June 26, 2020 – The prolonged period of hot weather continues through Saturday with moderate to high heat risk in the valley and foothills, with little overnight relief. Significant cooling trend develops during the weekend and continues into early next week.
Discussion
Clear skies cover the region early this morning as Thursday evening’s deep convection has died, and clouds associated with the upper low have shifted southeast of the forecast area. Satellite imagery shows an extensive marine layer all along the NorCal coast, and profiler data indicate its depth at around 1500-2000 ft near the Bay Area. A robust Delta Breeze continues with its cooling effect extending about a third of the way up the Sacramento Valley, and southward across the northern San Joaquin Valley as well.
Ridge rebounds across the region today in the wake of the departing low. The result will be one more day of intense heat across the northern Sacramento Valley where highs will once again be around 110 degrees with daily records in jeopardy. Further south, the Delta Breeze will bring slight cooling today to the Sacramento region and northern San Joaquin Valley. Elsewhere, many of the foothill and mountain areas will be a few degrees warmer given the synoptic warming and less cloudiness.
Synoptic cooling begins across the region on Saturday, and accelerates on Sunday, as the next upstream trough impacts NorCal and onshore flow spreads inland. Some showers will be possible in the high Sierra late on Sunday as a mostly dry cold front moves south.
Extended Discussion (Tuesday through Friday)
Little change to the extended forecast as model and ensemble guidance hold a general trough over much of the western US. Temperatures continue to favor a slight warm up, placing Valley highs in the 90s for much of the week while the foothills and mountains span the upper 60s to upper 80s.