Bismarck (BIS) — the National Weather Service forecast in plain English · Plaincast

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Dense fog in far southwest North Dakota this morning.

A warming trend to well above average temperatures is favored through early next week.

Dry through early next week, with low to medium chances for precipitation returning mid to late next week.

Update

The forecast remains in good shape. Surface observations and webcams show that widespread dense fog remains confined to Slope and Bowman Counties, with patchy dense fog across the rest of western North Dakota.

Discussion

An omega blocking pattern is spread across North America early this morning, with the CONUS ridge axis extending from eastern Montana through New Mexico. The ridge axis is forecast to slowly drift eastward through this weekend while being undercut by a shortwave traversing the southern US. The Northern Plains will remain under a south-southeast low-level/surface flow pattern through Saturday night, with breezy conditions at times. The stagnant pattern could maintain stubborn low clouds and overnight/morning fog into Saturday, although winds may be too strong for fog tonight into Saturday morning. That is not the case this morning though, as a Dense Fog Advisory remains in effect for Slope and Bowman Counties. Guidance continues to favor dense fog across most of western North Dakota this morning, but so far it has remained more low stratus than fog outside of the far southwest. The clouds pose a challenging temperature forecast. Early morning temperatures are in the upper teens to mid 20s to the east of the clouds and lower to mid 30s underneath the clouds. The high temperature forecast for this afternoon was trended cooler than the the blend-of-models forecast 50th percentile in western North Dakota, where confidence is higher in low clouds persisting through the day. It may still be warmer there than farther east though, with forecast highs today ranging from the upper 30s east to mid 40s far west. Breezy conditions and low clouds could keep overnight temperatures warmer than the deterministic the blend-of-models forecast values of lower 20s to lower 30s, but these are already warmer than the 50th percentile, so will refrain from deviating at this time. On Saturday, there is a higher probability that low clouds will clear as south- southeast surface winds increase to 20-30 mph, with gusts around 30-40 mph. This should allow warmer high temperatures in the lower 40s east to lower and mid 50s west. On Sunday, winds should begin to relax as the surface pressure gradient weakens. A mostly sunny sky is favored on Sunday with highs around 50 to 60.

From early to mid next week, a broader upper level ridge is forecast to emerge over the Plains and slide eastward through the Mississippi River Valley. This will transition flow aloft over the Northern Plains to southwesterly ahead of a progressive shortwave moving from southern California early Tuesday toward the Northern Plains on Wednesday. The forecast remains dry through Tuesday, with well above normal high temperatures in the mid 50s to lower 60s on Monday and lower to mid 50s on Tuesday. Ensemble confidence is high in the broad timing and trajectory of the shortwave, but cluster analysis reveals uncertainty in wave amplitude and its evolution from Thursday onward as a deeper trough digs into the western CONUS. All clusters bring precipitation across the region Wednesday into Thursday, although a GEFS-heavy cluster has notably lighter expected rainfall than the other 3. Temperatures may be cold enough for snow to mix in Wednesday night into Thursday, but the probability of measurable snow remains low and is limited to western North Dakota. The active pattern may continue into the following weekend, but ensembles show high spread in the evolution of the mid to late week western CONUS trough. A distinct cooling trend is advertised by the the blend-of-models forecast from mid to late next week, with temperatures favored to return closer to average.