textproduct: Bismarck

KEY MESSAGES

- Well above average temperatures and mostly dry conditions continue through Wednesday.

- Critical fire weather conditions are possible across most of western and parts of southern North Dakota on Wednesday.

- Active weather pattern Wednesday night through the end of the week, with medium to high precipitation chances and a strong cooling trend.

- Strong west to northwest winds are likely Thursday and Friday.

DISCUSSION

Issued at 251 PM CDT Tue Apr 21 2026

Quiet weather day today, with quasizonal flow aloft downstream of a deep closed low moving onshore over the western CONUS. Broad high pressure was centered over northern Minnesota, with a modest pressure gradient and boundary oriented northeast- southwest across western North Dakota. Mostly sunny with breezy southerly winds today, and afternoon highs in the lower 70s east to lower 80s west.

Forecast concerns increase Wednesday and continue through the end of the week. The aforementioned low approaches the region and an upper ridge builds in just downstream of the trough base, with low-level warm air advection boosting highs into the mid 70s north central to around 90 far west and south.

A Fire Weather Watch has been issued for western and parts of southern North Dakota for Wednesday, due to the combination of low relative humidity and strong winds. Southwest North Dakota compared to the northwest and James River Valley areas have slightly different environments. South to southeast winds will be sustained around mph across southwest North Dakota, with minimum relative humidity in the lower teens. Further north and east, winds will be stronger but dew points slightly higher, still leading to possible critical fire weather conditions. Joint probabilities of relative humidity less than 20 percent and winds of at least 15 mph favor western North Dakota, along the SD state line, and into the southern James River Valley, which is where we issued the watch for. Some uncertainty on conditions in the far south central and questions on what dew points end up looking like in the James River Valley. We are also favoring the fact that it will be the first widespread hot and windy day of the season, with forecast highs from mid 70s far north central to the upper 80s southwest and far south central. Right now the main climate sites to potentially break record highs are Dickinson (90 degrees in 1989) and Bismarck (89 degrees in 1990).

We continue to monitor thunderstorm potential Wednesday evening as the trough base and attendant low lift over the Northern Rockies and approach the region. This is also where the dew point question comes into play, with forecast instability varying amongst deterministic guidance. General thought is for marginal instability and bulk shear available, with potential for a few stronger storms, but likelihood of an isolated severe storm is low. 12Z HREF does paint a few max UH tracks across the forecast area, but will have to see how much moisture return we can get in the next 24 hours. Dew points across southeast North Dakota are in the upper 20s to lower 30s this afternoon, and looking upstream across the I-29 corridor and southern Minnesota, we have to look pretty far south to start seeing dew points in the 50s, which would severely limit any sort of convective potential, but would increase the fire weather potential.

As the upper low moves into the state on Thursday, precipitation chances increase early in the morning and through the day, although ensemble guidance is advertising a noticeable shift to the northwest, moving the center of the low out of the forecast area compared to what was being shown yesterday. With this shift, we have seen a significant decrease in forecast precipitation amounts, with the likelihood of exceeding a half inch of QPF only around 20 percent in the northwest corner of the state. Probabilities for more than an inch of snow are similar. The placement of the system would also favor much of central North Dakota to be dry slotted through the main push of moisture. The benefit of the shifting of the upper low is that it's not quite as slam dunk of a scenario for very strong winds, although still high confidence in needing an advisory on Thursday for the majority, if not all of the forecast area.

The continued story is then cooler air filters in, although with the low skewed further to the north we end up in more of a zonal flow aloft / diffuse surface pattern, with forecast highs a few degrees warmer than previous updates, which leads to more of a lower 40s to lower 50s forecast through the weekend. Winds will stay breezy through Saturday before diminishing more as flow finally begins to weaken. We still have low chances for precipitation Friday and Saturday, but with the system displaced not as confident in as much wrap-around precipitation. Still favored as snow, although NBM p-types are showing more of a mix across the south, especially during the day as our temperatures nudged up.

The other noticeable change with this forecast package issuance is increasing chances for precipitation on Sunday. As the upper low lifts further to the north, a secondary wave with a southern stream trough is projected to move through the Dakotas, and is further north than previous forecast iterations. This will continue chances for rain and snow through Sunday and into Monday. Temperatures are favored to moderate further into next week, although look to stay near to slightly below normal, and certainly not as warm as they have been to start this week.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1234 PM CDT Tue Apr 21 2026

VFR conditions expected through the TAF period. Breezy southerly winds will diminish overnight and become more variable before increasing again on Wednesday. A few high clouds this afternoon, with increasing clouds late in the period ahead of an approaching system.

BIS WATCHES/WARNINGS/ADVISORIES

Fire Weather Watch from Wednesday morning through Wednesday evening for NDZ001-009-017-018-031>033-040>048-050-051.