textproduct: Bismarck

KEY MESSAGES

- Dense fog across much of central and eastern North Dakota this morning.

- Medium to high chances for light rain in the eastern half of the state this evening into Saturday morning.

- Temperatures favored to remain near to slightly above average until late next week.

- High chances for showers and thunderstorms Sunday evening through Monday night for all but northwest North Dakota.

DISCUSSION

Issued at 500 AM CDT Fri Sep 25 2026

An upper level ridge is tilting through the Northern Plains early this morning over weak surface flow between broad high pressure that stretches from Michigan through southern Quebec and low MSLP ahead of a potent upper level trough over the Pacific Northwest. Dense fog has already developed across much of central and eastern North Dakota and may continue to expand westward until an hour or two after sunrise. The fog should lift by late morning, but there is uncertainty in how long low clouds could linger. The RAP, which tends to handle low stratus better than other deterministic models, favors a mostly cloudy sky prevailing along and east of Highway 83 through the entire day. Highs this afternoon are expected to reach the 70s where sunshine is more prevalent (western ND) and 60s where clouds are more prevalent (central and east). Model soundings to the south and east of Bismarck show favorable conditions for drizzle this morning. This may continue into the afternoon, but there will likely be a transition in drop-size distribution from drizzle to light rain showers. The showers will initially be isolated in the presence of only weak low level ascent, but a shortwave lifting north from the Central High Plains will increse chances for showers across the eastern half of the state this evening through tonight. Only light rain amounts are anticipated tonight, with ensembles favoring one to two tenths of an inch at most. Breezy conditions are expected today through tonight, with south-southeast winds around 15 to 20 mph. The breezy winds combined with extensive cloud cover will keep overnight low temperatures near record warm values in the mid to upper 50s.

Light rain should depart to the east Saturday morning as the Pacific Northwest trough ejects into Alberta/Saskatchewan and becomes stacked over its occluding surface cyclone. The attendant cold front is forecast to enter western North Dakota Saturday morning, slowly progressing eastward and reaching central North Dakota by late afternoon/early evening. There is a low chance for light rain ahead of the front in northwest North Dakota Saturday morning, but measurable precipitation is unlikely. The front will carry a much drier air mass and gusty west-northwest winds into western North Dakota, but the earlier timing of strongest winds (midday) compared to the lowest RH (late afternoon) should keep fire weather conditions below even near-critical levels. The warmest highs in the mid 70s on Saturday are likely to occur just ahead of the front due to compressional heating, with upper 60s and lower 70s expected elsewhere.

A cooler air mass will continue to filter into the region from the northwest on Sunday, but highs are still forecast to reach the mid 60s to lower 70s. By Sunday evening, shortwave energy ejecting from the base of a trough digging into northern California will begin approaching the Northern Plains. Lee cyclogenesis is forecast over Wyoming, eventually stretching into a positivly-tilted inverted trough on account of an approaching northern stream wave on Monday. Strong low level warm air advection/moisture transport ahead of the lead shortwave in an anomalously high precipitable water environment is expected to result in widespread showers with embedded thunderstorms across much of the state Sunday evening into Monday morning. Increasing MUCAPE on the order of 1000 J/kg may contribute to high rainfall rates, and there is a risk of training convection with forecast deep layer wind vectors perpendicular to low level moisture transport vectors. There may also be a conditional risk for strong to severe thunderstorms over this time period, but just a few hundred meters difference in elevated inflow layer could greatly regulate effective bulk shear, and point-specific model hodographs above 2 km are chaotic and generally not long. Due to the elevated nature of convection, the most likely hazard from a strong to severe storm through Monday morning would be large hail, for which low probabilities are highlighted by CSU machine learning guidance over southwest and south central North Dakota.

On Monday afternoon, the approaching northern stream wave under a coupled jet streak could produce another round of showers and thunderstorms that may or may not act as an extension of the first round. Afternoon thunderstorms would have a higher probability of being surface-based, but it is not a guarantee and would likely be limited to south central North Dakota along the inverted trough/cold front axis. A low CAPE/high shear environment could promote strong to severe storms Monday afternoon, with deep layer shear and wind vector orientation favoring a linear mode with damaging winds as the main hazard. Latest ensemble guidance has trended toward a quicker progression of the cold front pushing showers and thunderstorms off to the east Monday night, with dry weather now favored for most areas on Tuesday.

The latest NBM has focused its highest QPF probabilities along an axis from south central to northeast North Dakota where there are high chances (80 to 90 percent) for exceeding half an inch of rain and medium chances (50 to 70 percent) for exceeding one inch of rain from Sunday evening through Monday night. The 50 percent contour for at least half an inch of rain does touch Dickinson and Minot. But Williston, for example, only has a 40 percent chance for exceeding just a tenth of an inch. The QPF footprint is spatially consistent among global ensemble clusters. While QPF threshold probabilities from global ensembles are lower than their NBM counterparts, they may be biased too low by convective parameterization schemes.

Despite the passage of a cold front on Monday, the trend toward a drier and sunnier Tuesday has allowed its high temperature forecast to increase by a few degrees to around 65 to 70. Additional shortwaves could move along the international border through the rest of next week in what looks to be a progressive quasi-zonal flow pattern, but there are clear phasing discrepancies as early as late Tuesday in cluster analyses. Despite increasing spread in distributions, the NBM maintains near to slightly above average temperatures until the end of next week, with highs mainly in the 60s and lows in the 40s. A more distinct cooling trend is then favored for the first weekend of October.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 500 AM CDT Fri Sep 25 2026

Dense fog with LIFR/IFR ceilings will continue across central and eastern North Dakota this morning. Conditions should improve this afternoon, but MVFR ceilings are likely to prevail at KJMS and possibly KBIS. MVFR to IFR ceilings are once again favored across most of the state this evening through tonight. Some drizzle or light rain showers are possible at KJMS and surrounding areas during the day today, with more persistent light rain developing later this evening. Winds will become southeasterly around 15-20 kts later today, with gusts to near 30 kts in western North Dakota.

BIS WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 11 AM CDT /10 AM MDT/ this morning for NDZ004-005-012-013-019-020-022-023-025-035>037-046>048-050- 051-057>060-062.