April 18, 2018 – Light showers mainly over the mountains today through Thursday. Low snow levels with slippery roads higher elevations. Dry Friday through early next week. A few showers possible over the northern mountains middle of next week.
Discussion
Most of NorCal under high cloud cover this morning as a Pacific low now off the north coast approaches. Region of upper level diffluence will bring a threat of light showers today mainly to the mountains. Cold air associated with the low will keep snow levels relatively low for this time of year at between about 3500 and 4500 feet.
Main cold front associated with the low is forecast to dig southward today pushing across the coast mainly south of the San Francisco Bay Area tonight. Southward track of this system will keep heaviest precipitation south of the region with generally light showers expected south of interstate 80.
An inch or two of snow will be possible at the highest elevations but only very little snow is expected over the major interstate 80 and highway 50 Sierra passes. Cloud cover and cool airmass will keep daytime highs a little below normal. Upper trough axis shifts east of the state by mid day Thursday which should bring an end to the shower threat by early Thursday evening.
Upper ridging builds in over the west coast Thursday night and Friday with daytime highs climbing to about 10 degrees above normal by Friday afternoon. Fair skies and well above normal temperatures continue going into the weekend on Saturday as upper high pressure moves across the coast.
Extended discussion (Sunday through Wednesday)
High pressure ridging will bring dry and warm conditions over the weekend. Weak disturbances will flatten the ridge somewhat bringing some high cloudiness to the region Sunday but daytime high temperatures will remain well above normal.
A weak disturbance will bring just slightly cooler temperatures Monday and Tuesday. An upper low along the coast will approach Wednesday, bringing the potential for some showers over the mountains.