320
FXUS63 KUNR 020528
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1128 PM MDT FRI AUG 1 2025
KEY MESSAGES
- A MORE CONCENTRATED AREA OF THUNDERSTORMS WITH HEAVY RAIN AND
POTENTIAL FOR EXCESSIVE RAINFALL IS EXPECTED TO DEVELOP THIS
AFTERNOON INTO TONIGHT FROM NORTHWEST INTO CENTRAL SD. WE HAVE
ISSUED A FLOOD WATCH FOR FLASH FLOODING TO COVER THIS RISK.
- A SLIGHT RISK (LEVEL 2 OF 5) OF SEVERE STORMS CONTINUES FOR
MUCH OF THE SOUTH DAKOTA PORTION OF THE UNR AREA FOR TODAY INTO
TONIGHT, THOUGH THIS IS CONDITIONAL ON INITIATING CONVECTION
NEAR PEAK HEATING.
- OCCASIONAL BOUTS OF WILDFIRE SMOKE WILL CONTINUE TO BE POSSIBLE
FROM EITHER ROCKIES OR CANADIAN WILDFIRES.
- WARMER AND LESS ACTIVE (THOUGH NOT DRY) NEXT WEEK.
DISCUSSION
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 139 PM MDT FRI AUG 1 2025
A STATIONARY FRONT CONTINUES TO BE PARKED ON THE EASTERN SLOPES OF
THE ROCKIES, WITH A BROAD AND MOIST SOUTHEASTERLY LOW-LEVEL FLOW
CONTINUING ACROSS THE WESTERN PLAINS THAT EXTENDS WELL INTO CANADA.
ALOFT, THE MOST OBVIOUS FEATURE OUT THERE ON SATELLITE IS A WELL
DEFINED MCV OVER NORTHWEST SD. THIS MCV WILL DRIFT EAST AND BE A
FOCUS FOR CONVECTIVE ACTIVITY THIS AFTERNOON INTO TONIGHT. FROM THE
12Z HREF, THERE'S GROWING CONCERN THAT ACTIVITY THIS MCV INITIATES
WILL BE SLOW MOVING, WITH SOME TRAINING AS WELL. LPMM QPF FROM THE
HREF SHOWS A FAIRLY LARGE FOOTPRINT OF 3 TO 7 INCHES (PLUS) OF QPF
FROM NORTHEAST PERKINS, ACROSS NORTHERN ZIEBACH TO THE STANLEY/DEWEY
COUNTY LINE IN ABRS AREA. THIS MCV WILL BE FED BY ABOUT 30 KT SSE
WINDS AT H85, PWATS NEAR 1.6" AND IT WILL BE ON THE MUCAPE GRADIENT
WITH 1K-2K J/KG OF MUCAPE JUST TO THE SOUTHWEST OF THE MCV. SO FROM
THE SYNOPTIC SCALE, ALL THE INGREDIENTS ARE IN PLACE FOR A HEAVY
RAIN EVENT, IT'S JUST A QUESTION OF WHERE DO THE MESOSCALE FEATURES
SETUP. WITH ALL OF THIS IN MIND, WE DID COLLABORATE WITH ABR TO
ISSUED A FLASH FLOOD WATCH FOR FLASH FLOODING ACROSS NORTHWEST INTO
CENTRAL SD.
