textproduct: Bismarck

KEY MESSAGES

- Widespread showers and scattered thunderstorms late tonight through Monday.

- A few strong thunderstorms are possible Monday morning through Monday afternoon, with a conditional threat for a severe thunderstorm or two in the afternoon.

- High chance (60 to 90 percent) for at least 1 inch of rain over much of central North Dakota tonight through Monday night. Thunderstorms may also produce locally heavy rainfall.

- Near to slightly above normal high temperatures then expected through the mid to late workweek.

DISCUSSION

Issued at 230 PM CDT Sun Sep 27 2026

Cyclonic flow is found over the northern Plains this afternoon as a deep upper level low exits to the northeast out of the Canadian Prairies. A weak cold front slowly exiting to the southeast of the forecast area continues to promote some isolated showers across portions of our south central. Overall rain accumulations are expected to be very limited to non existent. Elsewhere clear skies are generally expected through the early to mid afternoon as a surface center of high pressure moves across the far northwest, before beginning to cloud back over as a second cold front associated with the Canadian Low beings to move in.

Late tonight into early Monday, a broad shortwave trough ejecting off a closed low over the western Canadian coast is expected to begin moving in the northern Plains. At the surface, a low pressure center developing on the lee side of the rockies is progged to be lifted up and across Wyoming into the Dakotas through the day, pushing an attendant warm front across southwestern through eastern North Dakota. At the same time, a moderately strong (50 to 60 knot) H7 jetstreak is expected to develop across south central into eastern North Dakota early Monday morning through Monday afternoon. With such ample sources of lift across the area, and with moisture returns increasing up ahead of the developing low center, widespread medium to high chances (60 to 90 percent). A fairly modest convective environment is also expected to develop by early Monday morning, with model MUCAPE values peaking up to around 1000 J/KG and bulk shear values around 35 to 40 knots. An interrogation of BUFKIT model soundings through early Monday afternoon indicates that much of the predicted instability should be fairly elevated about a robust cap, and above the better shear found below 1 KM AGL. The questions remains what will occur as we head into the later portions of Monday afternoon as the H7 jet begins to kick in. While the majority of short term CAMs advertise the robust capping over North Dakota persisting through the day, one of two of them do capture a storm or two becoming surface based by the mid to late afternoon. In such a circumstance, an isolated stronger to marginally severe thunderstorm or two cannot be ruled out, with the area to watch being southwestern and south central North Dakota into the northern James River Valley. The primary hazards associated with any severe thunderstorm that does develop would be large hail up to the size of a quarter, and damaging wind up to 60 MPH. Of note is a potential window during which an isolated tornado would become possible, mainly in late afternoon into the early evening as the surface low lifts into central and eastern North Dakota. While predicated on a surface based storm developing, the strong near surface shear near the triple point of the low could promote near surface (0-1km) SRH values around 150-200 KM and decently curved hodographs across the southern James River Valley. While the overall potential of a tornado remains low as this time, we will need to monitor forecast trends over the next 24 hours, especially if surface based storms become more likely.

Otherwise, moderate to heavy rainfall can be expected across portions of western and much of western North Dakota starting late tonight through Monday night. With high PWAT values exceeding 1.5" by the late afternoon, the NBM probability of exceeding 1.0" of rain accumulation is high (70 to 90 percent) across much of central North Dakota, with a low chance (20 to 40 percent) to exceed 3.0" over portions of the James River Valley. With such high PWATs, moderate to heavy rainfall approaching at least 0.5" to 1.0" per hour can also be expected where and when thunderstorms occur. As of this forecast cycle, the EFI highlights portions of central North Dakota for high values approaching 0.9-0.95 and a shift of tail values of 2, which indicates high confidence on an anomalously high precpitation event compared to our climatology. Of note is that a handful of CAMs capture training thunderstorm development along the warm front as it occludes over south central into northeastern North Dakota late Monday afternoon through Monday evening. If this scenario were to play out, localized flood can be anticipated despite the fairly dry, thirsty ground present over much of central North Dakota.

Looking ahead to the remainder of the workweek, near zonal to southwesterly flow is anticipated over the northern Plains through at least Wednesday promoting relatively dry somewhat warmer weather with highs broadly in the mid 60s to mid 70s. By Thursday, ensemble members advertise cooler weather with highs mainly in the 60s as a robust upper level passes far to the north through the Canadian Prairies, turning flow more northwesterly. By late Friday into the weekend, there's decent agreement that a clipper system passing through toward the Great Lakes Region will reinforce this cooling trend, promoting cooler highs mainly in the mid 50s to mid 60s, as well as some low chances (20 to 40 percent) for light rainfall over portions of north central into eastern North Dakota. Overall, the signal for widespread and accumulating precpitation during this period remains low at this time.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 230 PM CDT Sun Sep 27 2026

VFR ceilings and visibility are found at all terminals to begin the 18Z TAF period. Lowering ceilings and chances for precpitation are expected to increase beginning early tonight through Monday morning, with widespread MVFR and some IFR ceilings as well as widespread showers expected by the end of the TAF period. Some isolated thunderstorms will also be possible over portions of central North Dakota by early to mid Monday morning, though confidence remains too low to include mentions of such at any given terminal at this time. Light northwesterly winds this afternoon will becoming light and variable through the early evening as a center of high pressure moves to the north of the forecast area, then turn southeasterly overnight through the end the TAF period.

BIS WATCHES/WARNINGS/ADVISORIES

None.