textproduct: Bismarck

KEY MESSAGES

- Widespread showers and scattered thunderstorms are expected this morning into the afternoon, with another round of showers and storms impacting central and eastern parts of the state this evening through tonight.

- Excessive rainfall could cause localized flooding from south central North Dakota to the James River Valley this evening through tonight.

- A few thunderstorms may become strong this morning through tonight, with hail up to nickel size being the main hazard in addition to torrential rain.

- Mostly dry with near average temperatures from Tuesday into the weekend.

DISCUSSION

Issued at 502 AM CDT Mon Sep 28 2026

Shortwave energy ejecting from the base of a deep western CONUS trough is spreading over the Northern Plains this morning while the low level jet advects warm air and moisture into the region. These forcing mechanisms are responsible for areas of showers and thunderstorms. At 430 AM CDT, there were two distinct clusters of convection: one over north central North Dakota and another moving into far southwest and south central North Dakota, both traveling northeastward. The space between these two areas is likely to fill in eventually, but this may not occur until mid to late morning over the eastern third of the state. SPC mesoanalysis indicates 40 to 50 kts of effective bulk shear, but this may be too high and analyzed from the base of an inflow layer different from that of reality. While storms have been strong at times, would anticipate more intense and sustained updrafts with that amount of shear and up to 1000 J/kg MUCAPE. Through the rest of this morning and into the afternoon, the broader expanse of showers and storms will propagate northeastward into the Red River Valley in congruence with a mid level shortwave and the attendant low level warm air advection/moisture transport. Recent guidance has trended towards a drier afternoon across western and central North Dakota, although smaller clusters of more widely scattered showers and storms could be maintained by mid level frontogenesis across the south and a poleward advancing surface warm front across the north.

By early evening, the left exit region of an upper level jet will reach south central North Dakota over lower to mid level cyclogenesis adjacent to a strengthening low level jet. This is expected to produce another round of widespread showers and scattered thunderstorms across central and eastern North Dakota that could persist through tonight. This appears to be a favorable setup for training convection that could produce localized areas of flash flooding, with storm motion and deep layer wind vectors intersecting the low level jet and moisture transport vectors at an angle greater than 45 degrees, precipitable water approaching climatological maximum values, high deep layer RH, deep warm cloud depths, and skinny CAPE profiles. Nearly every CAM produces a narrow swath of at least 3 to 5 inches of total rainfall this morning through tonight. The most probable area for this to occur is from the Missouri River south of Lake Sakakawea to the Red River Valley north of Fargo. But only a small fraction within that broader area will see the excessively high rain amounts and risk for flooding.

With the forecast transitioning to a drier afternoon and much more active evening and overnight time period, the risk for severe thunderstorms has decreased. But there area still a handful of CAMs in both the HREF and REFS that produce UH tracks sufficient for severe weather during the late afternoon and evening from Lake Oahe to the James River Valley. If a storm is able to become surface-based with no inhibition late this afternoon, all hazards including a tornado would be possible. But the probability of this occurring is trending lower. Strong thunderstorms can still be expected though, both this evening through tonight and also with the first round of convection this morning into the early afternoon. The main hazard with stronger storms (aside from excessive rain and lightning) is expected to be hail up to nickel size.

Today will be cooler but humid, with highs in the upper 50s to upper 60s. Fog could develop across much of the area tonight into Tuesday morning as a surface ridge forms across western and north central North Dakota. Aside from morning fog and a few lingering early morning showers, Tuesday should be dry and sunnier with highs returning to the upper 60s to upper 70s. Dry weather continues on Wednesday as a deepening trough over central Canada pushes a cooler air mass down from the north. The timing of this cold front has sped up from previous forecasts, with highs across the north now only projected to reach the lower to mid 60s on Wednesday. The Wednesday night low temperature forecast has also cooled, with widespread mid 30s to lower 40s and a potential for patchy frost to develop in low-lying, sheltered areas. The cooler but seasonable air mass could hang around until a potential clipper arrives this weekend, but there is some ensemble support for a brief warm up to end the work week.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 502 AM CDT Mon Sep 28 2026

Multiple rounds of showers and thunderstorms are expected across the state through tonight, especially across south central and eastern North Dakota. MVFR to LIFR visibility can be expected with heavier showers and storms. The strongest storms could produce hail and gusty winds. MVFR to IFR ceilings are forecast to expand from southwest to northeast this morning. Western and south central North Dakota could return to VFR ceilings this afternoon, but areas from around KMOT to KJMS are likely to remain at least at MVFR through tonight. Winds will be easterly to southerly around 10-15 kts through much of the day today.

BIS WATCHES/WARNINGS/ADVISORIES

None.