511
FXUS63 KUNR 201120
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
520 AM MDT SAT JUN 20 2026
KEY MESSAGES
- ISOLATED SEVERE STORM THREAT SATURDAY, MAINLY OVER NORTHEAST WY
AND SOUTHWEST SD.
- BENEFICIAL RAINFALL EXPECTED SATURDAY INTO SUNDAY.
- COOLER TEMPERATURES FOR SUNDAY THROUGH TUESDAY, THEN A GRADUAL
WARM UP FOR THE REST OF NEXT WEEK.
UPDATE
ISSUED AT 1014 PM MDT FRI JUN 19 2026
04Z SURFACE ANALYSIS HAD WEAK HIGH OVER THE NORTHERN PLAINS. WATER
VAPOUR LOOP HAD NORTHWEST FLOW ALOFT OVER THE PLAINS, BUT UPSTREAM
CHANGES ON THE WAY PER A PAIR OF SHORTWAVE TROUGHS, ONE OVER THE
NORTHERN CA/OR COAST AND ANOTHER OVER BC. EFFECTS OF THESE WAVES
WILL IMPACT THE CWA THROUGH EARLY NEXT WEEK.
TONIGHT/SATURDAY MORNING, LOW LEVEL FLOW GRADUALLY TURNS SOUTHEAST
COURTESY OF LOW DEVELOPING OVER WY AHEAD OF CA/OR SHORTWAVE. WEAK
THETA-E ADVECTION MIGHT POP SOME SPRINKLES TONIGHT AND SHRA/TS
EAST OF THE BLACK HILLS SATURDAY MORNING, BUT LATEST GUIDANCE HAS
BACKED OFF A TAD. POPS HAVE BEEN ADJUSTED.
AS SHORTWAVE APPROACHES SATURDAY AFTERNOON/EVENING, SURFACE LOW
STRENGTHENS OVER NORTHEASTERN WY WITH BOUNDARY INTO THE NE
PANHANDLE. TONGUE OF 500-1500J/KG MEAN MUCAPE DEVELOPS OVER
NORTHEASTERN WY/SOUTHWESTERN SD WITH SUFFICIENT SHEAR FOR ISOLATED
SEVERE THUNDERSTORMS. LATEST SPC HREF GUIDANCE PORTRAYS BEST
ACTIVITY SOUTH OF CWA IN NE, SO HAVE LEFT ANY MENTION OF SEVERE
OUT OF THE FORECAST DATABASE. CLUSTERS OF SHRA/TS WILL MOVE
ACROSS CWA SATURDAY NIGHT INTO SUNDAY AFTERNOON AND THEN ANOTHER
BATCH MONDAY, WHICH MIGHT BE ACCOMPANIED BY ACTIVE STORMS AS BC
SHORTWAVE EVENTUALLY SLIPS SOUTHEAST INTO THE DAKOTAS. PWATS
DURING THIS PERIOD INCREASE TO 100-150% OF NORMAL PROVIDING FUEL
FOR BENEFICIAL RAINFALL.
FORECAST UPDATED TO ACCOUNT.
DISCUSSION
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 144 PM MDT FRI JUN 19 2026
CURRENT UPPER-AIR ANALYSIS AND WATER VAPOR IMAGERY DEPICT WEAK
TROUGHING OVER THE GREAT LAKES REGION AND SPLIT FLOW OFF THE WEST
COAST. THE SHORTWAVE THAT PRODUCED THUNDERSTORMS OVER PORTIONS OF
THE REGION LAST NIGHT HAS MOVED OFF TO THE EAST, LEAVING PARTLY
CLOUDY SKIES ACROSS WESTERN/CENTRAL SOUTH DAKOTA. SURFACE
OBSERVATIONS SHOW TEMPERATURES MAINLY IN THE 60S TO LOW 70S, WITH
DEW POINTS IN THE UPPER 30S TO LOW 40S ACROSS NORTHEAST WY AND 40S
TO LOW 50S ACROSS WESTERN SD. WINDS ARE GENERALLY NORTHWESTERLY AT
20KTS GUSTING TO 35KTS ACROSS NORTHWEST SD, WHILE WINDS ACROSS
SOUTHWEST SD INTO NORTHEAST WY ARE MORE NORTHERLY/NORTHEASTERLY AT
15KTS GUSTING TO 25KTS.
