Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201514
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
914 AM MDT WED MAY 20 2015

.UPDATE...
ISSUED AT 909 AM MDT WED MAY 20 2015

UPPER HIGH IS PUSHING DRIER AIR INTO THE NORTHERN PLAINS. SKIES
ARE BECOMING CLEAR FROM NORTH TO SOUTH...AND PRECIP IS
DIMINISHING. SURFACE HIGH PRESSURE IS DRAPED ACROSS THE CWA.
WINDS ARE LIGHT AND VARIABLE WITH TEMPS RISING INTO THE 40S AND
LOWER 50S. ADJUSTED SKY GRIDS AND POPS TO MATCH CURRENT
TRENDS...BUT REST OF FORECAST LOOKS ON TRACK.

&&

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
ISSUED AT 250 AM MDT WED MAY 20 2015

08Z SURFACE ANALYSIS HAD HIGH PRESSURE OVER THE DAKOTAS. WATER
VAPOR LOOP HAD UPPER LOW SPINNING OVER NORTH CENTRAL NE.
DEFORMATION ZONE -RASN ACROSS SOUTHERN SD STARTING TO WANE AS
MOISTURE PLUME IS CUTOFF AND MAIN FORCING SHIFTS NORTHEAST ON 90KT
JET STREAK ACROSS THE MIDDLE MO RIVER VALLEY. FEW INCHES OF SNOW
OVER THE HIGHER ELEVATIONS PER WEB CAMS/ROAD REPORTS SINCE TUESDAY
AFTERNOON. 00Z NAM/GFS AND LATEST RAP SHOW PRECIPITATION WANING
THROUGH THE MORNING HOURS WITH MOST SYNOPTIC SCALE ACTIVITY/LIFT
DONE BY 18Z. LOW LEVEL INSTABILITY SUGGESTS A FEW POPCORN SHOWERS
POSSIBLE THIS AFTERNOON ACROSS THE FAR SOUTH GIVEN RESIDUAL LOW
LEVEL MOISTURE...BUT DRIER AIR INFILTRATING BOUNDARY LAYER UNDER
SURFACE HIGH MAY LIMIT ACTIVITY TO SPRINKLES/VIRGA. TEMPERATURES
WILL COOL AND BE BELOW GUIDANCE ACROSS THE SOUTH BUT NEAR GUIDANCE
ACROSS THE NORTH WHERE CLEARING SKIES WILL MAKE FOR A PLEASANT
DAY...ALBEIT BELOW NORMAL.

TONIGHT/THURSDAY...WEAK UPPER RIDGE BUILDS INTO THE NORTHERN PLAINS
AS SURFACE HIGH SHIFTS INTO THE MIDDLE MS RIVER VALLEY. FROST MAY
OCCUR OVER PARTS OF THE SD PLAINS AND LATER SHIFTS WILL NEED TO
ASSESS FOR HEADLINES. WEAK RETURN FLOW EXPECTED THURSDAY WITH WARM
AIR ADVECTION PUSHING TEMPERATURES INTO THE 60S ON THE PLAINS AND
50S IN THE BLACK HILLS.

THURSDAY NIGHT...UPPER FLOW BECOMES SOUTHWEST IN RESPONSE TO UPPER
LOW/TROUGH OVER THE WEST COAST. SHORTWAVE MOVING THROUGH WY MAY
PRODUCE SMALL POPS OVER THE FAR SOUTHWEST LATE. TEMPERATURES WILL BE
NEAR GUIDANCE.

.LONG TERM...FRIDAY THROUGH TUESDAY
ISSUED AT 250 AM MDT WED MAY 20 2015

THE NEXT LOW PRESSURE SYSTEM TO EJECT OUT OF THE WESTERN CONUS
TROF WILL BEGIN TO IMPACT THE AREA ON FRIDAY...WITH CHANCES FOR
SHOWERS AND THUNDERSTORMS INCREASING FROM SOUTHWEST TO NORTHEAST
ACROSS THE CWA INTO FRIDAY EVENING. MEDIUM RANGE MODELS SEEM TO BE
IN BETTER AGREEMENT ON THE TRACK OF THE SYSTEM...WITH SOME
DIFFERENCES ON TIMING AND WHERE HEAVIER RAINFALL MAY DEVELOP. THE
BEST CHANCES FOR MORE WIDESPREAD PCPN STILL LOOK TO BE FROM LATE
FRIDAY INTO SUNDAY MORNING...WITH THE THREAT FOR HEAVIEST RAINFALL
GENERALLY BEING SATURDAY AFTERNOON AND NIGHT. SATURDAY LOOKS TO BE
THE MOST FAVORABLE DAY FOR STRONGER THUNDERSTORMS AS WELL...
ESPECIALLY FROM THE BLACK HILLS AREA AND EASTWARD. AS THE SYSTEM
WEAKENS TO THE NORTH AND EAST OF THE AREA LATE IN THE
WEEKEND...SOUTHWEST FLOW ALOFT WILL REMAIN OVER THE REGION. THIS
WILL KEEP THE UNSETTLED PATTERN CONTINUING INTO EARLY NEXT WEEK.
TEMPERATURES WILL STAY BELOW AVERAGE THROUGH THE WEEKEND WITH
CLOUDS AND MOISTURE ACROSS THE AREA. WILL LIKELY SEE A WARMING
TREND TO NEAR AVERAGE TEMPERATURES EARLY NEXT WEEK.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING
ISSUED AT 535 AM MDT WED MAY 20 2015

LOW PRESSURE ALOFT WILL WEAKEN AND SHIFT EAST OF THE REGION
TODAY. AREAS OF LIGHT RAIN/SNOW WITH MVFR/IFR CONDITIONS OVER
SOUTHERN SD AND FAR NORTHEAST WY WILL CONTINUE EARLY THIS
MORNING...WITH PCPN TAPERING OFF AND CONDITIONS IMPROVING TO VFR
FROM NORTH TO SOUTH THROUGH THE REST OF THE MORNING AND MIDDAY
HOURS. VFR CONDITIONS WILL PERSIST ACROSS NORTHWEST SD.


&&

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

$$

UPDATE...POJORLIE
SHORT TERM...HELGESON
LONG TERM...26
AVIATION...26



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