textproduct: Bismarck

KEY MESSAGES

- A little cooler today, with highs in the lower 70s to lower 80s. Aside from a few morning showers, the rest of the day should remain dry.

- Low to medium chances (20 to 40 percent) for isolated to scattered showers and thunderstorms on Wednesday. A few storms may become strong to severe in south central North Dakota during the afternoon and evening.

- Near to slightly above average temperatures favored mid week through the weekend.

UPDATE

Issued at 1015 AM CDT Tue Aug 18 2026

Quiet weather is found across western and central North Dakota this morning. Patchy fog found earlier across the northwest and north central has all but lifted, leaving clear conditions across the board. A small area of weak to moderate radar returns continues to move across the south central at this time, though a farily dry above surface layer is expected to greatly limit the amount of precpitation reaching the ground. No major adjustments to the forecast were performed with this update, as it remains broadly on track.

UPDATE Issued at 709 AM CDT Tue Aug 18 2026

A small area of showers anchored to a low level baroclinic zone continues to propagate southeastward into central North Dakota early this morning, and was over Lake Sakakawea at 645 AM CDT. These showers may persist into the mid morning hours and reach the James River Valley. Very little measurable rain is expected, and the probability of lightning remains very low. Elsewhere, patchy fog has developed across northern North Dakota. Visibility observations under half a mile have recently become more prevalent, and this is confirmed in some webcam imagery. A Special Weather Statement for the patchy dense fog has been issued. The fog should lift by around 9 AM CDT.

DISCUSSION

Issued at 419 AM CDT Tue Aug 18 2026

The Northern Plains lie under a west-northwest cyclonic flow pattern early this morning between a Hudson Bay low and Desert Southwest ridge. Despite a surface high pressure analyzed over southern Saskatchewan, enough low level convergence/frontogenesis is present to have produced an area of scattered showers along the Missouri River Valley from northeast Montana into northwest North Dakota. CAMs that show some semblance of this activity bring it southeastward through central North Dakota this morning, although prognostics of the low level forcing weaken over time. An occasional, brief thunderstorm cannot be ruled out, but there does not appear to be enough CAPE to support sustained lightning. Aside from these morning showers, a quiet weather day is anticipated as surface high pressure slides southeastward into North Dakota. Today will be a little cooler than yesterday for most, with highs in the lower and mid 70s north and east to lower 80s southwest.

From tonight into Wednesday, mid level shortwave energy is forecast to approach the region from the northwest, with a surface trough deepening over western North Dakota by Wednesday afternoon. Several CAMs show weak, elevated convection entering western North Dakota late tonight into Wednesday morning, but PoPs remain lower than 20 percent over this time period due to sparse coverage and very low RH projected in the sub-cloud layer. But Wednesday afternoon could see an uptick in both coverage and intensity of convection over central North Dakota in response to diurnal heating, a pooling of low level moisture downwind of the surface trough, and perhaps a coinciding increase in DCVA. MLCAPE could increase above 1000 J/kg over south central North Dakota by mid to late Wednesday afternoon with deep layer shear initially only around 25 kts, but increasing over time. Values of 0-3 km shear are actually quite similar to those in the 0- 6 km layer, which is reflected in forecast hodographs that do show a varying degree of low level curvature depending on location. Residual CIN and dry-air entrainment in the upper levels could work against sustained updraft growth, but the environment is still forecast to be supportive of a few marginally severe thunderstorms from south central North Dakota to the James River Valley Wednesday afternoon and evening. Shear and deep layer wind vector orientation to the surface trough favor a mixed storm mode, but the weak nature of the forcing may put a slight tilt towards a more predominant discrete mode.

Despite the passage of the aforementioned shortwave(s) on Wednesday, as well as another one that could brush northern and eastern parts of the state on Thursday, broad mid to upper level rising height tendencies are in the forecast mid to late week. This brings the high temperature forecast back into the 80s Wednesday and Thursday, closer to 90 in the southwest quadrant of the state on Thursday. Friday may be a few degrees cooler as another shortwave passes by to the north and east. Ensemble guidance shows a highly-amplified wave pattern developing heading into the weekend, with an upstream ridge being tilted into the Northern Plains and eventually flattened by a southern Canadian shortwave early next week. But there is notable timing uncertainty in the latter feature, which leaves a near- average temperature forecast in place through the weekend for now. After Wednesday, rain/thunderstorm chances remain very low until late Saturday into Sunday when height falls associated with the southern Canadian shortwave could begin spreading into the region.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 1015 AM CDT Tue Aug 18 2026

Patchy fog has developed across northern North Dakota early this morning, but is unlikely to impact KXWA or KMOT. A small area of showers is moving through central North Dakota early this morning, and should pass to the north and east of KBIS between 12Z and 14Z. Aside from the early morning fog, VFR conditions are expected to prevail through the forecast period. Winds will remain light and variable, with 5-10 kt northwest winds this afternoon.

BIS WATCHES/WARNINGS/ADVISORIES

None.