textproduct: Bismarck

KEY MESSAGES

- Moderate to high chances for showers and thunderstorms through Labor Day. Isolated to scattered severe thunderstorms are possible.

- Unseasonably warm and humid through the Labor Day, then trending cooler.

- Windy on Tuesday, with near-critical to critical fire weather conditions across southwest and south central North Dakota.

UPDATE

Issued at 145 AM CDT Mon Sep 7 2026

Widely scattered showers and thunderstorms continue across northwest and north central North Dakota late tonight. Greater coverage of convection exists just north of the Canadian border, and also more recently in far northeast Montana. 850 mb warm air advection, moisture transport, and frontogenesis are likely to maintain convection through the night, and coverage may increase at the nose of the low level jet in far northwest North Dakota. Still expecting widespread showers and thunderstorms spreading into far western North Dakota by sunrise Labor Day morning as a lead shortwave ejects off the Northern Rockies.

UPDATE Issued at 1009 PM CDT Sun Sep 6 2026

Water vapor energy shows a wave moving across northwestern North Dakota. This wave is causing showers and thunderstorms across the northwest into the north central. Heavy rain and lots of lightning are possible with these storms. There is a chance that one of these cells could become slightly stronger leading to large hail and strong winds but the chances remain low at this time. The current forecast remains on track.

UPDATE Issued at 716 PM CDT Sun Sep 6 2026

A large supercell continues in McKenzie County and is likely producing hail larger than golf balls at times, otherwise most thunderstorm activity has ended over the forecast area for the meantime. 0Z sounding at KBIS shows a stout cap after convection from earlier today, which along with the SPC mesoanalysis page indicates further initiation unlikely in the south central this evening. Thunderstorm development remains possible in the southwest this evening, though increasing CIN appears to be winning out. Despite this, increasing LLJ, WAA, and a strong shortwave will likely bring another round of showers and thunderstorms initially tonight and through much of the day Monday.

DISCUSSION

Issued at 332 PM CDT Sun Sep 6 2026

A general unsettled pattern to bring isolated to scattered thunderstorms, possibly severe, through tonight. High amounts of instability, mostly elevated, will continue through tonight. Meanwhile a weak pseudo warm front near a developing low will be draped across much of the state through tonight. Aloft sees falling heights as the upper level ridge moves east and southwest flow takes its place. Models also indicate a low level jet may return this evening through tonight. All this combined will return widespread chances for showers and thunderstorms through tonight. Today's storms have left plenty of remnant boundaries across the state, How these interact with each other could influence severe weather tonight as well. Overall the stronger severe weather will be located to anywhere with higher shear which currently analyzed in the north and west. Elsewhere has less shear, although high amounts of instability may be just enough for stronger pulse like storms. Overall a hail threat up to golf ball size will be possible with any stronger storm through tonight, with rotating storms in the higher sheared areas having the better potential for the bigger hail. The wind threat is modest through tonight. DCAPE is high, although 0 to 3 km shear is lacking as are low level lapse rates. Thus winds 60 to perhaps 70 mph are possible. There still remains a low tornado threat through tonight. This is highly dependent on boundary interactions, although there is some increased SRH and 0 to 1 KM shear through tonight. Of note are some increased non supercell parameters through this evening. Overall confidence in surface based storms through tonight is low, yet a tornado is possible along any boundary interactions. High pwats over 1.5 inches will continue to bring a heavy rain and localized flooding threat. If confidence in any one area for heavy rain increase then perhaps a flood watch may be needed tonight and perhaps again on Monday. Otherwise look for mild lows in the 60s tonight. Patchy fog may also return tonight to areas without thunderstorms and some clearing. Confidence was not high enough to include fog at this time.

Surface low then moves across the state on Labor Day bringing more isolated to scattered severe thunderstorms. Timing wise, severe storms could be ongoing in the morning as a low level jet continues ahead of the low in the morning. As the low pushes through following by a cold front, thunderstorms could continue through the day from west to east through the day. A few thunderstorms could then develop along a trailing front tomorrow evening, although this may be more uncertain depending how much the daytime convection impacts the atmosphere. All hazards remain possible. Increased shear and instability will support large hail to golf ball sized. Meanwhile, the potential for line development could bring strong winds to 70 mph. There also remains a conditional tornado threat for Monday as dewpoints remain high and a weak warm front lifts ahead of the low. Storms would have to be surface based to increase the tornado threat. Currently SPC has a Marginal Risk for severe weather. CSU-MLP severe outlooks shown all threats possible for Monday. Thus anyone with outdoor plans for Monday should continue to be weather aware on Monday. Highs for Labor Day will continue to be warm with 80s for most of the area, and 70s north. Breezy southerly winds will be found until a breezy westerly wind moves in behind the low. Precipitation diminishes Monday night, with lows cooling in the 50s to near 60.

The main concern for Tuesday remains strong winds. Both the NBM and ECMWF EFI support advisory criteria winds of sustained speeds between 30 and 40 mph and gusts of 45 to 55 mph. Tuesday will be much cooler with highs from the upper 60s northwest to lower 80s southeast, but also drier with minimum humidity falling to around 25 to 35 percent. The combination of strong winds and lower RH will likely bring near- critical to critical fire weather conditions to all of southwest and some south central North Dakota, with critical conditions especially possible in the far southwest where RH could fall closer to 20 to 25 percent. A few showers may also be found Tuesday, mainly in the north. Cooler temperatures remain in the forecast on Wednesday, but with winds not nearly as strong yet still breezy at times. Ensembles have now trended toward a quick warmup on Thursday due to a transient ridge, followed by a distinct cooling trend heading into next weekend, but with increasing spread due to synoptic scale wave phasing uncertainty. There could be an increased fire weather threat on Thursday, especially in the southwest. Limited chances for precipitation also look to be Wednesday through Friday.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 145 AM CDT Mon Sep 7 2026

Widespread showers and thunderstorms are expected to move across the state from west to east Monday morning into the afternoon. Heavier showers and storms could produce torrential rain reducing visibility to IFR levels. A few storms could be severe with large hail and strong, erratic wind gusts. Outside of showers and storms, MVFR to IFR ceilings are forecast to develop across northern and eastern North Dakota late tonight into Monday morning, impacting KMOT and possibly KJMS. Winds will remain southeasterly around 10-20 kts through Monday morning. A cold front entering the state this afternoon will shift winds to the west.

BIS WATCHES/WARNINGS/ADVISORIES

None.