November 29, 2018 – Wet pattern continues through the weekend with several weather systems forecast to affect the region. A stronger system moves through today with valley rain, mountain snow, thunderstorms and gusty southerly winds. That will be followed by a colder system over the weekend.
Discussion
Cold front moving through early this morning accompanied by a narrow band of heavy rain. Fortunately, the lines of heavier showers have mostly missed the recent burn scars (Carr and Camp Fires) so far. Earlier in the night, a large area of moderate rain occurred ahead of the cold front bringing a half inch to an inch of rain to areas north of I-80. The lines of heavier showers are now moving into the foothills and Sierra east of the Central Valley, and their relatively fast movement to the east will limit more significant flooding. An urban and small stream flood advisory continues for much of the area through 6 AM.
Gusty southerly winds continue, especially right ahead of the cold front where gusts of 35 to 45 mph are likely early this morning. Winds may subside a bit for an hour or so behind the front, but the potential for some strong gusts will continue through the morning.
Much of the valley may see a relative respite from precipitation (just some scattered showers) during the morning commute hours, but it’s still looking like another significant line of showers and thunderstorms will spread inland by mid to late-morning as the surface and upper low approach.
Will continue the winter storm warning through early Friday (for up to 2-3 feet over the higher Sierra) with snowfall rates expected to increase. The flash flood/debris flow watch for the Camp, Mendocino Complex and Carr, Hirz-Delta fires has been extended through today as the threat for stronger convection will linger across much of the region until about sunset.
Mostly a dry day and more settled weather on Friday (although some lingering showers are possible over the Sierra) before the next Pacific Storm moves through NorCal Friday night and Saturday. Snow levels will be lower with this colder system (between 3500 and 4000 feet over the Sierra), and even though the QPF will be lower, significant snow is expected, especially at lower elevations, and therefore mountain travel impacts are likely. Preliminary snowfall amounts of around a foot at 4500 feet with 18-20 inches along the crest. Some lingering showers possible over the mountains Sunday.
Extended Discussion (Monday through Thursday)
Extended models aim the next Pacific Frontal system into NorCal early next week but differ on timing a bit. Will to mention cool and unsettled weather. Snow levels come up a bit as a Pacific low starts to move onshore but still fairly low for this time of year at between 3000 and 4000 feet. QPF and snow levels would indicate mountain travel impacts again by mid week but continued poor model run to run consistency makes for low confidence in details.