396
FXUS63 KBIS 130619
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
119 AM CDT SAT SEP 13 2025
KEY MESSAGES
- SEVERAL ROUNDS OF SCATTERED SHOWERS AND THUNDERSTORMS THROUGH
THE MIDDLE OF NEXT WEEK.
- MEDIUM TO HIGH PROBABILITIES FOR AT LEAST AN INCH OF RAIN
ACROSS THE WESTERN HALF OF THE STATE THROUGH THIS WEEKEND.
- ISOLATED SEVERE THUNDERSTORMS POSSIBLE TONIGHT THROUGH SUNDAY
NIGHT.
- TEMPERATURES FAVORED TO REMAIN NEAR TO ABOVE AVERAGE THROUGH
THE MIDDLE OF NEXT WEEK.
UPDATE
ISSUED AT 116 AM CDT SAT SEP 13 2025
INTENSITY OF CONVECTION HAS TRENDED DOWNWARD OVER THE PAST COUPLE
HOURS, WITH THE STRONGEST STORMS REMAINING OFF TO THE SOUTH IN
NORTHWEST SOUTH DAKOTA. THAT SAID, THE LOW PROBABILITY RISK FOR A
MARGINALLY SEVERE STORM WILL CONTINUE THROUGH TONIGHT. THE GREATEST
CONCERN IMPACT-WISE THOUGH IS FOR EXCESSIVE RAINFALL WHERE STORMS
TRAIN OVER A SIMILAR AREA. OVERALL, THERE ARE NO MAJOR CHANGES TO
FORECAST THINKING. CURRENT CONDITIONS AND LATEST ENSEMBLE DATA WERE
BLENDED INTO THE FORECAST FOR THIS UPDATE.
UPDATE
ISSUED AT 952 PM CDT FRI SEP 12 2025
STORMS OVER SOUTHERN PORTIONS OF OUR AREA HAVE WEAKENED, BUT AN
AREA OF STORMS CONTINUE OVER FAR NORTHWEST NORTH DAKOTA, THOUGH
THESE HAVE REMAINED RATHER TAME. THE QUESTION IS WHAT WILL
OCCUR WITH THE NEXT WAVE LIFTING NORTH THROUGH WESTERN SOUTH
DAKOTA. AN UNSTABLE ATMOSPHERE REMAINS IN PLACE OVER WESTERN AND
PARTS OF CENTRAL NORTH DAKOTA, BUT THE AMOUNT OF SHEAR FOR THE
STORMS TO WORK WITH APPEARS TO BE A BIT ON THE MEAGER SIDE. SO,
DO NOT DOUBT THE POTENTIAL IS THERE FOR SOME ISOLATED STORMS TO
PULSE UP A BIT NOW AND THEN AND BECOME SEVERE, BUT DO NOT EXPECT
THIS TO HAVE MUCH IN COVERAGE.
UPDATE ISSUED AT 712 PM CDT FRI SEP 12 2025
** MESOSCALE UPDATE **
AN ISOLATED SEVERE THUNDERSTORM RISK WILL PERSIST THROUGH ABOUT
9 PM CDT IN SOUTH CENTRAL ND. AN ADDITIONAL RISK OF ISOLATED TO
SCATTERED SEVERE THUNDERSTORMS WILL BEGIN ACROSS SOUTHWEST ND
AFTER ABOUT 11 PM CDT/10 PM MDT, THEN SPREADING NORTH AND EAST
THROUGH THE NIGHT.
AS OF 00 UTC, ISOLATED SUPERCELLS ARE ONGOING IN SOUTH CENTRAL
ND SOUTH THROUGH SOUTHWEST OF BISMARCK/MANDAN, ALONG A SURFACE
CONVERGENCE AXIS/WIND SHIFT THAT EXTENDS FROM NEAR LINTON INTO
THE HETTINGER AREA. MLCAPE ON THE ORDER OF 3000 J/KG AND DEEP-
LAYER SHEAR ON THE ORDER OF 30-35 KT IS SUPPORTING AT LEAST
TRANSIENT SUPERCELL STRUCTURES, AND THIS CAPE-SHEAR SETTING IS
EXPECTED TO CONTINUE FAVORING A LARGE HAIL AND PERHAPS DAMAGING
WIND GUST RISK WITH THIS ACTIVITY IN THE NEAR TERM. HOWEVER, THE
STORMS REMAIN FOCUSED NEAR THE BOUNDARY, AND UNFAVORABLE OUTFLOW
INTERACTIONS ALONG WITH SLOWLY-INCREASING BOUNDARY LAYER-BASED
CIN AS SUNSET APPROACHES SUGGESTS THESE STORMS WILL GRADUALLY
DIMINISH BY ABOUT 02 UTC. IN THE MEANTIME, AN ISOLATED SEVERE
RISK WILL CONTINUE, THOUGH HIGH TROPOSPHERIC MOISTURE CONTENT
AND DUAL-POL RADAR SIGNATURES SUGGEST LOCALLY HEAVY RAINFALL IS
ALSO A CONCERN, AND ADJACENT-STORM HYDROMETEOR SEEDING MAY ALSO
BE REDUCING PEAK HAIL SIZES WITH INDIVIDUAL STORMS.
