textproduct: Bismarck

KEY MESSAGES

- Periodic low to medium chances for showers and thunderstorms late tonight through Monday.

- A few storms may be strong to severe in southwest and south central North Dakota during the day Sunday, far western North Dakota Sunday night, and central and eastern North Dakota on Monday.

- Temperatures are favored to remain near to slightly above normal through next week, with highs mostly in the 80s.

UPDATE

Issued at 144 PM CDT Sat Aug 22 2026

Quiet weather continues with some fair weather cumulus developing over the James River Valley.

UPDATE Issued at 911 AM CDT Sat Aug 22 2026

Quiet weather continues with high pressure settled over the area. No changes needed at this time.

UPDATE Issued at 633 AM CDT Sat Aug 22 2026

The forecast for today remains on track. Quiet weather will prevail under surface high pressure.

DISCUSSION

Issued at 413 AM CDT Sat Aug 22 2026

A highly-amplified upper level wave pattern lies over North America early this morning, with a ridge axis along the Rockies and a trough axis from Hudson Bay to the Southern Appalachian Mountains. Surface high pressure is centered over southeast Saskatchewan, which is keeping the local weather very quiet. The surface high will morph into an elongated ridge and slide over the Red River Valley by the end of the day as the upper ridge axis begins to pivot off the Northern Rockies. Quiet weather will continue through the daytime hours, with high temperatures this afternoon ranging from the mid 70s northeast to mid 80s southwest.

A mid level shortwave will eject off the Northern Rockies by this evening, cutting through the ridge axis. The increasing downstream warm-air advection, moisture transport, isentropic lift, etc. could generate showers and thunderstorms in eastern Montana tonight, spreading into western North Dakota early Sunday morning. MUCAPE could exceed 1000 J/kg with effective bulk shear near 30 kts in the southwest Sunday morning, but convection should remain elevated, and most CAMs are only simulating scattered showers and isolated thunderstorms. The 00Z NAMnest is an outlier with a couple of clusters of strong to severe storms with bowing segments in the southwest Sunday morning and into the afternoon. Proximity model soundings at Dickinson do show higher RH at the base of the EML and higher equilibrium levels in the NAMnest, but its hodographs could best be described as chaotic. Therefore, the risk for severe weather Sunday morning into the early afternoon is very low, but not zero. This could change later Sunday afternoon as diurnal heating opens the potential for surface or mixed-layer based convection. However: 1) there is high confidence in a strong capping inversion above the boundary layer, 2) a moist southeasterly surface flow is not conducive to efficient boundary layer mixing, and 3) mid level clouds and/or anvil shading from morning convection could limit diurnal heating to some extent. CAMs do show an increased probability in stronger convection over south central North Dakota mid to late Sunday afternoon along the eastern gradient of the buoyancy pool, where CIN may be relatively weaker. Still looking at a CAPE/ shear parameter space supportive of only marginally severe storms though. But regardless of intensity, there are still medium chances (30 to 60 percent) for showers and thunderstorms across much of western and central North Dakota Sunday afternoon and evening as the shortwave moves through. Increased confidence in the aforementioned southeasterly flow and cloud cover has cooled the high temperature forecast into the lower and mid 80s for all but far southwest North Dakota on Sunday.

By Sunday night, a much more potent shortwave/upper low will be ejecting off the Canadian Rockies into the southern prairie provinces. Clusters of thunderstorms forming off the Montana Rockies late Sunday afternoon could cross into western North Dakota Sunday night before dissipating. If this convection is maintained, it could be strong to severe as it moves into a higher buoyancy air mass with increasing shear. The 06Z HRRR appears to show a reasonable worst-case scenario with a broken line of strong to severe storms extending from the Canadian to South Dakota borders entering the state after 10 PM CDT. Simulated surface winds gusts in the 06Z HRRR are much lower in western North Dakota though than they are in eastern Montana earlier in the evening.

The thunderstorm forecast on Monday remains uncertain and may end up highly dependent on the eastward propagation of the occluded front attendant to the potent Canadian upper low. Both CAPE (~2000 J/kg) and shear (~35 kts) directly ahead of the front are projected to be sufficient for severe storms. But very few ensemble members are generating any convection along the front, likely due to an absence of mid to upper level forcing. Broad mid level height falls do eventually spread into northern North Dakota, but that may lag behind the surface front. The latest NBM has reduced PoPs to only 20 to 30 percent Monday afternoon and evening, and kept mentionable PoPs east of Highway 83. But location uncertainty in the surface front at 00Z Monday evening ranges from as far west as Minot to Dickinson (NAM) to as far east as Devils Lake to Jamestown (a small subset of GEFS members). The progression of the front is also likely to play a role in high temperatures on Monday. Strong mixing in the dry post-frontal air mass could allow temperatures to approach 90 in southwest and south central North Dakota, with at least lower 80s elsewhere. This is assuming a slightly quicker frontal progression, which ensembles do tilt towards.

Ensemble guidance shows the Canadian low digging southeastward on Tuesday, but with variance in its trajectory. That uncertainty may dictate how much temperatures cool off on Tuesday, but the NBM has trended slightly warmer than previous iterations with highs in the mid/upper 70s north to lower/mid 80s south. Regardless, Tuesday is likely to be a windier day, with northwest winds gusting as high as 35 mph. There could also be some diurnally-driven showers across the north Tuesday afternoon. Ensembles favor a return to northwest flow between an eastern CONUS trough and western CONUS ridge for the second half of next week, with uncertainty on when or if the ridge might get pushed eastward. Ensemble clusters that are more heavily ECMWF-weighted are much more progressive in breaking down the ridge, while some GEFS-heavy clusters keep the ridge to our west into next weekend. The NBM broadly maintains near average temperatures through the end of next week, but is starting to trend slightly above average in southwest and south central North Dakota considering that average temperatures themselves are now beginning to cool at this time of year.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 144 PM CDT Sat Aug 22 2026

Afternoon fair weather cumulus over the James River Valley is resulting in some low end VFR ceilings, though should erode later today into this evening. South-southeast winds will be on the increase overnight into Sunday morning. Over western North Dakota, scattered showers and thunderstorms will be possible late overnight into Sunday morning, possibly affecting the KDIK and KXWA terminals. Given high confidence, have mentioned in the KDIK TAF.

BIS WATCHES/WARNINGS/ADVISORIES

None.