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July 27, 2020 – Slightly above average temperatures for today and Tuesday, followed by a cooling trend. Mountain thunderstorm chances will continue again this afternoon. Breezy Delta winds into next week.
GOES-West infrared satellite imagery reveals mostly clear skies across much of interior central and northern California this early Monday morning. The marine stratus is blanketing the coastline from the Oregon/California border through Santa Barbara County with the Fort Ord Profiler measuring the marine layer at around 1,500 ft deep. The 2.9 mb surface pressure gradient from San Francisco to Sacramento is promoting a healthy Delta Breeze with gusts over 25 kt gust at Travis Air Force Base.
Northern California finds itself nestled between a ridge positioned to our east in the Rockies and a trough just to our west. High resolution short-term models advertise another opportunity of mountain thunderstorms again this afternoon with the latest HRRR painting CAPE in excess of 800-1000 J/kg, particularly in portions of Plumas and Shasta Counties.
Main threats will be lightning, small hail, and gusty winds. Outside the mountains, high temperatures will range from the 90s around the Delta, northern San Joaquin Valley, and southern Sacramento Valley, with upper 90s to low 100s for the northern Sacramento Valley.
Upper level ridge then builds off the southern California coast on Tuesday as much of the northern Pacific is influenced by an upper level trough. A quick-moving shortwave will ripple through the flow on Wednesday, and will drop back temperatures by several degrees.
Little day-to-day change is expected from Wednesday to Thursday as the upper level high anchors in the Desert Southwest with dry, southwest flow aloft for central and northern California.
Extended Discussion (Friday through Monday)
For the extended period which covers July 31st into early August, the synoptic pattern will be governed by a stout Four Corners ridge.
Equally persistent, ensembles favor longwave troughing off the Pacific Northwest coast. Generally speaking, northern California remains in between this pair of features which will keep daily temperatures close to seasonal norms.
Triple digit temperatures will be possible over the northern Sacramento Valley by the weekend. The 00Z ECMWF favors a stronger ridge centered over Arizona which would support an uptick in 500-mb heights over the western U.S. This results in some minor temperature forecast uncertainties when compared to other solutions.
Overall, this pattern should keep dry conditions in place with occasional breezy conditions around the Delta and over the higher elevations.