textproduct: Bismarck

KEY MESSAGES

- Rain showers continue into this evening south central ND into the James River Valley before departing to the east-northeast tonight. Slight chance of showers elsewhere.

- Lows tonight into Tuesday morning dip into the upper 20s to lower 30s. Freeze Warnings and Frost Advisories have been issued. Cold temperatures again possible Tuesday night/Wednesday morning, mainly east.

- Unsettled weather pattern develops mid to end of the week. Greatest and most widespread chances (about 30 to 60 percent) come Thursday into Friday.

DISCUSSION

Issued at 223 PM CDT Mon May 18 2026

Current surface analysis places low over the upper midwest with notable frontal boundary stretching to the southwest through the central plains. High remains over southern Saskatchewan into central Montana. Upper level analysis places trough over Saskatchewan southward towards the central Rockies. Southeast flow over our area with some embedded short waves is resulting in broad shower activity over much of South Dakota into southeast/south central North Dakota.

For tonight, ongoing showers will continue into this evening before departing to the east/northeast. In the meantime, surface high settles into the area, mainly western locations, with cool air continuing to slide in. This will result in sub freezing temperatures over parts of western and north central North Dakota, therefore a Freeze Warning has been issued. Further east, confidence is a little lower as to how cold it will get given the persistant cloud cover. With that said, lows look to dip close to or reach freezing, so have decided to go with a Frost Advisory for that area even though technically "frost" will not form, but sensitive plants could be damaged, especially if temperatures are a degree or two lower than forecast.

Trough pushes east early Tuesday, with a low amplitude ridge passing over for Tuesday into Wednesday. Expect a gradual warm- up for high temperatures, but Tuesday night may see some freezing lows, mainly over our east given the high passing over and clearing skies.

Next trough digs in over the western CONUS on Thursday with our flow shifting southwesterly before the system closes off and ejects to the northeast to close out the week. Greatest chances for precipitation come Thursday into Friday (about 30 to 60 percent chance). Warming trend expected going into the weekend with NBM temperature spreads being quite confident in seeing well above average temperatures by late weekend.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1253 PM CDT Mon May 18 2026

Low stratus over the state will continue to bring widespread MVFR with localized IFR ceilings through the rest of today into the overnight hours. Improvement is expected late tonight over far western North Dakota, then over much of western and parts of north central North Dakota Tuesday morning.

BIS WATCHES/WARNINGS/ADVISORIES

Freeze Warning from 1 AM CDT /midnight MDT/ to 9 AM CDT /8 AM MDT/ Tuesday for NDZ001>005-009-010-012-017>020-022-031>033- 040-041-043-044-055>059. Frost Advisory from 1 AM CDT /midnight MDT/ to 9 AM CDT /8 AM MDT/ Tuesday for NDZ013-023-025-035>037-042-046>048-050-051- 060>062.