textproduct: Bismarck

KEY MESSAGES

- Isolated severe thunderstorms are possible Saturday afternoon through Saturday night, and again Sunday afternoon through Sunday night. The main hazards will be large hail and damaging winds.

- Daily chances for showers and thunderstorms continue through next week.

- High temperatures will generally be in the mid 70s to lower 80s through midweek next week, before warming up late in the week.

UPDATE

Issued at 535 PM CDT Fri Jul 18 2025

Only some minor adjustments to sky cover with this update. Scattered to broken, mainly low VFR clouds remain over a good portion of western and central ND. Surface high pressure over southern Saskatchewan and into eastern Montana and western ND will move east tonight, settling over eastern ND Saturday morning. This should bring a quiet night as far as showers and thunderstorms go, although there is a small chance of overnight or early Saturday morning convection in/near the southwest portion of the state. We will probably see patchy, if not areas of low stratus and fog as we get into the late evening and more likely the overnight hours. Previous fcst has this covered. Will see how it plays out this evening. Updated text products will be transmitted shortly.

DISCUSSION

Issued at 246 PM CDT Fri Jul 18 2025

This afternoon, the synoptic pattern was characterized by longwave troughing across the northern part of the CONUS, with a sharp trough and immediate downstream ridge in the western Canadian Prairies. The center of a weak surface high was analyzed in southern Saskatchewan, with a few showers exiting our far eastern counties as an upper shortwave moves out. Cloud cover has been a bit more widespread than expected, and is relatively low, with a scattered deck around 2 to 4k feet. Highs this afternoon are in the lower 70s to lower 80s.

Cloud cover is expected to diminish this evening, with the exception of parts of the James River Valley. Forecast soundings in parts of central North Dakota are fairly convinced that fog will develop, so broad-brushed an area of patchy fog across most of the central for late tonight into Saturday morning. Lows will be in the upper 40s to mid 50s.

The aforementioned trough and attendant closed low are progged to drop south through the day Saturday, while the ridge quickly moves over western North Dakota while being flattened as the closed low expands. As flow to our west begins to turn just a bit southwesterly and embedded impulses move through, precipitation chances begin to increase through the day Saturday. Low chances start in the southwest, before probabilities expand north and increase in the afternoon as a surface low deepens in south central Montana. Breezy southeast winds will help advect in dew points around 60 degrees F, leading to a ribbon of increased instability along the ND/MT state line, and bulk shear around 40 to 45 knots will be sufficient for supercells. Storm mode and the overall progression is still a bit fuzzy, with today's CAMs run really increasing the spatial coverage of convection, leading to higher overall chances of precipitation, as well as speeding up the timing of development. Any early afternoon thunderstorms would likely be subsevere, but can't rule out multiple rounds of thunderstorms in general, especially for places south and west of the Missouri River. Advertising isolated severe thunderstorms with hail up to the size of golf balls and wind gusts up to 60 mph, with the most likely window of severe weather the late afternoon through the evening.

Troughing aloft becomes more pronounced across the Pac NW on Sunday, leading to continued southwest flow across the Dakotas. Blended POPs are already in the 40 to 60 percent range through the day Sunday, with some potential for holdover from the previous night's showers and thunderstorms. Sunday has been highlighted in machine learning guidance as a day to watch, with continued moisture advection leading to higher instability across much of the forecast area, and overlapping with modest bulk shear. There is some concern for mid-level capping with height rises relatively neutral, but if storms do manage to form, there is certainly potential for them to be severe. Currently carrying mention of isolated severe thunderstorms for the majority of the forecast area. Slow storm motion and high PWATs could lead to locally heavy rainfall and potentially some isolated flooding concerns as well.

The overall pattern is quite consistent Saturday through Wednesday, with highs generally in the mid 70s to lower 80s and overnight lows in the mid 50s to lower 60s. Troughing out west stays persistent through midweek, with daily low to medium chances for showers and thunderstorms. Late in the week, ensembles favor flow to become more zonal and temperatures warm up into the widespread 80s, with medium probabilities for highs to return to the 90s. Above normal temperatures are favored through the end of the month, with the active pattern continuing through much of this time.

AVIATION /00Z TAFS THROUGH 00Z SUNDAY/

Issued at 535 PM CDT Fri Jul 18 2025

VFR conditions to begin the 00Z TAF period. Expect mostly VFR conditions this evening. Late this evening or more likely after midnight, we may see patchy to areas of fog develop over portions of central into eastern ND. As we get into Saturday there is also some indication of low stratus being pulled up into southwest ND from the south. A little more confident in the patch fog late evening and overnight, over the stratus later Saturday. Will probably add some mention of fog at KJMS and KBIS to begin with and see how things go this evening. Late in the period there is the potential for thunder moving into western ND, but at this time too much uncertainty to include at KXWA or KDIK. Generally light easterly flow tonight, with a southeast flow on Saturday, becoming breezy with gust to around 25kts at western sites in the afternoon.

BIS WATCHES/WARNINGS/ADVISORIES

None.