textproduct: Bismarck

KEY MESSAGES

- Low to medium chances of showers and thunderstorms in western North Dakota late this afternoon and evening, and in central North Dakota tonight into Thursday. Isolated severe thunderstorms are possible, mainly in western North Dakota this evening.

- Low chances of thunderstorms Friday and Saturday, then medium to high chances for showers and thunderstorms Sunday through early next week.

- Expect a warming trend through the end of the week, then cooling somewhat late this weekend into early next week.

UPDATE

Issued at 636 AM CDT Wed Sep 2 2026

An area of showers and thunderstorms redeveloped over north central ND since about 09Z, and radar trends suggest a low chance of that activity is prudent close to the ND/SD border the next 1 to 3 hours. Otherwise, low clouds are expanding into southwestern ND at this hour as moisture return begins to increase. Only minor changes were made to the forecast with this update cycle.

DISCUSSION

Issued at 332 AM CDT Wed Sep 2 2026

Early this morning, broad surface high pressure extends across the Red River Valley region, with light east-southeast winds across western and central ND as a lee-side pressure trough deepens in central MT. Middle- and upper-level flow is in the process of starting to turn southwesterly, a process that is expected to be complete by this afternoon. GOES nighttime microphysics RGB imagery reveals stratus developing in western and southern SD, in an area where richer low-level moisture is apparent in surface observations. There remains a low to medium chance that area of stratus will develop and/or advect into southwestern ND this morning, with an accompanying low probability of fog.

For the better part of today, warm and dry weather is forecast with highs mainly in the 80s F. Southeast winds will increase concurrent with a strengthening surface pressure gradient in western ND, with gusts up to 30 mph expected. Increasing low- level moisture beneath an EML-related capping inversion will tend to keep relative humidity values elevated above 30% and that in turn will mitigate the risk of critical fire weather conditions. Late afternoon and evening surface dewpoints in the upper 50s to lower 60s F beneath steep midlevel lapse rates will contribute to 1500-2000 J/kg of MLCAPE in western ND. This will yield a low and conditional risk of severe thunderstorms, though capping at the base of the EML and weak forcing for ascent lends considerable uncertainty in this scenario. By late afternoon and evening, a surface warm frontal zone is forecast to be in place across eastern MT and western ND, with deep boundary layer mixing of a hot and drier air mass in south central MT intersecting with that warm frontal zone somewhere over southeast or east central MT. In general, low-level convergence appears modest near the warm frontal zone, but may be somewhat enhanced near the differential mixing zone in southeastern MT. That could support isolated deep convective initiation upstream of southwestern ND, but MLCIN is forecast to be greatest in the southwestern ND portion of the surface warm frontal zone. Cooler midlevel temperatures in northwestern ND will yield lower MLCIN there, but that may be offset by the weaker forcing for ascent (e.g., weaker low-level convergence) than further southwest. The net result is a broad, 20 percent probability of thunderstorms in western ND late this afternoon and this evening, with attendant risk of large hail and damaging winds. Effective-layer shear is on the order of 30 kt, so we are messaging quarter size hail as the main hazard, along with the possibility of damaging wind gusts to 60 mph given the high- based nature of any storms that develop. A handful of members in the 00z HREF simulated moderate updraft helicity tracks across southwestern ND in support of marginal supercell structures, so if confidence in convective initiation becomes greater in later forecast updates, peak hailstone sizes that we message may be increased a bit.

As the boundary layer cools during the evening, we would expect any evening thunderstorms in western ND to gradually diminish or become more elevated in nature as they progress eastward. Low- and midlevel warm air advection is nonetheless forecast to be ongoing tonight across northwest and central ND, supporting a low chance of showers and thunderstorms through the night. The steep lapse rates aloft and further increases in low-level moisture will result in strong elevated bouyancy (MUCAPE on the order of 2000-3000 J/kg) tonight in the face of 30-40 kt of effective-layer shear even across central ND. Most forecast soundings reasonably depict significant CIN for most unstable parcels originating around the maximized layer of warm air advection near 850 mb, suggesting that overall intensity of any overnight convection will be tempered. However, in some cases, the depth of the moist layer becomes sufficient in forecast soundings to reduce CIN for the layers that possess the large bouyancy. While the overall setting of weak synoptic-scale ascent, a warm EML aloft, and lack of CAM-based signals for robust storms overnight tends to suggest the risk of strong to severe storms will be minimized in central and northwestern ND overnight, a low and very conditional risk of an isolated severe storm even across central ND is apparent if the moist layer ends up deeper than the consensus of guidance expects.

A low to medium chance of showers and thunderstorms continues Thursday and into Thursday evening in north central and into eastern ND, including the James River Valley, both due to early-day warm air advection aloft, and large bouyancy in the afternoon and early evening. Once again, forcing for ascent is apt to be weak (unless a slightly stronger impulse embedded in southwest flow aloft comes to fruition as a small subset of 00z model simulations suggest). However, a conditionally-favorable CAPE-shear setting is once again forecast to be in place, mainly from the Turtle Mountain region southward into the James River Valley. A drier air mass will move into western ND behind a surface trough during the afternoon, resulting in a dry forecast along and west of the Highway 83 corridor Thursday afternoon.

A warming trend will begin Thursday and continue Friday, and potentially into Saturday amid low- and mid-level warm air advection downstream of an upper-level trough in the Pacific northwest. It appears that 850 mb temperatures will rise into the 25 C range in at least southwest ND by Friday, with some ensemble members suggesting an even warmer air mass will reach the area. This is consistent with the relatively small spread in NBM forecast temperatures that peak in the mid 90s F on Friday over most of western and south central ND. Both Thursday and Saturday are forecast to have highs in the 80s to lower 90s F as well, though ensemble spread begins to increase Saturday with regard to whether or not a cool frontal zone will shift into western and northern parts of the area. A low probability of thunderstorms will exist Friday and Saturday, mainly in central ND per ensemble-based guidance.

A cooling trend is forecast beginning Sunday, with medium to high chances of showers and thunderstorms Sunday, Labor Day, and into Tuesday. A majority of ensemble members suggest southwest flow and one or more noteworthy shortwave troughs will eject from the northwestern U.S. trough during this period. As a result, the NBM continues to advertise 48-hour probabilities for 0.50" or more of precipitation ranging from around 50% in northern ND to 30% in southern ND from Sunday through Tuesday. However, we do note that a minority cluster of global ensembles (about 20 percent of them) drive a stronger trough through the Canadian Prairies during this period, which would in turn suppress southwest flow aloft and result in a cooler and drier outcome.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 636 AM CDT Wed Sep 2 2026

IFR ceilings in stratus have developed and moved into far southwestern ND early this morning, and satellite trends suggest a medium to high probability of these ceilings at least briefly impacting the KDIK terminal this morning. Those ceilings will lift and dissipate by late morning, leaving VFR conditions to prevail across western and central ND today and tonight. Light east to southeast winds this morning will increase to 10-15 kt in central ND this afternoon and evening, and to around 20 kt with gusts to 30 kt in western ND. There is a low chance of thunderstorms in western ND this evening, and in northwest and central ND tonight. However, confidence in thunderstorm development is low due to a warm capping layer aloft, precluding any mention of them in the 12Z TAFs.

BIS WATCHES/WARNINGS/ADVISORIES

None.