November 29, 2019 – Snow and rain showers continue with travel impacts through the Friday. Much cooler temperatures are in store for the rest of the week. A wetter and warmer winter storm is expected over the weekend bringing additional travel problems in the higher mountains. Active weather looks to persist into next week.
RGB satellite imagery this morning is rather busy as the broad area of low pressure continues to move eastward. The western and northern portion of the Sacramento Valley is clear while the eastern and southern portion of the CWA has mix of low clouds. Radar imagery reflects this as well, with light rain and snow showers being observed over the Sierra. Rain and snow will linger throughout the morning, with chances decreasing as we head into the afternoon and evening hours. Unfortunately, the mountainous region won’t get too much of a break as the next storm system is forecast to arrive on Saturday.
The forecast for this weekend is a bit tricky. We ended up keeping our Winter Storm Watch out; however, it has been split into two segments to better highlight timing for those traveling this holiday weekend. Snow levels will start out very low on Saturday, around 2000-2500 ft or so, but WAA associated with the incoming moisture will raise the snow levels. For the I-80 corridor over the Sierra snow levels will rise to 6000 ft to over 7000 ft (near pass levels) by Sunday, while areas north of I-80 rise to 4000 ft rising to 6000 ft. Initially, this will be a very impactful event with low snow levels, but the impacts should lessen late Sunday into Monday as snow levels rise to near or above the major Sierra pass levels. Precipitation is still likely, but will slowly taper off throughout the day and into early Tuesday morning.
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While the mountains see wind and snow, the Valley will see rain and wind. Contemplated a High Wind Watch for Zone 18 and 19 (portions of Solano, San Joaquin, and Stanislaus counties), but confidence just wasn’t there to hoist one. Model data and return intervals show decent winds at the 850 level both Saturday and Sunday, with the best chances for stronger winds being over MTR and EKA’s CWA early on. It’s seems more likely that we could at least meet advisory level winds for this event. This will have to be re-evaluated by the day shift.
Extended Discussion (Tuesday through Friday)
Continued wet weather continues through next week. Ensemble guidance continues to show a deep closed, upper low progressing towards the California coast on Tuesday. There may be a brief break in precipitation Tuesday afternoon before this system moves into the area bringing precipitation back to NorCal. Snow levels look to be at or above pass levels Tuesday and Wednesday, limiting the heavy snow to higher peaks. The closed low may transition to an open wave again Wednesday night as it progresses east into the Great Basin. Some breezy winds may be seen Thursday as this system moves out and another strong closed low moves towards the west coast. Rain and snow may be possible again next weekend.