textproduct: Bismarck

KEY MESSAGES

- Medium to high chances (40 to 80 percent) for showers this afternoon through this evening south central and into the James River Valley, low chances elsewhere.

- Cold overnight low temperatures near or slightly below freezing tonight (west and north central), and Tuesday night (southwest, central, and east).

- Temperatures warming back to above normal by late in the work week and for the weekend, with near daily chances for showers and a few thunderstorms.

UPDATE

Issued at 645 AM CDT Mon May 18 2026

Webcams and observations showing some dense fog across north western and north central North Dakota this morning. This fog should diminish by mid to late morning, however have issued an SPS for its potential impacts on the morning commute. Otherwise low clouds remain across the area. Shower activity has diminished, although some pockets of drizzle are still possible. The next round of rain is starting to take shape in western South Dakota. Left PoPs as is as we continue to monitor the progression of this next round. Lastly SPC does have southeastern North Dakota in a general risk for thunderstorms today. The better instability is in South Dakota and further south today. Perhaps some lightning is possible this afternoon with heavier showers, however, the overall threat for thunderstorms today is very low.

DISCUSSION

Issued at 357 AM CDT Mon May 18 2026

Upper level trough will push across the state later today bringing the next round of showers. Before doing so, lingering low level moisture will bring abundant cloud cover and cooler temperatures this morning through today. A few rain showers and pockets of drizzle will also be found this morning, along with some patchy fog, as a result of this lingering low level moisture. An increased gradient on the surface of the exiting surface low may also bring some breezy north winds today to southern and eastern portions. Temperatures today will be quite cool and generally in the 40s, with some lower 50s. Later today through this evening, the mentioned upper level wave will move through bringing more organized showers to the state. Best chances for these showers remain across south central and eastern portions of the state where the better synoptic lift is. Isolated to perhaps scattered showers are possible elsewhere. QPF will be much less from this second wave, with the higher amounts being a tenth to a quarter of an inch in the southeast. The mentioned wave moves eastward tonight, although a few showers may linger as it does so especially in the west. Perhaps a rain snow mix is possible from these lingering showers. Cooler temperatures will also be found tonight with lows in the 30s. Depending if clouds can clear, some frost is possible. Low level moisture looks to linger, although some far western portions could at least partially clear which may be the area to monitor tonight for frost. Although not in the forecast, perhaps some patchy fog is also possible tonight into Tuesday morning with light winds and lingering low level moisture. Surface high will push this low level moisture eastward on Tuesday. Some isolated showers are possible in the morning as it does so, then look for clearing skies and slightly warmer temperatures in the 50s. Breezy northwest winds could also linger in the east for Tuesday. This surface high combined with ridging aloft will bring clearing skies tonight and colder temperatures. Most areas are forecast in the 30s, with some areas in the central and east could see temperatures near to slightly below freezing. Widespread frost is still likely, with perhaps some freeze highlights also needed. There still remains some uncertainty if we fully clear out and if a switch to a breezy southerly flow occurs overnight. Will continue to message the cold temperatures, yet hold off on any highlights at this time for Tuesday night into Wednesday morning.

A breezy southerly flow is then forecast for Wednesday, with another broad trough pattern approaching the state. Warmer temperatures will return as a result with highs forecast in the 70s. Some lower RH values may also return, although recent rainfall should help with fuels. This trough pattern could also bring some isolated to scattered showers and thunderstorms in the afternoon and evening for Wednesday. Broad trough pattern then looks to continue through the end of the upcoming week. This is forecast to bring seasonable temperatures and near daily chances for showers and thunderstorms. Instability looks limited during the work week, thus the chances for severe thunderstorms looks low at this time. Daily high temperatures in the 60s with lows in the upper 30s to mid 40s are also expected, limiting the frost and freeze threat for the end of the week. Warmer temperatures are then possible for the upcoming weekend with highs in the 70s Saturday to perhaps near 80 on Sunday. Current NBM chances for precipitation this coming weekend are low, although zonal flow aloft and some weak instability could change this with each forecast update. These warming temperatures could also bring lower RH values in the afternoon this weekend. Winds generally look light, which should limit the fire weather threat.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 645 AM CDT Mon May 18 2026

Low clouds will continue through much of the day today, bringing MVFR to periods of IFR ceilings. Some areas of fog are also being report across northwestern and north central portions this morning bringing LIFR conditions. Fog could last through the mid to late morning hours, and generally from KXWA to KMOT. The next round of showers is expected to return this afternoon through this evening, and will be more confined to the south and east, although most sites will have at least slight chances for rain showers. Any shower has the potential to bring MVFR to IFR conditions. Tonight will see shower activity diminish, although low clouds could linger bringing MVFR to isolated IFR ceilings. Some low VFR ceilings may be found for western sites late tonight into early Tuesday morning. Patchy fog may also return tonight, although confidence is not high enough to include at this time. A breezy north wind may also be found throughout much of the forecast period.

BIS WATCHES/WARNINGS/ADVISORIES

None.