April 17, 2017 – A series of weak storms expected through Thursday. Dry and warmer weather late in the week.
Discussion
Skies remain cloudy across interior NorCal early this morning with a few light showers persisting. Temperatures are milder across most of the region compared to 24 hours ago and generally range from the upper 30s and 40s in the mountains to the lower to mid 50s elsewhere.
Moist southwest flow will continue today with some light showers expected at times in the valley despite short-wave ridging aloft. Showers will be more numerous over the mountains where upslope flow may give some areas as much as a 1/2 inch of rain today. High snow levels will limit snowfall accumulations to areas near the crest of the northern Sierra.
The next wave moves in by this evening and continues precip across the area into Tuesday. Orographic enhancement may lead to another inch or two of QPF in the mountains while much of the valley is expected to see less than 1/2 an inch. Snow levels lower a bit below the pass levels with a few inches of snowfall accumulation possibly leading to some travel impacts.
Still looks like some potential for thunderstorms Tuesday afternoon as the main band of cloudiness shifts east and south of the region by midday allowing for increased surface heating. Models indicate approach of subtle short-wave embedded in SW flow late in the day along with cooling mid-level temps.
A brief break expected Wednesday, then the next weaker system is forecast to bring a return of light precipitation Wednesday night into early Thursday.
Extended discussion (Friday through Monday)
Model forecasts for the extended forecast period starting Friday are in good agreement with advertising the development of an upper level ridge over the eastern Pacific and extending into northern California. The stable atmosphere will allow for temperatures to warm up between 5 and 10 degrees above normal across interior northern California for Friday and into the coming weekend.
Uncertainty still exists as to the progression of the upper level trough that is forecast to develop just off the coast of the Pacific northwest. Current forecast tracks have the weather making system and associated vorticity spin remaining northward, but the northernmost portions of the Sacramento valley and northern mountains may receive a few sprinkles of rain and light snow for elevations higher than 8000 feet. No significant accumulations of precipitation are expected at this time for this forecast period.