AS FOR THE SEVERE THREAT, THE 18Z UNR SOUNDING IS A BIT WORRISOME,
WITH STRONG CAPPING CENTERED AT ABOUT 725 HPA. SO WE'RE GOING TO
NEED FORCING OF SOME VARIETY TO GET THINGS GOING. WHERE IS THAT
FORCING COMING FROM OUTSIDE OF THE MCV? THAT'S LOOKING A BIT
NEBULOUS. WITH THE SOUTHEAST WINDS, WE DO HAVE THE CONVERGENCE ZONE
ON THE NORTH SIDE OF THE HILLS. WE STILL SEE THIS WITH THE
HRRR/HREF, THOUGH INITIATION OF THIS TERRAIN INDUCED ACTIVITY HAS
BEEN PUSHED CLOSER TO 00Z. OTHERWISE, YOU HAVE TO GO THE MOUNTAINS
OF CO/WY TO SEE A WEAK SHORTWAVE ON WATER VAPOR. EVENTUALLY, THIS
SHOULD INITIATE STORMS OVER SOUTHEAST WY. THE GREATEST SEVERE
PROBABILITIES WITH THIS WILL BE CLOSER TO WHEN IT INITIATES
SOUTHWEST OF THE UNR AREA, WITH THIS ACTIVITY NOT MOVING INTO
WESTERN PORTIONS OF THE UNR AREA UNTIL TONIGHT, WITH THOSE
CONVECTIVE REMNANTS PUSHING ACROSS WESTERN SD THROUGH TONIGHT. I
GUESS WHAT WE'RE GETTING AT IS THAT TODAY'S SEVERE RISK IS VERY MUCH
CONDITIONAL ON ACTUALLY SEEING STORMS DURING PEAK HEATING, WITH ANY
ACTIVITY OVERNIGHT THAT COMES OFF THE HIGHER TERRAIN TO THE WEST
UNLIKELY TO BE SEVERE.
FOR SATURDAY, THE MCV WILL BE FARTHER EAST, WITH MORE SUN RESULTING
IN WARMER TEMPERATURES FOR SATURDAY, THOUGH SOUTHEASTERLY WINDS WILL
KEEP A RISK OF ISOLATED TO SCATTERED DIURNAL ACTIVITY GOING,
ESPECIALLY IN/NEAR THE BLACK HILLS. FOR SATURDAY NIGHT, IT LOOKS
LIKE WE SEE SCRAPS COMING OFF THE HIGH TERRAIN TO THE WEST ONCE
AGAIN, BUT HAZARDS WITH THIS ACTIVITY LOOKS LOW.
THIS THEME OF DIURNAL ACTIVITY LOOKS TO CONTINUE INTO NEXT WEEK,
THOUGH WITH SOME CHANGES. FIRST, THE EPS SHOWS THE JET DRIFTING
NORTH THROUGH THE WEEK, EVENTUALLY ENDING UP OVER MT/ND. THIS WILL
ALLOW HEAT TO SLOWLY BUILD, WITH THE PRIMARY ZONE OF CONVECTIVE
ACTIVITY SHIFTING NORTH AND EAST AS WELL. THOUGH SUNDAY LOOKS TO
PROVIDE FAIRLY WIDESPREAD DIURNAL ACTIVITY BEFORE THIS PRIMARY STORM
TRACK SHIFTS AWAY FROM THE UNR AREA. AS FOR THE HEAT, THE WOST OF IT
WILL REMAIN SOUTH OF THE AREA, BUT 90S WILL AT LEAST START TO SHOW
UP ON WEATHER MAPS ACROSS WESTERN SOUTH DAKOTA AGAIN NEXT WEEK.
THOUGH LOOKING DRIER, IT WON'T BE COMPLETELY DEVOID OF PRECIP NEXT
WEEK, IT'S JUST DRY DAYS WILL FINALLY START TO OUTNUMBER WET DAYS
WITH A RATHER TYPICAL AUGUST WEATHER PATTERN LOOKING TO SET IN.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1121 PM MDT FRI AUG 1 2025
STORMS WILL CONTINUE TO PUSH EASTWARD ACROSS WESTERN SOUTH DAKOTA
LATE TONIGHT INTO EARLY FRIDAY MORNING, WITH LOCAL MVFR/IFR
CONDITIONS. VFR CONDITIONS ARE THEN EXPECTED FOR MUCH OF SATURDAY.
THE NEXT CHANCE FOR STORMS WILL BE SATURDAY EVENING.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION/KEY MESSAGES...MPG
AVIATION...13
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