420
FXUS63 KUNR 182344
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
544 PM MDT FRI SEP 18 2026
KEY MESSAGES
- COOL AND WET THIS WEEKEND, WITH DAILY PRECIPITATION IN THE
REGION.
- GRADUAL WARMUP EARLY NEXT WEEK.
DISCUSSION
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 213 PM MDT FRI SEP 18 2026
CURRENT WATER VAPOR AND UPPER AIR MODELS SHOW SOUTHWEST FLOW OVER
THE FORECAST AREA, AS UPPER LOW DIGS INTO THE ROCKIES. 18Z SURFACE
ANALYSIS DEPICTS A LOW OVER SOUTHEASTERN SD, WITH FRONTAL BOUNDARY
STRETCHING INTO CENTRAL NEBRASKA. WINDS ARE GENERALLY LIGHT OUT OF
THE NORTH, WITH TEMPERATURES IN THE 60S TO UPPER 70S.
OUT AHEAD OF THE UPPER LOW, A DISTURBANCE WILL LIFT UP INTO THE
REGION THIS EVENING. THE LINE OF SHOWERS/STORMS IS CURRENTLY IN
CENTRAL WYOMING MOVING NORTHEAST, EXPECTED TO ENTER THE FORECAST
AREA IN A FEW HOURS. GENERALLY LIGHT PRECIPITATION WITH THE
EVENING PRECIPITATION, BUT ACCUMULATIONS NEARING A TENTH OF AN
INCH MAY BE POSSIBLE IN HEAVIER PRECIP CORES. PRECIPITATION MAY
LINGER INTO THE OVERNIGHT HOURS, AND SOME SHOWERY DEVELOPMENT IS
POSSIBLE AGAIN DURING THE DAY SATURDAY. THERE'S A LOW-END CHANCE
FOR A SEVERE STORM SATURDAY AFTERNOON, GIVEN SOME CAPE VALUES
500-1000 J/KB, HOWEVER WEAK EFFECTIVE SHEAR (20-30KTS).
ATTENTION THEN TURNS TO THE MAIN EVENT, AS THE UPPER LOW MOVES
OVER WYOMING LATER SATURDAY INTO SUNDAY. WIDESPREAD PRECIPITATION
IS EXPECTED TO MOVE INTO THE REGION OVER THIS TIMEFRAME. HEAVIEST
AMOUNTS ARE EXPECTED SUNDAY MORNING AND AFTERNOON AND WILL TAPER
OFF FROM WEST TO EAST SUNDAY NIGHT INTO MONDAY. LREF PROBABILITIES
FOR 24 QPF 0.5" OR MORE HAS A BULLSEYE OF 70-90% OVER THE BLACK
HILLS INTO SOUTHWESTERN SD. PROBABILITIES FOR 1" OR MORE QPF RANGE
FROM 30-60% IN THE SAME AREA. EXPECT COOLER TEMPERATURES AS WELL
AS THE LOW MOVES INTO THE PLAINS, WITH HIGH TEMPERATURES SUNDAY
ONLY REACHING AROUND 60 OVER THE PLAINS, AND THE LOW TO MID 50S
OVER THE BLACK HILLS.
BY THE LATTER HALF OF MONDAY, THE PATTERN CHANGES AGAIN AS UPPER
RIDGING BUILDS OVER THE PLAINS, BRINGING A GRADUAL WARMING TREND
MONDAY THROUGH MUCH OF NEXT WEEK. TEMPERATURES CLIMB BACK TO AT OR
ABOVE NORMAL BY TUESDAY AND WEDNESDAY.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 534 PM MDT FRI SEP 18 2026
A CLUSTER OF THUNDERSTORMS WILL CROSS NE WY THIS EVENING INTO FAR
WESTERN SD, AND MAY HAVE GUSTY/VARIABLE WINDS WITH IT. CHANCES FOR
PRECIPITATION WILL CONTINUE OVERNIGHT INTO SATURDAY AS A LARGE
SYSTEM CROSSES THE REGION. IFR/LIFR CIGS WILL RETURN TO THE
WESTERN SD PLAINS LATE TONIGHT AND CONTINUE THROUGH SATURDAY
MORNING. AREAS OF DENSE FOG ARE ALSO EXPECTED WITH LIFR VSBY. CIGS
COULD SEE SOME GRADUAL IMPROVEMENT THROUGH THE DAY TOMORROW BUT
SHOULD STILL BE LIMITED TO NO HIGHER THAN MVFR, ESPECIALLY IF
RAINFALL IS ACCOMPANIED.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION...DYE
AVIATION...13
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