359
FXUS63 KUNR 070752
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
152 AM MDT THU AUG 7 2025
KEY MESSAGES
- HOT TODAY WITH HEAT INDICES 100-105F SOUTH-CENTRAL SD
- MARGINAL TO SLIGHT (LEVEL 1-2 OF 5) RISK OF SEVERE
THUNDERSTORMS TONIGHT AND FRIDAY AFTERNOON/EVENING
- SEASONALLY DRIER FOR THE WEEKEND INTO NEXT WEEK
DISCUSSION
(TODAY THROUGH WEDNESDAY)
ISSUED AT 144 AM MDT THU AUG 7 2025
07Z SURFACE ANALYSIS HAD LOW OVER KBYG, WHICH WAS ALONG A FRONTAL
BOUNDARY FROM WESTERN ND INTO ID. MODEST LOW LEVEL JET (KUDX
RADAR HAD 30KTS JUST OFF THE SURFACE) IMPINGING ON FRONTAL
BOUNDARY WITH ACCAS/ISOLATED TS OVER SOUTHEAST MT. THIS ELEVATED
CONVECTION MAY AFFECT FAR NORTHWEST SD EARLY THIS MORNING.
NIGHTTIME MICROPHYSICS LOOP DEPICTED BLOSSOMING STRATUS/FOG OVER
PARTS OF NE, WHICH WILL CREEP INTO THE FAR SOUTHERN REACHES OF
THE CWA INDICATIVE OF THE SOUPY ATMOSPHERE THAT WILL BLANKET THE
EASTERN REACHES OF THE CWA TODAY. WIDENING OUR VIEW, WATER VAPOUR
LOOP HAD SOUTHWEST FLOW OVER THE CWA IN RESPONSE TO UPPER TROUGH
SLIPPING SOUTHEAST INTO THE NORTHWEST CONUS FROM SOUTHWEST CANADA.
EFFECT OF THIS SYSTEM THE MAIN FORECAST CONCERN.
TODAY THROUGH FRIDAY, UPPER TROUGH MOVES THROUGH THE NORTHERN
PLAINS. WY SURFACE LOW WILL DEEPEN SOME AS IT COMBINES WITH
SOUTHWEST FLOW ALOFT TO CREATE DEEP BOUNDARY LAYER MIXING AND
STRONG PUSH OF DRY AIR TODAY. DRY LINE WILL SURGE INTO PARTS OF
NORTHEASTERN WY/SOUTHWESTERN SD WITH PLUMMETING DEW POINTS BEHIND
IT. THERMAL RIDGE PEAKS PUSHING TEMPERATURES WELL INTO THE 90S
WITH SOME 100S FROM SOUTHWEST INTO CENTRAL SD LIKELY (HREF >80%
CHANCE). STICKY TD/S IN THE MID 60S TO LOWER 70S WILL COMBINE WITH
FORECAST MAXT TO CREATE 100-105F HEAT INDICES (HREF >80% CHANCE)
OVER CENTRAL SD LEADING TO THE ISSUANCE OF A HEAT ADVISORY THIS
AFTERNOON/EARLY EVENING. SHIFTING OUR GAZE FURTHER NORTH SHOWS
STRONG BUOYANCY/MODERATE SHEAR BY TONIGHT, BUT WITH SIGNIFICANT
SBCIN. SURFACE BASED CONVECTION CHANCES NOT ZERO, BUT NOT LOOKING
GREAT. HOWEVER, SUPPORT IS MUCH HIGHER INTO ND WITH THE POTENTIAL
FOR CONVECTION TO SLIP INTO FAR NORTHWEST SD TONIGHT WITH
RESULTANT DAMAGING WIND/LARGE HAIL THREAT ALONG OUTFLOW OR
OUTFLOW-INDUCED CONVECTION. A SMATTERING OF CAMS SUPPORT. AS
SURFACE LOW SHIFTS EAST TONIGHT, TRAILING COLD FRONT WILL MOVE
INTO THE CWA, EXITING THE AREA LATER FRIDAY. FRONT MAY BE
CONVECTIVELY ENHANCED WITH GUSTY NORTHERLY WINDS LATE TONIGHT.
