Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 221530
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
930 AM MDT TUE JUL 22 2014

.UPDATE...
ISSUED AT 929 AM MDT TUE JUL 22 2014

UPDATED FORECAST TO REMOVE POPS FROM THE REST OF THE MORNING PERIOD.
OTHERWISE THE FORECAST REMAINS ON TRACK.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
ISSUED AT 218 AM MDT TUE JUL 22 2014

08Z SURFACE ANALYSIS HAD COOL FRONT FROM CENTRAL MT INTO CENTRAL
WY AND THEN EAST THROUGH NORTHERN NE. WATER VAPOUR SHOWED UPPER
RIDGE OVER THE FOUR CORNERS AREA WITH HEIGHTS STARTING TO RISE
OVER THE CWA AND SEVERAL WEAK WAVES ROTATING AROUND IT FROM WY
INTO THE DAKOTAS. ONE WAVE KICKED OFF A SMALL CLUSTER OF TSRA
MOVING INTO CENTRAL SD AND ANOTHER OVER CENTRAL WY...HEADING
NORTHEAST. WILL MAKE LAST MINUTE CHANGES TO PACKAGE TO ACCOUNT FOR
THESE WIGGLES.

TODAY/EARLY THIS EVENING...SURFACE RIDGE BUILDS BACK INTO WY/MT AS
SURFACE HIGH SLIDES EAST OF THE CWA INTO THE UPPER MIDWEST. RETURN
FLOW ON BACK SIDE OF HIGH WILL MORPH WESTERN END OF COOL FRONT INTO
LEE TROUGH AS IT MOVES NORTHEAST TODAY TO SIT FROM CENTRAL MT INTO
THE NE PANHANDLE. UPSLOPE FLOW POOLS MOISTURE ALONG BOUNDARY
RESULTING IN 1-2KJ/KG MLCAPE AND WEAKENING MLCIN...ESPECIALLY OVER
THE HIGHER TERRAIN...BY MID-AFTERNOON. 0-6KM SHEAR INCREASES TO
20-30M/S AS 40KT MID-LEVEL NORTHWESTERLY WINDS COMBINE WITH 10KT
EAST/SOUTHEAST BOUNDARY LAYER FLOW. MAIN QUESTION IS WHETHER LOW
LEVEL CONVERGENCE/TERRAIN INFLUENCE CAN OVERCOME LACK OF A CLEAR
SHORTWAVE AND BUILDING HEIGHTS. SUSPECT WE/LL SEE A COUPLE OF
SUPERCELLS TIED TO TERRAIN/LOW LEVEL CONVERGENCE FEATURES BY LATE
AFTERNOON...BUT THEN QUICKLY DYING AROUND SUNSET. LOCAL WRF SEEMS TO
SUPPORT THIS SCENARIO. LARGE HAIL WILL BE THE MAIN THREAT...BUT AS
STORMS COLLAPSE DAMAGING WINDS POSSIBLE. TEMPERATURES WILL BE 5-15F
COOLER THAN YESTERDAY GIVEN LOWER TROPOSPHERIC FORECAST SOUNDINGS.

OVERNIGHT...UPPER LEVEL RIDGE CONTINUES TO BUILD OVER CWA WITH
MAINLY DRY WEATHER EXPECTED. LOWS NEAR GUIDANCE.

WEDNESDAY...UPPER/THERMAL RIDGE OVER THE NORTHERN PLAINS WITH
SHORTWAVE MOVING FROM NV INTO MT/WY CREATING LOW PRESSURE ALONG LEE
TROUGH IN CENTRAL WY/MT. NARROW RIBBON OF 2-3KJ/KG MLCAPE DEVELOPS
FROM SOUTHEAST MT INTO THE NE PANHANDLE...INTERSECTING THE BLACK
HILLS. LOW LEVEL SOUTHEASTERLY FLOWS PICK UP NOTICEABLY WITH
15-25M/S 0-6KM BULK SHEAR. SHORTWAVE SHOULD MOVE INTO CWA DURING
PEAK HEATING AND CREATE ISOLATED SEVERE TSRA. INTERESTING FEATURE
WITH THIS SETUP IS PERSISTENT MOISTURE CONVERGENCE ALONG EASTERLY
SLOPES OF BLACK HILLS AND SUPERCELL FORECAST MOVEMENT LESS THAN
10KTS OVER TERRAIN/ADJACENT PLAINS. PRECIPITABLE WATERS SURPASS 150
PERCENT OF NORMAL. POSSIBLE FLASH FLOOD EVENT SETTING UP...BUT WILL
HOLD OFF ON ANY HEADLINES UNTIL TIMING OF FEATURES BECOMES CLEARER.
TEMPERATURES WILL WARM UP SOME...AND COULD BE QUITE WARM WEDNESDAY
NIGHT GIVEN 30-40KT LOW LEVEL JET.

&&

.LONG TERM...THURSDAY THROUGH MONDAY
ISSUED AT 218 AM MDT TUE JUL 22 2014

UPPER-LEVEL RIDGE WILL REMAIN OVER THE ROCKIES AND HIGH PLAINS
DURING THE MIDDLE AND LATTER PART OF THE WEEK...WITH VERY WARM
CONDITIONS PERSISTING. A STRONG UPPER TROF WILL SLIDE ACROSS
SOUTHERN CANADA...WITH WEAKER ENERGY CROSSING THE NORTHERN PLAINS
ON THURSDAY. THIS WILL BRING A CHANCE OF THUNDERSTORMS TO THE
AREA. AS THE UPPER TROF SLIDES EAST...THE UPPER RIDGE WILL
RETROGRADE WEST...BRINGING PREDOMINANTLY NORTHWEST UPPER FLOW TO
THE NORTHERN PLAINS. THIS WILL RESULT IN COOLER TEMPERATURES FOR
THE REST OF THE EXTENDED PERIOD...ALONG WITH MAINLY DRY
CONDITIONS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 523 AM MDT TUE JUL 22 2014

MOSTLY VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD.
ISOLATED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE ACROSS THE
AREA THROUGH LATE TONIGHT. SOME THUNDERSTORMS MAY BE SEVERE LATE
THIS AFTERNOON AND INTO THIS EVENING.


&&

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

$$

UPDATE...10
SHORT TERM...HELGESON
LONG TERM...15
AVIATION...15






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