668
FXUS63 KBIS 231148
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
648 AM CDT SUN AUG 23 2026
KEY MESSAGES
- ISOLATED TO SCATTERED SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS
WESTERN AND SOUTH CENTRAL NORTH DAKOTA THIS AFTERNOON AND
EVENING. POTENTIAL HAZARDS INCLUDE HAIL UP TO THE SIZE OF PING
PONG BALLS, DAMAGING WINDS UP TO 70 MPH, AND TORRENTIAL
DOWNPOURS.
- CONDITIONAL RISK FOR ISOLATED SEVERE THUNDERSTORMS IN CENTRAL
AND EASTERN NORTH DAKOTA MONDAY AFTERNOON AND EVENING.
POTENTIAL HAZARDS INCLUDE LARGE HAIL UP TO 2 INCHES IN
DIAMETER AND DAMAGING WINDS UP TO 70 MPH.
- TEMPERATURES GENERALLY FAVORED TO REMAIN NEAR AVERAGE THROUGH
NEXT WEEK.
- NEAR-CRITICAL FIRE WEATHER CONDITIONS COULD DEVELOP IN PARTS
OF WESTERN NORTH DAKOTA ON MONDAY, AND THE FAR SOUTHWEST ON
TUESDAY.
UPDATE
ISSUED AT 644 AM CDT SUN AUG 23 2026
THE FORECAST FOR TODAY REMAINS ON TRACK. CURRENT CONDITIONS AND
TRENDS WERE BLENDED IN FOR THIS UPDATE.
DISCUSSION
ISSUED AT 422 AM CDT SUN AUG 23 2026
AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE TEXAS PANHANDLE
THROUGH WESTERN NORTH DAKOTA EARLY THIS MORNING, WITH A
SHORTWAVE EJECTING OFF THE NORTHERN ROCKIES PRECEDING A DEEPER
CLOSED LOW OVER WESTERN WASHINGTON. THE SHORTWAVE WILL BE THE
MAIN FOCUS FOR SHOWERS AND THUNDERSTORMS DEVELOPING IN WESTERN
AND CENTRAL NORTH DAKOTA LATER THIS MORNING THROUGH THIS
EVENING. A HANDFUL OF MODELS BRING SOME WEAKER ELEVATED
CONVECTION INTO SOUTHWEST NORTH DAKOTA BY MID MORNING, BUT
THERE IS BETTER CONSENSUS FOR AN INCREASE IN BOTH COVERAGE AND
INTENSITY BEGINNING IN NORTHWEST NORTH DAKOTA EARLY THIS
AFTERNOON AND SPREADING SOUTH AND EASTWARD THROUGH THE LATE
AFTERNOON AND EVENING HOURS. SHOWERS AND STORMS WILL DEVELOP
OVER A BOUNDARY LAYER WITH A SOUTHERLY, MOISTURE-RICH RETURN
FLOW, ALTHOUGH THERE IS SOME QUESTION WHETHER AN MCS OVER
SOUTHWEST SOUTH DAKOTA AND NORTHERN NEBRASKA EARLY THIS MORNING
COULD IMPEDE MOISTURE TRANSPORT TO SOME EXTENT. THAT UNCERTAINTY
ASIDE, DIURNAL HEATING SHOULD CONTRIBUTE TO CAPE INCREASING AS
HIGH AS 2000 J/KG WITH DEEP LAYER SHEAR FORECAST TO INCREASE
FROM 30 KTS IN THE AFTERNOON TO 40 KTS IN THE EVENING. THERE
ARE SOME FACTORS THAT COULD DAMPEN THE INTENSITY OF CONVECTION,
