textproduct: Bismarck

KEY MESSAGES

- Isolated to scattered severe thunderstorms are possible this afternoon and evening. Expected hazards include hail as large as 2 inches in diameter and damaging winds up to 70 mph, with a tornado possible.

- Hot and humid today, with high temperatures and heat index values around 95 to 100.

- Windy on Monday, with critical fire weather conditions possible in parts of southwest and south central North Dakota.

- Cooler on Tuesday, then becoming hot once again by the end of the week.

DISCUSSION

Issued at 443 AM CDT Sun Jul 19 2026

An upper ridge axis is pivoting back through the Northern Plains early this morning. Underneath the ridge, a plume of mid level moisture transport has initiated scattered showers and isolated thunderstorms over south central North Dakota, slowly drifting eastward. SPC mesoanalysis shows this activity to be on the outer fringes of MUCAPE of just a few hundred J/kg, with effective bulk shear no greater than 20 kts. We therefore do not anticipate this convection intensifying as it shifts into the James River Valley before dissipating later this morning. The thermal ridge is forecast to enter the western Dakotas this afternoon, allowing high temperatures to soar into the 90s to around 100. The hottest temperatures are expected in the southwest quadrant of the state. Dewpoints are forecast to remain in the 60s for most areas through the afternoon, and could even reach the lower 70s from the James River Valley to the Turtle Mountains. The combination of heat and humidity brings the maximum heat index forecast to around 100 across southwest and much of central North Dakota. Confidence in higher dewpoints led to the expansion of the Heat Advisory to now cover all counties along and south of Highway 200 within our forecast area. Some thought was given to expand into parts of north central North Dakota, including Minot, but there was not enough confidence in widespread heat impacts that far north. The area of greatest concern within the Heat Advisory is south central North Dakota where forecast maximum heat indices are closer to 105 than 100, and the maximum wet-bulb globe temperature risk is solidly in the Extreme category.

There is a conditional risk for isolated to scattered severe thunderstorms this afternoon and evening, but aspects of this part of the forecast are no more certain, and may even be less certain, than they were yesterday. A shortwave digging into central Saskatchewan later today will force a lowering of mid level heights over the Northern Plains as a surface trough slides in from the west. The biggest question remains when and where, and now perhaps if, convective initiation (CI) will occur. Every 6-hour cycle of CAMs since yesterday has shown increasingly lower coverage of convection and lower odds of CI even happening. And if CI does occur, CAMs now favor it more in southwest/south central North Dakota than the north. This may be due to a higher probability of convective temperatures being breached as there are no discernible differences in the magnitude of convergence along the surface trough, and the magnitudes of height falls are higher farther to the north. Forecast MLCIN may be just a touch stronger than yesterday, and some forecast soundings in north central North Dakota appear to be much more strongly capped. If CI does occur, it is not a given that storms will become severe as dry-air entrainment could hinder updraft growth and sustainment. However, if storms are able to become well-established, MLCAPE approaching 3000 J/kg and effective bulk shear around 40 kts and later increasing to near 50 kts would be more than sufficient for severe weather. Another aspect that has grown more uncertain is storm mode. Previously, shear and deep layer wind vectors were forecast to be perpendicular to the surface trough, strongly favoring a discrete mode. But in more recent forecast guidance, the surface trough has taken on a slightly more positive tilt while the aforementioned vectors have turned more due easterly rather than east-southeast. The angle of separation between the boundary axis and these vectors is still greater than 45 degrees, and with weak deep layer forcing in a capped environment, we still think a discrete mode would be favored initially. Long hodographs with subtle concave and convex curvatures would favor splitting supercells, which has shown up as a solution in CAMs. High LCLs and inverted-v soundings farther south could support damaging winds with any storm mode and could accelerate outflow to cause upscale growth into a mixed/cluster storm mode. No changes have been made to our most likely hazard forecasts of 2 inch diameter hail and 70 mph damaging winds. The setup of high CAPE with moderate to strong deep layer shear along a vorticity-rich surface boundary with low baroclinicity remains such that a tornado cannot be ruled out. The risk for severe weather will diminish after midnight with storms either dissipating or exiting the forecast area to the south and east.

A cold front remains scheduled to sink through the region on Monday, but not in time to keep temperatures from reaching the lower to mid 90s across southern North Dakota. In northern North Dakota though, highs on Monday could be limited to the lower and mid 80s. Windy conditions are expected on Monday in a cold air advection regime with a tightening isobaric gradient and mean mixed layer winds around 25-35 kts. This could translate to surface gusts approaching 45 mph. Dewpoints will also become lower on Monday, and could fall into the 40s from southwest into south central North Dakota, yielding humidity as low as 20 percent. Critical fire weather conditions remain possible along and south of I-94 and west of Highway 83, but forecast confidence in the magnitude of sustained winds is not yet high enough to issue a Fire Weather Watch. The mid level shortwave trough trailing the cold front could bring widely scattered showers and thunderstorms into northern parts of the state late Monday afternoon evening, but there should not be enough instability or shear to support a severe risk.

A final note about the shorter-term forecast is that we are monitoring the potential for near-surface smoke entering western and central North Dakota later today, which could linger through Monday. Only patchy smoke has been added to the forecast for now as it has not yet been mixed down to the surface upstream. There is higher confidence in smoke aloft moving over the region later today and persisting through Monday when the HRRR is simulating notably high concentrations of vertically- integrated smoke.

Ensemble guidance remains confident in Tuesday being a cooler and dry day with high pressure settled over the US Northern Plains and Canadian prairie provinces. NBM high temperatures on Tuesday remain in the mid 70s northeast to mid 80s southwest. Confidence continues to increase that the upper ridge will eventually shift from the Rockies back into the central CONUS in time for next weekend, with a couple possible shortwave passages leading its return. This could return very hot temperatures to the region, with the NBM already advertising widespread highs around 100 on Saturday.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 443 AM CDT Sun Jul 19 2026

Scattered showers and isolated thunderstorms will continue in south central North Dakota early this morning. Some brief visibility restrictions are possible if a heavier shower or storm moves over a terminal. Later this afternoon and evening, isolated to scattered severe thunderstorms could develop across southwest and central North Dakota. These storms would be capable of large hail, strong and erratic wind gusts, and IFR visibility from heavy rain. VFR conditions are expected to prevail outside of heavier showers and thunderstorms, but smoke from western wildfires could begin reducing visibility across western and north central North Dakota by this evening. If current forecast trends hold, a mention of FU may need to be added to the TAFs at KXWA, KDIK, and KMOT. Primarily southerly winds this morning, which may become gusty in parts of central North Dakota, then shifting to the northwest in the afternoon and evening as a frontal boundary moves through.

BIS WATCHES/WARNINGS/ADVISORIES

Heat Advisory from 1 PM CDT /noon MDT/ this afternoon to 9 PM CDT /8 PM MDT/ this evening for NDZ017>020-022-023-025-031>033- 035>037-040>044-046>048-050-051-057>062.