Dry weather with sunny days and cool overnight temperatures continue. Valley frost and fog possible in the overnight and morning hours through Saturday. Precipitation expected Sunday with minor mountain travel impacts and light valley rain. Potential for freezing and sub freezing overnight lows behind the system.
Discussion
Ridge of high pressure that has been over the region will begin to break down as a weak wave drops down from the north over Oregon. Morning temperature will bottom out in the mid 30s. Winds are light and also shifting to a southerly direction. This may allow for more fog to develop in the central part of the valley for this morning compared with yesterday.
Temperatures will begin a cooling trend today. By Saturday a weak dry wave will have passed through the region. The main change will be in the cooler air the system advects over the region for the day.
Saturday night into Sunday a stronger cold system will rapidly move into the region. Models are starting to settle in on the late Saturday night through Sunday evening for the timing of the storm.
Not a lot of precipitation is expected and models have decreased precipitation from yesterdays runs. Less then a tenth of and inch is expected in the valley and less than half an inch in the mountains.
Behind this system Sunday night into Monday colder air will filter in over the region for a cold morning start. Northerly winds will also develop where winds gusts between 30 to 40 mph will be possible in the valley late Sunday night through Monday morning.
Extended Discussion (Tuesday through Friday)
Upper level ridge will be building into NorCal for the start of the extended period. Cold air behind the weekend trough will be in place and that will bring a stretch of chilly weather with daytime highs running 7 to 15 below average.
The overnight lows will be more impactful as we will see them fall to near to below freezing.
The coldest nights will be Monday and Tuesday night with a 70-95% chance of seeing lows 32 or lower in the Valley and a 30-70% of 28 or lower.
Right now it doesn’t look like we will set any new daily record low temperatures but some areas will be close both Tuesday and Wednesday morning. Temperatures gradually warm towards the end of the week as the APEX of the ridge pushes over us.
The forecast becoming more uncertain late week into next weekend as ensemble solutions diverge. Troughing will be building over the Pacific but it’s unclear how quick the upper level ridge pushes east.
The IVT (integrated water vapor transport) charts don’t show any very wet systems at this point but some rain and snow chances will be possible late week into next weekend depending on how quick the ridge pushes east.