OTHERWISE, STRONGER FORCING FOR ASCENT UPSTREAM FROM EASTERN WY
INTO WESTERN SD WILL CONTINUE TO RESULT IN INCREASING COVERAGE
OF STORMS. EXTRAPOLATION OF CURRENT MOTIONS SUGGESTS A LARGER
COMPLEX OF SHOWERS AND THUNDERSTORMS COULD ENTER SOUTHWESTERN ND
AFTER ABOUT 11 PM CDT, AS LONG-SIGNALED BY MOST CAMS. THERE WILL
BE AN ATTENDANT RISK OF DAMAGING WINDS AND LARGE HAIL WITH THIS
ACTIVITY, TOO, BUT LOW- AND MIDLEVEL WINDS ARE FORECAST TO BE
MODEST, WHICH MAY MITIGATE THE OVERALL RISK TO SOME EXTENT.
DISCUSSION
ISSUED AT 336 PM CDT FRI SEP 12 2025
THIS AFTERNOON, AN ELONGATED UPPER LEVEL LOW EXTENDED
SOUTHWEST-NORTHEAST ACROSS THE WESTERN CONUS, WITH THE BASE OF
A TROUGH DIGGING INTO THE SOUTHWEST, LEADING TO SOUTHWEST FLOW
ALOFT OVER THE DAKOTAS. A SURFACE LOW WAS ANALYZED TO OUR SOUTH,
WITH A WARM FRONT EXTENDING ACROSS FAR SOUTHEAST NORTH DAKOTA.
THERE WAS AN ADDITIONAL BOUNDARY AND ASSOCIATED WIND SHIFT
ACROSS THE NORTHWEST, AND A FEW THUNDERSTORMS HAVE BEEN
DEVELOPING ALONG THIS BOUNDARY. ALTHOUGH NOT SEVERE STORMS, ONE
DID PRODUCE A BRIEF TORNADO IN WILLIAMS COUNTY, LIKELY DUE TO
ENHANCED LOW- LEVEL VORTICITY ALONG THE BOUNDARY AND TAPPING
INTO SOME ELEVATED INSTABILITY, WITH SPC MESO PAGE SHOWING AN
UNCAPPED ENVIRONMENT ACROSS PARTS OF WESTERN NORTH DAKOTA. THERE
IS LOW CONFIDENCE IN STORM DEVELOPMENT AND LOCATION FOR THE
REST OF THE AFTERNOON, WITH NO PRONOUNCED SYNOPTIC FORCING.
ISOLATED STORMS ARE DEVELOPING IN SOUTHEAST MONTANA, ALTHOUGH
THEY ARE MOVING SLOWLY AND ARE PROGRESSING INTO AN ENVIRONMENT
THAT IS STILL RELATIVELY CAPPED. IF THESE CAN BE SUSTAINED,
THOUGH, THEY WILL BE MOVING INTO SOUTHWEST NORTH DAKOTA EARLIER
THAN EXPECTED. WE ALSO CAN'T RULE OUT A STORM OR TWO DEVELOPING
AHEAD OF THE MAIN WAVE, AND ANYTHING THAT FORMS COULD BE
POTENTIALLY STRONG TO SEVERE, ESPECIALLY IN THE AREA THAT IS
EITHER WEAKLY CAPPED OR NOT CAPPED AT ALL OUT WEST.
THE CHANCE FOR SHOWERS AND THUNDERSTORMS INCREASES THIS EVENING
AND INTO THE OVERNIGHT HOURS AS A STRONGER SHORTWAVE EJECTS OUT
OF THE TROUGH BASE, WITH PRECIPITATION CHANCES INCREASING TO 70
TO 90 PERCENT ACROSS SOUTHWEST NORTH DAKOTA TONIGHT. WE ARE ALSO
CARRYING A MENTION OF SCATTERED SEVERE THUNDERSTORMS (LEVEL 2
OUT OF 5) IN THIS AREA, AND ISOLATED SEVERE THUNDERSTORMS (LEVEL
1 OUT OF 5) ACROSS THE REMAINDER OF WESTERN AND CENTRAL NORTH
DAKOTA. HIGH-RES GUIDANCE IS GENERALLY AGREEING ON THE SAME
PROGRESSION ALTHOUGH SOME DIFFERENCES IN TIMING, WITH A BROAD
WINDOW OF 9 PM TO MIDNIGHT CDT FOR THE MAIN WAVE OF STORMS
MOVING INTO SOUTHWEST NORTH DAKOTA. THESE STORMS ARE PROJECTED
TO LIFT NORTH AS A MID-LEVEL WAVE ALIGNS WITH AN UPPER JET
STREAK, LEADING TO STRONG HEIGHT FALLS AND WIDESPREAD SHOWERS
AND THUNDERSTORMS. CURRENT HAZARDS WE ARE MESSAGING ARE HAIL UP
TO THE SIZE OF GOLF BALLS AND WIND GUSTS UP TO 60 MPH, WITH
SUFFICIENT BUOYANCY BUT WEAK SHEAR. 12Z HREF MAX UH TRACKS SHOW
A SMATTERING OF TRACKS TONIGHT INTO SATURDAY MORNING, ALTHOUGH
NONE VERY LONG OR PRONOUNCED, WHICH WOULD FIT WITH THE LACK OF
SHEAR BEING ADVERTISED IN GUIDANCE. WITH THE FREQUENT
BACKBUILDING AND RELATIVELY SLOW STORMS WE'VE BEEN SEEING
YESTERDAY AND TODAY SO FAR, ALSO HAVE TO CONSIDER HEAVY RAINFALL
AS A THREAT, WITH CONTINUED ABNORMALLY HIGH PWATS.
