textproduct: Bismarck

KEY MESSAGES

- Near average temperatures are favored to continue through next week, with Monday being a slightly warmer day.

- There is a 20 to 40 percent chance of light rain showers moving from northwest North Dakota this morning to south central North Dakota this afternoon.

- Medium chances (30 to 60 percent) for showers and thunderstorms late Saturday night through Monday.

UPDATE

Issued at 905 AM CDT Fri Aug 21 2026

Patchy fog over eastern parts of the area continues to gradually dissipated as we warm up this morning. Otherwise, a few showers continue to move through northwest/north central North Dakota. Latest guidance has some of these continuing to push towards the southeast as the day goes on, with possibly a weak thunderstorm. For morning update have adjusted timing/position of the higher chances in line with latest guidance.

UPDATE Issued at 653 AM CDT Fri Aug 21 2026

Patchy fog persists in the Turtle Mountains, Devils Lake Basin, and northern James River Valley areas early this morning. Most of the fog appears to be causing little to no impacts, but a more concentrated area of dense fog has settled over northern Pierce County. Conditions should improve from 8 to 9 AM CDT.

Scattered light showers are moving into northwest North Dakota early this morning. The near-term forecast was refined to better align with observed trends. The showers should hold together into central North Dakota around midday, but recent model guidance now tends to favor showers diminishing before they reach the southern James River Valley by late afternoon.

DISCUSSION

Issued at 429 AM CDT Fri Aug 21 2026

Northwest flow aloft continues over the Northern Plains early this morning while the upstream western CONUS ridge is beginning to become more amplified. A shortwave embedded in the northwest flow is depicted on water vapor imagery over southern Saskatchewan and is forecast to move from northwest to southeast North Dakota through this afternoon. Scattered showers have been ongoing with this wave since late last evening, and most guidance suggests these will hold together at least until reaching central North Dakota around midday. A couple of CAMs have hinted at a strong thunderstorm between the Missouri and James River Valleys this afternoon, but it is difficult to find model support for CAPE higher than 100-200 J/kg. An occasional brief thunderstorm cannot be ruled out at any point with this activity, but the probability of lightning is not high enough to carry a mention in the forecast.

The surface pattern this morning is very benign, with broad ridging extending from Alberta/Saskatchewan through the Missouri River Valley. Shallow fog has developed from near the Turtle Mountains to the northern James River Valley and back west towards Lake Sakakawea. The fog could reduce visibility in low lying areas before clearing by mid morning. The high temperature forecast for today is similar to what was observed yesterday, generally ranging from the upper 70s far north to upper 80s far southwest. The center of the surface high pressure will become more focused over Saskatchewan, Manitoba, and into North Dakota tonight. NBM spread for low temperatures tonight is small, but would not be surprised to see colder percentiles in the 40s verify. On Saturday, the surface high/ridge slides into the Red River Valley as the highly-amplified upper level ridge begins to shift off the Northern Rockies. Highs on Saturday are projected to remain similar or be just a touch cooler at most locations, with mid 70s to mid 80s.

Shortwave energy preceding a potent Pacific Northwest upper low will begin ejecting off the Northern Rockies Saturday night. The Pacific Northwest low will push the upper ridge axis into the High Plains, but with embedded shortwave energy and underlying moisture return. Recent consensus guidance has trended to a slower progression of the synoptic scale wave pattern, but the NBM has actually refined PoPs to higher percentages and a more focused corridor moving from southwest North Dakota early Sunday morning to northwest-south central North Dakota Sunday afternoon. Model soundings show strong capping, and deterministic guidance would suggest QPF outpacing a ribbon of higher CAPE. Therefore, any convection during the day Sunday is favored to remain elevated, with a very low risk for severe weather. Medium shower and thunderstorm chances (around 30 to 60 percent) expand across all of western and central North Dakota Sunday evening. But despite increasing buoyancy, even for elevated parcels, confidence in any severe threat through Sunday remains low. Monday could be a different story though if the slower progression of the potent upper low comes to fruition. Ensembles now favor an occlusion of the low over Saskatchewan on Monday, with the primary surface frontal boundary attendant to the low moving through western and central North Dakota during the day. The environment downstream of the surface front could become supportive of severe thunderstorms, with CAPE as high as 2000 J/kg and deep layer shear around 35 to 45 kts. But there is still too much uncertainty in forecast details to begin messaging a severe threat at this time. The post-frontal air mass could become hot, dry, and breezy, which may lead to near-critical fire weather conditions in western North Dakota Monday afternoon.

The occluded low is forecast to track southeastward, reaching the Great Lakes late Wednesday. In its wake, the upper ridge is forecast to rebound from the Southern Rockies through the Northern High Plains ahead of another potent trough digging into the Pacific Northwest. Ensemble spread grows by the end of next week, but there are hints that the Pacific Northwest trough could break down the ridge and transition flow aloft to quasi-zonal. A slight warmup continues to be advertised for Sunday and Monday, with highs reaching the lower 80s to lower 90s, followed by a return to near or slightly below temperatures that could last through the rest of next week.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 653 AM CDT Fri Aug 21 2026

Patchy fog has developed across central and eastern North Dakota early this morning. The fog is unlikely to impact any TAF sites, but terminals to the east of KMOT and north of KJMS could see reduced visibility until around 14Z. VFR conditions are otherwise expected through the forecast period. Light rain showers will move from northwest North Dakota this morning into central North Dakota around midday, likely diminishing in the mid to late afternoon. The rain is unlikely to cause categorical flight restrictions, and may only fall over KXWA this morning and possibly KBIS in the late morning and early afternoon. Light and variable winds early this morning will increase to around 10 kts this afternoon, with a north to northwest direction in central North Dakota and a northeast to east direction in western North Dakota.

BIS WATCHES/WARNINGS/ADVISORIES

None.