textproduct: Bismarck

KEY MESSAGES

- Seasonable temperatures are favored through the weekend, with highs mostly in the 60s and 70s and lows in the 40s and 50s.

- Medium to high chances for showers and a few thunderstorms on Wednesday.

UPDATE

Issued at 644 AM CDT Tue Sep 22 2026

Current conditions and trends have been blended into the forecast for this update. The only notable change as a result was a lowering of wind speeds through the morning. Once diurnal mixing commences, south-southeast winds should increase to around 20 to 25 mph, with gusts as high as around 35 mph.

DISCUSSION

Issued at 337 AM CDT Tue Sep 22 2026

Weak mid to upper level flow over the Northern Plains early this morning, with a ridge over eastern Manitoba/western Ontario and a trough approaching the Upper Mississippi River Valley. Meanwhile, low level to surface southerly return flow is increasing as a result of lee troughing along the slopes of the Northern Rockies and broad high pressure stretched across the northern Great Lakes. The southerly return flow has lead to an increase in low stratus across southern parts of the state. The low clouds may continue to expand through the morning and linger in some areas through the afternoon, keeping high temperatures in the upper 50s to mid 60s. Wherever sunshine is more plentiful, upper 60s and lower 70s can be expected for highs this afternoon. South-southeast winds could increase to around 20-25 mph with gusts as high as 35 mph this afternoon as the lee trough shifts eastward while the downstream high remains in place. A persistent south-southeast breeze through tonight should keep low temperatures in the mid 40s to lower 50s.

The benign mid to upper level flow pattern will turn southwesterly on Wednesday with the arrival of a shortwave that is spinning over the Great Basin this morning. Chances for showers begin to increase in southwest North Dakota early Wednesday morning with the arrival of DCVA and underlying warm air advection, spreading northeastward through through the morning and into the afternoon. A few thunderstorms will be possible across central North Dakota in the afternoon, but model soundings show convection should remain elevated with only up to around 500 J/kg MUCAPE and effective bulk shear 25 kts or less. Shower and thunderstorm chances diminish from west to east during the afternoon and evening. However, there is a low chance for convective initiation along the lee surface trough in western North Dakota late Wednesday afternoon. Any thunderstorms in this time and space would more likely be surface-based with up to 1000 J/kg CAPE and 30 kts deep layer shear, which could result in a stronger storm. Whether storms actually develop here remains highly uncertain though as low level warm air advection and the 700 mb trough may not be properly phased to provide stronger support for ascent.

Showers and associated cloudiness limit forecast highs to the 60s in central and northwest North Dakota on Wednesday, with the southwest warming into the lower and mid 70s. Behind the departure of the shortwave, upper level ridging is forecast to amplify on Thursday, warming forecast high temperatures back into the lower 70s east to lower 80s west. By Friday morning, a deeper trough is forecast to land on the Pacific Northwest while a ridge axis remains in place over the Mississippi River Valley, briefly turning flow aloft northerly. A shortwave is forecast to lift off the Foothills of Colorado/Wyoming early Friday, bringing medium chances for rain across the state from south/southwest to north/northeast Friday through Friday night. Forecast QPF is light (ensemble mean around a few hundredths to a couple tenths of an inch), and there is little to no chance for a thunderstorm. Most locations are likely to see a slight cool down in high temperatures on Friday due to the increased shower chances and associated cloud cover.

On Saturday, the deeper upstream trough is forecast to swing northeastward into the Canadian prairie region, picking up the shortwave responsible for Friday's rain chances. This could lead to a warmer Saturday, but the southern Canadian trough could begin to drive a cold front through the region by Saturday afternoon. Ensembles tend to favor southwest flow through the weekend as a deep but progressive trough moves across the western CONUS. This trough is responsible for widespread medium rain chances in the forecast from Sunday night through Monday and into Tuesday. But there is considerable uncertainty in the evolution of this trough. One potential outcome is for the base of the trough to cut off from the northern stream, which would leave the Northern Plains under split flow with a much lower rain potential. Ensemble clusters show mean height fields to be broad and smooth late Sunday through Monday, making it difficult to discern if one particular outcome is more probable than others. NBM temperature distributions do begin to shift cooler early next week, but remain close to late September averages.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 644 AM CDT Tue Sep 22 2026

Areas of MVFR ceilings are expected across southern North Dakota this morning, and may continue into the afternoon. Confidence in a period of prevailing MVFR is highest at KJMS. VFR conditions are otherwise expected through this afternoon. MVFR to IFR ceilings are then forecast to spread from south to north across the western half of the state this evening through tonight. South-southeast winds will increase to around 15-20 kts this afternoon, with gusts around 25-30 kts. A slight decrease in wind speed to around 10-15 kts is expected this evening through tonight, but higher gusts should be less common.

BIS WATCHES/WARNINGS/ADVISORIES

None.