLY RETURN
FLOW MAY DEVELOP OVER NORTHEASTERN WY LATE IN THE NIGHT. ENSEMBLE
CONSENSUS SUGGESTS HIGH LIKELIHOOD IN A BUILDING MIDLEVEL TO UPPER-
LEVEL RIDGE OVER THE ROCKIES TOMORROW AND SATURDAY, SHIFTING OVER
THE HIGH PLAINS BY SUNDAY. THE AFOREMENTIONED UPPER LOWS OVER THE
PACIFIC WILL GRADUALLY APPROACH THE ROCKIES THIS WEEKEND INTO
MONDAY, SUPPORTING LEE CYCLOGENESIS. COMBINED WITH A STRENGTHENING
HIGH OVER THE GREAT LAKES, THE RESULTING PRESSURE GRADIENT WILL
SUPPORT BREEZY SOUTH/SOUTHWEST FLOW OVER MUCH OF THE AREA SATURDAY,
WITH THE STRONGEST WINDS LIKELY OCCURRING OVER SOUTH CENTRAL SD.
HERE, ADVISORY-LEVEL GUSTS ARE NOT OUT OF THE QUESTION (CHANCES ~10-
30% IN LATEST EPS). LEADING LOW-LEVEL TROF CROSSES THE AREA LATE
SATURDAY ONLY TO BE REPLACED WITH A MORE AMPLIFIED TROF SUNDAY INTO
MONDAY, WHICH WILL LIKELY SUPPORT ROBUST LOW-LEVEL WARM-AIR
ADVECTION AND ANOTHER ROUND OF STRONG SOUTH/SOUTHWEST WINDS. AS A
RESULT, WELL ABOVE NORMAL (AND NEAR-RECORD) TEMPERATURES RETURN
SUNDAY, WITH EPS/GEFS/GEPS ALL SHOWING NEAR-DEFINITE 70+ DEGREE
TEMPERATURES OVER THE PLAINS. ALTHOUGH SOMEWHAT OF A WARM OUTLIER
COMPARED TO OTHER ENSEMBLES, THE GEFS FAVORS A BROAD AREA OF
PROBABLE TO LIKELY 80+ DEGREE TEMPERATURES FROM SOUTHWESTERN TO
SOUTH CENTRAL SD, WHICH IT CONTINUES INTO MONDAY DUE TO SLOWER
PROGRESSION OF THE ASSOCIATED TROF. ALSO OF NOTE, GFS PRESSURE
GRADIENTS LATE SUNDAY NIGHT SUPPORT THE POTENTIAL FOR STRONG
DOWNSLOPE WINDS OVER THE NORTHERN AND NORTHEASTERN FOOTHILLS; THIS
POTENTIAL IS BACKED UP BY EPS PROBABILITIES OF WIND GUSTS OF AT
LEAST 34 KT, WHICH REACH 40-60% OVER THIS LOCALIZED AREA BY AROUND
06Z MONDAY.
BY MONDAY NIGHT, THE APPROACHING MIDLEVEL TROF IS EXPECTED TO DEEPEN
OVER THE WESTERN CONUS, WITH AN AXIS GENERALLY EXTENDING FROM THE
GREAT BASIN NORTHEASTWARD THROUGH MT. ROBUST MIDLEVEL TO UPPER-LEVEL
Q-VECTOR CONVERGENCE DOWNSTREAM OF THE TROF AXIS WILL APPROACH OUR
AREA BY TUESDAY MORNING, THOUGH LATEST DETERMINISTIC GUIDANCE
SUGGESTS SOME WEAKENING IN THIS FORCING AS IT DOES SO. NONETHELESS,
SOME CORRIDORS OF ENHANCED LOW-LEVEL/MIDLEVEL FRONTOGENESIS CROSS
THE REGION THEREAFTER, WHICH COULD PROMOTE AREAS OF PRECIPITATION AS
PWATS SURGE TO 125-175% OF NORMAL. OVERALL, ENSEMBLES--PARTICULARLY
THE EPS--APPEAR BULLISH ON PRECIPITATION CHANCES, WITH GENERALLY 30-
70% CHANCES FOR TOTAL QPF OF AT LEAST 0.5". GIVEN A LACK OF A ROBUST
FORCING SIGNAL, HOWEVER, I AM SOMEWHAT SKEPTICAL OF THESE AMOUNTS.
BARRING SIGNIFICANT CHANGES IN THE TRACK OR STRENGTH OF THE SYSTEM,
WE MAY NEED TO TREND TOWARD LOWER PRECIPITATION PERCENTILES IN
FUTURE FORECAST PACKAGES. I DO HAVE HIGHER CONFIDENCE IN MUCH COOLER
TEMPERATURES, AND LIKELY BELOW NORMAL, TEMPERATURES, WITH
DETERMINISTIC GLOBAL MODELS AND THEIR ENSEMBLE MEANS ALL SUGGESTING
NEGATIVE 850 MB TEMPERATURE ANOMALIES OF AT LEAST A FEW DEGREES BY
WEDNESDAY.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1040 PM MDT THU OCT 24 2024
VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD.
FIRE WEATHER
ISSUED AT 212 PM MDT THU OCT 24 2024
A DEVELOPING UPPER-LEVEL RIDGE OVER THE WESTERN U.S. WILL SUPPORT
WARMING TEMPERATURES THROUGH THE WEEKEND AS DRY WEATHER
CONTINUES. AS A PAIR OF LOW-LEVEL TROUGHS MOVE THROUGH THE REGION
SATURDAY AND SUNDAY, PERIODS OF BREEZY SOUTH TO SOUTHWEST WINDS
ARE ALSO EXPECTED. COMBINED, THE WARM, DRY WEATHER AND WINDY
CONDITIONS MAY SUPPORT ELEVATED OR NEAR- CRITICAL FIRE WEATHER
CONDITIONS.
FOR NOW, THE MOST LIKELY TIME PERIOD FOR WIDESPREAD NEAR-CRITICAL
FIRE WEATHER CONDITIONS IS SUNDAY AFTERNOON. HOWEVER, LOCALIZED
NEAR-CRITICAL CONDITIONS ARE ALSO POSSIBLE SATURDAY (MAINLY FROM
SOUTHWESTERN TO SOUTH CENTRAL SD), SUNDAY NIGHT (PRIMARILY OVER
THE NORTHERN FOOTHILLS, WHERE DOWNSLOPE WINDS MAY LEAD TO POOR
RELATIVE HUMIDITY RECOVERY), AND MONDAY AFTERNOON (ACROSS SOUTH
CENTRAL SD).
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...SHERBURN
AVIATION...POJORLIE
FIRE WEATHER...SHERBURN
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