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KEY MESSAGES

- Isolated to scattered severe thunderstorms expected over much of western and central North Dakota through this evening.

- Isolated to scattered severe thunderstorms possible over central into eastern North Dakota on Wednesday.

- Low to medium chances of showers and thunderstorms Thursday through the remainder of the week.

- Highs in the 70s and 80s through the workweek, warming into the 80s and lower 90s for the weekend.

UPDATE

Issued at 700 PM CDT Tue Jun 2 2026

** MESOSCALE DISCUSSION **

Thunderstorms have formed along the pre-frontal wind shift/ differential mixing boundary from near Fessenden southward to the Pettibone, Tappen, Napoleon, Wishek, and Ashley areas. In this area, capping has been eroded in the absence of the high clouds that have resulted in more MLCIN further west. There is large bouyancy with MLCAPE around 2000 J/kg, but effective shear is generally less than 30 kt, and those vectors are oriented parallel to the wind shift. This means that we have seen and will continue to expect multicell, pulse-type storms along this axis, with a marginal risk of hail to around half dollar size and damaging wind gusts up to 60 mph. Note that given the weak shear environment, hail diagnostic tools such as MRMS and single-radar MESH will tend to overestimate hail sizes with these storms.

Further west, storms along/ahead of the cold front, e.g., in Sioux County, have struggled to become established in the face of larger MLCIN. Similarly, post-frontal convection, such as that near Glen Ullin and Center as of 00 UTC, has also been struggling to intensify. These areas of convection represent only a low risk of intensification and severe-storm risk for the remainder of the evening. As observational trends allow, we will cancel western and northern portions of the Severe Thunderstorm Watch early in collaboration with SPC.

CJS

UPDATE Issued at 410 PM CDT Tue Jun 2 2026

** MESOSCALE DISCUSSION **

A severe hail and wind risk will continue across central ND the next several hours, with only a low tornado risk. In this scenario, the main hazards will be from large hail and damaging winds, which is why a Severe Thunderstorm Watch has been issued.

Technical discussion: As of 21z, thunderstorms including some previous marginal supercell structures are focused in the McHenry, Pierce, and Sheridan County areas. This is along a pre- frontal trough, and possibly where the cold frontal zone has begun to merge with that trough, resulting in additional low- level convergence. MLCAPE on the order of 2000 J/kg and effective-layer shear on the order of 35-40 kt in that zone favor the marginal supercell structures with an attendant large hail and damaging wind risk. However, anvil-level flow does weaken with northward extent, and the orientation of deep-layer shear vectors to the surface boundaries suggests gradual upscale growth will occur in this area if or when additional initiation occurs.

Further southwest, the prefrontal surface trough is seen on radar fine-line from near Mercer to Price, Crown Butte Lake, and Carson. The 18z KBIS RAOB sampled residual capping with MLCIN around -50 J/kg. As surface temperatures reach the mid 80s F, that capping becomes minimized, but high-level clouds spreading across Grant, Morton, and into Burleigh Counties casts some doubt on the timing of convective initiation. We believe that eventually additional development will occur in south central ND, but robust development may take some time and additional frontal lift to overcome the residual capping layer. The highest probability of development may initially be over Sioux and southern Grant Counties, where satellite trends suggest more robust upstream development occurring in an area where downstream high-cloud shading is less prevalent.

There is also a low to medium probability that the line of cumulus from Kidder south into Emmons Counties, on the edge of richer low-level moisture representing a differential heating boundary, could result in pre-frontal initiation. However, deep- layer shear is weaker there and would result in more marginal, multicellular type of storms.

Generally-speaking, low-level hodographs are relatively small, and accordingly, low-level SRH ahead of the front in the buoyant sector is 100 m2/s2 or less. Deep-layer shear vectors are also oriented parallel to the front, favoring upscale-growing and messy modes. This all suggests that the tornado risk is low overall.