COLD FRONT WILL BECOME FOCUS FOR STRONG/SEVERE CONVECTION FRIDAY
AFTERNOON/EVENING, BUT WITH HIGHEST THREAT EAST OF THE CWA. POST-
FRONTAL ENVIRONMENT WILL BE CHARACTERIZED BY WEAK
BUOYANCY/MODERATE SHEAR AND LITTLE SBCIN, WHICH MAY BE CONDUCIVE
TO ISOLATED SEVERE THUNDERSTORMS. TEMPERATURES TODAY WILL BE NEAR
GUIDANCE, ESPECIALLY WHERE DRY AIR PREVAILS. TEMPERATURES FRIDAY
WILL BE TRICKY WITH COLD FRONT MODULATING READINGS, SO CONFIDENCE
IS LOWER.
FOR THE WEEKEND INTO NEXT WEEK, NORTHWEST FLOW ALOFT BECOMES
WESTERLY. DRIER AIR WILL BE IN PLACE, BUT IT IS AUGUST SO WHILE
POPS WILL DROP OFF, WE'LL PROBABLY HAVE SOME ISOLATED CONVECTION
IN/NEAR THE CWA THROUGH THE PERIOD. TEMPERATURES WILL BE
SEASONALLY WARM.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1024 PM MDT WED AUG 6 2025
LOW STRATUS AND PATCHY FOG MAY DEVELOP OVER SOUTH CENTRAL SD
AFTER 09-10Z, DISSIPATING AFTER 15Z. GUSTY SOUTHERLY WINDS ARE
EXPECTED ACROSS THE WESTERN SD PLAINS THURSDAY AFTERNOON AHEAD OF
AN APPROACHING FRONT. GUSTS OF UP TO 30 KT EXPECTED, MAINLY
TOWARDS SOUTH CENTRAL SD. WINDS OVER NE WY AND NW SD WILL SHIFT
FROM SOUTH TO NORTHWEST BY THURSDAY AFTERNOON AS THE FRONT BEGINS
TO MOVE ACROSS THE REGION. THERE'S ALSO A CHANCE FOR TSRA OVER FAR
NORTHEASTERN WY INTO NORTHWESTERN SD THURSDAY EVENING.
FIRE WEATHER
ISSUED AT 144 AM MDT THU AUG 7 2025
DEEP BOUNDARY LAYER MIXING WILL PROMOTE THE DEVELOPMENT OF VERY
DRY AIR (HREF >80% CHANCE <15% MINRH) OVER THE FAR SOUTHWEST
REACHES OF THE CWA THIS AFTERNOON ALONG WITH GUSTY WEST/SOUTHWEST
WINDS AT TIMES. BEST COMBINATION OF MINRH/GUSTY WINDS WILL EXTEND
FROM WRIGHT, WY TO KIEN. COLLABORATION WITH LAND MANGERS
YESTERDAY INDICATE FUELS OVER PARTS OF THE CWA ARE NOW CRITICAL.
THUS, WILL UPGRADE FIRE WEATHER WATCH TO RED FLAG WARNING WHERE
FUELS/METEOROLOGICAL CONDITIONS WARRANT.
UNR WATCHES/WARNINGS/ADVISORIES
SD...HEAT ADVISORY FROM NOON MDT /1 PM CDT/ TODAY TO 7 PM MDT /8 PM
CDT/ THIS EVENING FOR SDZ014-032-043-046-047-049-077.
RED FLAG WARNING FROM NOON TODAY TO 8 PM MDT THIS EVENING FOR
SDZ322.
WY...RED FLAG WARNING FROM NOON TODAY TO 8 PM MDT THIS EVENING FOR
WYZ315.
DISCUSSION/KEY MESSAGES...HELGESON
AVIATION...WONG
FIRE WEATHER...HELGESON
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