742
FXUS63 KUNR 231721
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1021 AM MST TUE DEC 23 2025
KEY MESSAGES
- WINDY, MAINLY DRY AND UNSEASONABLY WARM THIS WEEK.
- RECORD TO NEAR-RECORD HIGH TEMPERATURES ON CHRISTMAS.
- CHANCE OF SNOW AND MUCH COLDER, BUT SEASONAL, THIS WEEKEND.
DISCUSSION
(TODAY THROUGH MONDAY)
ISSUED AT 122 AM MST TUE DEC 23 2025
LATEST UPPER LEVEL ANALYSIS SHOWS SLIGHTLY ZONAL FLOW OVER THE
FORECAST AREA WITH A BUILDING RIDGE OVER THE CENTRAL CONUS AND A
DEEPENING TROUGH IN THE EASTERN PACIFIC EXTENDING FROM A STRONG
UPPER LOW OFF THE COAST OF BRITISH COLUMBIA. WATER VAPOR SATELLITE
HAS A WELL DEFINED CHINOOK ARCH OVER COLORADO THAT EXTENDS
NORTHWARD INTO EASTERN WYOMING (OFF THE LARAMIE RANGE). AT THE
SURFACE, TWO EAST-WEST FRONTAL BOUNDARIES ARE SITUATED OVER THE
AREA. ONE BOUNDARY EXTENDS ACROSS NORTHWESTERN SOUTH DAKOTA, WHILE
THE SECOND BOUNDARY EXTENDS THROUGH NORTHERN WYOMING INTO
SOUTHWESTERN SOUTH DAKOTA AND NORTHERN NEBRASKA. ADDITIONALLY,
HIGH PRESSURE IS CENTERED OVER SASKATCHEWAN WITH RIDGING EXTENDING
DOWN TO THE BOUNDARY IN NORTHWEST SOUTH DAKOTA. TEMPERATURES AT
0830Z ARE MILD, MAINLY IN THE 30S, WITH A FEW READINGS IN THE
LOWER 40S IN THE FOOTHILLS AROUND RAPID CITY.
THE UPPER RIDGE OVER THE CENTRAL PLAINS WILL BUILD TODAY AND SHIFT
SLIGHTLY EAST AS THE EASTERN PACIFIC TROUGH DEEPENS. THIS WILL
CREATE A MORE PRONOUNCED SOUTHWEST FLOW PATTERN IN THE UPPER LEVELS.
THE NORTHERN SURFACE FRONT WILL WASH OUT AS SURFACE HIGH PRESSURE
DROPS INTO THE EASTERN DAKOTAS. THIS SET-UP WILL ALLOW FOR RETURN
FLOW TO DEVELOP OVER THE FORECAST AREA THIS AFTERNOON WITH A MODEST
PRESSURE GRADIENT DUE TO THE PROXIMITY OF THE SOUTHERN FRONTAL
BOUNDARY. BREEZY SOUTHEASTERLY WINDS WILL BE COMMON EAST OF THE
BLACK HILLS TO THE NORTH/EAST OF THE BOUNDARY, WHILE BREEZY
SOUTHWEST WINDS DEVELOP ON THE WEST/SOUTH SIDE OF THE BOUNDARY
ACROSS PORTIONS OF NORTHEASTERN WYOMING. IT WILL BE SLIGHTLY
COOLER TODAY, ESPECIALLY AFTER THE RECORD WARMTH ON MONDAY, BUT IT
WILL STILL BE UNSEASONABLY WARM.
SOUTHERLY FLOW AND WARM AIR ADVECTION TONIGHT COMBINED WITH 30-35KT
WINDS IN THE LOWER LEVELS, WILL KEEP TEMPERATURES FROM DROPPING OFF
ACROSS THE SOUTHERN 2/3RDS OF THE AREA, WITH SOME LOCATIONS IN THE
HILLS AND FOOTHILLS WARMING OVERNIGHT.
A WEAK, MOISTURE STARVED IMPULSE ROUNDS THE RIDGE WEDNESDAY MORNING
AS THE SOUTHERN SURFACE FRONTAL BOUNDARY LIFTS NORTHWARD. THE TIMING
OF THESE TWO FEATURES, COMBINED WITH THE LOWER SUN ANGLE THIS TIME
OF THE YEAR, WILL LIMIT THE DAYTIME HEATING POTENTIAL BY A FEW
DEGREES. TEMPERATURES WILL CONTINUE TO BE UNSEASONABLY WARM,
BUT WILL LIKELY REMAIN BELOW RECORD HIGHS. RECORDS FOR SELECTED
LOCATIONS WEDNESDAY INCLUDE KUNR 67F, KRAP 62F, GILLETTE 62F, HOT
SPRINGS 62F, CAMP CROOK 52F, AND WINNER 59F).
MODEL CONSENSUS AND CERTAINTY HAS INCREASED OVER THE PAST 24 HOURS,
WITH THE UPPER RIDGE REMAINING ANCHORED IN PLACE OVER THE CENTRAL
PLAINS THROUGH FRIDAY. MODELS STILL INDICATE WEAK IMPULSES ROUNDING
THE RIDGE CHRISTMAS, CHRISTMAS NIGHT AND FRIDAY, BUT ARE KEEPING
850MB TEMPS AROUND +15F. RECORD HIGHS ARE A LITTLE LOWER IN SPOTS ON
CHRISTMAS THAN WEDNESDAY, THUS THERE IS THE POTENTIAL FOR RECORD
WARMTH CHRISTMAS DAY. (RECORDS ARE: KUNR 63F, KRAP 60F, GILLETTE
55F, HOT SPRINGS 62F, CAMP CROOK 52F, AND WINNER 66F). ADDITIONALLY,
A 40-50KT LOW LEVEL JET WILL AID IN WARMING. THERE WILL ALSO BE A
CHANCE FOR SOME VERY LIGHT RAIN SHOWERS/SPRINKLES WITH THESE
IMPULSES.
THE UPPER RIDGE BREAKS DOWN AFTER CHRISTMAS. THE EASTERN PACIFIC
UPPER TROUGH SWINGS THROUGH THE REGION SATURDAY AND CLOSES OFF AN
UPPER LOW OVER ONTARIO SATURDAY NIGHT. NORTHERLY FLOW BEHIND THE
TROUGH WILL RESULT IN MUCH COLDER, BUT SEASONAL, TEMPERATURES FOR
THE WEEKEND. PRECIPITATION CHANCES WILL BE MINIMAL, WITH SOME SNOW
SHOWERS POSSIBLE WITH THE OVERRUNNING OF COLD AIR. BRISK
NORTHWEST WINDS, ESPECIALLY OVER THE SOUTH DAKOTA PLAINS, MAY RESULT
IN SUB-ZERO WINDCHILLS SATURDAY NIGHT.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY)
ISSUED AT 1021 AM MST TUE DEC 23 2025
VFR CONDITIONS TO CONTINUE THROUGH THE VALID FORECAST PERIOD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...SMITH
AVIATION...HINTZ
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