Late-season winter storm to bring significant rain/snow and breezy winds

May 14, 2019 – Dry and mild weather continues for most of the region today, then rain chances increase and spread southward Wednesday. Cool, wet and breezy weather expected to continue into next week.

Discussion

Advertisement

Satellite imagery shows high clouds beginning to spread across NorCal early this morning as the initial frontal system approaches northwest California. The marine layer has deepened a bit and onshore gradients are a little stronger helping to usher in a little cooler temperatures into the Central Valley. Current readings range from the mid 30s in the mountain valleys to the 50s to lower 60s across the Central Valley.

Today will mark the beginning of the transition back to cooler and wetter weather that will last into next week. Radar is picking up some light precipitation off the northwest coast of California that will spread inland across the far northern portion of the state today as the initial frontal system stalls and weakens. Latest ops models continue trend of a developing a stronger system off the coast on Wednesday before it moves inland across the region Wednesday night and Thursday bringing precipitation, gusty winds and cooler temperatures.

The upper trough is forecast to move in later Wednesday night and Thursday turning precip more convective and leading to a better chance of thunderstorms along with bringing lowering snow levels to the northern Sierra. Accumulating snow will be possible across the higher elevations into early Friday where local amounts approaching 2 feet will be possible, and a winter storm watch has been posted.

Extended Discussion (Saturday through Tuesday)

Unsettled weather is going to continue into the extended period as we remain in a troughing pattern. Both the EC and GEFS ensembles are in good agreement with another trough axis moving through NorCal early Sunday. This will bring increasing shower chances Saturday with rain likely Saturday night into Sunday. Snow levels over the weekend look to be around 6500 feet and we will likely see mountain travel impacted especially Saturday night likely continuing into Sunday afternoon. We do see some CAPE build into the valley Sunday and could possibly see some thunderstorms but will hold off for now on putting them in the forecast.

The EC and GEFS ensembles split a bit as we head into early next week but both continue to show us in a long wave troughing pattern. This will keep shower chances in the forecast. Standardized anomalies for temperatures will continue to run -2 to -3 deviations from normal. This will translate into well below normal temperatures continuing, running 10 to 20 degrees below normal.