991
FXUS63 KUNR 291725
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1125 AM MDT THU JUL 29 2021
DISCUSSION
(TODAY THROUGH WEDNESDAY)
ISSUED AT 234 AM MDT THU JUL 29 2021
08Z SURFACE ANALYSIS HAD HIGH PRESSURE OVER ND HAD PUSHED COLD
FRONT INTO SOUTHERN WY/NE. WATER VAPOUR LOOP SHOWED UPPER RIDGE
OVER THE CENTRAL PLAINS WITH NOTABLE WAVE/MONSOONAL MOISTURE OVER
THE FOUR CORNERS REGION, WRAPPING INTO THE NORTHERN ROCKIES.
EASTERLY 850-700MB FLOW FEEDING WEAK CONVECTION OVER NORTHEAST WY
INTO NORTHWEST SD PER THETA-E ADVECTION/WEAK MUCAPE. MAIN CONCERN
THIS FORECAST REVOLVES AROUND FOUR CORNERS WAVE.
TODAY THROUGH FRIDAY, WAVE FLATTENS UPPER RIDGE AS IT MOVES INTO THE
NORTHERN PLAINS TONIGHT INTO FRIDAY. SURFACE HIGH DRIFTS SOUTHEAST
MAINTAINING EASTERLY COMPONENT/LOW LEVEL UPSLOPE FLOW. UPPER WAVE
WILL SUPPORT LEE TROUGH AS IT MOVES EASTWARD TONIGHT. 500-750J/KG
MLCAPE DEVELOPS THIS AFTERNOON/EVENING ACROSS THE FAR SOUTHWEST
SIXTH OF THE CWA AS 0-6KM BULK SHEAR SETTLES AROUND 35KTS.
ISOLATED STRONGER STORMS MAY DEVELOP FOR THOSE AREAS DURING PEAK
HEATING. CLUSTER OF SHOWERS/STORMS AHEAD OF WAVE WILL MOVE ACROSS
THE CWA TONIGHT INTO FRIDAY. CURRENT THINKING IS BEST CHANCE FOR
BENEFICIAL RAINS WILL BE FROM NORTHEAST WY INTO SOUTHERN SD. GIVEN
PWATS 150-200% OF NORMAL, LOCALLY HEAVY RAINS MAY OCCUR. MAIN
BAND OF PRECIPITATION DIMINISHES FRIDAY NIGHT. TEMPERATURES WILL
BE NOTICEABLY COOLER, ESPECIALLY FRIDAY.
FOR THE WEEKEND INTO THE FIRST HALF OF NEXT WEEK, UPPER RIDGE WILL
CONTINUE TO DOMINATE THE WEATHER. NORTHWEST FLOW ALOFT OVER THE
WEEKEND TRANSITIONS TO WEST/SOUTHWEST FLOW MID-WEEK. TEMPERATURES
WILL BE SEASONABLE AS WEAK DISTURBANCES BRING TRANSIENT CHANCES
FOR STORMS.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1125 AM MDT THU JUL 29 2021
ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS MUCH OF
THE AREA THROUGH LATE AFTERNOON, WITH SHOWERS AND STORMS BECOMING
MORE WIDESPREAD FROM NORTHEAST WY TO WESTERN SD TONIGHT. MVFR
CONDITIONS COULD DEVELOP WITH HEAVIER SHOWERS AND AREAS OF MVFR
CEILINGS ARE LIKELY LATER TONIGHT INTO FRIDAY MORNING. INCREASING
SMOKE FROM WILDFIRES IN SOUTH CENTRAL CANADA WILL ALSO LIKELY
REDUCE VSBYS AT TIMES IN MANY AREAS, ESPECIALLY TONIGHT INTO
FRIDAY.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION...HELGESON
AVIATION...26
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