Cool, unsettled weather continues with showers, high elevation snow showers and isolated afternoon thunderstorm chances through Tuesday. Dry and warming conditions expected later this week and into the weekend.
Discussion
Current radar shows some light showers up in Shasta County early this morning, with a more impressive band of precipitation just to the west over the northern California Coast. Observed precipitation over the past few hours up in the vicinity of Shasta Lake area is a couple hundredths of an inch of rain.
Showers are expected to spread inland today as the next system moves through, with the majority of the precipitation expected to fall north of Interstate 80, especially Shasta County. Total precipitation amounts will generally range anywhere from a couple hundredths up to an inch with locally higher amounts over the higher elevations of the southern Cascades. Snow levels will be around 4500 to 6000 feet this morning, rising to around 5000 to 6500 feet this afternoon. Snow amounts of less than an inch up to 4 inches will be possible, with locally higher amounts over Lassen Park area.
Isolated thunderstorms are also forecast for this afternoon and evening, bringing the potential for brief downpours, small hail, dangerous lightning and gusty winds with any thunderstorms that develop. The latest National Blend of Models (NBM) probabilistic data advertises a 10 to 25 percent probability of thunderstorm development for mainly the northern Sacramento Valley and surrounding terrain this afternoon, with lingering chances (5 to 15 percent probability) on Tuesday afternoon up in the mountains.
Breezy to locally gusty winds will accompany this wave, with winds out of the south to southwest direction. Gusts of 20 to 35 mph will be possible across the northern and central Sacramento Valley today, including the cities of Redding, Red Bluff and Chico, with locally higher wind gusts over the Sierra Nevada. Wind speeds decrease in the afternoon.
Lingering isolated showers Tuesday will be followed by drier and warmer weather on Wednesday and Thursday. Temperatures on Wednesday will still be trending below normal, but will be rising closer to normal or even slightly above normal for Thursday. The warming trend will continue into the extended forecast period.
Extended Discussion (Friday through Monday)
Ensembles and clusters continue to indicate a high likelihood that NorCal will be under the periphery of a strong blocking ridge that sets up over the PacNW/southern BC/southern AB late in the week and through the weekend. NBM probabilities of highs exceeding 90 degrees remain high (75-95% by Sunday) for the Central Valley over the weekend. Areas of moderate heat risk develop as early as Friday in the Sacramento Valley, then become widespread across the Central Valley over the weekend, so heat-sensitive groups should practice heat safety.
The lower atmosphere won’t be completely dried out (PWAT’s are forecast to be at or above seasonal average and increase over the weekend under east-southeast flow aloft), but deep convection is unlikely through at least Saturday due to capping from warm mid- level temperatures. By Sunday, there will be a slight chance for late-day showers or thunderstorms over the Sierra south of Lake Tahoe as the cap weakens.