Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 232039
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
239 PM MDT THU APR 23 2015

.SHORT TERM...THIS EVENING THROUGH FRIDAY NIGHT
ISSUED AT 237 PM MDT THU APR 23 2015

HIGH RESOLUTION MODELS ARE KEYING ON THE DEVELOPMENT OF ISOLATED TO
SCATTERED CONVECTION ACROSS THE BLACK HILLS REGION AND WEST CENTRAL
SOUTH DAKOTA THIS EVENING AND AGAIN FRIDAY. SO FAR TODAY ONE LONE
PERSISTENT CELL HAS DRIFTED SOUTHEAST FROM THE NORTHERN HILLS AND
MAINTAINED IT/S INTENSITY FOR A FEW HOURS.  THIS WAS UNDER LESS THAN
IDEA CONDITIONS OF TEMPERATURES IN THE LOWER 60S WITH TD/S JUST IN
THE UPPER 30S.  AS MOISTURE CONTINUES TO INCREASE ACROSS WEST
CENTRAL SOUTH DAKOTA THIS AFTERNOON...WOULD EXPECT STORM COVERAGE TO
INCREASE AS WELL...ESPECIALLY ACROSS THE BLACK HILLS AND SOUTHERN
PORTIONS OF THE FORECAST AREA /WHERE A DEEPENING SECONDARY SURFACE
LOW IS SHOW IN ADVANCE OF A MIDLEVEL SHORTWAVE/.  THE CLEARING SKIES
HAVE PROMOTED SOME DESTABILIZATION OF THE LOWER TROPOSPHERE EARLY
THIS AFTERNOON.  CURRENT LAPS DATA SUGGESTS UPWARDS TO 500 J/KG OF
ML CAPE ALONG THE SOUTHERN BORDER OF THE STATE AND WITHIN THE
HILLS.  STORMS THAT FORM LATER THIS AFTERNOON MAY PUSH THE STRONG
ENVELOPE...WITH GUSTY WIND AND SMALL HAIL BEING THE PRIMARY
THREAT...HOWEVER THE THREAT OF WIDESPREAD SEVERE WEATHER IS LOW.
FOR THE OVERNIGHT...THE AFOREMENTIONED SHORTWAVE WILL LIFT NORTHEAST
FROM THE CENTRAL HIGH PLAINS...AHEAD OF THE FEATURE...MIDLEVEL
THETA-E ADVECTION ALONG A STRENGTHENING LLJ WILL PROMOTE THE
POSSIBILITY OF ADDITIONAL CONVECTION ACROSS WEST CENTRAL SOUTH
DAKOTA.  THE SHORT TERM MODELS PROG WEAK INSTABILITY ALOFT...SO WILL
CONTINUE A THUNDER MENTION INTO MIDNIGHT...THEREAFTER...WILL CARRY A
SHOWER MENTION EAST AS THE LLJ VEERS TOWARD THE EAST CENTRAL PART OF
THE STATE.  WILL CONTINUE TO KEEP SLIGHT CHANCE TO CHANCE POPS GOING
ACROSS MUCH OF THE FORECAST AREA ON FRIDAY AS THE SHORTWAVE LIFTS
NORTHEAST.  THE BETTER FORCING SEEMS TO FOCUS OVER THE SOUTHERN AND
WESTERN HALF/S/ OF THE CWA...POP CHANCES ARE HIGHEST IN THESE
LOCATIONS.  PROXIMITY SOUNDINGS INDICATE ENOUGH SOLAR DRIVEN
DESTABILIZATION /AND WEAK COOLING ALOFT/ FOR A THUNDER MENTION
DURING THE AFTERNOON HOURS ON FRIDAY.  SEVERE WEATHER HOWEVER IS
ONCE AGAIN NOT ANTICIPATED.

TEMPERATURES FOR TONIGHT AND TOMORROW ARE A PRODUCT OF THE CONSALL
BLEND...WHICH INDICATE LOWS GENERALLY IN THE 40S FOR MUCH OF THE
FORECAST AREA.  THIS SEEMS PLAUSIBLE WITH THE MOISTURE ADVECTION IN
ADVANCE OF THE APPROACHING TROUGH.  ENOUGH BREAKS IN THE CLOUDS
FRIDAY WILL PROMOTE SIMILAR HIGHS...RANGING IN THE 60S TO LOWER 70S
OVER THE SOUTH...MID 60S FOR THE NORTH...AND 50S OVER THE ELEVATED
TERRAIN OF THE BLACK HILLS.

