Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 041736
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1136 AM MDT SAT JUL 4 2015

.UPDATE...
ISSUED AT 1057 AM MDT SAT JUL 4 2015

UPDATED FORECAST TO ACCOUNT FOR ISOLATED CONVECTION THAT COULD
DRIFT INTO NORTHEASTERN WYOMING LATER THIS AFTERNOON FROM THE
BIGHORNS AND HIGHER TERRAIN OF WYOMING. SOME OF THE HIGH
RESOLUTION MODELS HAVE BACKED OFF ON FIRING STORMS IN THE BLACK
HILLS THIS AFTERNOON...BUT FORECAST SOUNDINGS ERODE NEARLY ALL OF
THE CIN BY LATE AFTERNOON. FOR THIS REASON...WILL STILL KEEP
ISOLATED CHANCES FOR STORMS IN THE BLACK HILLS THIS AFTERNOON.
OTHERWISE...SCATTERED CONVECTION SHOULD FIRE OFF ALONG THE SURFACE
TROUGH IN CENTRAL SOUTH DAKOTA AFTER 21Z TODAY. GIVEN CAPE AND
SHEAR PARAMETERS...SOME OF THE STORMS COULD BE SEVERE.

&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 224 AM MDT SAT JUL 4 2015

08Z SURFACE ANALYSIS HAD LOW PRESSURE OVER NORTHERN MB WITH COLD
FRONT INTO NORTHWEST MT...LOW ALONG FRONT IN NORTH CENTRAL
MT...AND TROUGH INTO CENTRAL WY. MODEST LOW LEVEL JET IN PLACE PER
KUDX VWP AND MODEL DEPICTIONS. WEAK THETA-E ADVECTION SUPPORTING
ISOLATED -SHRA/TS ACROSS CENTRAL PORTIONS OF CWA EARLY THIS
MORNING. THIS ACTIVITY WILL SLOWLY SHIFT EAST THIS MORNING AS LOW
LEVEL JET SHIFTS EAST. MEANWHILE...WEAK SHORTWAVE OVER THE CENTRAL
DAKOTAS SHIFTS SOUTHEAST AND ANOTHER SUGGESTED ON WATER VAPOUR
OVER MT DROPS SOUTHEAST. FEATURE WILL SUPPORT MOVEMENT OF
AFOREMENTIONED SURFACE TROUGH INTO SOUTHERN SD TODAY. AROUND
2KJ/KG MLCAPE POOLS ALONG SURFACE TROUGH WITH 15-20M/S 0-6KM BULK
SHEAR THIS AFTERNOON. IT ISN/T CLEAR WHERE UPPER SUPPORT/NON-
SUPPORT WILL COME FROM...PERHAPS MT SHORTWAVE...OR PERHAPS
SHORTWAVE RIDGE BEHIND CENTRAL DAKOTAS SHORTWAVE WILL PROMOTE
SUBSIDENCE. IF CONVECTION CAN INITIATE ALONG SURFACE
TROUGH...SEVERE STORMS POSSIBLE GIVEN INSTABILITY/SHEAR. ANY
SUPERCELL WILL MOVE VERY SLOWLY WITH LOCALIZED FLASH FLOOD THREAT.
GIVEN DEGREE OF UNCERTAINTY...WILL LET DAY SHIFT ASSESS NEED FOR
ANY HEADLINES. TEMPERATURES WILL BE QUITE WARM TODAY AND NEAR
GUIDANCE.

TONIGHT...ANY DIURNALLY DRIVEN ACTIVITY WILL MOVE EAST AS TROUGH
MOVES EAST. COLD FRONT DROPS INTO FAR NORTHWEST REACHES OF CWA
TOWARD MORNING WITH SHRA/TSRA CHANCES ALONG IT. LOW LEVEL JET/THETA-
E ADVECTION EAST OF CWA. TEMPERATURES NEAR GUIDANCE.

SUNDAY...COLD FRONT SINKS SLOWLY SOUTHEAST AS IT BECOMES PARALLEL TO
UPPER FLOW AND SLOWS DOWN. UPPER TROUGH/SHORTWAVE TAIL DROPS FROM
SOUTH CENTRAL CANADA INTO MT/ND/SD. RATHER STRONG INSTABILITY FROM 2-
4KJ/KG MLCAPE DEVELOPS AND OF COLD FRONT WITH MARGINAL 0-6KM BULK
SHEAR FOR SEVERE THUNDERSTORMS...EXCEPT JUST ALONG/BEHIND COLD
FRONT. GIVEN DEGREE OF INSTABILITY...SEVERE STORMS POSSIBLE.
ACTIVITY WILL CONGEAL INTO A BLOB OF SHRA/TSRA LATE IN THE
DAY/EVENING HOURS AND SCOOT EAST. HIGH POPS WARRANTED
ALONG/SOUTHEAST OF COLD FRONT. TEMPERATURES WILL BE TRICKY GIVEN
CLOUDS/COLD AIR ADVECTION BEHIND FRONT.

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 224 AM MDT SAT JUL 4 2015

THE NRN PLAINS SYSTEM WILL EXIT THE CWA BY MON MRNG...WITH DRIER
WEATHER EXPECTED INTO AT LEAST EARLY TUESDAY. FLOW ALOFT WILL
BECOME MORE ZONAL BY MIDWEEK...WITH INCREASING CHANCES FOR SHOWERS
AND STORMS LATER TUESDAY THROUGH WEDNESDAY. BEYOND THAT...A TROF
IS FORECAST TO DEVELOP ALONG THE WEST COAST LATE IN THE
WEEK...WITH FLOW ALOFT OVER THE NRN PLAINS EVENTUALLY BECOMING
SOUTHWESTERLY. WILL KEEP LOWER CHANCES FOR SHOWERS AND
THUNDERSTORMS IN THE FORECAST FOR LATE NEXT WEEK.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z SUNDAY
ISSUED AT 1136 AM MDT SAT JUL 4 2015

ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED TO
DEVELOP THIS AFTERNOON INTO TONIGHT...MOSTLY TO THE EAST OF THE
BLACK HILLS. A FEW OF THE STORMS COULD BE STRONG TO SEVERE...
ESPECIALLY TOWARD CENTRAL SD...WITH LARGE HAIL AND STRONG WIND GUSTS
POSSIBLE. LOCAL AND BRIEF MVFR CONDITIONS ARE POSSIBLE WITH ANY
HEAVIER STORMS.

&&

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

$$

UPDATE...MCKEMY
SHORT TERM...HELGESON
LONG TERM...13
AVIATION...26



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