373
FXUS63 KUNR 300444
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1044 PM MDT FRI MAY 29 2026
KEY MESSAGES
- STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED SATURDAY AFTERNOON
AND EVENING WITH PRIMARY HAZARDS OF LARGE HAIL QUARTER TO GOLF
BALL SIZE, DAMAGING WINDS IN EXCESS OF 60 MPH, AND HEAVY
RAINFALL.
- UNSETTLED CONDITIONS WITH DAILY CHANCES OF SHOWERS AND
THUNDERSTORMS CONTINUE INTO THE MIDDLE OF NEXT WEEK.
DISCUSSION
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 254 PM MDT FRI MAY 29 2026
HARD TO RULE OUT AN ISOLATED THUNDERSTORM FIRING THIS
AFTERNOON/EVENING OVER THE BLACK HILLS REGION OR ACROSS CAMPBELL
COUNTY WYOMING, BUT OTHERWISE ONE MORE WARM AND BREEZY DAY IS IN
STORE FOR NORTHEASTERN WYOMING AND WESTERN SOUTH DAKOTA. SOME
SCATTERED ELEVATED SHOWER ACTIVITY WITH EMBEDDED THUNDER IS ALSO
POSSIBLE TONIGHT INTO SATURDAY MORNING, ESPECIALLY ACROSS OUR SOUTH
DAKOTA PLAINS.
THE MAIN SHOW REMAINS SATURDAY, WITH SPC MAINTAINING A SLIGHT RISK
OF SEVERE THUNDERSTORMS ACROSS OUR CENTRAL AND SOUTHERN SOUTH DAKOTA
PLAINS, AND A MARGINAL RISK FOR JUST ABOUT THE REST OF THE CWA.
SIGNALS ARE "MIXED" WITH REGARD TO THE SEVERE WEATHER
POTENTIAL...NOT A SLAM-DUNK OR HIGH-END SETUP BY ANY MEANS, YET
STILL POTENTIAL HAZARDS TO DISCUSS. LIFT WON'T BE AN ISSUE...STORMS
ARE EXPECTED TO FIRE OFF THE NORTHERN ARC OF A DRYLINE INTO THE
NEBRASKA PANHANDLE, AND AHEAD OF AN APPROACHING NEGATIVELY-TILTED
TROUGH LIFTING ACROSS WYOMING. MOISTURE ALSO WON'T BE A
PROBLEM...SURFACE MOISTURE ADVECTION IS UNDERWAY TODAY WITH DEW
POINTS ALREADY EXCEEDING 50 DEGF IN OUR SOUTHEAST COUNTIES, AND A
STRONG SOUTH-SOUTHEAST FLOW THROUGHOUT OUR ATMOSPHERIC COLUMN WILL
CONTINUE TO STREAM MOISTURE NORTHWARD TONIGHT AND SATURDAY. SURFACE
AND NEAR-SURFACE WINDS BACKED TO SOUTHEASTERLY SATURDAY WILL ASSIST
IN TRANSPORTING THIS MOISTURE WESTWARD AND POOLING IT UP AGAINST THE
BLACK HILLS CORRIDOR, AS WELL AS ENHANCE STORM-RELATIVE INFLOW. TDS
WILL REMAIN LOWER WEST OF THE BLACK HILLS ACROSS NORTHEASTERN
WYOMING, YET STILL SUFFICIENT TO SUPPORT CONVECTION WITH THE
STRONGEST SYNOPTIC FORCING APPROACHING FROM THE WEST. INSTABILITY
(THE PROCLIVITY OF AIR PARCELS TO WANT TO RISE, AKA FUEL FOR STORMS)
WON'T REALLY BE A PROBLEM EITHER...RAP AND NAMNEST FORECAST SOUNDING
SUPPORT 1,500 TO 2,500 J/KG SBCAPE WITH STEEP LOW-LEVEL LAPSE RATES,
AND EVEN THE BLENDED HREF MEAN REACHES AT LEAST 1,000 TO 1,500 J/KG,
WITH THE GREATEST INSTABILITY FOCUSED FROM THE BLACK HILLS EASTWARD
ACROSS THE SOUTH DAKOTA PLAINS GIVEN THE INFLUX OF MOISTURE IN THIS
REGION. HOWEVER, WHAT WILL BE LACKING IN THIS SETUP IS WIND SHEAR.
NO MODEL GUIDANCE IS BROADLY REACHING 30KTS OF DEEP LAYER SHEAR OR
EBWD, AND 0-1KM AND 0-3KM SHEAR AND STORM RELATIVE HELICITY VALUES
STAY FAIRLY LOW DESPITE SFC WINDS BACKED INTO THE SOUTHEAST ACROSS
THE SOUTH DAKOTA PLAINS. THIS KEEPS OUR REGION SOLIDLY IN A MULTI-
CELL TO CLUSTER REGIME AS STORMS INITIATE...LOCAL ENHANCEMENTS TO
DIRECTIONAL AND/OR SPEED SHEAR WILL BE NEEDED TO NUDGE A CELL TO
TRANSIENT SUPERCELL STATUS. OVERALL, THE LACK OF SHEAR WILL DO VERY
LITTLE TO ASSIST IN STORM ORGANIZATION/LONGEVITY OR PROVIDE GOOD
UPDRAFT/DOWNDRAFT SEPARATION (YET FORCING LOOKS GOOD TO SUSTAIN
CONVECTION), SUGGESTING OUR SEVERE WEATHER RISK MAY BE MORE "PULSY"
AND EPISODIC IN NATURE THROUGHOUT THE EVENT.
