501
FXUS63 KBIS 280256
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
956 PM CDT SUN JUL 27 2025
KEY MESSAGES
- ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE OVERNIGHT, MAINLY
IN WESTERN NORTH DAKOTA AFTER 3 AM CDT/2 AM MDT.
- SCATTERED SEVERE THUNDERSTORMS ARE POSSIBLE MONDAY, WITH THE
POTENTIAL FOR LARGE HAIL UP TO GOLF BALL SIZE AND DAMAGING
WINDS UP TO 70 MPH. THERE IS POTENTIAL FOR A SIGNIFICANT
SEVERE THUNDERSTORM EVENT TO OCCUR IF THE INGREDIENTS ALL
COME TOGETHER.
- TEMPERATURES REMAIN BELOW NORMAL (MOSTLY IN THE 70S) THROUGH
THE WORK WEEK.
UPDATE
ISSUED AT 956 PM CDT SUN JUL 27 2025
CHANGES WITH THIS UPDATE WERE MAINLY TO ADD PATCHY FOG INTO THE
FORECAST LATE TONIGHT AND MONDAY MORNING IN SOUTHWEST AND PARTS
OF SOUTH CENTRAL ND, AND TO INCREASE THUNDERSTORM CHANCES MONDAY
MORNING GENERALLY ALONG AND WEST OF HIGHWAY 83.
UNCERTAINTY REMAINS WITH HOW STORMS WILL EVOLVE LATE TONIGHT AND
MONDAY, BUT CONFIDENCE IS BEGINNING TO INCREASE IN A COMPLEX OF
STRONG-SEVERE STORMS IMPACTING WESTERN AND PARTS OF CENTRAL ND
AS EARLY AS LATE TONIGHT, AND CONTINUING THROUGH THE DAY ON
MONDAY. WE ARE CURRENTLY CONTINUING TO MESSAGE THE MAIN HAZARDS
AS HAIL UP TO GOLF BALL SIZE AND DAMAGING WIND GUSTS UP TO 70
MPH. HOWEVER, SEVERAL INGREDIENTS ARE IN PLACE THAT COULD RESULT
IN AN ORGANIZED, FORWARD-PROPAGATING MESOSCALE CONVECTIVE SYSTEM
(I.E., BOW ECHO) DEVELOPING SOMEWHERE ACROSS WESTERN OR CENTRAL
ND MONDAY. PREDICTABILITY OF THESE TYPE OF SYSTEMS, ESPECIALLY
AT THE TIME OF DAY WE'RE TALKING ABOUT HERE, IS INHERENTLY LOW.
HOWEVER, AS MENTIONED, THERE ARE SEVERAL INGREDIENTS THAT ALIGN
WITH TYPICAL SETTINGS THAT DO GENERATE THESE TYPE OF SYSTEMS,
AND NEWLY- ARRIVING 00 UTC CAMS (I.E., HRRR, 3-KM NAM- NEST, AND
NSSL WRF- ARW) ARE SIMULATING THIS POTENTIAL EVOLUTION.
WE SEE TWO POTENTIAL SCENARIOS/OUTCOMES LATE TONIGHT/MONDAY:
1) STRONG-SEVERE STORMS MOVE ACROSS WESTERN AND CENTRAL ND (60%
CHANCE OF THIS SCENARIO). IF THIS SCENARIO OCCURS, THEN THERE IS
A MEDIUM TO HIGH CHANCE THAT AN ORGANIZED, BOWING COMPLEX WITH
SIGNIFICANT WINDS DEVELOPS IN PARTS OF SOUTHERN ND AND/OR
NORTHERN SD, BUT EXACTLY WHERE IS UNCERTAIN AT THIS TIME RANGE.
2) EARLY-DAY STORMS POSE ONLY AN ISOLATED STRONG-SEVERE RISK,
AND THEN THE PRIMARY SEVERE-STORM RISK ENDS UP DISPLACED TO THE
SOUTH IN SD AND MN LATER IN THE DAY (40% CHANCE OF THIS SCENARIO)
TECHNICAL DETAILS ON THE POTENTIAL LATE NIGHT AND MONDAY SEVERE
STORMS FOLLOW: A SEASONBLY-MOIST AIR MASS REMAINS IN PLACE THIS
EVENING WITH DEWPOINTS IN THE MID 60S F TO LOWER 70S F ACROSS ND
TO THE NORTH OF A SEMI-DIFFUSE, QUASI-STATIONARY SURFACE FRONT.
