Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 312333
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
533 PM MDT FRI JUL 31 2015

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 204 PM MDT FRI JUL 31 2015

20Z ANALYSIS SHOWS SFC HIGH PRESSURE CENTERED OVER THE FORECAST
AREA WITH AN UPPER RIDGE BUILDING OVER THE WESTERN CONUS. MESO
ANALYSIS SHOWS MLCAPE CURRENTLY RANGING FROM 250-500J/KJ OVER
NORTHEASTERN WYOMING AND THE BLACK HILLS. SOME RELATIVELY FLAT CU
CURRENT NOTED OVER PARTS OF NERN WY AND THE BLKHLS. IF THE
CONVECTION MANAGES TO OVERCOME THE SYNOPTIC SCALE SUBSIDENCE OVER
THE REGION DURING THE REST OF THE AFTN...EXPECT ISOLATED SHORT
DURATION THUNDERSTORMS WHICH MAY RESULT IN GUSTY SFC WINDS.

A 25-30KT LL JET WILL DEVELOP OVER FAR WRN SD THIS EVENING
INCREASING THE MID-LEVEL THETA-E ADVECTION AND INCREASING THE
INSTABILITY ALOFT. MAY SEE ISOLATED ELEVATED THUNDERSTORMS
DEVELOP OVER FAR NERN WY/THE BLKHILLS THIS EVENING WHICH COULD
POSSIBLY CONTINUE THOUGH MUCH OF THE NIGHT IN THE ELEVATED
UNSTABLE LAYER...MOVING GRADUALLY SOUTHEAST OVERNIGHT. A WEAK
FRONTAL BOUNDARY WILL MOVE SOUTHWARD ACROSS THE FORECAST AREA ON
SATURDAY. DUE TO INSTABILITY AND LL FORCING ALONG AND NEAR THE
FRONT WILL INCLUDE A LOW CHANCE OF THUNDERSTORMS OVER SOUTHWESTERN
AND SOUTH CENTRAL SOUTH DAKOTA THROUGH THE DAY ON SATURDAY. HAVE
ALSO INCLUDED A SLIGHT CHANCE OF THUNDERSTORMS OVER THE CENTRAL
AND SOUTHERN BLACK HILLS ON SATURDAY AFTN AS CONVERGENCE ALONG
THE BOUNDARY COMBINED WITH DIURNAL HEATING MAY BE STRONG ENOUGH TO
OVERCOME THE SUBSIENCE BEHIND THE FRONT. HIGH TEMPERATURES ON THE
PLAINS ON SATURDAY ARE EXPECTED TO RANGE FROM THE UPPER 80S TO THE
UPPER 90S

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 204 PM MDT FRI JUL 31 2015

GFS/ECMWF STILL IN DECENT AGREEMENT WITH THE OVERALL
PATTERN FOR MUCH OF NEXT WEEK. HOWEVER...TIMING DIFFERENCES REMAIN
WITH IMPULSES MOVING THROUGH THE NORTHERN PLAINS...ESPECIALLY
FURTHER OUT IN TIME.

SUNDAY WILL BE WARM AND DRY AS UPPER RIDGE BUILDS ACROSS THE HIGH
PLAINS. HIGHS WILL BE IN THE 90S ON THE PLAINS WITH RELATIVE
HUMIDITY DROPPING TO AROUND 15 PERCENT AGAIN OVER NORTHEAST WY AND
FAR WESTERN SD. WINDS SHOULD STAY RELATIVELY LIGHT ACROSS THE AREA.

CHANCES FOR THUNDERSTORMS WILL BEGIN TO INCREASE EARLY IN THE
WEEK...STARTING LATE ON MONDAY...AS RIDGE WEAKENS ENOUGH TO ALLOW A
SERIES OF DISTURBANCES TO CROSS THE REGION. LOW LEVEL MOISTURE WILL
INCREASE AS EAST-SOUTHEAST WINDS BECOME RATHER PERSISTENT ACROSS THE
AREA THROUGH MIDWEEK...ESPECIALLY OVER AND EAST OF THE BLACK HILLS.
TIMING FOR BETTER CHANCES OF STORMS IS STILL UNCERTAIN AT THIS
POINT...BUT THE MIDDLE PART OF THE WEEK LOOKS TO BE THE MOST
FAVORABLE PERIOD. TEMPERATURES WILL BE NEAR AVERAGE THROUGH MUCH OF
THE WEEK.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING
ISSUED AT 529 PM MDT FRI JUL 31 2015

SCT CLDS OVR NERN WY AND BLK HLS WL DISSIPATE THIS EVENING. ISOLD TSTMS
MAY DVLP OVR SWRN SD TONITE AND MOV ACRS SCNTRL SD. LGT WNDS WL SHIFT
TO THE NW SAT MRNG BEHIND A COLD FRONT.

&&

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

$$

SHORT TERM...10
LONG TERM...26
AVIATION...55


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