Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 280537
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1137 PM MDT WED MAY 27 2015

.UPDATE...
ISSUED AT 547 PM MDT WED MAY 27 2015

LATEST WATER VAPOUR/RADAR LOOPS SHOWED PRIMARY WAVE -TSRA HEADING
EAST/NORTHEAST AND WILL EXIT THE CWA LATER THIS EVENING. AFTERNOON
RAP PICKS UP ON NEXT SHORTWAVE OVER SOUTHWEST WY...WHICH WILL PUSH
INTO WESTERN REACHES OF THE CWA OVERNIGHT...SO HAVE UPPED POPS IN
THE WEST LATE TO ACCOUNT.

&&

.SHORT TERM...THIS EVENING THROUGH THURSDAY NIGHT
ISSUED AT 225 PM MDT WED MAY 27 2015

CLOSED UPPER LOW OVER THE PAC NW WILL CONTINUE TO SLOWLY PUSH
EAST IN THE PERIOD. A EASTERN PERIPHERY WEAK IMPULSE/JET STREAK IS
IN THE PROCESS OF LIFTING NE OUT OF WY...SUPPORTING SCT-NUMEROUS
SHRA AND TS ACROSS THE FA. JET STREAK WILL LIFT NE THIS
EVENING...WITH FORCING AND ASSOCIATED CONVECTION LIFTING NE. HIRES
ANALYSIS FIELDS INDICATE AOA 1000-1500 J/KG OF CAPE MAINLY IN A
NORTH/SOUTH AXIS ON THE SD PLAINS. AS CONVECTION LIFTS NE INTO
THIS AREA OF HIGHER INSTABILITY...A FEW STRONGER STORMS CAN BE
EXPECTED. BEST CHANCES/COVERAGE OF SHRA/TS WILL BE ACROSS NW SD
WHERE THE BEST LL CONVERGENCE AND LSA WILL OVERLAP. LL SFC TROUGH
WILL SHIFT SE INTO THE FA THIS EVENING...EVENTUALLY STALLING OVER
SCENTRAL SD. MAIN UPPER LOW OVER THE PAC NW IS EXPECTED TO DRIFT
EAST OVERNIGHT...EVENTUALLY SUPPORTING AN INCREASE IN LSA AND
ASSOCIATED DEEP CYCLONIC FLOW...POTENTIALLY SUPPORTING LINGERING
SHRA INTO THE FAR WESTERN FA BY LATE IN THE NIGHT. DRIED MOST
PLACES OUT AFTER MIDNIGHT...WITH A SLIGHT UPTICK TO CHANCE POPS
OVER THE FAR WEST TOWARD DAWN. DEEP CYCLONIC FLOW WILL SPREAD OVER
THE AREA AND SUPPORT INCREASING LSA OVER MOST OF THE REGION
THURSDAY. MORE THAN SUFFICIENT LL MOISTURE IN PLACE/DIURNAL
HEATING/AND ENHANCED CONVERGENCE ALONG A STALLED SFC TROUGH WILL
SUPPORT WIDESPREAD CONNECTIVE SHOWERS OVER THE FA...ESP IN THE BH
WHERE CIN WILL BE NEGLIGIBLE. A FEW STRONGER STORMS WILL BE
POSSIBLE OVER SCENTRAL SD AHEAD OF THE SFC TROUGH WHERE ONGOING
MOISTURE TRANSPORT IN THE WARMER SECTOR WILL SUPPORT ML CAPES OF
AROUND 1500 J/KG BY AFTERNOON. HOWEVER...SHEAR REMAINS QUITE
LIMITED WITH 20-25 KNOTS PROGGED WHERE THE HIGHEST CAPE WILL BE.
THE MAIN CONCERN IS LOCALLY HEAVY RAINFALL OVER THE BH. STEEP LL
LAPSE RATES/HIGH PW/S OVER AN INCH/ENHANCED CONVERGENCE PER EDDY
EFFECTS/AND SLOW STORM MOTION VECTORS WILL BE IN PLACE OVER THE BH
FOR MUCH OF THUR AFTERNOON. WOULD NOT BE SURPRISE TO SEE A
WIDESPREAD HALF INCH OF RAIN ACROSS MUCH OF THE BLACK HILLS WHICH
COULD AGGRAVATE ONGOING FLOODING CONCERNS. A SECONDARY TROUGH WILL
SHIFT SOUTH THUR NIGHT AND SUPPORT AN ENHANCED AREA OF CONVERGENCE
WITH SHRA CHANCES CONTINUING OVERNIGHT. KEPT POPS FAIRLY HIGH
THROUGH THUR NIGHT...WITH A SOUTHWARD SHIFT AS THE MAIN TROUGH
AXIS SHIFTS SOUTH ALONG WITH LSA.

.LONG TERM...FRIDAY THROUGH WEDNESDAY
ISSUED AT 225 PM MDT WED MAY 27 2015

UPPER LEVEL TROF WILL SHIFT EAST OF THE NORTHERN PLAINS ON FRIDAY
AS SURFACE HIGH PRESSURE DROPS SOUTH OUT OF CANADA. LINGERING
SHOWERS ARE EXPECTED ON FRIDAY...SHIFTING SOUTH THROUGHOUT THE DAY
AS DRIER AIR MOVES IN. COOL HIGH PRESSURE WILL KEEP TEMPERATURES
SLIGHTLY BELOW AVERAGE ON SATURDAY...WITH A FEW SHOWERS AND
THUNDERSTORMS POSSIBLE IN THE AFTERNOON AS A WEAK WAVE PASSES
THROUGH. THERMAL RIDGE WILL BUILD INTO THE REGION SUNDAY AND
MONDAY...ALLOWING FOR A WARMUP...WITH SMALL CHANCES OF SHOWERS AND
THUNDERSTORMS. GREATER PRECIPITATION CHANCES RETURN FOR THE MIDDLE
OF NEXT WEEK AS UPPER FLOW BECOMES SOUTHWESTERLY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1124 PM MDT WED MAY 27 2015

-SHRA/-TSRA WILL CONTINUE OVERNIGHT ACROSS NORTHEAST WY/FAR
WESTERN SD WITH LOCAL MVFR CIGS/VSBYS. ACTIVITY WILL EXPAND OVER
THE ENTIRE AREA THURSDAY WITH MVFR CIGS/VSBYS ASSOCIATED WITH THE
HEAVIER PRECIPITATION.

&&

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

$$

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


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