THE 00 UTC BISMARCK SOUNDING DISPLAYED A RESIDUAL WARM NOSE, BUT
ITS ACTUAL MLCIN WAS LESS THAN FORECAST BY GUIDANCE, AND VERY
STEEP LAPSE RATES CONTRIBUTED TO STRONG BOUYANCY, WHICH EXTENDS
ACROSS THE STATE CONCURRENT WITH THE RICH MOISTURE SURMOUNTED BY
STEEP LAPSE RATES ALOFT. WATER VAPOR IMAGERY SUGGESTS AN IMPULSE
GENERATING CONVECTION IN CENTRAL MT AS OF MID EVENING, AND MODEL
GUIDANCE SUGGESTS THAT FEATURE -- AND THE RIGHT-ENTRANCE REGION
OF A 70-KT 300-MB JET STREAK -- WILL REACH WESTERN AND CENTRAL
ND BY MONDAY MORNING. FORECAST SOUNDINGS LATE TONIGHT AND MORESO
ON MONDAY DAYTIME FEATURE STRONG BOUYANCY (MUCAPE ON THE ORDER
OF 2500-3500 J/KG, STRONG EFFECTIVE-SHEAR (50-60 KT), SUFFICIENT
DCAPE FOR WIND DAMAGE (EVEN WITH INITIALLY-ELEVATED STORMS), AND
SUFFICENTLY-CONCAVE, ENLARGING HODOGRAPHS IN THE 0-3-KM LAYER TO
SUPPORT LOW- AND MIDLEVEL MESOCYCLONE DEVELOPMENT. DEEP-LAYER
SHEAR VECTORS ARE LARGELY PARALLEL TO THE SURFACE FRONTAL ZONE
TO THE SOUTH, WHICH FAVORS UPSCALE-GROWING, LINEAR STORMS, AND
SOME FORECAST HODOGRAPHS DISPLAY INTENSE 0-3-KM SHEAR MAGNITUDES
OF 30-40 KT, WHICH IS COMMONLY OBSERVED WITH SIGNIFICANT
DAMAGING WIND EVENTS IF AN ORGANIZED CONVECTIVE SYSTEM DEVELOPS.
HAVING SAID ALL OF THAT, THIS CONVECTION IS INITIALLY EXPECTED
TO BE ELEVATED, AND WILL BE HIGHLY SENSITIVE TO EVOLUTION OF THE
LOW-LEVEL MOIST LAYER GIVEN SOME RESIDUAL CAPPING ALOFT. TIMING
OF THE IMPULSE AND CONVECTION PRIOR TO PEAK DIURNAL HEATING ALSO
CASTS SOME UNCERTAINTY ON ITS ABILITY TO BE MAINTAINED. THIS IS
WHY THE SECOND POTENTIAL SCENARIO EXISTS, WHEREIN THE EARLY-DAY
STORMS WEAKEN IN THE FACE OF CAPPING OVER WESTERN AND CENTRAL
ND, AND LATER-DAY STORMS END UP FORMING WELL SOUTH OF THE LOCAL
AREA CLOSE TO SURFACE FRONTAL ZONE IN SD/MN, ONCE DIURNAL
HEATING IS ABLE TO ERODE BOUNDARY-LAYER-BASED CIN.
UPDATE
ISSUED AT 656 PM CDT SUN JUL 27 2025
AS OF EARLY EVENING, CAPPING REMAINS IN PLACE AND HAS INHIBITED
BOUNDARY LAYER CONVECTION IN WESTERN AND CENTRAL ND, WITH THE 00
UTC BISMARCK SOUNDING REVEALING A NOTABLE INVERSION JUST ABOVE
850 MB. OBJECTIVE MESOANALYSIS OUTPUT SUGGESTS ONLY NORTHWESTERN
ND HAS MINIMIZED MLCIN, CONSISTENT WITH EARLIER MODEL FORECASTS.
SATELLITE IMAGERY DOES SUGGEST A WEAK UPSTREAM IMPULSE NORTH OF
THE GLASGOW AREA IS PROGRESSING EASTWARD, SO A LOW CHANCE FOR
THUNDERSTORM DEVELOPMENT (AND CONDITIONAL SEVERE-STORM RISK) IS
CONTINUING IN PARTS OF THE AREA THIS EVENING, MAINLY NORTHWESTERN
ND. THE PRIMARY SURFACE FRONTAL ZONE STRETCHES FROM CENTRAL MN
WESTWARD TOWARD PIERRE, SD, AND THEN NORTHWEST INTO CENTRAL MT.
