February 20, 2018 – Below normal temperatures and periods of showers mainly over the mountains will persist through the week. Stronger system may move across the area early next week.
With a cold airmass in place, current temperatures are chilly with most Valley locations ranging from the mid 20s to mid 30s. However, winds have prevented overnight temperatures to drop significantly. Dry conditions are anticipated on Tuesday with highs in the 50s across the Valley. While not as cold as previous nights due to increasing cloud cover, Wednesday morning lows could be near or below freezing throughout much of the Central Valley resulting in areas of frost. Therefore, a Hard Freeze Warning continues for areas below 2000 feet through Wednesday morning.
Unseasonably low heights will persist along the West Coast with a series of short waves pivoting through the main feature Wednesday into the weekend. These systems are expected to bring periods of showers generally over the mountains with a stronger wave moving in Thursday into Friday. Models indicate some precipitation activity making its way across the Valley late this week, but any precipitation amounts are expected to be less than 0.10 inches.
QPF amounts will be limited with these systems, but a few inches of snow will be possible at pass levels. This may be enough to cause some slick roads, but not expecting major impacts. Snow levels down to 1000 feet could give a dusting down to the foothills and lower elevations of Shasta county. In addition to shower activity, temperatures will remain below normal through the period as cold air continues to filter in.
Extended discussion (Saturday through Tuesday)
A weak shortwave will clip the northern portions of the state Saturday into Sunday, and could bring a few snow showers to the northern mountains and Sierra Nevada. Most of the region will likely remain dry over the weekend however under dry northerly flow.
A subtle but perhaps meaningful pattern shift toward wetter weather is looking a bit more likely for next week. Shortwave troughs will continue to drop out of the north, but may remain a bit farther offshore as they do, allowing them to tap into more abundant moisture. These systems will still originate from Alaska / western Canada, so the colder airmass should persist. The GFS and ECMWF have come into better agreement on this solution, which gives us a degree of confidence in this pattern shift. The net result: potential for wetter (but not abundantly wet) weather along with moderate to heavy mountain snow and low snow levels.