TODAY WILL BE MOSTLY DRY AS THE SHORTWAVE CONTINUES TO MOVE OFF TO
THE EAST, LEADING TO HIGH TEMPERATURES MAINLY IN THE 70S TO LOW 80S
OVER THE PLAINS AND 60S FOR THE BLACK HILLS. WINDS WILL REMAIN GUSTY
THROUGH THE AFTERNOON BEFORE TRANSITIONING TO A SOUTH/SOUTHEASTERLY
FLOW LATE TONIGHT. ELEVATED FIRE WEATHER CONDITIONS WILL BE PRESENT
TODAY DUE TO THE GUSTY WINDS IN COMBINATION WITH THE LOWER RH
VALUES, ESPECIALLY OVER NORTHEAST WY.
SATURDAY IS EXPECTED TO BE MORE UNSETTLED AS A SHORTWAVE MOVES IN
THE REGION FROM THE SOUTHERN STEAM OF THE SPLIT FLOW. SPC CURRENTLY
HAS NORTHEAST WY, THE BLACK HILLS, AND SOUTHWEST SD IN A MARGINAL
RISK, WITH A SLIGHT RISK IN THE FAR SOUTHERN PORTIONS OF FALL RIVER
AND OGLALA LAKOTA COUNTIES. WITH THE GENERALLY SOUTHERLY FLOW
DEVELOPING TONIGHT, DEW POINTS LOOK TO INCREASE INTO THE LOW 50S
SATURDAY MORNING ACROSS NORTHEAST WY (~40 TO 55% CHANCE, 12Z HREF)
AND SOUTHWEST SD (~75 TO 90% CHANCE, 12Z HREF). MEAN SURFACE-BASED
CAPE VALUES LOOK TO BE ON THE LOW TO MODERATE SIDE AT ~700 TO 900
J/KG (12Z HREF) FOR THE LATE MORNING/EARLY AFTERNOON FOR NORTHEAST
WY. 0-6KM WIND SHEAR IS LEANING TOWARDS MODERATE LEVELS OVER
NORTHEAST WY, WITH THE HREF SHOWING VALUES RANGING BETWEEN 30 TO
45KTS FOR THE EARLY AFTERNOON. STORMS ARE EXPECTED TO FORM OVER
NORTHEAST WY DURING THE EARLY AFTERNOON AND AGAIN LATER IN THE
EVENING; HOWEVER, WITH MARGINAL DEW POINTS AND SHEAR VALUES ON THE
EDGE FOR SUPERCELL DEVELOPMENT, THE LIKELIHOOD FOR SEVERE WEATHER
REMAINS UNCERTAIN FOR MUCH OF THE REGION. THE BETTER CHANCE FOR
SEVERE WEATHER WILL BE FOR EAST-CENTRAL WY INTO THE NE PANHANDLE,
WHERE DEW POINTS WILL BE HIGHER AND SHEAR VALUES WILL BE MORE
CONSISTENT.
SHOWERS AND STORMS WILL LINGER INTO SUNDAY, PROVIDING MUCH-NEEDED
RAINFALL ACROSS THE REGION. QPF VALUES ARE TRENDING TOWARDS AT LEAST
0.50" FOR MOST LOCATIONS, WITH HIGHER AMOUNTS EAST OF THE BLACK
HILLS, WHERE 1.00" TO 1.50" IS NOT OUT OF THE QUESTION. IF GUIDANCE
CONTINUES TO TREND IN THIS DIRECTION, THIS WEEKEND WILL PROVE VERY
BENEFICIAL FOR THE REGION. UNSETTLED WEATHER IS EXPECTED TO CONTINUE
INTO THE WEEK AHEAD, WITH PRECIPITATION CHANCES POSSIBLE ON MOST
DAYS. COOLER TEMPERATURES WILL BE PRESENT TO START OFF THE WEEK,
WILL A GRADUAL WARM UP FOR THE REST OF THE WEEK.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 515 AM MDT SAT JUN 20 2026
EXPECT GRADUALLY DETERIORATING CONDITIONS TODAY AS AN UPPER LEVEL
DISTURBANCE MOVES INTO THE REGION. MOIST SE UPSLOPE FLOW WILL
DEVELOP TODAY WITH STRATUS EXPECTED ON THE WESTERN SD PLAINS, ESP
INVOF THE BLACK HILLS. SHOWERS AND THUNDERSTORMS EXPECTED THIS
AFTERNOON AND EVENING, WITH CONVECTION DEVELOPING OVER WY AND
SPREADING EAST. MORE PERSISTENT SHOWERS ARE EXPECTED TONIGHT INTO
SUNDAY, ESP ACROSS NW SD. EXPECT WIDESPREAD STRATUS LATER TONIGHT
WITH IFR TO LOCAL LIFR CONDS.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
UPDATE...HELGESON
DISCUSSION...SCHULTZ
AVIATION...JC
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