Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 231755
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1155 AM MDT THU JUL 23 2015

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 322 AM MDT THU JUL 23 2015

UPPER LEVEL ANALYSIS HAS A BROAD AREA OF HIGH PRESSURE OVER THE
SOUTHERN PLAINS WITH A SHORTWAVE TROF DIGGING INTO THE PACIFIC
NORTHWEST. WEST TO SOUTHWEST FLOW IS PRESENT ACROSS THE NORTHERN
PLAINS WITH A WEAK CLUSTER OF STORMS MOVING ACROSS SOUTHEAST SD.
SKIES ARE PARTLY CLOUDY TO CLEAR ACROSS WESTERN SD. AT THE
SURFACE...THERE IS AN AREA OF LOW PRESSURE OVER EASTERN MONTANA
WITH A WEAK COLD FRONT EXTENDING BACK INTO MONTANA. AHEAD OF THE
COLD FRONT IS A LEE TROF EXTENDING THROUGH WESTERN SOUTH DAKOTA.
TEMPERATURES AT 3 AM ARE IN THE 60S TO LOWER 70S.

TODAY...SHORTWAVE ENERGY AHEAD OF THE PAC NW TROF WILL CROSS
NORTHERN AND WESTERN PORTIONS OF THE FORECAST AREA BY AFTERNOON.
AT THE SURFACE...THE COLD FRONT WILL MOVE INTO NORTHWESTERN SOUTH
DAKOTA AND NORTHEASTERN WYOMING...PROVIDING A FOCUS FOR SOME
AFTERNOON SHOWERS AND STORMS. FORECAST SOUNDINGS ACROSS NORTHWEST
AND FAR SOUTH CENTRAL SD SHOW CAPE VALUES OF 500-1500 J/KG...BUT
SHEAR VALUES ARE LESS THAN 20KTS. THUS ANY STRONGER STORMS THAT
OCCUR WILL LIKELY BE NEAR THE FRONTAL BOUNDARY WHERE LOCAL SHEAR
VALUES WILL BE HIGHER. TEMPERATURES AHEAD OF THE COLD FRONT WILL
BE RATHER WARM WITH READINGS IN THE MID TO UPPER 90S. WINDS WILL
ALSO BE A FACTOR WITH GUSTY SOUTHERLY WINDS AHEAD OF THE FRONT
WITH GUSTY WESTERLY/NORTHWESTERLY WINDS BEHIND THE FRONT.

TONIGHT...WESTERN TROF OPENS UP AND LIFTS NORTH ACROSS THE
NORTHERN ROCKIES. WEAK SHORTWAVE ENERGY WILL CONTINUE TO LIFT
ACROSS FAR NORTHEAST WYOMING AND FAR NORTHWEST SOUTH
DAKOTA...KEEPING A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE
FORECAST. ELSEWHERE PARTLY CLOUDY TO MOSTLY CLEAR SKIES WILL
PREVAIL WITH MILD TEMPERATURES CONTINUING. LOWS WILL FALL INTO THE
UPPER 50S BEHIND THE FRONT ACROSS NORTHEAST WYOMING AND THE BLACK
HILLS...WITH TEMPS IN THE 60S TO LOWER 70S AHEAD OF THE FRONT
ACROSS THE SD PLAINS.

FRIDAY...BROAD RIDGE REMAINS ANCHORED ACROSS THE SOUTHERN PLAINS
WITH WESTERLY UPPER FLOW ACROSS THE FAR NORTHERN PLAINS. SURFACE
HIGH PRESSURE WILL MOVE EASTERLY ACROSS THE DAKOTAS EARLY IN THE
DAY...WITH SOUTHERLY RETURN FLOW PICKING UP LATE IN THE DAY. WEAK
UPPER LEVEL SHORTWAVE WILL CROSS THE AREA DURING THE AFTERNOON
AND EVENING...GIVING THE AREA A CHANCE FOR SOME SHOWERS AND
THUNDERSTORMS. HIGH TEMPERATURES ON FRIDAY WILL BE SLIGHTLY COOLER
THAN TODAY...IN THE 80S TO LOWER 90S. LOW TEMPERATURES FRIDAY
NIGHT WILL BE IN THE MID 50S TO UPPER 60S.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 322 AM MDT THU JUL 23 2015

UPPER RIDGE WILL SHIFT EASTWARD TOWARD THE GREAT LAKES SATURDAY
AS A LEE TROF OVER MT DRAWS MORE HUMID AIR OVER WESTERN-CENTRAL
SD TO PRODUCE THUNDERSTORMS EAST OF THE BLACK HILLS...WHILE
NORTHEASTERN WY DRIES OUT. ANOTHER LONG WAVE TROF OVER THE PACIFIC
COMES ONSHORE AND MOVES INLAND OVER THE ROCKIES...AND DEEP UPPER
LOW FORMS OVER SOUTHERN CANADA... BRINGING A COLD FRONT THROUGH
THE NORTHERN PLAINS MONDAY. MODELS IN FAIRLY CLOSE AGREEMENT ON
THE STORM TRACK...BUT GFS HAS THE LOW MUCH DEEPER WITH A TIGHT
PRESSURE GRADIENT BEHIND THE FRONT THAT COULD PRODUCE VERY GUSTY
WINDS MONDAY INTO EARLY TUESDAY MORNING. ZONAL FLOW THEN REPLACES
THE HIGHER- AMPLITUDE FLOW THROUGH MIDWEEK WITH SLIGHTLY COOLER
THAN SEASONAL TEMPERATURES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1138 AM MDT THU JUL 23 2015

A FEW STORMS COULD INITIATE ALONG A COLD FRONT IN FAR NORTHWESTERN
SD AND NORTHEASTERN WY THIS AFTERNOON. OTHERWISE, VFR CONDITIONS
SHOULD PERSIST. WINDS WILL SHIFT FROM SOUTHWEST TO NORTHWEST AND
BE GUSTY AT TIMES PRIOR TO SUNSET.

&&

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

$$

SHORT TERM...15
LONG TERM...55
AVIATION...WARD


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