Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 101734
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1134 AM MDT THU JUL 10 2014

.UPDATE...
ISSUED AT 836 AM MDT THU JUL 10 2014

14Z SURFACE ANALYSIS HAD TROUGH FROM NORTHEAST MT INTO SOUTH
CENTRAL SD. SHORTWAVE OVER SOUTHWEST ND SUPPORTING WEAK LOW ALONG
TROUGH AS WELL AS ELEVATED CONVECTION ACROSS SOUTHEAST MT THROUGH
NORTHWEST SD. 12Z KUNR SOUNDING SHOWED THAT WITHOUT DECENT LOW
LEVEL MOISTURE ADVECTION...AFTERNOON CONVECTION MAY STRUGGLE
AGAINST MLCIN AND CWA WILL BE UNDER IMPLIED SUBSIDENCE REGION
BEHIND SOUTHWEST ND SHORTWAVE. 12Z MODEL GUIDANCE IS STARTING TO
SUGGEST A LATER START...BUT TD/S WELL INTO THE 60S ARE NOT TOO FAR
AWAY AND MOISTURE WILL LIKELY POOL ALONG SURFACE TROUGH.
ADDITIONAL SHORTWAVE ENERGY MOVES INTO THE CWA THIS
EVENING...WHICH WOULD LIKELY ENHANCE TSRA DEVELOPMENT. 0-6KM BULK
SHEAR WILL BE SUFFICIENT FOR SUPERCELLS INITIALLY...WITH
CONVECTION POSSIBLY BUILDING UPSCALE TONIGHT.

UPDATE WILL ADDRESS LATEST RADAR TRENDS AS WELL AS TWEAKING TIMING
OF ACTIVITY THIS AFTERNOON/TONIGHT.

&&

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 220 AM MDT THU JUL 10 2014

ACTIVE WESTERLY FLOW WILL CONTINUE IN THE PERIOD AS SEVERAL
IMPULSES ADVANCE AROUND THE PERIPHERY OF THE WESTERN CONUS RIDGE.
LL FRONTAL ZONE WILL WAVER ACROSS THE AREA...PROVIDING THE FOCUS
FOR SHRA/TS...WITH SOME STORMS POSSIBLY BECOMING SEVERE. ONE SUCH
IMPULSE IS IN THE PROCESS OF ADVECTING THROUGH THE WESTERN
FA...SUPPORTING ELEVATED POS THETA-E ADV...EVIDENCE WELL AT H7.
THIS IMPULSE WILL HELP LIFT THE NEARLY STALLED FRONTAL BOUNDARY
BACK NORTH AS A WARM FRONT...WITH ANOTHER IMPULSE LATER THIS
AFTERNOON EJECTING INTO THE AREA AND SUPPORTING A SFC TROUGH
THROUGH THE AREA...AND PROVIDING THE FOCUS FOR RENEWED TS
DEVELOPMENT THIS AFTERNOON. STALLED UPPER TROUGH OVER THE EASTERN
PAC WILL CONTINUE TO SUPPORT SW FLOW IMPULSES INTO THE REGION
THROUGH FRIDAY.

