textproduct: Bismarck

KEY MESSAGES

- Widespread rain showers developing in western North Dakota late this afternoon and evening, continuing through Friday and spreading into central and eastern North Dakota Friday afternoon through Friday night.

- Medium to high chances for an axis of at least half an inch of rain in western North Dakota, with low to medium chances for exceeding 1 inch of rain.

- Near to slightly below normal temperatures through Friday, warming to well above normal by the end of the holiday weekend.

UPDATE

Issued at 945 AM CDT Thu May 21 2026

The band of rain is still sitting over the far northwestern corner of the state. Forecast still remains on track so no adjustments were needed at this time.

UPDATE Issued at 702 AM CDT Thu May 21 2026

Some shallow ground fog has developed in far southwest North Dakota early this morning. This should quickly burn off within an hour or two. Otherwise, the forecast for today remains on track.

DISCUSSION

Issued at 421 AM CDT Thu May 21 2026

The main story in the shorter term forecast period is the expectation for beneficial rainfall across much of western and to a lesser extent, parts of central North Dakota late this afternoon through Friday night.

Synopsis: An upper level low is spinning over southwest Saskatchewan early this morning, with a trough axis extending southwestward to southern Idaho. A near-stationary surface trough is located from the southeast corner of Saskatchewan to northeast Wyoming. As the closed upper low continues to spin across southern Saskatchewan throughout the day, the base of the upper trough will dig southeastward through southern Wyoming and spin up another closed circulation over the Black Hills Friday morning. The southern closed low is forecast to become the predominant feature on Friday and spin northeastward into the Red River Valley Friday night, with some uncertainty on the evolution of and/or interaction with the northern closed low. All the while, the surface trough will become inverted as it attaches to lee cyclogenesis in northeast Colorado by tonight. By the time the Colorado low ejects northeastward on Friday, another surface low could form near the Black Hills and create a double-barrel surface low that attends to the southern upper low.

The main focus for continuous showers through Friday morning is along the inverted trough axis in western North Dakota. Ensemble systems continue to hone in on a corridor of highest rain amounts, but there is still some spread that now appears to be dependent on model resolution. Global ensembles favor a corridor of highest mean QPF and threshold probabilities from around Lemmon, SD to Minot. In high-resolution ensembles, this same axis is shifted westward from between Bowman and Hettinger to Stanley. Regardless of location, all ensemble systems show high probabilities for at least half an inch of rain and low to medium probabilities for at least one inch of rain. But the HREF contains higher probabilities for exceeding one inch, and its probability-matched mean QPF shows a corridor of 1.5 to 2 inches, with localized areas even exceeding 3 inches. These higher rain projections by CAMs are undoubtedly being driven by training convection, for which there appear to be high chances of occurring this evening into the overnight hours. Ingredients supporting this include skinny CAPE profiles with up to 1000 J/kg, high deep-layer RH, and favored storm motions parallel to the inverted trough. The main risk from thunderstorms will be heavy downpours. There does not appear to be enough shear to support stronger convection, but some small hail and gusty winds cannot be ruled out. Given the seasonal moisture deficits, the risk for flooding is very low. But there could be ponding of water in urban, low-lying, and poor drainage areas where the heaviest rain falls.

The inverted surface trough is forecast to shift very little, if at all on Friday. This will continue to produce showers over western North Dakota, but weaker buoyancy should keep rainfall rates lower on Friday. By Friday afternoon, the nearly-stacked low over South Dakota will begin to push a large area of mostly stratiform rain with some possible embedded convective elements into south central and southeastern North Dakota. This shield of rain will progress north-northeastward through the evening and into Friday night. Most areas in central and eastern North Dakota will see only a 3-6 hour period of rainfall at most, but the wrap-around deformation zone could stall over part of south central North Dakota for a longer duration rainfall. For areas along and east of Highway 83, there are low (north) to medium (south) chances for exceeding half an inch of rain through Friday night, with only very low chances for exceeding one inch.

High temperatures today are forecast to reach around 65 to 70 degrees, except in the far west where thicker cloud cover and developing showers could keep highs closer to 60. With increasing confidence in widespread rain and clouds on Friday, the high temperature forecast has in turn cooled into the mid 50s to mid 60s, which may still be a little too warm. Lows tonight should stay in the 40s. Friday night could be cooler, particularly in the southwest where there are higher odds for decreasing cloud cover. If a clear sky does emerge there, lows falling to near freezing cannot be ruled out.

Confidence remains high in a strong warming trend through the holiday weekend, along with with drier conditions as a ridge tries to build over the central CONUS. The preceding low pressure system now looks a tad slower to depart the region, which could keep highs on Saturday in the mid 60s to mid 70s and allow diurnal showers to develop. There could also be some weaker shortwave energy crossing the region on Sunday in a transitory quasi-zonal flow regime. The ridge finally does look to become well established on Memorial Day, albeit with some placement uncertainty of its axis. The NBM continues to advertise highs in the mid 80s to near 90 for the holiday. Well above normal temperatures remain favored to close out May, with highs mostly in the 80s. Precipitation chances remain uncertain beyond Memorial Day, driven by whether or how much the ridge will block a deep western CONUS trough from advancing eastward. But there does appear to be consensus for either southwest or southerly flow aloft over the Northern Plains next week, which would eventually point towards increased chances for showers and thunderstorms.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 945 AM CDT Thu May 21 2026

A band of more persistent rain was approaching KXWA at the start of the TAF period, and this could persist near or over the terminal through the morning and into the afternoon.

From late this afternoon through tonight, a significant increase in showers is expected across the state, with thunderstorms also possible during the late afternoon and evening. Ceilings could fall to MVFR levels under rain, and the heaviest showers and storms could briefly reduce visibility to IFR levels. In the southwest, there is higher confidence in prevailing MVFR to IFR ceilings later this evening through tonight regardless of rainfall.

Western North Dakota will see variable winds around 5-10 kts through the forecast period, becoming northerly around 10-15 kts for a period of time this afternoon. Central North Dakota should see southerly winds increasing to 15-25 kts later this morning and afternoon, then becoming southeasterly around 10-15 kts this evening through tonight.

BIS WATCHES/WARNINGS/ADVISORIES

None.