184
FXUS63 KUNR 160514
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1014 PM MST SAT FEB 15 2025
KEY MESSAGES
- VERY COLD TONIGHT ACROSS NORTHWESTERN SD WITH WIND CHILLS OF -25
TO -30F.
- RECORD TO NEAR-RECORD COLD AIR IN PLACE FOR MONDAY THROUGH
THURSDAY, BRINGING US THE COLDEST AIR OF THE WINTER SEASON.
ALTHOUGH WIND SPEEDS WILL BE MOSTLY UNDER 15-20 MPH, WIND
CHILLS WILL FALL TO -25 TO AROUND -40F FOR MUCH OF THE AREA
DURING THIS TIME.
- A PERIOD OF PROLONGED, LIGHT-TO-MODERATE SNOWFALL IS EXPECTED
SUNDAY EVENING THROUGH TUESDAY NIGHT, ESPECIALLY AFFECTING
NORTHEASTERN WYOMING, THE BLACK HILLS, AND SOUTHWESTERN SOUTH
DAKOTA. SNOWFALL AMOUNTS OF 2 TO 6 INCHES, WITH LOCALLY HIGHER
AMOUNTS, WILL BE POSSIBLE IN THESE AREAS OVER THE 2-DAY PERIOD.
- SNOW WILL COME TO AN END ON WEDNESDAY. THEREAFTER, A WARMING
TREND WILL TAKE PLACE TOWARD THE END OF THE WEEK, AND ESPECIALLY
NEXT WEEKEND.
DISCUSSION
(THIS EVENING THROUGH SATURDAY)
ISSUED AT 150 PM MST SAT FEB 15 2025
THE LATEST WATER VAPOR IMAGES AND 500-MB ANALYSIS SHOWED A BROAD/
LARGE UPPER TROUGH OVER MOST OF THE CONUS. FLOW ALOFT WAS WEST-
NORTHWEST, WITH A SHORT-WAVE TROUGH CROSSING THE CWA THAT PRODUCED
THE 1-2 INCHES OF SNOW OVER THE PAST 18 HOURS OR SO. THE ARCTIC
FRONT WAS WELL SOUTH OF THE CWA AND A 1037-MB HIGH PRESSURE WAS
MOVING SOUTH TOWARD SOUTHERN SASKATCHEWAN. FINALLY, A RATHER
TIGHT 850- TO 700-MB BAROCLINIC ZONE WAS OVER THE CWA, AND THIS
WILL BE THE FOCUS FOR ISENTROPIC LIFT AND FRONTOGENESIS THE NEXT
SEVERAL DAYS -- LEADING TO A PROLONGED SNOWFALL EVENT.
QUIET WEATHER WITH LITTLE IF ANY SNOW IS EXPECTED TONIGHT AS LOWS
DROP TO THE SINGLE DIGITS BELOW ZERO IN MOST AREAS, WITH SOME COLDER
SPOTS ACROSS NORTHWESTERN SD. MINIMUM WIND CHILLS WILL BE MOSTLY
-10 TO NEAR -30F, LOWEST MAINLY OVER FAR NORTHWESTERN SD.
A FRIGID AIR MASS WILL REMAIN ACROSS THE REGION THROUGH THURSDAY,
WITH TEMPERATURES NEAR RECORD-LOW VALUES (BOTH LOWS AND DAYTIME
HIGHS). A REINFORCING SHOT OF ARCTIC AIR IS EXPECTED TO GRADUALLY
PUSH INTO THE REGION SUNDAY NIGHT AND MONDAY. AT THIS POINT, HIGHS
WILL STRUGGLE TO GET ABOVE ZERO ACROSS AT LEAST MUCH OF THE SD
PLAINS MONDAY AND TUESDAY, POSSIBLY WEDNESDAY AS WELL, ESPECIALLY
NORTH AND EAST OF THE BLACK HILLS. LOWS WILL BE WELL BELOW ZERO,
WITH DANGEROUS WIND CHILLS OF -25 AROUND -40F EXPECTED AT TIMES
IN MANY AREAS DURING THE OVERNIGHT AND MORNING HOURS. WINDS WILL
BE GUSTING TO 20-25 MPH IN SPOTS MONDAY AS THE COLDER AIR PUSHES
IN, BUT WILL BE RELATIVELY LIGHT AFTER THAT. WILL CONTINUE THE
EXTREME COLD WATCH FOR FAR NORTHWESTERN SD FROM SUNDAY NIGHT INTO
WEDNESDAY. THIS IS WHERE THE GREATEST POTENTIAL FOR THE COLDEST
TEMPERATURES AND WIND CHILLS IS EXPECTED.
