textproduct: Bismarck

KEY MESSAGES

- Scattered showers and thunderstorms today, then widespread showers with isolated to scattered thunderstorms Tuesday evening through Wednesday.

- A few thunderstorms could become strong along and between Highways 85 and 83 this afternoon, and from northwest to south central North Dakota Tuesday evening into Tuesday night.

- Temperatures favored to remain near to below normal through the week, with highs mostly in the 60s Wednesday and Thursday, and 70s all other days.

- Strong northwest winds are possible in western and south central North Dakota on Wednesday.

DISCUSSION

Issued at 513 AM CDT Mon Jun 15 2026

Cyclonic northwest flow prevails over the Northern Plains early this morning. An embedded shortwave over southeast Saskatchewan that coincides with a weak surface/low-level west-to-east oriented cold front is preparing to cross the international border. A broken line of widely scattered showers with an occasional thunderstorm has been associated with this activity through the night, and high-resolution model guidance suggests it will continue into North Dakota through the morning. The highest chances for rain this morning are in northwest North Dakota where forcing may be supplemented by left exit region jet dynamics. The leading edge of DCVA associated with the shortwave is forecast to clear the state by the afternoon while the western side of the cold front pushes south more quickly than the eastern side. A continuous stream of cyclonic vorticity is anticipated over the region through the afternoon, which combined with diurnal heating is expected to result in scattered showers and thunderstorms. There have been and continues to be mixed signals on the threat ceiling for storms this afternoon. CAPE is forecast to be highest in central and eastern North Dakota at around 500-1000 J/kg. In contrast, deep layer shear is forecast to be much stronger over western North Dakota at around 40-50 kts (and unidirectional), with a sharp cutoff to only 10-20 kts central and east. It is possible that there may be just enough overlap in the higher CAPE and shear to allow stronger thunderstorms to develop, with a very low but non- zero probability for a severe storm. This potential corridor shows up in HREF maximum UH tracks along and between Highways 85 and 83, although the maximum values of UH themselves are lower than what CAMs typically simulate for a severe thunderstorm. Therefore, a reasonable high-end expectation for the strongest storm(s) today would be hail up to nickel size and wind gusts to around 50 mph.

Breezy northwest winds are expected to return this afternoon, strongest in southwest North Dakota where gusts could approach 40 mph. Forecast highs today are in the upper 60s to mid 70s. Showers and thunderstorms should diminish through the evening, giving way to a quiet overnight period with lows in the 40s. An upper level jet streak is forecast to curl from the Canadian Rockies into the Northern High Plains by Tuesday morning. The placement of its left exit region over a 700 mb shortwave and low level warm air advection could produce a broad area of light rain showers over western and central North Dakota Tuesday morning and afternoon, with little to no chance of thunderstorms until at least late afternoon. The NBM shows Tuesday to be the warmest day of the week for most locations with highs in the lower 70s to lower 80s, but wonder if this may be too warm given the expected increase in cloud cover and rain chances. In any case, winds should at least be much lighter on Tuesday.

A potent shortwave is forecast to eject off the Canadian Rockies by Tuesday evening and dig into the Upper Mississippi River Valley on Wednesday. Several clusters of showers and thunderstorms are being depicted by CAMs ahead of the shortwave traveling through the state late Tuesday afternoon through early Wednesday morning, with the highest probabilities focused from around Williston to Bismarck to Jamestown. There is an emerging signal for a highly conditional severe thunderstorm threat with this activity, with the two key conditions being 1) whether, or for how long, storms will remain rooted in the boundary layer and 2) how much CAPE and shear would be available for elevated convection. Any convection that remains rooted in the boundary layer Tuesday evening would experience very strong effective bulk shear around 50-60 kts. CAPE is less certain, with projections ranging anywhere from just a few hundred to near 1500 J/kg. The highest probability for a severe storm would be in northwest North Dakota early Tuesday evening, with chances lowering in space and time. But the 06Z HRRR, while clearly an outlier, is attention-grabbing with a few very strong UH tracks through south central North Dakota into late Tuesday night. The probability of a storm realizing the amount of CAPE and shear that would be needed to produce storms of this magnitude seems very low, especially considering both MUCAPE and effective bulk shear (using RAP 2-7 km shear as a proxy) are forecast to decrease over time and space. We will therefore not message a severe potential at this time, but this aspect of the forecast will need to be monitored closely.

The risk for even just garden-variety thunderstorms is forecast to significantly lower for Wednesday as the digging shortwave brings a more stable air mass and weaker mid level winds over the state. But widespread rain showers are likely to continue through at least the afternoon. The favored axis for highest QPF Tuesday evening through Wednesday afternoon has taken a slight northward shift, with 3 out of 4 ensemble clusters placing it from near Williston to Fargo. But threshold probabilities along this corridor have also risen to high chances for at least 0.25", medium chances for at least 0.5", and low chances for at least 0.75". The biggest forecast concern during the day Wednesday could be for strong northwest winds. Deterministic models show an initial push of cold air advection and pressure rises late Tuesday night/early Wednesday morning with around 40-50 kts mixing potential, but the time of day should limit gusts of that magnitude, at least temporally. A secondary surge thereof could pass through Wednesday afternoon, but this one carries much higher uncertainty in placement and timing, and model soundings show uncertainty in the depth of the mixed layer. Regardless of magnitudes, probabilities for impactful winds on Wednesday range from high in the southwest to low in the northeast. The ECMWF EFI reflects this thinking with its wind gust values approaching 0.8 and inclusion of a shift-of- tails contour. The NBM has shown a run-to- run cooling trend but still keeps highs in the mid to upper 60s on Wednesday. This still may be around 5 to 10 degrees too warm for any areas that see persistent cloud cover and rain showers throughout the day, which could be much of the state.

A northwest flow pattern is favored to prevail through the end of the work week, with increasing ensemble spread on whether that will hold through the weekend or transition to a progressive and amplified quasi-zonal flow. Thursday looks to remain cool with lingering shower chances (20-40 percent) and highs still in the 60s. Despite the increasing uncertainty in the synoptic pattern, NBM maximum temperature spreads remain low given the forecast time range and show a slight warm up into the 70s through the weekend.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 513 AM CDT Mon Jun 15 2026

Widely scattered showers with an occasional thunderstorm will spread southeastward across the state through the morning. This activity is unlikely to greatly impact aviation. This afternoon, scattered showers and thunderstorms are expected across much of western and central North Dakota, with higher probabilities and greater coverage expected in central North Dakota compared to the west. Thunderstorms could produce small hail, erratic wind gusts, and downpours reducing visibility to MVFR/IFR levels. Showers and storms should diminish through the evening. Aside from afternoon and early evening thunderstorms, VFR conditions are otherwise expected to prevail. Winds will become westerly around 10-15 kts this morning, then turn to the northwest and increase to 15-25 kts this afternoon.

BIS WATCHES/WARNINGS/ADVISORIES

None.