INCLUDING MID LEVEL LAPSE RATES LESS THAN 6 C/KM AND A CAPPING
INVERSION THAT BOUNDARY LAYER MIXING AND COOLING ALOFT FROM
HEIGHT FALLS MAY NOT BE ABLE TO FULLY ERODE. NEVERTHELESS,
RECENT CAMS HAVE CERTAINLY HONED IN ON AN OUTCOME THAT INCLUDES
A FEW SEVERE THUNDERSTORMS OVER PARTS OF WESTERN AND CENTRAL
NORTH DAKOTA FROM MID AFTERNOON THROUGH THIS EVENING. A LACK OF
A WELL-DEFINED SURFACE BOUNDARY AND A MIXTURE OF SHEAR AND DEEP
LAYER WIND VECTOR ORIENTATION TO THE DEWPOINT/CAPE GRADIENT
WOULD SEEMINGLY POINT TOWARD A MULTICELL/CLUSTER STORM MODE,
WHICH FITS WITH CAMS' REFLECTIVITY SIMULATIONS. CONFIDENCE IN
SUSTAINED SUPERCELLULAR STRUCTURE IS LOW, SO HAVE LIMITED OUR
MOST LIKELY MAXIMUM HAIL SIZE FORECAST TO PING PONG BALLS FOR
NOW. IF UPSCALE GROWTH CAN LEAD TO MORE ORGANIZED CONVECTION,
DAMAGING WINDS UP TO 70 MPH COULD EMERGE AS THE DOMINANT SEVERE
HAZARD, ESPECIALLY IN THE EVENING WHEN 0-3 KM SHEAR COULD
INCREASE TO 35 KTS. DESPITE LOW LCLS AND 0-1 KM SHEAR GREATER
THAN 10 KTS, MODEL HODOGRAPHS DO NOT APPEAR TO BE SUPPORTIVE OF
TORNADOGENESIS. WHILE INSTANTANEOUS RAINFALL RATES COULD BE
QUITE HIGH WITH THESE STORMS, THEIR FORWARD PROPAGATION SHOULD
LIMIT THE RISK FOR LOCALIZED FLOODING, WITH URBAN AREAS BEING A
POSSIBLE EXCEPTION.
BACK TO THE WEST, THE DEEPER CLOSED LOW IS FORECAST TO EJECT
OFF THE CANADIAN ROCKIES THIS EVENING. LEE CYCLOGENESIS IS
ALREADY UNDERWAY FROM ALBERTA THROUGH CENTRAL MONTANA, BUT THE
LEE TROUGH/COLD FRONT IS NOT FORECAST TO REACH WESTERN NORTH
DAKOTA UNTIL LATER TONIGHT. MODELS HAVE SHOWN MIXED SIGNALS ON
WHETHER STRONG TO SEVERE CONVECTION ASSOCIATED WITH THE TROUGH
IN CENTRAL/EASTERN MONTANA THIS AFTERNOON AND EVENING WILL
SURVIVE INTO WESTERN NORTH DAKOTA LATER TONIGHT. MORE RECENT
GUIDANCE HAS TRENDED TO A LOWER PROBABILITY OF CONVECTIVE
MAINTENANCE, WHICH MAY BE DUE IN PART TO THE INCREASED
PROBABILITIES OF THUNDERSTORMS IN NORTH DAKOTA STABILIZING THE
AIR MASS IN BETWEEN THE TWO CONVECTIVE SYSTEMS. MUCAPE IS
ACTUALLY PROJECTED TO REMAIN AS HIGH AS 2000 J/KG THROUGH THE
NIGHT IN WESTERN NORTH DAKOTA, BUT MODEL SOUNDINGS REVEAL THE
MOST-UNSTABLE LAYER TO BE HIGHLY-CAPPED. DEPENDING ON THE
TIMING OF DECAYING CONVECTION, THERE COULD BE SOME HIGHER WIND
GUSTS SNEAKING ACROSS THE MONTANA BORDER AROUND MIDNIGHT.
