520
FXUS63 KUNR 041700
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1058 AM MDT SAT JUL 4 2009
DISCUSSION
REMAINING LOW STRATUS OVER PARTS OF WESTERN AND
CENTRAL SOUTH DAKOTA SHOULD MIX INTO A CU DECK DURING THE EARLY
AFTERNOON. CAP WILL WEAKEN ENOUGH FOR NEW CONVECTION BY
18Z...ESPECIALLY OVER NORTHEASTERN WYOMING AND THE BLACK HILLS AREA.
THIS ACTIVITY WILL CONTINUE INTO THE EVENING HOURS. MAIN THREAT
FOR SEVERE WEATHER WILL BE WEST OF THE CWA AHEAD OF AN APPROACHING
WAVE...AND NEAREST SURFACE BOUNDARY. SHEAR WILL BE SUFFICIENT FOR
ISOLATED STRONG TO SEVERE THUNDERSTORMS DURING PEAK HEATING.
SUNDAY...UPPER TROUGH APPROACHING THE WEST COAST ALLOWING UPPER
RIDGE TO AMPLIFY OVER THE NORTHERN PLAINS. THERMAL RIDGE BEGINS TO
BUILD WITH A COUPLE OF WEAK WAVES. THE SURFACE BOUNDARY WILL LIFT
INTO MT/ND/NORTHWEST SD...FOCUSING TSRA ACTIVITY. SUMMER-LIKE
TEMPERATURES FORESEEN. SHEAR AGAIN SUFFICIENT FOR ISOLATED SEVERE
THUNDERSTORMS DURING PEAK HEATING.
MONDAY...UPPER LOW DEVELOPS NEAR OR WITH UPPER/THERMAL RIDGE OVER
THE CWA. FORECAST SOUNDINGS SUGGEST WE/LL BE CAPPED WITH PLENTY OF
SUNSHINE AND TEMPERATURES ABOVE 90F OVER MANY LOCATIONS.
EXTENDED...AN UPPER RIDGE IS FORECAST TO TAKE UP A POSITION OVER THE
NORTHERN PLAINS FOR THE MIDDLE OF NEXT WEEK. THIS WILL RESULT IN A
PERIOD OF WARMER AND DRIER WEATHER. BY THE END OF THE WEEK THE GFS
SHOWS A MORE ZONAL/ACTIVE PATTERN WHILE THE ECMWF REDEVELOPS A WRN
U.S. RIDGE. THE CURRENT FORECAST PACKAGE REINTRODUCES A SLGT
CHANCE FOR MOST AREAS THU NIGHT WHICH IS A PRETTY GOOD COMPROMISE
AT THIS POINT.
AVIATION...WIDESPREAD MVFR...WITH LOCALIZED IFR
CONDS CONTINUE
FROM THE BLKHLS EWD AND INTO SOUTHWESTERN AND SOUTH CENTRAL SOUTH
DAKOTA. CIGS AND VSBYS ARE EXPECTED TO IMPROVE DURING THE
AFTERNOON IN WRN SOUTH DAKOTA AS THE UPPER LEVEL SHORT WAVE AND
ASSCD SFC TROUGH MOVE OUT OF THE AREA. THERE IS A CHANCE OF
AFTERNOON AND EVENING THUNDERSTORMS...ESPECIALLY ACROSS NORTHEASTERN
WYOMING...AND OVER AND NEAR THE BLACKH HILLS.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
HELGESON/CARPENTER
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