textproduct: Bismarck

KEY MESSAGES

- Below normal temperatures continue this weekend, with highs about 5 to 10 degrees below average.

- High chances for rain showers (~70-100%) Sunday night into Monday. The greatest chances are over central and eastern North Dakota.

- Becoming windy late Sunday, with the strongest winds expected on Monday before diminishing Monday night. Gusts to 50 mph are possible over western North Dakota.

DISCUSSION

Issued at 225 PM CDT Sat Sep 12 2026

This afternoon, broadly zonal flow was present over the Northern Plains, with a Hudson Bay low to the northeast and a secondary closed low just offshore of the Pacific Northwest. A shortwave aloft associated with the Hudson Bay low was over the central Canadian Prairies. At the surface, broad high pressure extended from east central Alberta into northwest North Dakota.

An embedded vort max in the mean flow has been producing light radar returns across southwest North Dakota throughout the day so far today, although we have to see any confirmation of any rain making it to the surface, which is not too surprising given the high ceilings. Northwest winds are a bit breezy with the surface pressure gradient, but will be diminishing through the rest of the day as the surface high continues to push across the state. Highs this afternoon will be in the upper 50s to upper 60s. Lows tonight will be seasonably chilly, mainly in the upper 30s to mid 40s, although we could see some mid 30s across the International Border.

We did contemplate whether or not a Frost Advisory would be needed tonight. Although the surface high moving in would typically favor temperatures dropping well below guidance, latest deterministic guidance is advertising a shortwave diving south from the Canadian Prairies overnight tonight. Recent CAMs runs are all in agreement on scattered precipitation across at least central North Dakota tonight, with forecast RH and BUFKIT soundings showing midlevel clouds extending across the forecast area. This, plus current satellite imagery showing widespread cloud cover upstream across southern Alberta and Saskatchewan, has us wondering how much clouds will clear out even as the surface high moves through and subsequently how much temperatures will drop below the deterministic NBM which is already skewed close to the 25th percentile. Some isolated frost is still possible mainly across our four northwest counties and into Renville and Bottineau Counties, but at this point we are not confident enough in widespread impacts to go ahead with an advisory. Forecasters this evening will re- evaluate.

On Sunday, the aforementioned deep closed low will continue to move onshore into the Pacific Northwest, with downstream shortwave ridging across the Northern Plains that will warm temperatures some for Sunday and Monday. Highs rebound back into the lower 60s to lower 70s on Sunday, and then the mid 60s to mid 70s on Monday. As the low approaches the region, expect widespread showers and occasional thunderstorms to start late Sunday evening across western North Dakota, expanding east through the night and Monday. NBM PoPs continue to be quite high especially for areas along and east of Highway 83, with a rainy Monday morning commute expected. This is the dividing line of a 50/50 chance for more than 0.50 inches of rain (east) and less than that (west). Showers and thunderstorms will end rather quickly from west to east through the day Monday as the upper low lifts northeast.

The main threat will be for localized heavy rain, with PWATs forecast around 1.5 inches which is towards the upper end of climatology for mid September. We are also expecting strong winds with this system, starting southeasterly on Sunday and switching to westerly on Monday behind the front that moves through. ECMWF EFI highlights southwest North Dakota as the area of most concern with a shift of tails across much of the forecast area, so current thought is wind gusts of 50 to 55 mph across western North Dakota on Monday.

We quickly return to zonal flow on Tuesday, with highs in the 60s but lighter winds after the early week system. Moderate chances for rain return on Wednesday as a progressive embedded wave moves in as synoptic flow turns more southwesterly across the region. NBM temperature percentiles signal a return to near normal temperatures by the end of the work week.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1242 PM CDT Sat Sep 12 2026

VFR conditions expected through the 18Z TAF period. A few isolated rain showers continue in far southwest North Dakota, but any precipitation coming out of them will be very light. Breezy northwest winds will continue to diminish through the day today, with light and variable winds overnight before southeast winds start to increase at the end of the TAF period. Another round of light rain showers is possible overnight, although low confidence in any timing and location, although would be low impact overall.

BIS WATCHES/WARNINGS/ADVISORIES

None.