A CONDITIONAL THREAT FOR SEVERE STORMS CONTINUES IN CENTRAL AND
EASTERN NORTH DAKOTA ON MONDAY, BUT CONFIDENCE IN CONVECTIVE
INITIATION IS QUITE LOW. EVEN THOUGH SEVERAL FORCING MECHANISMS
ARE FORECAST TO BE PRESENT, INCLUDING MID LEVEL HEIGHT FALLS/
DCVA, LOW LEVEL WARM AIR CONVERGENCE, AND SURFACE CONVERGENCE
ALONG THE FRONTAL BOUNDARY ATTENDANT TO THE CANADIAN LOW, THERE
MAY NOT BE ENOUGH OF AN ALIGNMENT OF THESE FEATURES TO ENSURE
DEEP MOIST CONVECTION INITIATES, AND THERE ARE A NUMBER OF
POSSIBLE SCENARIOS AND COMBINATIONS THEREOF BEING DISPLAYED BY
THE SUITE OF CAMS. FIRST, THERE IS POTENTIAL FOR ELEVATED
MORNING CONVECTION MOVING ACROSS NORTHERN NORTH DAKOTA AHEAD OF
THE SURFACE FRONT IN AN AREA WHERE STRONGER WARM AIR ADVECTION
ON THE MESOSCALE COULD OVERLAP WITH STRONGER HEIGHT FALLS AS
THE CANADIAN UPPER LOW SPINS OVER SOUTHERN SASKATCHEWAN. THIS
MAY OR MAY NOT PLAY A ROLE IN AFTERNOON CONVECTION IF IT
OCCURS. A CAPPING INVERSION WILL ALMOST CERTAINLY DELAY
SURFACE-BASED CONVECTION UNTIL LATE AFTERNOON AND EARLY
EVENING. THEN IT BECOMES A QUESTION OF WHETHER STRONG ENOUGH
FORCING WILL COME INTO ALIGNMENT FOR SUSTAINED DEEP MOIST
CONVECTION. DESPITE THE LOW PROBABILITIES FOR CONVECTIVE
INITIATION AND COVERAGE, THE THREAT CEILING MAY BE HIGHER THAN
TODAY, WITH CAPE AROUND 2000-2500 J/KG AND DEEP LAYER SHEAR
CLOSER TO 40-50 KTS. UNLIKE TODAY, THERE IS A CLEAR FAVORING OF
A DISCRETE STORM MODE WITH SHEAR AND DEEP LAYER WIND VECTORS
PERPENDICULAR TO THE SURFACE BOUNDARY. MODEL HODOGRAPHS ARE
LONG AND MOSTLY STRAIGHT, BUT WITH ENOUGH CURVATURE TO SUPPORT
SPLITTING SUPERCELLS. THE MOST LIKELY MAXIMUM HAIL SIZE
FORECAST FOR MONDAY HAS THEREFORE BEEN INCREASED TO 2 INCHES IN
DIAMETER, WITH THE MAXIMUM WIND GUST FORECAST REMAINING AT 70
MPH ON ACCOUNT OF FORECAST DCAPE AROUND 1000-1500 J/KG. SIMILAR
TO TODAY, THE TORNADO RISK ON MONDAY APPEARS TO BE LOW ON
ACCOUNT OF MODELED HODOGRAPH STRUCTURE, DESPITE LOW LCLS AND
MODEST LOW LEVEL SHEAR.