LOOKING AT SOME MORE PARAMETERS BY HAZARD...BRIEF TORNADO RISK SEEMS
LOW GIVEN A LACK OF A DOMINANT SUPERCELL STORM MODE AND WEAK LOW-
LEVEL SHEAR AND HELICITY, BUT NOT NECESSARILY ZERO, ESPECIALLY IF
ANY STORM MERGERS OR "NUDGERS" OCCUR OR TERRAIN OR STORM OUTFLOWS
CAN LOCALLY ENHANCE SHEAR. DESPITE NOT HITTING OUR IDEAL TARGET FOR
EBWD AND LOW SHIP VALUES, DECENT CAPE IN THE HAIL GROWTH ZONE PER
MODEL FORECAST SOUNDINGS AND 700-500MB LAPSE RATES OF 7.0-8.0
DEGC/KM MAY ALLOW STRONGER CELLS TO PULSE AND PRODUCE A FEW
INSTANCES OF QUARTER TO GOLF BALL SIZE HAIL, AND WE CONTINUE TO SEE
SEVERE HAIL ANALOGS IN THIS RANGE APPEARING ON THE FORECAST
SOUNDINGS TODAY. ENVIRONMENTAL PARAMETERS AREN'T PERFECT FOR
DAMAGING WINDS EITHER, BUT PWATS AND DCAPE MAY BE MARGINALLY HIGH
ENOUGH TO SUPPORT SOME WET MICROBURSTS (GUSTS 50-70 MPH), AND THE
HREF ENSEMBLE MAX WIND GUST DOES SUPPORT THIS WITH A FEW STORMS.
FINALLY, PWATS EXCEEDING 1.00 INCH (ESPECIALLY EAST OF THE BLACK
HILLS) NOT ONLY EXCEED THE 90TH PERCENTILE BUT APPROACH
CLIMATOLOGICAL MAXIMUMS FOR LATE MAY PER SPC SOUNDING CLIMATOLOGY,
SO VERY HEAVY RAINFALL IS EXPECTED. OVERALL STORMS SHOULD BE MOVING
PROGRESSIVELY REDUCING THE FLOOD RISK, BUT INITIAL CELLS FROM THE
BLACK HILLS WESTWARD MAY BE SLOWER AND MAY CLUSTER, AND WE'LL ALSO
HAVE TO WATCH FOR ANY SPOTS THAT EXPERIENCE MULTIPLE STORM HITS OR
CELL TRAINING FOR A LOCALIZED RISK OF FLASH FLOODING.
GIVEN ALL OF THE ABOVE AND THEMES NOTED IN THE CAMS, GENERAL
EXPECTATION IS FOR INITIAL STORMS TO FIRE ACROSS NORTHEASTERN
WYOMING AND THE BLACK HILLS BETWEEN NOON AND 2 PM WITH ADDITIONAL
CELLS INBOUND FROM THE NEBRASKA PANHANDLE AROUND THIS TIME OR
SHORTLY THEREAFTER AS WELL, PERHAPS POSING INITIAL PRIMARY RISKS OF
LARGE HAIL AND VERY HEAVY RAIN, BEFORE EVERYTHING BEGINS TO MERGE
AND GROW UPSCALE INTO A BOW/LINE OF CONVECTION AS IT CROSSES THE
BLACK HILLS AND TRACKS NORTHEAST ACROSS OUR SOUTH DAKOTA PLAINS OVER
THE AFTERNOON AND EVENING WITH SLIGHTLY LESS HAIL THREAT BUT MORE OF
A DAMAGING WIND THREAT, PERHAPS NOT CLEARING OUR EASTERN COUNTIES
UNTIL MIDNIGHT OR SO. THIS LINE IS ALSO EXPECTED TO LAY DOWN 0.40 TO
0.90 INCHES OF RAINFALL AS IT TRACKS NORTHEAST, WITH LOCALLY HIGHER
AMOUNTS.
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS IS EXPECTED SUNDAY
AFTERNOON AND EVENING WITH A MARGINAL RISK OF SEVERE THUNDERSTORMS
ACROSS PORTIONS OF OUR SOUTH DAKOTA PLAINS, BUT OVERALL COVERAGE AND
INTENSITY WILL LIKELY BE LESS COMPARED TO SATURDAY. ENOUGH
INSTABILITY MAY STILL BE AVAILABLE TO SUPPORT MARGINALLY-SEVERE HAIL
OR GUSTY WINDS IF A FEW ROBUST CELLS CAN DEVELOP. UNSETTLED WEATHER
STILL LOOKS TO CONTINUE WELL INTO THE MIDDLE OF NEXT WEEK WITH DAILY
CHANCES OF SHOWERS/STORMS, AND TEMPERATURES REMAINING IN THE 70S AND
80S.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1040 PM MDT FRI MAY 29 2026
ISOLATED SHOWERS AND THUNDERSTORMS ARE STILL POPPING UP AROUND NE
WY AND SW SD. THESE STORMS ARE WEAKENING, AND WILL CONTINUE TO
WEAKEN, AS WE GO INTO THE OVERNIGHT HOURS. GUSTY WINDS WILL ALSO
FADE OUT.
FOR TOMORROW, SHOWERS AND THUNDERSTORMS (SOME STRONG TO SEVERE
AND CAPABLE OF STRONG, ERRATIC WINDS AND HAIL) WILL DEVELOP ACROSS
NORTHEASTERN WY AFTER AROUND 20 TO 22Z TOMORROW AND MOVE INTO
WESTERN SD LATE IN THE TAF PERIOD.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...KSMITH
AVIATION...GS
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