ONE OR MORE DIFFERENTIAL MIXING ZONES EXIST IN EASTERN MT AND
WESTERN ND, AND HAVE BEEN RESPONSIBLE FOR OCCASIONAL SHALLOW
CUMULUS DEVELOPMENT. ONE SUCH DIFFERENTIAL MIXING ZONE MAY ALSO
EXTEND FROM NEAR ESTEVAN AND CROSBY TOWARD PLENTYWOOD, MT, AND
INTO THE GLASGOW VICINITY, AND WILL BE MONITORED AS THE UPSTREAM
IMPULSE INTERACTS WITH IT THE NEXT COUPLE OF HOURS FOR SIGNS OF
CONVECTIVE INITIATION. HAVING SAID THAT, THE LACK OF MASS-FIELD
RESPONSES ACROSS THE AREA (E.G., LACK OF STRONGER SURFACE
PRESSURE FALLS), COMBINED WITH THE CAPPING, RENDERS CONFIDENCE
IN THUNDERSTORM DEVELOPMENT THIS EVENING LOW. THE MAIN CHANGE
WITH THIS FORECAST UPDATE CYCLE WAS TO FOCUS POPS THIS EVENING
IN FAR WESTERN, NORTHWEST, AND TO A LESSER-EXTENT NORTH CENTRAL
ND, AND TO LIMIT THEM TO THE 20 TO 30 PERCENT RANGE.
DISCUSSION
ISSUED AT 136 PM CDT SUN JUL 27 2025
CURRENTLY, SKIES WERE PARTLY CLOUDY ACROSS WESTERN AND CENTRAL
ND. A THUNDERSTORM THAT DEVELOPED OVER SOUTHEAST MONTANA AND
MOVED INTO SOUTHWEST ND A LITTLE EARLIER THIS AFTERNOON HAS NOW
DISSIPATED. WE REMAIN MOIST AND UNSTABLE ACROSS MOST OF THE
FORECAST AREA, ALTHOUGH THE FAR SOUTHWEST IS RELATIVELY DRY WITH
DEWPOINTS IN THE MID 50S. THERE IS A FRONTAL BOUNDARY DRAPED
ACROSS SOUTHEAST ND, WITH SCATTERED THUNDERSTORMS OVER THE FAR
SOUTHEAST PORTION OF THE STATE. GENERALLY WEAK SURFACE HIGH
PRESSURE WAS LOCATED OVER WESTERN AND CENTRAL ND. THERE IS
ABOUT 1500-2000 J/KG OF MLCAPE ACROSS WESTERN AND CENTRAL ND BUT
FORECAST SOUNDINGS INDICATE SOME WEAK MID-LEVEL CAPPING
REMAINING. SPC MESO-ANALYSIS SHOWS THE CAP ERODING OVER
NORTHWEST PORTION OF THE STATE. EFFECTIVE SHEAR IS GENERALLY
AROUND 30 KNOTS WEST TO 40 KNOTS CENTRAL. CAMS ARE NOT SHOWING
MUCH IN THE WAY OF CONVECTION THROUGH THE REST OF THIS AFTERNOON
AND EARLY EVENING. HOWEVER WITH BOUNDARIES LINGERING BEHIND
OVERNIGHT AND EARLY MORNING CONVECTION, THE AFOREMENTIONED
INSTABILITY AND SHEAR, IF A STORM COULD BREAK THE CAPPING, A
STRONG TO SEVERE STORM WOULD BE POSSIBLE WITH THE MAIN THREATS
BEING WINDS TO 60 MPH AND HAIL UP TO PING PONG BALL SIZE. IF I
WERE TO GUESS, WITH THE DISSIPATING CIN NORTHWEST, THIS WOULD BE
A GUESS FOR THE MORE LIKELY AREA FOR CI LATE AFTERNOON OR EARLY
EVENING, AND WITH THE SOUTHWEST (WITH DRIER AIR IN PLACE) THE
LEAST LIKELY. HOWEVER, CAN'T REALLY ELIMINATE ANY AREA FOR
POSSIBLE CONVECTION. COVERAGE DOES LOOK TO BE MINIMAL,
ESPECIALLY WHEN COMPARED TO LAST NIGHT.