CJS

DISCUSSION

Issued at 151 PM CDT Tue Jun 2 2026

Relatively well stacked low pressure is present over southern Saskatchewan. This low will very gradually slide eastward over the next couple days. During this timeframe, an associated very slow moving cold frontal boundary currently draped north to south over western North Dakota will slide eastward. This frontal boundary will likely become quasistationary, and possibly retrograde, at times. Showers and thunderstorms are present and will continue to frequently develop along and ahead of this frontal boundary.

High pressure over the Great Lakes region will continue advecting moisture from the Gulf of America into the Northern Plains. This added moisture, with boundary layer dewpoints in the mid 50s to low 60s will help produce a buoyant atmosphere. In addition, deep layer shear along and ahead of the front is generally progged at around 35 to 45 kts with a southwesterly component. Combined, this should produce the conditions for isolated to scattered severe thunderstorms this afternoon and evening. With the southwesterly component of the 0 to 6 km bulk shear vectors and a north to south frontal boundary, suspect clusters are the most likely thunderstorm mode along most of the front. Considering there is already a clusterish line of showers and thunderstorms along the frontal boundary, suspect a limited timeframe for any discrete cells to develop this afternoon. Though one has already developed near the Turtle Mountains as of this writing. This means that while there may be a window for golf ball size hail and an isolated tornado threat, this may wind up being a case where widespread marginal severe thunderstorms prevail overall. In addition, slow moving storm motions with the potential for training could lead to heavy rain and a localized flooding event.

Of note, a mesoanalyst will produce a mesoanalysis discussion within the next hour or two. This will provide even further details in regard to the severe weather threat based on the evolving severe weather environment. Depending on how the environment evolves, changes to the above threat expectations are not out of the question.

While there may be initial LLJ development this evening mainly over the eastern half of the state, it does not look to persist through the night. Therefore, while isolated to scattered showers and thunderstorms are likely to persist through at least parts of the area through tonight, the severe threat will likely wane rapidly as the sun sets, instability decreases, and capping increases. Still, a few strong storms are not entirely out of the question overnight.

For Wednesday, the aforementioned frontal boundary will continue to gradually shift eastward and as such, so will the severe threat. Therefore, concur with SPC that the highest severe potential for Wednesday will be in the south central (mainly east of Hwy 83) and in eastern North Dakota. The biggest threats will remain strong winds and large hail, though an isolated tornado threat could return mainly in the far southeast, including the southern James River Valley of ND.

Gulf moisture will be, at least temporarily, cut off behind the frontal boundary. However, a deepening low pressure over the Central Plains could bring the return of showers and thunderstorms mainly to southern North Dakota Thursday through Friday. The severe threat is favored to remain south for the most part at this time, though will keep an eye on that over the next couple days. Saturday is favored to remain mostly dry, after which periodic showers and thunderstorms are possible to start next week. CSU machine learning suggests at least low severe weather potential most days to start next week.

Slightly above average temperatures with highs in the mid 70s to low 80s are expected to continue through Friday. Well above average temperatures are then expected to return this weekend and are favored to continue into the middle of next week. Lows will start out mostly in the mid 40s to low 50s before increasing to the 50s to low 60s next week.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 641 PM CDT Tue Jun 2 2026

Showers and thunderstorms continue along a cold frontal boundary that is draped across central North Dakota from just east of KBIS northeastward to just east of Langdon. Near this front, expect the potential for additional SHRAs/TSRAs...some of which could be severe...to impact potentially KJMS amd KBIS over the next few hours with MVFR of lower CIGS/VSBYS. SHRA/TSRA activity is then expected to shift east with the cold front as it expands in coverage through around 03/06Z...with additional SHRAs/TSRAs rotating around the upper level low across southern Saskatchewan impacting the western terminals overnight and working its way eastward during the daytime hours Wednesday. Overall, an unsettled period with low confidence in timing of TSRA activity and therefore limited lower CIGS/VSBYs to mainly prob30 groups.

BIS WATCHES/WARNINGS/ADVISORIES

None.