Cooler temperatures return to the forecast, but when do showers return for NorCal?
After the sunny and warm start to the week with highs above average, our forecast is making a cooler transition.
Highs have stayed in the mid to upper 80s from the weekend through Monday in the valley. This won't be the case on Tuesday as cooler air spills in from the west thanks to strong Delta Breezes.
Afternoon highs stay cool through the day as many reach for the mid-70s. Cooler than Monday's highs by about 10 degrees.
The Cooler Pattern
An area of high pressure that has kept the warmth and sunshine in place has now moved off to the east, allowing cool air to spill into the region.
Our pattern has made a transition to what we call an 'onshore flow', meaning air comes in from the sea and moves inland. Increasing Delta Breezes, building up the marine layer along the coast, and keeping temperatures in the valley cooler as we make the transition.
Temperatures will hold near to slightly below average through Friday with highs in the low 70s.
With an area of low pressure off the coast, this will add an increase of precipitation to the region Tuesday through mid-week in the form of a few isolated showers and thunderstorms. Yet, most stay dry.
The bigger change we're watching is another low pressure system moves in by Friday that would bring better shower and storm chances.
Will NorCall see thunderstorms soon?
The best chances for thunderstorms Tuesday through Wednesday will be mainly across the Sierra and portions of the Northern Valley.
Many of these storms will pop up during the late afternoon and evening, producing small hail, lightning, brief heavy rain, and gusty winds.
By Wednesday, storm chances move further south along the Sierra Nevada Mountain range.
Friday's rain and snow chances
A weak system will move inland from the Gulf of Alaska by the end of the week, bringing the best chance of showers Thursday night into Friday.
The valley will have a chance of showers starting late Thursday through the day Friday. The foothills and Sierra will have a chance of rain showers during the day and high-elevation snow overnight.
This won't bring a wash-out finish to the week, but it will make things soggy. As it brings scattered showers to the valley, light snow to the Sierra, and cooler temperatures regionwide. With just enough instability we can't rule out a few isolated thunderstorms too as this system moves in
Precipitation amounts are expected to be less than 0.10" in the valley with around 0.50" over the foothills and mountains.
Snow levels will stay high with this system. Snow levels start up around 8,000 ft. Thursday afternoon and stay mainly above 7,000 feet as the system passes by Friday evening.
With higher snow levels, travel impacts over the Sierra will be minimal, yet roads will be slick at times.
Highs by Friday will range from the upper 60s to low 70s across the valley, with low 60s in the foothills and 40s across the Sierra.
Weekend outlook
The storm is forecast to clear out just in time for the weekend.
There may be a few leftover showers over the foothills and Sierra but most of these will be light and clearing out by Saturday evening.
Once the rain wraps up the weekend will feature more sun and warming temperatures with highs reaching the mid-upper 70s.
Make sure to stay with the CBS Sacramento First Alert weather team for updates to the forecast this week.
