Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 241709
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1109 AM MDT FRI APR 24 2015

.UPDATE...
ISSUED AT 1104 AM MDT FRI APR 24 2015

CURRENT SURFACE ANALYSIS SHOWS A FRONTAL BOUNDARY EXTENDING FROM
CENTRAL SOUTH DAKOTA SOUTHWESTWARD INTO SOUTHWESTERN SOUTH DAKOTA
AND THAN NORTHWESTWARD INTO CENTRAL MONTANA. SOUTH OF THE FRONTAL
BOUNDARY...TEMPERATURES HAVE ALREADY WARMED ABOVE FORECAST
HIGHS...THUS HAVE UPDATED TEMPS IN SOUTH CENTRAL SOUTH DAKOTA TO
REFLECT THIS TREND.

&&

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
ISSUED AT 329 AM MDT FRI APR 24 2015

UPPER LEVEL ANALYSIS HAS RIDGE AXIS JUST TO THE EAST OF THE
NORTHERN PLAINS WITH DEEP TROF ACROSS THE WESTERN CONUS. CLOSED
LOW IS ENTERING THE PACIFIC NORTHWEST AT THE MOMENT WITH ANOTHER
NEARLY CLOSED LOW OVER THE FAR SOUTHWEST. UPPER FLOW OVER THE
NORTHERN PLAINS IS WEST SOUTHWEST WITH WEAK SHORTWAVE ENERGY
CROSSING THE AREA. RAIN SHOWER ACTIVITY HAS DIMINISHED OVERNIGHT
WITH JUST A MID LEVEL CLOUD DECK REMAINING. AT THE SURFACE...A
WEAK TROF OF LOW PRESSURE RESIDES OVER WESTERN SOUTH DAKOTA WITH
HIGH PRESSURE BUILDING IN FROM THE NORTH. TEMPERATURES ARE IN THE
40S AND 50S AT 3AM...WITH LIGHT WINDS.

FOR TODAY...UPPER LEVEL RIDGE AXIS SHIFTS FURTHER EAST AS WESTERN
TROF SLIDES INTO THE FOUR CORNERS REGION. MAJORITY OF MODELS ARE
SHOWING A VERY WEAK NORTHERN STREAM SHORTWAVE LIFTING THROUGH
WESTERN SOUTH DAKOTA TODAY. AT THE SURFACE...TROF OF LOW PRESSURE
AND WEAK FRONTAL BOUNDARY WILL SLOWLY PUSH SOUTHEAST INTO SOUTH
CENTRAL SOUTH DAKOTA BY MID DAY. CHANCES FOR SHOWERS WILL INCREASE
THIS MORNING AND INTO THE AFTERNOON AS ATMOSPHERE
DESTABILIZES...BEST CHANCES GENERALLY OVER THE BLACK HILLS AND
SOUTHWESTERN SD. THUNDERSTORMS ARE EXPECTED THIS AFTERNOON...
ESPECIALLY FROM THE BLACK HILLS THROUGH SOUTH CENTRAL PORTIONS OF
SD. A STRONG STORM OR TWO IS POSSIBLE OVER SOUTH CENTRAL SD IN THE
VICINITY OF THE SURFACE TROF THIS AFTERNOON. TEMPS WILL IN THE 60S
TO NEAR 70 DEGREES ACROSS THE PLAINS.

TONIGHT...WEAK UPPER SHORTWAVE THAT CROSSES THE AREA TODAY WILL
PHASE WITH THE LARGER TROF SWINGING OUT OF THE SOUTHWEST CONUS AND
PUSH WELL SOUTHEAST OF THE FORECAST AREA OVERNIGHT. SHOWER/TSTM
ACTIVITY SHOULD SHIFT QUICKLY EAST DURING THE EVENING HOURS. WEAK
UPPER LEVEL ENERGY IN WEST-SOUTHWEST FLOW MAY KEEP A FEW LIGHT
SHOWERS GOING OVERNIGHT...MAINLY ACROSS SOUTH CENTRAL SOUTH
DAKOTA. LOW TEMPERATURES WILL FALL INTO THE 40S.

ON SATURDAY...UPPER LEVEL CLOSED LOW CROSSES THE CASCADES AS NEXT
TROF DEEPENS ACROSS THE WESTERN CONUS. UPPER FLOW BECOMES MORE
SOUTHWESTERLY OVER THE NORTHERN PLAINS WITH ADDITIONAL SHORTWAVE
ENERGY CROSSING THE AREA. SHOWERS AND ISOLATED THUNDER WILL
INCREASE IN COVERAGE FROM WEST TO EAST ACROSS THE AREA WITH BEST
CHANCES FROM THE BLACK HILLS INTO NORTHWEST SOUTH DAKOTA DURING
THE AFTERNOON. TEMPERATURES WILL BE COOLER WITH THE EXTENT OF
CLOUD COVER EXPECTED. HIGHS WILL ONLY REACH THE 50S ACROSS WESTERN
PORTIONS OF THE AREA...WITH LOW 60S ACROSS THE SOUTH DAKOTA
PLAINS. CLOUDY SKIES AND PRECIP CHANCES CONTINUE IN SATURDAY NIGHT
WITH LOWS FALLING INTO THE UPPER 30S TO MID 40S.

.LONG TERM...SUNDAY THROUGH THURSDAY
ISSUED AT 329 AM MDT FRI APR 24 2015

GFS/GEM/ECMWF CONTINUE TO SHOW UPPER LOW CLOSING OFF OVER THE
SOUTHERN PLAINS SUNDAY. AS FLOW SPLITS...WEAKER NORTHERN STREAM
TROF SLOWLY SLIDES THROUGH THE NORTHERN PLAINS SUNDAY/EARLY
MONDAY. DECENT CHANCE OF SHOWERS SUNDAY/EARLY MONDAY WITH WEAK
FORCING AND STEEP MID LEVEL LAPSE RATES. UPPER LEVEL RIDGE BUILDS
ACROSS THE ROCKIES EARLY NEXT WEEK...WITH DRY WEATHER AND WARMER
TEMPERATURES.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z SATURDAY
ISSUED AT 1104 AM MDT FRI APR 24 2015

SCT SHRA/TSTMS EXPECTED THIS AFTN AND TONIGHT...ESPECIALLY FROM
THE BLKHLS EWD INTO CNTRL SD. LCL MVFR CIGS/VSBY WITH THE PCPN.
RATHER WDSPRD STRATUS EXPECTED TO DEVELOP ACROSS MUCH OF THE AREA
AFT MIDNIGHT WITH IFR CIGS.

&&

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

$$

UPDATE...MLS
SHORT TERM...15
LONG TERM...7
AVIATION...JOHNSON



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