046
FXUS63 KUNR 080750
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
150 AM MDT FRI AUG 8 2025
KEY MESSAGES
- MARGINAL (LEVEL 1 OF 5) RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON/EVENING
- SEASONALLY DRIER FOR THE WEEKEND INTO NEXT WEEK WITH NEAR
NORMAL TEMPERATURES
DISCUSSION
(TODAY THROUGH THURSDAY)
ISSUED AT 148 AM MDT FRI AUG 8 2025
07Z SURFACE ANALYSIS HAD OUTFLOW BOUNDARY ENHANCED COLD FRONT
TRAILING ND MCS TO KRAP TO CENTRAL WY. GUSTS WITH THESE FEATURES
FROM 50-55MPH WERE COMMON NEAR THE SD/ND BORDER EARLIER THIS
MORNING. WATER VAPOUR LOOP HAD UPPER TROUGH OVER THE NORTHERN
ROCKIES WITH 80KT JET STREAK AHEAD OF IT STARTING TO SUPPORT NEW
CONVECTION OVER SOUTHEAST MT, WHICH IS MOVING NORTHEAST. MAIN
CONCERN IS UPPER TROUGH.
TODAY/TONIGHT, UPPER TROUGH MOVES ACROSS THE NORTHERN PLAINS.
SOUTHEAST MT CONVECTION WILL MOVE NORTHEAST EARLY THIS MORNING,
CLIPPING THE FAR NORTHWEST CORNERS OF THE CWA. COLD FRONT WILL
DRIVE SOUTHEAST INTO SOUTH-CENTRAL SD BEFORE IT LOSES THE OUTFLOW
BOOST AND BECOMES PARALLEL TO UPPER FLOW. EXPECT A PERIOD OF GUSTY
WINDS BEHIND THE COLD FRONT. AHEAD OF THE FRONT LATE THIS
AFTERNOON/EVENING, BEST CHANCE OF SEVERE THUNDERSTORMS EAST OF
THE CWA. POST FRONTAL ENVIRONMENT GIVES ~1KJ/KG SBCAPE, WEAK
SBCIN, AND MODEST SHEAR WHICH WOULD BE SUFFICIENT TO POP ISOLATED
SEVERE THUNDERSTORMS (ESPECIALLY OVER SOUTHERN SD) AS UPPER TROUGH
INFLUENCE OVERSPREADS THE AREA, WHICH IS WHAT THE SPC HREF
PORTRAYS. HOWEVER, SOME GUIDANCE IS QUITE AGGRESSIVE WITH LOW-
LEVEL DRYING WHICH WILL NIP ACTIVE CONVECTION IT THE BUD. LATER
SHIFTS CAN TAKE A CLOSER LOOK. MUCH DRIER AIR WILL INVADE TONIGHT
(AT THE LATEST) LEADING TO A REFRESHING SLEEPING NIGHT.
TEMPERATURES WILL BE TRICKY THIS AFTERNOON PER FRONTAL POSITION
UNCERTAINTY, BUT NEAR GUIDANCE TONIGHT.
SATURDAY THROUGH NEXT WEEK, NORTHWEST FLOW ALOFT BECOMES WESTERLY
AND THEN SOUTHWESTERLY AS UPPER RIDGE OVER THE CENTRAL CONUS
SLOWLY AMPLIFIES. SEASONALLY WARM TEMPERATURES EXPECTED AS THERMAL
RIDGE EXPANDS ASSISTED BY DOWNSLOPE FLOW. GREENNESS VALUES ARE
STARTING TO TAIL OFF PER NVDI TRENDS AND THUS, SUSPECT WE MIGHT
END UP WITH SOME HOTTER DAYS NEXT WEEK AS AUGUST DRYING RAMPS UP
AND SOME VEGETATION STARTS TO CURE. LIMITED POPS IN THE FORECAST,
BUT DON'T BE SURPRISED IF SOME GET ADDED AS ATMOSPHERIC WIGGLE
TIMING BECOMES CLEARER.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1106 PM MDT THU AUG 7 2025
MAINLY VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. A COLD
FRONT WILL MOVE THROUGH THE AREA OVERNIGHT, WITH GUSTY NORTHWEST
WINDS TO 35 KNOTS EXPECTED ACROSS THE SD PLAINS FROM 06Z THROUGH
THE REMAINDER OF THE TAF PERIOD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...HELGESON
AVIATION...DYE
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