TODAY...SHRA/TS CLUSTER WILL CONTINUE TO SHIFT EAST ACROSS THE
WESTERN HALF OF THE FA...BEING AIDED BY VIGOROUS POS THETA-E ADV AT
THE BASE OF A STAUNCH EML. CONVECTION IS EXPECTED TO SPREAD INTO
WESTERN SD...POSSIBLY LINGERING INTO LATE MORNING. AMPLE DEEP LAYER
MOISTURE WILL BUILD INTO THE REGION...WITH LL GOMEX MOISTURE
COUPLING WITH UPPER LEVEL MONSOON MOISTURE FROM THE SW CONUS. THIS
WILL SUPPORT PW VALUES WELL OVER ONE INCH ACROSS MUCH OF THE
FA...APPROACHING 2 INCHES OVER SCENTRAL SD. SOME THREAT FOR
LOCALIZED HEAVY RAIN...AND POTENTIAL FLASH FLOODING IF BACK BUILD
CELLS DEVELOP. HOWEVER...CERTAINLY NOT HIGH ENOUGH FOR ISSUANCE OF A
FLASH FLOOD WATCH...GIVEN STORM MOTION VECTORS. THE MAIN CONCERN
TODAY WILL BE THE THREAT FOR SEVERE STORMS. MORNING CONVENTION MAY
SUPPORT A HAIL THREAT WITH STRONGER CORES GIVEN DEEP LAYER BULK
SHEAR VALUES IN EXCESS OF 40 KNOTS. HOWEVER...THE MAIN CONCERN FOR
SEVERE WEATHER WILL BE WITH AFTERNOON AND EVENING TS/S AS THE NEXT
IMPULSE ADVECTS INTO THE REGION. AMPLE LL MOISTURE UNDER STEEP MID
LEVEL LAPSE RATES WILL SUPPORT ML CAPE IN EXCESS OF 2000 J/KG OVER
MUCH OF THE AREA...ESP IF SUFFICIENT INSOLATION IS REACHED...WHICH
MAY BE AN ISSUE EARLY IN THE AFTERNOON GIVEN ELEVATED CONVECTION AND
CLOUDS. SFC TROUGH WILL BE IN PLACE ACROSS THE REGION THIS AFTERNOON
PER THIS MORNING/S IMPULSE. THIS FEATURE WILL PROVIDE THE FOCUS FOR
NEW CONVECTION THIS AFTERNOON...WITH THE NEXT APPROACHING IMPULSE.
STORMS WILL ALSO LIKELY FIRE OVER THE NORTHERN/CENTRAL BLACK HILLS
WHERE CAPPING WILL BE WEAK AND LL CONVERGENCE STRONG. PASSING UPPER
JET STREAK WILL SUPPORT DEEP LAYER SHEAR IN EXCESS OF 35 KNOTS
ACROSS MOST OF THE REGION AND WHEN COUPLED WITH ML CAPE EXPECTED IN
EXCESS OF 2000 J/KG...STORMS WILL HAVE A GOOD CHANCE TO GROW UPSCALE
AND BECOME SEVERE...ESP ACROSS THE BLACK HILLS AND SE INTO SCENTRAL
SD. HAVE ADJUSTED POPS FOR THIS. CONVECTION WILL TREND EAST THROUGH
EVENING...WITH THE LINGERING LL FRONTAL ZONE PROVIDING FOCUS FOR
POSSIBLE ELEVATED STORMS OVERNIGHT ACROSS SOUTHERN AREAS.

FRIDAY...ANOTHER IMPULSE WILL SUPPORT AN UNDULATION OF THE LL
FRONTAL ZONE IN PLACE...SUPPORTING CHANCES FOR SHRA/TS...ESP IN THE
LATE AFTERNOON AND OVERNIGHT. STORMS WILL LIKELY FIRE OVER WY AND
SHIFT EAST ACROSS THE FA THROUGH THROUGH FRIDAY NIGHT. INCREASING
FAST FLOW ALOFT PER THE SETTLING MID LEVEL JET WILL SUPPORT A SEVERE
THREAT ACROSS THE AREA...ESP WHEN COUPLED WITH AMPLE LL MOISTURE AND
RESULTING CAPE ALONG AND NEAR THE STALLED FRONTAL ZONE ACROSS THE
REGION. ADJUSTED POPS ACCORDINGLY. ALSO ADJUSTED HIGH TEMPS DOWN FRI
GIVEN CONCERNS ON CLOUD COVER/PRECIP/AND LL EASTERLY MOIST UPSLOPE
FLOW.

&&

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 220 AM MDT THU JUL 10 2014

UPPER LEVEL RIDGING WILL BE IN PLACE ACROSS MUCH OF THE WESTERN
CONUS DURING THE EXTENDED PERIOD. NORTHWESTERLY FLOW ALOFT WILL ALSO
PERSIST OVER THE NORTHERN PLAINS AS AN UPPER LOW DRIFTS ACROSS SOUTH
CENTRAL CANADA INTO THE GREAT LAKES. A SERIES OF SHORTWAVES WILL
MOVE SOUTHEASTWARD ACROSS THE AREA SATURDAY INTO SUNDAY...BRINGING A
CHANCE OF SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL BE NEAR TO
SLIGHTLY ABOVE AVERAGE THIS WEEKEND. COOLER AND DRIER WEATHER IS
EXPECTED FOR THE FIRST HALF OF NEXT WEEK AS COLD FRONT PUSHES INTO
THE REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1133 AM MDT THU JUL 10 2014

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED LATE THIS
AFTERNOON...THROUGH THIS EVENING ACROSS MUCH OF THE AREA. THESE
STORMS COULD PRODUCE BRIEF MVFR CONDITIONS. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD.


&&

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

$$

UPDATE...HELGESON
SHORT TERM...JC
LONG TERM...13
AVIATION...15





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