February 12, 2018 – Cooler temperatures this week. A chance of light rain/snow showers over the mountains this morning, Wednesday and Wednesday night and late next weekend.
Discussion
Upper low over the Great Basin with a shortwave dropping down the Sierra Cascade range this morning bringing a few light showers. Snow levels remain quite low at around 3000 feet or less but precipitation amounts are quite light so impacts should remain minimal. Temperatures will remain cooler this week than last week but still come in just a bit above normal for this time of year. A few light showers will remain possible over the northern Sierra through tonight as the upper low continues to dig southward.
Surface high pressure building over the Pacific northwest behind the retreating low will bring a tightening northerly gradient across norcal. This gradient combined with good upper level support will bring breezy north winds to the north state today. Models predict surface gradients of about 8 mb from Medford to Sacramento. At this time expect winds for the most part to remain below wind advisory criteria. Surface gradients and windspeeds should max out this evening then decrease quickly overnight and during the Tuesday morning hours. High pressure pushing in off the Pacific will bring dry conditions and fair skies on Tuesday. Temperatures warm as well on Tuesday to several degrees above normal.
Another inside slider type trough will drop through the Pacific Northwest and northeast California on Wednesday. This system will bring increased cloud cover to most of the north state and a chance of showers over the northern mountains and Sierra Cascade range Wednesday afternoon and night. Daytime highs on Wednesday will drop down to close to normal for this time of year. Another round of breezy north winds will follow on Thursday with warmer temperatures and clearing skies.
Extended discussion (Friday through Monday)
Ridge of high pressure will rebuild across interior NorCal late this week into Saturday as an upper level disturbance exits the area. As a result, a gradual warming trend and dry conditions are anticipated. Daytime temperatures will remain 5-15 degrees above average with Valley highs reaching the mid 60s to mid 70s.
The upper level ridge will be displaced as an upper level trough drops down from the Pacific NW Sunday into early next week. However, forecast models are beginning to show better agreement compared to previous forecast runs. This system could bring snow and rain to the mountains with snow levels as low as 1500 feet.