367
FXUS63 KUNR 062307
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
507 PM MDT TUE JUN 6 2023
DISCUSSION
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 214 PM MDT TUE JUN 6 2023
LITTLE CHANGE IN THE FORECAST OVER THE PAST 12-24 HOURS. CONDITIONS
THROUGH TOMORROW WILL DEVIATE ONLY MODESTLY FROM PERSISTENCE.
INCREASING COVERAGE OF THUNDERSTORMS AND A PERIOD OF NEAR TO
SLIGHTLY BELOW AVERAGE TEMPERATURES CONTINUE TO LOOK LIKELY LATE
THIS WEEK INTO EARLY IN THE WEEKEND. GIVEN WEAK FLOW/SHEAR AND
INCREASING PWATS, LOCALLY HEAVY RAINFALL CANNOT BE RULED OUT DURING
THIS TIME. MORE ACTIVE PATTERN POSSIBLE EARLY NEXT WEEK, BUT
CONFIDENCE IS LOW IN TIMING OF ANY MIDLEVEL/UPPER-LEVEL FLOW
TRANSITION GIVEN PSEUDO-BLOCKING PATTERN OVER MUCH OF THE CONUS.
WATER VAPOR IMAGERY THIS AFTERNOON SHOWS UPPER RIDGING IN PLACE OVER
THE NORTH CENTRAL CONUS, WITH AN UPPER HIGH CENTERED NEAR THE CN/US
BORDER TO OUR EAST. COMPARED TO YESTERDAY, COVERAGE OF CU IS LIMITED
AT THIS HOUR, WITH SHALLOW CU (PER VIS/IR/CLOUD PHASE DISTINCTION
RGB) LIMITED TO THE NORTHERN BLACK HILLS AND FROM THE SANDHILLS
NORTHWARD THROUGH CENTRAL SD. MORE ROBUST CU AND SOME THUNDERSTORMS
ARE EVIDENT OVER THE BIGHORNS. LIKE YESTERDAY, SURFACE FEATURES OVER
THE REGION REMAIN RELATIVELY ILL-DEFINED, THOUGH A SURFACE TROF WAS
RECENTLY ANALYZED FROM EASTERN MT SOUTHWARD INTO THE LEE OF THE
BIGHORNS. GENERALLY LOWER PRESSURES TO THE WEST AND HIGHER PRESSURES
TO THE EAST CONTINUE TO SUPPORT LARGELY SOUTHERLY/SOUTHEASTERLY FLOW
AWAY FROM THE BLACK HILLS, WITH TERRAIN-DRIVEN FLOW CLOSER TO THE
HILLS. ABOVE AVERAGE TEMPERATURES CONTINUE, WITH EARLY AFTERNOON
TEMPERATURES IN THE 70S TO 80S AREA-WIDE.
CONVECTIVE COVERAGE MAY INCREASE OVER CAMPBELL COUNTY LATER THIS
AFTERNOON IF OUTFLOW CAN EMERGE FROM ONGOING STORMS OVER THE
BIGHORNS OR IF MOISTURE CONVERGENCE CAN INCREASE IN THE VICINITY OF
THE AFOREMENTIONED WEAK TROF. FOR NOW, THIS DOES NOT LOOK PROBABLE.
EITHER WAY, THE ENVIRONMENT CONTINUES TO LOOK UNSUPPORTIVE OF
CONVECTIVE ORGANIZATION, WITH MLCAPE < 500 J/KG AND PALTRY DEEP-
LAYER SHEAR. ANY SHOWER/STORM ACTIVITY SHOULD DIMINISH AFTER SUNSET.
OVER THE NEXT FEW DAYS, MIDLEVEL RIDGING OVER THE CENTRAL CONUS WILL
BECOME INCREASINGLY SQUEEZED BY A SLOWLY PROGRESSING TROF OVER THE
SOUTHWESTERN CONUS AND A BROADENING LONGWAVE TROF OVER THE EASTERN
CONUS. IN TIME, THE RIDGE IS PROJECTED TO BECOME RATHER ELONGATED AS
IT SHIFTS SLIGHTLY WESTWARD, EXTENDING FROM THE SOUTHERN PLAINS
NORTHWESTWARD THROUGH AB/SK. AS A SHORTWAVE APPROACHES IN THE
BROADER CYCLONIC FLOW TO OUR EAST, PWATS WILL GRADUALLY INCREASE
THROUGH FRIDAY, CLIMBING TO 150-175% OF NORMAL IN SPOTS. MEANWHILE,
INCREASING DEFORMATION/FGEN AND MOISTURE CONVERGENCE ALONG THE
EASTERN PERIPHERY OF THE RIDGE SHOULD LEAD TO A NW-SE ORIENTED ZONE
OF FAVORABLE ASCENT ACROSS THE AREA. IN SHORT, EXPECTING AN INCREASE
IN COVERAGE OF SHOWERS/STORMS IN THE FRIDAY TO SATURDAY TIME FRAME.
WEAK FLOW ALOFT WILL PROMOTE SLOW-MOVING STORMS, POTENTIALLY LEADING
TO LOCALLY HEAVY RAINFALL. HOWEVER, SOILS SHOULD BE CAPABLE OF
ABSORBING ANY MOISTURE THAT FALLS. A BACKDOOR COLD FRONT ASSOCIATED
WITH THE AFOREMENTIONED SHORTWAVE SHOULD BRING SLIGHTLY COOLER TEMPS
FOR THE WEEKEND--LIKELY NEAR OR SLIGHTLY BELOW AVERAGE. BEYOND
SUNDAY, FORECAST CONFIDENCE DECREASES OWING TO DIVERGING MODEL
GUIDANCE.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 506 PM MDT TUE JUN 6 2023
VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD. THE ONLY EXCEPTION
WILL BE WITH ISOLATED THUNDERSTORMS EARLY THIS EVENING OVER
NORTHEAST WY, PRIMARILY WEST OF THE KGCC TERMINAL.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION...SHERBURN
AVIATION...JC
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