IN NON-CONVECTIVE FORECAST NEWS, TODAY WILL BE SEASONABLY WARM
AND HUMID WITH HIGHS MOSTLY IN THE 80S AND DEWPOINTS RISING
INTO THE MID 50S TO MID 60S. IT WILL ALSO BE A BIT BREEZY WITH
SOUTHEAST WINDS AROUND 15-20 MPH. MONDAY IS FAVORED TO BE THE
WARMEST DAY OF THE UPCOMING WEEK FOR MOST AREAS, WITH
WIDESPREAD HIGHS AROUND 85 TO 90. THE POST-FRONTAL AIR MASS IN
WESTERN NORTH DAKOTA WILL BECOME VERY DRY AND COULD FEATURE
GUSTY NORTHWEST WINDS MONDAY AFTERNOON, WHICH MAY LEAD TO NEAR-
CRITICAL FIRE WEATHER CONDITIONS. THE SOUTHERN CANADIAN LOW,
WHICH WILL BECOME NEARLY-STACKED MONDAY NIGHT, IS FORECAST TO
DIVE SOUTHEASTWARD INTO THE RED RIVER VALLEY ON TUESDAY. THIS
BRINGS SLIGHTLY COOLER DAYTIME TEMPERATURES AND STRONGER
NORTHWEST WINDS INTO THE FORECAST AS THE SURFACE PRESSURE
GRADIENT GETS SQUEEZED BETWEEN THE LOW AND HIGH PRESSURE
BUILDING OVER ALBERTA AND SASKATCHEWAN. RH COULD BE LOW ENOUGH
IN THE FAR SOUTHWEST FOR ANOTHER AFTERNOON OF NEAR-CRITICAL
FIRE WEATHER CONDITIONS ON TUESDAY. THE NBM HAS ALSO INCREASED
POPS FOR DIURNALLY-DRIVEN SHOWERS IN THE NORTHWEST CYCLONIC
FLOW REGIME TUESDAY AFTERNOON, JUST IN THE TURTLE MOUNTAINS
AREA FOR NOW BUT COULD SEE THAT EXPANDING WITH FUTURE FORECAST
UPDATES. THE DOWNSTREAM LOW CONTINUES A SOUTHEASTWARD TRAJECTORY
TOWARD THE GREAT LAKES ON WEDNESDAY AS SURFACE RIDGING SLIDES
INTO THE NORTHERN PLAINS AND THE UPPER LEVEL RIDGE BEGINS TO
REAMPLIFY OVER THE ROCKIES. A DEEPER TROUGH DIGGING INTO THE
PACIFIC NORTHWEST ON THURSDAY COULD PUSH THE UPPER RIDGE BACK
INTO THE NORTHERN PLAINS BY THE END OF THE WEEK, WITH ENSEMBLE
SPREAD ON THE SYNOPTIC PATTERN INCREASING THEREAFTER. ENSEMBLE
CLUSTERS NOW TEND TO FAVOR MORE OF A QUASI-ZONAL FLOW PATTERN
HEADING INTO NEXT WEEKEND, WHICH IS EVIDENT IN DETERMINISTIC
GUIDANCE. BUT THERE IS STILL SOME SUPPORT FOR YET ANOTHER
REEMERGENCE OF THE UPPER LEVEL RIDGE SOMEWHERE BETWEEN THE
ROCKIES AND GREAT PLAINS. THE POTENTIAL QUASI-ZONAL FLOW IS
REFLECTED IN THE NBM RETURNING DAILY LOW TO MEDIUM SHOWER AND
THUNDERSTORM CHANCES TO THE FORECAST FROM FRIDAY ONWARD. THE
TEMPERATURE OUTLOOK FOR MID TO LATE NEXT WEEK REMAINS CLOSE TO
AVERAGE, WITH HIGHS MOSTLY IN THE UPPER 70S TO MID 80S AND LOWS
MOSTLY IN THE 50S.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 644 AM CDT SUN AUG 23 2026
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL INCREASE FROM WEST
TO EAST THIS MORNING THROUGH THIS EVENING. A FEW STORMS COULD
BE SEVERE, PARTICULARLY IN SOUTHWEST AND SOUTH CENTRAL NORTH
DAKOTA FROM MID AFTERNOON THROUGH EARLY EVENING. IF A STORM
MOVES OVER A TERMINAL, IFR VISIBILITY AND STRONG WIND GUSTS CAN
BE EXPECTED, WITH LARGE HAIL AND A BRIEF MVFR CEILING POSSIBLE.
A FEW SHOWERS AND STORMS COULD LINGER INTO THE OVERNIGHT HOURS
OR RE-ENTER WESTERN NORTH DAKOTA LATE TONIGHT. OUTSIDE OF
SHOWERS AND STORMS, VFR CONDITIONS AND SOUTH TO SOUTHEAST WINDS
AROUND 10-20 KTS ARE EXPECTED THROUGH THE FORECAST PERIOD.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...HOLLAN
DISCUSSION...HOLLAN
AVIATION...HOLLAN
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