743
FXUS63 KUNR 271137
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
537 AM MDT SUN SEP 27 2026
KEY MESSAGES
-ANOTHER LOBE OF TROPICAL MOISTURE EXPECTED SUNDAY INTO MONDAY,
SUPPORTING MORE CHANCES FOR RAIN
-COOL SUNDAY, ESPECIALLY ON THE SD PLAINS
-SEASONAL AND DRY AFTER MONDAY
UPDATE
ISSUED AT 1032 PM MDT SAT SEP 26 2026
RECENT CAMS AND 00Z NAM SUGGEST A FEW SHOWERS COULD DEVELOP OVER
NORTHWESTERN SD OVERNIGHT, THOUGH CONFIDENCE TOO LOW TO INCLUDE ANY
MENTIONS IN GRIDS. PATCHY FOG HAS BEGUN TO DEVELOP OVER SOUTH
CENTRAL SD, THIS FOG SHOULD CONTINUE TO DEVELOP OVER PORTIONS OF
SOUTH CENTRAL SD THROUGH LATE TONIGHT INTO TOMORROW MORNING AS
MOISTURE CONTINUES TO STREAM INTO THE REGION. MADE NO MAJOR CHANGES
TO THE FORECAST ASIDE FROM SOME MINOR TWEAKS TO POPS FOR TOMORROW.
STILL EXPECTING MOSTLY CLOUDY SKIES AND ISOLATED TO SCATTERED
SHOWERS ACROSS WESTERN SD TOMORROW AFTERNOON WITH CHANCES FOR
SHOWERS AND STORMS INCREASING IN THE EVENING HOURS AS WARM FRONT
LIFTS THROUGH THE AREA.
DISCUSSION
(THIS AFTERNOON THROUGH FRIDAY)
ISSUED AT 1059 AM MDT SAT SEP 26 2026
UPPER TROUGH WILL REMAIN IN PLACE THROUGH EARLY NEXT WEEK OVER
THE WESTERN CONUS, SUPPORTING MAINLY WSW FLOW ALOFT. PATTERN
CHANGE EXPECTED TOWARD NEXT WEEKEND AS A STRONG NE PAC UPPER
TROUGH DIVES INTO THE PAC NW AND SUPPORTS A COUPLE STRONGER UPPER
TROUGHS AND ASSOCIATED SFC LOW'S ACROSS SOUTHERN CANADA AND THE
NORTHERN CONUS, FLATTENING THE FLOW ALOFT. SFC TROUGH HAS PUSHED
THROUGH MOST OF THE FA. A PERIOD OF BREEZY WINDS CAN BE EXPECTED
INTO THE AFTERNOON, ESP IN THE LEE OF THE BLACK HILLS. NOT MUCH IF
ANY COOL AIR WITH THIS FRONT, JUST A DRIER AIRMASS. UPPER TROUGH
WILL DROP INTO THE SW CONUS SUNDAY AND DIRECT TROPICAL MOISTURE NE
ACROSS THE ROCKIES. MEANWHILE LOW LEVEL SE RETURN FLOW WILL
DEVELOP, PUSHING LL MOISTURE BACK WEST INTO THE REGION. THIS WILL
SUPPORT MUCH COOLER CONDS ON THE SD PLAINS FOR SUNDAY, ESP ALONG
THE EAST SLOPES OF THE BH WHERE MOIST UPSLOPE FLOW WILL BE IN
PLACE. EXPECT MOSTLY CLOUDY SKIES THERE WITH LIGHT SHOWERS OR
DRIZZLE POSSIBLE. ISOLATED LIGHT RAIN SHOWERS WILL ALSO BE
POSSIBLE ACROSS THE REMAINDER OF THE SD PLAINS AS POS THETA-E ADV
WILL BE ONGOING THROUGH THE DAY. MAIN LOBE OF DEEP MOISTURE WILL
ARRIVE IN THE EVENING VIA A LEAD IMPULSE, SUPPORTING A GOOD CHANCE
OF SHOWERS AND ISOLATED TS. ANOTHER WINDOW OF HIGHER CHANCES OF
SHOWERS AND STORMS CAN BE EXPECTED MONDAY AFTERNOON AS THE SFC
TROUGH MOVES THROUGH THE AREA, WITH A FEW STRONGER STORMS POSSIBLE
ON THE SD PLAINS. THINGS DRY OUT AFTER MONDAY WITH SEASONAL TEMPS
EXPECTED INTO THE UPPER 60S TO LOW 70S THE REST OF THE WEEK, LOWS
IN THE 40S/50S. MODELS ARE STILL INDICATING A STRONGER COLD FRONT
NEXT WEEKEND, WHICH COULD BRING SOME FROST AS THE UPPER TROUGH
OVER THE NE PAC SHIFTS EAST AND FORCES COLD AIR SOUTH OUT OF
CANADA. HOWEVER, THE DEGREE OF CAA WITH THIS SYSTEM STILL VARIES
SUBSTANTIALLY AMONG THE VARIOUS FORECAST MODELS AND ENSEMBLES,
WITH TEMPERATURE SPREADS REALLY LARGE.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 533 AM MDT SUN SEP 27 2026
PATCHY FOG AND LOW CLOUDS HAVE REDEVELOPED EARLY THIS MORNING
ACROSS WESTERN AND CENTRAL SD. CIGS WILL BE MVFR, AT TIMES IFR,
BUT VSBY IS EXPECTED TO DROP TO IFR OR LOWER (< 1 SM) DUE TO
PATCHY FOG ACROSS SOME LOCATIONS OVER THE WESTERN SD PLAINS. VFR
CONDITIONS WILL CONTINUE THROUGH NE WY.
SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS ARE LIKELY TODAY
WITH INCREASED CHANCES THIS EVENING, INTO TOMORROW/MONDAY, AS A
SYSTEM MOVES ACROSS THE REGION.
UNR WATCHES/WARNINGS/ADVISORIES
SD...DENSE FOG ADVISORY UNTIL 9 AM MDT /10 AM CDT/ THIS MORNING FOR
SDZ032-043-046-047-049-077.
WY...NONE.
UPDATE...WONG
DISCUSSION...JC
AVIATION...GS
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