Afternoon and evening thunderstorms the next several days with the most widespread chances today. Scattered thunderstorms in the mountains will be capable of producing heavy rain with localized flooding, hail and strong winds. Temperatures will remain below normal then start increasing to near to slightly above normal by mid-week.
Discussion
A few showers linger over Shasta and Tehama counties early this morning, leftovers from Sunday’s deep convection. An isolated thunderstorm is also moving south over far eastern Shasta County. Elsewhere, partly to mostly cloudy skies cover the region. Current temperatures are pretty similar to those from 24 hours ago and are mainly in the 40s to lower 50s in the mountains, and in the mid 50s to around 70 in the Central Valley. The main low center that’s been responsible for importing the moisture and instability into NorCal is currently located over southern Nevada and will shift east today. However, a weak trough is forecast to linger over central and southern California through at least mid-week as ridging over the eastern Pacific is held at bay.
Enough moisture and instability will remain in place for late-day showers and thunderstorms over the Coast Range, northern Sacramento Valley and Sierra/Cascades.
Today and Tuesday look rather active again, then thunderstorm chances may retreat further to the east by Wednesday and Thursday as ridging noses in from the Pacific. Stronger storms will be accompanied by lightning, heavy rain, hail and gusty winds. Temperatures will remain near to below normal early this week before warming slightly by mid-week.
Area waterways continue to run fast and cold due to snowmelt, creating dangerous conditions for even experienced swimmers. Use extreme caution near waterways!
Extended Discussion (Friday through Monday)
Ensemble guidance and cluster analysis supports a troughing pattern to continue off the coast of Southern California. This will result in continued afternoon and evening thunderstorm potential over the mountains late-week, and potentially into the weekend. The best chances will be along the Sierra Crest, south of US Highway 50 (10 to 25 percent probability of thunderstorm development).
Temperatures will trend warmer through the end of the week and into Saturday. The National Blend of Models (NBM) advertises a 50 to 95 percent probability of reaching 90 degrees for the daytime high temperature Thursday through Saturday for most of the Valley, excluding the immediate vicinity of the Delta.
Even with the warming temperatures, widespread Minor HeatRisk remains over interior NorCal with a just few patches of Moderate HeatRisk, as daytime highs will only be reaching near to slightly above normal for mid-June.
The increasing potential of a trough/closed low moving inland over the coast on Sunday has high temperatures gradually trending downward for Sunday into early next week. The NBM shows this trend, although there is a fairly wide spread in exactly how much cooling, due to variations in the track and depth of the trough.