.LONG TERM...SATURDAY THROUGH THURSDAY
ISSUED AT 237 PM MDT THU APR 23 2015

VERY ACTIVE NEAR TERM PERIOD WITH LONG WAVE TROUGH MOVING INTO
CENTRAL PLAINS AND AFFECTING NORTHERN PLAINS WEATHER FRIDAY AND
SATURDAY AND THEN NEXT SYSTEM...A DEEPENING TROUGH OVER THE
WESTERN CONUS CLOSING OFF AND MOVING INTO THE SOUTHERN
PLAINS...SUNDAY THROUGH TUESDAY. STRONG RIDGE WILL BUILD EAST INTO
WESTERN SOUTH DAKOTA TUESDAY. ACTIVE NORTHERN STREAM WILL COMMENCE
WITH RIDGE BUILDING INTO SOUTHERN CANADA WARMER TEMPERATURES AND
DRY.

SATURDAY ON THE BACKSIDE OF UPPER LOW OVER SOUTHEAST NEBRASKA.
SCATTERED SHOWERS IN THE MORNING AND THEN WITH HEATING OF THE DAY
AND COLD FRONT MOVING SOUTH INTO WESTERN SOUTH DAKOTA ISOLATED
THUNDER CONTINUES INTO SATURDAY EVENING. STRONGER WAVE MOVES OUT
OF BOTTOM OF TROUGH SATURDAY NIGHT WITH DIFFLUENCE ALOFT AND
TROUGH CLOSING OFF...BECOMING NEGATIVELY TILTED. SHOWERS CONTINUED
OVER NIGHT.

SUNDAY SHOWERS CONTINUING THROUGH THE DAY AS UPPER TROUGH MOVES
EAST INTO THE WESTERN DAKOTAS. CLOSED LOW MOVES INTO THE TEXAS
PANHANDLE THROUGH MONDAY WITH THE NORTHERN TROUGH AND COOLER MORE
STABLE AIR KEEPING RAINSHOWERS OVER WESTERN SOUTH DAKOTA THROUGH
MONDAY EVENING.

RIDGE BUILDS IN FROM THE WEST TUESDAY WITH WARMER DRIER AIR.
HIGHS IN THE 60S. WEDNESDAY WARMER WITH HIGHS IN THE 70S AND DRY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1127 AM MDT THU APR 23 2015

LATEST HIGH RESOLUTION MODELS ARE FOCUSING THE DEVELOPMENT OF
SHOWERS AND THUNDERSTORMS ACROSS SOUTHWEST SOUTH DAKOTA THIS
AFTERNOON WITH THE ACTIVITY SPREADING NORTHEAST THROUGH THE
EVENING. ADDITIONAL SHOWERS AND THUNDERSTORMS ARE SHOWN TO DEVELOP
OVER THE BLACK HILLS AND POSSIBLY NORTHWEST SOUTH DAKOTA LATE THIS
AFTERNOON AND EVENING. MOST OF THE ACTIVITY WILL BE SCATTERED AND
FAIRLY WEAK...HOWEVER AN ISOLATED STRONG STORM CAPABLE OF GUSTY
ERRATIC WIND AND HAIL CANNOT BE RULED OUT...ESPECIALLY ACROSS
SOUTHWEST SOUTH DAKOTA. THIS ACTIVITY MAY IMPACT THE KRAP TERMINAL
AFTER 00Z THIS EVENING. OTHERWISE A FRONT WILL DROP SOUTH
OVERNIGHT...ALLOWING FOR A WIND SHIFT TO NORTHERLY. THE TIMING OF
THE FRONT WILL BE KEY FOR THE KRAP TERMINAL AS A LATER ARRIVAL
WOULD ALLOW FOR GOOD LOW LEVEL MOISTURE RETURN AND POSSIBLY MVFR
STRATUS. AT THIS POINT...WE ARE LEANING AGAINST STRATUS AT KRAP.


&&

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

$$

SHORT TERM...WFO UNR/JACOBS
LONG TERM...WFO UNR/POWER
AVIATION...WFO UNR/JACOBS






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