FXUS63 KUNR 061458
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
857 AM MDT SAT SEP 6 2008

.DISCUSSION...LATEST WATER VAPOR IMAGERY SHOWS A BROAD TROUGH ACROSS
THE NORTH CENTRAL CONUS WITH SOME SHORTWAVE ENERGY EMBEDDED IN THE
FLOW. THE FIRST SHORTWAVE IS MOVING OFF INTO EASTERN SD/NEB. RAIN IS
STILL AFFECTING MAINLY TRIPP CO IN SC SOUTH DAKOTA BUT IT SHOULD BE
MOVING EAST OF THERE DURING THE NEXT COUPLE OF HOURS. ANOTHER
SHORTWAVE IS NOTED MOVING INTO SOUTHEASTERN MONTANA ATTM WITH MORE
SHOWERS. SAT IMAGERY SHOWS SUBSIDENCE BETWEEN THESE TWO SHORTWAVES
HAS BROKEN UP THE CLOUD COVER OVER MOST OF THE SOUTH DAKOTA PORTION
OF THE FORECAST AREA THIS MORNING...BUT THE BREAK WILL BE BRIEF AS
INSTABILITY WILL INCREASE AGAIN LATE THIS MORNING/EARLY THIS AFTN
DUE TO DIURNAL HEATING AND THE SHORTWAVE APPROACHING FROM MONTANA.
EXPECT TO SEE SCATTERED SHOWERS DEVELOP AGAIN...WITH THE BEST CHANCE
OF RAIN OVER NORTHEASTERN WYOMING...ALONG WITH NORTHWESTERN AND WEST
CENTRAL SOUTH DAKOTA. ENOUGH INSTABILITY WILL BE PRESENT FOR AN
ISOLATED THUNDERSTORM OR TWO. THE NAM IS INDICATING AFTERNOON CAPE
VALUES AROUND 100 J/KG AND LI VALUES AROUND -1.0 C.

BOTH THE NAM AND GFS ARE SHOWING A BROAD SWATH OF PRECIP MOVING
ACROSS THE CWA THIS EVENING. WEAK SURFACE HIGH PRESSURE WILL THEN
MOVE OVER THE AREA EARLY SUNDAY MORNING BRINGING A BRIEF BREAK IN
THE SHOWER ACTIVITY BEFORE ANOTHER SHORTWAVE MOVES ACROSS THE CWA
LATE SUNDAY AFTERNOON INTO SUNDAY NIGHT. EXPECT THE BULK OF THE
PRECIP TO OCCUR AFTER 00Z...WHEN THE BEST OMEGA WILL BE PRESENT
ALONG THE SOUTH DAKOTA AND NEBRASKA BORDER. THIS WAVE WILL BRING THE
BEST CHANCE OF SHOWERS TO THE CWA. NORTHWEST FLOW ALOFT WILL REMAIN
OVER THE REGION THROUGH SUNDAY NIGHT. TEMPERATURES WILL BE ON THE
COOL SIDE THROUGH MONDAY WITH HIGHS MAINLY IN THE 60 AND LOWS IN THE
40S. HIGHER ELEVATIONS OF THE BLACK HILLS WILL DIP BELOW FREEZING.

EXTENDED...THE UPPER TROUGH WILL FINALLY PUSH EAST OF THE AREA
MONDAY...WITH UPPER LEVEL RIDGING MOVING INTO THE REGION. THIS WILL
BRING DRY AND WARMER WEATHER FOR THE EARLY PART OF NEXT WEEK.
ANOTHER UPPER LEVEL TROUGH WILL APPROACH FROM THE NORTHWEST ON
WEDNESDAY...ALONG WITH A COLD FRONT. THIS WILL BRING A CHANCE FOR
SHOWERS AND THUNDERSTORMS WEDNESDAY AND WEDNESDAY NIGHT. SEASONABLY
MILD AND DRY WX LOOKS TO BE ON TAP FOR THE LATTER PART OF NEXT WEEK.

&&

.AVIATION...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS EXPECTED
AGAIN TODAY...PERHAPS REDUCING CONDITIONS TO MVFR AT TIMES.
OTHERWISE...VFR CONDITIONS ARE EXPECTED.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$











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