textproduct: Bismarck

KEY MESSAGES

- Low to medium chances (30 to 50 percent) for thunderstorms through tonight. Isolated to scattered severe storms are possible, mainly in the south.

- Showers and thunderstorms return through the week. Isolated severe storms are possible in the south again Wednesday. - A cooling trend is expected through Friday, followed by a warming trend through the weekend and into early next week.

UPDATE

Issued at 1235 AM CDT Wed Aug 12 2026

Severe thunderstorm watch remains in effect until 1 AM CDT. Convection currently over Stutsman county has shown a downward trend over the past hour or so, although there are still some localized intensification. Activity should be pushing out of Stutsman county in the next 30 minutes or so. Do not intend to extend the watch. Sub-severe convection also indicated over Adams/Hettinger counties and into western Grant county. This activity is pushing east southeast and should be out of the forecast area in the next hour or so. Current thinking is that this activity may be strong at time but should remain below severe levels. Made some updates to pops and sky cover based on latest radar and satellite data.

UPDATE Issued at 958 PM CDT Tue Aug 11 2026

Scattered supercells persist in south central ND as of 0245Z, but coverage is gradually diminishing concurrent with gradual increases in MLCIN. Radar trends and CAMs -- especially time- lagged HRRR cycles -- suggest the severe-storm risk will continue until around 05Z, while continuing to slowly decrease. In the interim, sufficient CAPE and deep-layer shear remain in place to support large hail (mainly 1 to 2 inches in diameter with the most-intense supercells), and perhaps damaging wind gusts up to 60 mph. Recent CAMs suggest the risk of storms is rapidly ending in southwestern ND as of late evening, and that the odds of redevelopment after 05Z in south central ND are lower than previously anticipated. Nonetheless, a low chance of storms is prudent late tonight with broad, albeit modest midlevel warm air advection expected.

UPDATE Issued at 706 PM CDT Tue Aug 11 2026

Scattered supercells have evolved over southwestern ND after initiating on a weak confluence zone. They are occurring in an environment characterized by 2000-3000 J/kg of MLCAPE and effective-layer shear on the order of 50 kt. Hodographs have sufficient length to support supercells, and have favored splitting storms, with a slight preference toward the right- moving supercells being dominant once they are well-established. This scenario is expected to continue the next 1-2 hours with scattered supercells capable of producing large hail mainly up to around 2 inches in diameter. There's some uncertainty in how far eastward these storms will sustain given warmer midlevel capping both with eastward extent and with time, but several CAMs suggest they will persist into south central ND through late evening, e.g., beyond 02Z. Otherwise, the earlier storms in the southern James River Valley have weakened, likely as a result of increasing MLCIN in an environment that already had more residual midlevel capping than elsewhere per the 18z KABR RAOB. Nonetheless, a low chance of isolated development remains, as evidenced by visible satellite imagery showing attempts at updraft development in Emmons County recently.

DISCUSSION

Issued at 240 PM CDT Tue Aug 11 2026

Currently quasi-zonal flow is over the Northern Plains, with a broad ridge over the Southern Plains. The severe storms in the James River Valley this morning have mostly moved into South Dakota. At the surface weak high pressure is in the region.

The severe storm risk today looks very conditional. There is plenty of CAPE with dew points in the 60s and 70s across the south, however the Bismarck 18z sounding shows a strong cap. So the majority of the CAPE (2727 J/kg) is elevated. What might start the event before sunset is the convective temperature is 84, however there is plenty wildfire smoke aloft that might prohibit that. Shear across the area is around 50kts so organized. Most of the CAMS keep convection happening until close to sunset when maybe the jet stream speed max connects with them. There is some storms starting to fire on the Black Hills, but that is near the stationary front. Whatever boundary kicked off storms in our east is still there and has some cumulus trying but currently hitting the cap. If or when storms go the hazards are 2 inch hail and 70mph winds. Thunderstorms are possible through tonight and into the morning, especially in the south central.

The rest of this week will be much cooler, below average in fact, in the 70s. The upper pattern will turn northwest Wednesday, before turning to the southwest Thursday. Daily chances of showers and thunderstorms are possible, including overnight through Saturday morning in the active southwest flow. There is currently a level 1 risk of severe storms again Wednesday in the south, with current hazards being golf balls and 70mph winds. It is possible that over an inch of rain could fall between today and Saturday morning across our forecast area. Thursday and Friday look very breezy from a pressure gradient. This weekend looks warmer in the lower 80s, then maybe back to average early next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1235 AM CDT Wed Aug 12 2026

Convection currently over Stutsman county is expected to impact KJMS TAF at 06Z-07Z, with MVFR-IFR visibilities and MVFR ceilings, along with gusty and erratic winds. Elsewhere, VFR conditions are expected to begin the 06Z TAF period. Low stratus/fog is possible early Wednesday morning. For the time being only included a TEMPO at KBIS for low stratus, but certainly can't rule out low stratus/fog at any TAF site, but mainly the southern Taf sites. Another round of thunderstorms is possible again Wednesday afternoon and evening.

BIS WATCHES/WARNINGS/ADVISORIES

None.