SHOWERS AND THUNDERSTORMS CONTINUE LIFTING NORTH THROUGH THE
MORNING SATURDAY BEFORE THERE WILL LIKELY BE A BIT OF A LULL, AT
LEAST IN THE AMOUNT OF WIDESPREAD CONVECTION. ADDITIONAL ROUNDS
OF PRECIPITATION ARE EXPECTED AS MORE WAVES EJECT FROM THE
TROUGH BASE THAT WILL SLOWLY BE ROTATING ACROSS THE REGION, WITH
PERSISTENT MEDIUM CHANCES FOR SHOWERS AND THUNDERSTORMS THROUGH
MONDAY. WE ARE CARRYING A MENTION OF ISOLATED SEVERE STORMS ON
SATURDAY AND SUNDAY, WITH FORECAST INSTABILITY SLOWLY DECREASING
THROUGH THE WEEKEND. OF MORE CERTAINTY IS THE POTENTIAL FOR
WIDESPREAD RAIN AMOUNTS OF AT LEAST AN INCH, WITH CURRENT NBM
PROBABILITIES HIGHLIGHTING MEDIUM TO HIGH CHANCES FOR THIS
THRESHOLD THROUGH THE WEEKEND ACROSS THE WESTERN HALF OF THE
STATE. THE LIKELIHOOD OF AT LEAST 3 INCHES OF RAIN IS AROUND 10
PERCENT IN AN AREA FROM STANLEY TO LEMMON, ALTHOUGH OVERALL
RAINFALL AMOUNTS COULD BE QUITE VARIABLE FROM THUNDERSTORMS
MOVING THROUGH. WE CONTINUE TO SEE AN ELEVATED QPF SIGNAL IN THE
EFI, WITH A SHIFT OF TAILS OVER PARTS OF WESTERN AND CENTRAL
NORTH DAKOTA ON SATURDAY AND SUNDAY.
TEMPERATURE WISE, HIGHS SATURDAY THROUGH TUESDAY WILL BE IN THE
LOWER 70S TO LOWER 80S, BEFORE NBM TEMPERATURE PROBABILITIES
SHOW SIGNS OF A COOL DOWN FOR THE MIDDLE TO END OF NEXT WEEK AS
FLOW ALOFT TURNS MORE CYCLONIC. LOW PRECIPITATION CHANCES
CONTINUE FOR THE BACK HALF OF NEXT WEEK, ALTHOUGH NOT AS HIGH OR
AS WIDESPREAD AS WHAT WE'RE SEEING FOR THE NEXT FEW DAYS.
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 116 AM CDT SAT SEP 13 2025
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DRAMATICALLY INCREASE IN
COVERAGE DURING THE OVERNIGHT HOURS, IMPACTING ALL TAF SITES EXCEPT
KJMS. CEILINGS WILL DECREASE QUITE DRAMATICALLY AS THUNDERSTROMS
OVERSPREAD THE REGION, WITH MVFR PREVAILING. THERE IS ALSO THE
POTENTIAL FOR FOG IN THE NORTH, WHICH COULD IMPACT KXWA AND KMOT. IF
IT WERE TO FORM IT WOULD SIGNIFICANTLY REDUCE VISIBILITY INTO
IFR/LIFR. CEILINGS WILL SLOWLY IMPROVE SATURDAY, WITH POCKETS OF IFR
IN THE MORNING GIVING WAY TO PREVAILING MVFR BY MID-AFTERNOON.
SHOWER/STORM COVERAGE WILL ALSO DECREASE THROUGHOUT THE DAY. WITH
RECENT PRECIPITATION AND LIGHT WINDS SATURDAY NIGHT, FOG WILL BE A
CONCERN, BUT THAT THREAT LOOKS TO BE JUST OUTSIDE OF THE CURRENT TAF
PERIOD.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...HOLLAN/JJS/CJS
DISCUSSION...JONES
AVIATION...BR/WFO FGF
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