248
FXUS63 KUNR 160538
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1138 PM MDT MON SEP 15 2025
KEY MESSAGES
- WEAK COOL FRONT BRINGS GUSTY SHOWERS/STORMS THROUGH TONIGHT
- UPPER LOW DROPS INTO THE NORTHERN PLAINS FOR THE REST OF THE
WEEK WITH A COOLING TREND AND GOOD CHANCES FOR PRECIPITATION
- GENERALLY DRIER AND WARMER WEATHER EXPECTED FOR THE WEEKEND
DISCUSSION
(THIS EVENING THROUGH MONDAY)
ISSUED AT 201 PM MDT MON SEP 15 2025
19Z SURFACE ANALYSIS HAD WEAK COOL FRONT FROM ND INTO NORTHERN
ID. WATER VAPOUR LOOP HAD AN UPPER LOW OVER SOUTHWEST MT. WEAK
LEAD SHORTWAVE OVER EASTERN EASTERN WY WITH BETTER LOOKING WAVE
OVER WESTERN WY. 18Z KUNR SOUNDING WAS WELL-MIXED UP TO ~550MB
WITH WEAK MLCIN. THESE TWO FEATURES WILL CONSPIRE WITH THE COOL
FRONT TO PRODUCE OUR SENSIBLE WEATHER TONIGHT.
TONIGHT, SHORTWAVES AHEAD OF THE LOW WILL ASSIST THE DEVELOPMENT
OF HIGH-BASED CONVECTION OVER WY THIS AFTERNOON, SPREADING INTO
WESTERN SD TONIGHT. MINIMAL BUOYANCY IN THE WEST WILL COMBINE WITH
DEEPLY MIXED BOUNDARY LAYER TO SUPPORT GUSTY ISOLATED/SCATTERED
SHOWERS/TS, PARTICULARLY WITHIN THE DAY 1 MARGINAL DEPICTION. AS
YOU GO FURTHER EAST OF THE BLACK HILLS, THE CAP WILL LIKELY
PREVENT STRONGER CONVECTION TO DEVELOP. TEMPERATURES WILL BE NEAR
GUIDANCE.
TUESDAY, COOL FRONT HANGS UP OVER SOUTH-CENTRAL SD AS UPPER LOW
SAUNTERS INTO WY. BETTER CAPE/SHEAR SETS UP ALONG THE COOL FRONT
WITH A MARGINAL RISK OF SEVERE THUNDERSTORMS LATER IN THE
AFTERNOON/EVENING HOURS. SPC HREF SUPPORTS THINKING WITH UPDRAFT
TRACKS. PWATS RISE TO 150-200% OF NORMAL, SO LOCALLY HEAVY RAIN
MAY OCCUR. TEMPERATURES WILL COOL DOWN BEHIND THE FRONT, BUT STILL
BE WARM AHEAD OF IT.
WEDNESDAY THROUGH FRIDAY, UPPER LOW WILL MEANDER OVER THE NORTHERN
PLAINS WITH RATHER HIGH PWATS SLOWLY SHIFTING EAST BUT NOT BEFORE
LOCALLY HEAVY RAIN POTENTIALLY FALLS WEDNESDAY PER ENSEMBLE OUTPUT.
HOWEVER, THE LOCATION OF THE HEAVIEST RAIN VERY UNCERTAIN GIVEN
INABILITY OF GUIDANCE TO RESOLVE MOVEMENT OF THE UPPER LOW.
TEMPERATURES WILL BE COOL - ABOUT 5-10F BELOW NORMAL.
NEXT WEEKEND, UPPER LOW (IN THEORY) SLOWLY MOVES AWAY LEADING TO A
RETURN TO SEASONALLY MILD TEMPERATURES.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1130 PM MDT MON SEP 15 2025
MOSTLY VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. NORTHWEST
WINDS WILL BECOME NORTHERLY TOWARDS OR SHORTLY AFTER DAYBREAK.
VCSH ARE ANTICIPATED NEAR TAF SITES TOWARDS THE END OF THE TAF
PERIOD HOWEVER NOT ENOUGH CONFIDENCE ON TIMING TO THROW INTO THE
FORECAST JUST YET.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...HELGESON
AVIATION...MELO
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