LATER TONIGHT AND THROUGH THE DAY MONDAY WE SEE A MORE POTENT
IMPULSE IMPACTING THE LOCAL AREA. CAMS SHOW A GENERAL TIMEFRAME
OF 08-12 UTC WHEN CONVECTION MAY MOVE INTO THE WEST. THIS IS
FROM A WAVE CURRENTLY OVER THE WESTERN U.S. THAT TRACKS ACROSS
THE NORTHERN ROCKIES AND INTO THE NORTHERN HIGH PLAINS TONIGHT
AND ACROSS THE FORECAST AREA ON MONDAY. CONVECTION COULD
CONTINUE THROUGH THE DAY ON MONDAY AS THE WAVE TRACKS ALONG THE
INTERNATIONAL BORDER. THE AFTERNOON AND EVENING HOURS WOULD BE
THE FAVORED TIMEFRAME FOR STRONG TO SEVERE CONVECTION, BUT
AGAIN, I DON'T THINK YOU CAN COMPLETELY RULE OUT SEVERE MORNING
CONVECTION EITHER. AS WE DO GET INTO THE AFTERNOON HOURS, THINK
THE SEVERE POTENTIAL WILL DISSIPATE ACROSS THE NORTH, AND
EVENTUALLY IN THE SOUTH MONDAY EVENING. SPC HAS A SLIGHT RISK
OVER PORTIONS OF THE SOUTHWEST AND SOUTH CENTRAL. THIS WOULD
SEEM REASONABLE GIVING THE CURRENT TIMING. ALTHOUGH INSTABILITY
LOOKS TO DIMINISH IN THE SOUTH THROUGH THE AFTERNOON/EVENING
TIMEFRAME, THERE SHOULD BE A WINDOW WHEN WE WOULD SEE SUFFICIENT
INSTABILITY, COMBINED WITH STRONG SHEAR, TO SUPPORT LARGE HAIL
TO THE SIZE OF GOLF BALLS AND WINDS TO 70 MPH. THIS WINDOW WILL
BE GREATER TO THE SOUTH OF THE FORECAST AREA, BUT A LOT WILL
DEPEND UPON THE EVOLUTION OF THE AFOREMENTIONED SHORTWAVE AND
IT'S ATTENDANT SURFACE BOUNDARY AS WE GO THROUGH THE OVERNIGHT
HOURS AND MONDAY MORNING. PERHAPS IT'S A LITTLE SLOWER AS WE SEE
A GREATER AREA OF STRONG INSTABILITY AND SHEAR ACROSS WESTERN
AND CENTRAL ND, RESULTING IN A LONG AFTERNOON AND EVENING OF
STRONG TO SEVERE CONVECTION. ON THE OTHER HAND, PERHAPS THE
PROGRESSION OF THE SYSTEM IS SUCH THAT STRONG TO SEVERE
CONVECTION IS MOSTLY TO OUR SOUTH. FOR THE TIME BEING, INCLUDING
AT LEAST A PORTION OF THE SOUTHWEST AND SOUTH CENTRAL WITHIN
THE SLIGHT RISK (LEVEL 2 OF 5) FOR SEVERE STORMS SEEMS
REASONABLE.
ONCE CONVECTION (WHEREVER IT IS) ENDS ON MONDAY AFTERNOON OR
EVENING, IT LOOKS LIKE THE THREAT FOR STRONG TO SEVERE STORMS
WILL BE LIMITED TO THE SOUTHWEST PORTION OF THE STATE ON
TUESDAY. THEN GOING THROUGH THE REST OF THE WORK WEEK THE THREAT
FOR SEVERE STORMS LOOKS TO BE MINIMAL, AND IF ANY, ALSO
CONFINED TO THE SOUTHWEST PORTION OF THE STATE. TEMPERATURES
THROUGH THE WORK WEEK ARE EXPECTED TO REMAIN BELOW NORMAL
(MAINLY IN THE 70S TO LOWER 80S) UNTIL POSSIBLY TRENDING BACK
UP BY THE WEEKEND.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 956 PM CDT SUN JUL 27 2025
VFR CONDITIONS AND LIGHT WINDS ARE EXPECTED THROUGH ABOUT 09 UTC,
WITH ONLY A LOW CHANCE OF A THUNDERSTORM. HIGHER PROBABILITIES
OF THUNDERSTORMS AND ATTENDANT LOCALIZED IFR/MVFR CONDITIONS ARE
FORECAST TO ENTER WESTERN ND LATE TONIGHT, AND CENTRAL ND
MONDAY MORNING, AS A STRONGER DISTURBANCE MOVES INTO THE AREA.
SPECIFIC TIMING AND COVERAGE OF THE LATE NIGHT AND MONDAY
ACTIVITY IS UNCERTAIN, SO ONLY PROB30 GROUPS WERE INCLUDED IN
THE 00 UTC TAFS. PATCHY FOG AND MVFR TO IFR CEILINGS IN STRATUS
WILL ALSO LIKELY (60-80% CHANCE) DEVELOP ALONG THE ND/SD
BORDER, AND ESPECIALLY INTO SOUTHWESTERN ND, LATE TONIGHT AND
MONDAY MORNING ON MOIST EAST-NORTHEAST WINDS. KDIK IS THE
TERMINAL MOST LIKELY TO BE IMPACTED BY LOW CEILINGS FROM ABOUT
12 TO 18 UTC MONDAY.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...CJS
DISCUSSION...TWH
AVIATION...CJS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page