April 10, 2018 – A weak Pacific weather system will bring some light precipitation to northern California today followed by a colder and wetter system Wednesday and Thursday. Dry weather returns later in the week, but more rain is expected Sunday.
Discussion
Warm-advection ahead of the approaching cold front resulted in some sprinkles and light showers earlier in the night. Partly to mostly cloudy skies cover the region as the more extensive cloud cover has lifted off to the northeast. With all the cloud cover and a mild airmass in place, current temperatures are considerably milder (5-15 degrees in most areas) compared to 24 hours ago and generally range from the 40s and 50s in the mountains to the upper 50s to mid 60s in the valley.
Cold front presently off the NW coast of California will spread southeast and weaken as the upper trough shears with much of energy quickly lifting into the PacNW. Precipitation is expected to be generally on the light side with a narrow band of rain forecast to reach the Sacramento region by mid to late-afternoon. Snow levels will be above Sierra Pass levels with this initial system.
A second system, presently seen on satellite imagery dropping southeastward through the Gulf of Alaska, will follow Wed/Wed night and is forecast to be stronger bringing a bit more rain, mountain snow, breezy winds and colder temperatures. A few showers may linger Thursday before tapering off Thursday night. Snow levels should come “crashing down” Wed nite before lowering to around 2500-3000 feet on Thu when the precip should decrease. 850 mbs temps and 1000-500 mbs thickness values drop to <=zero deg C/<540 dam over much of the CWA by early, early Thu morning which makes snow amounts a little heavier over the Sierra.
Locally, a storm total of a foot or so is forecast for the Sierra up to Lassen NP. The colder air should result in snow to liquid ratios at least 12:1, if not higher over the higher elevations, quite high for this time of year indicative of the cold GOA/NErn Pac air associated with this 2nd system.
Thursday will be a cold spring day in NorCal with maxes in the upper 50s to low 60s in the Valley some 9 to 15 degrees or so below normal. Warmer and drier weather forecast for Friday as the Pacific ridge rebuilds over the region.
Extended discussion (Saturday through Tuesday)
Dry with warming Saturday as upper ridge moves through. Pacific front spreads precip over western portions of the CWA Sunday morning and across much of Interior NorCal by Sunday afternoon. Front moves through by Sunday night with upper trough keeping unsettled weather Monday. Light to moderate precipitation expected with this storm. Drier weather returns Tuesday under short wave upper ridging.