PRECIP-WISE, A PROLONGED PERIOD OF LIGHT-TO-MODERATE SNOWFALL IS
EXPECTED WITH THE REINFORCING SHOT OF ARCTIC AIR SUNDAY NIGHT INTO
TUESDAY NIGHT. THE MORE PERSISTENT SNOWFALL WILL BE WHERE ISENTROPIC
LIFT AND FRONTOGENESIS OCCUR ALONG THE TIGHTER PART OF THE
BAROCLINIC ZONE. AT THIS POINT, IT LOOKS TO SET UP MOST FAVORABLY
FOR MORE IMPACTFUL ACCUMULATIONS FROM NORTHEASTERN WY TO THE BLACK
HILLS AND SOUTHWESTERN SD. LREF CHANCES FOR AT LEAST AN INCH OF
SNOWFALL ARE 70 TO NEAR 100 PERCENT ACROSS THESE AREAS, WITH 20 TO
OVER 50 PERCENT CHANCES FOR 3 INCHES OR MORE IN MOST OF THE SAME
AREAS DURING THIS TIME. THESE PERCENTAGES ARE BASED ON ABOUT 10:1
SNOW RATIOS, SO WITH THE FLUFFY SNOWFALL EXPECTED (UP TO AROUND
20:1), THE PERCENTAGES FOR THESE AMOUNTS WILL BE HIGHER. ALTHOUGH
ONE COULD ARGUE FOR AN ADVISORY OR WATCH AT THIS TIME, THERE IS
PLENTY OF TIME UNTIL THE LONG-DURATION EVENT COMMENCES, AND THE
MESSAGING FOR THIS HAS ALREADY STARTED. WILL CONTINUE TO MONITOR
TONIGHT AND MONDAY WHEN SOME HIGHLIGHTS LIKELY WILL BE NEEDED.
HAVING SAID THAT, THE WPC WINTER STORM OUTLOOK PROBABILITIES ARE
STILL LESS THAN 10%, AND THE PROBABILISTIC WSSI ONLY INDICATES
MINOR IMPACTS.
MILDER AIR WILL EVENTUALLY RETURN TO THE REGION LATE NEXT WEEK, BUT
HOW QUICKLY AND TO WHAT EXTENT IS STILL UNCERTAIN. THERE IS NOW SOME
BETTER ENSEMBLE AGREEMENT FOR AT LEAST NEAR-AVERAGE TEMPERATURES
RETURNING NEXT WEEKEND.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1011 PM MST SAT FEB 15 2025
MAINLY VFR CONDS ARE EXPECTED THROUGH THE VALID TERMINAL PERIOD.
SCT-BKN MID CLOUD MAY MOVE ACROSS NORTHEAST WYOMING AND THE BLACK
HILLS OVERNIGHT. SOME POSSIBLE MVFR CIGS/VSBYS ARE POSSIBLE LATE
IN THE TERMINAL PERIOD ACROSS NORTHEAST WYOMING.
UNR WATCHES/WARNINGS/ADVISORIES
SD...EXTREME COLD WATCH FROM SUNDAY EVENING THROUGH WEDNESDAY MORNING
FOR SDZ001-002-014-078.
WY...NONE.
DISCUSSION/KEY MESSAGES...BUNKERS
AVIATION...HINTZ
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