Unusually wet late season storm system brewing

May 13, 2019 – Dry and mild weather expected today and most of Tuesday before a pattern change develops by mid-week that will lead to cooler, breezier and wetter weather for the remainder of the week.

Discussion

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Clear to partly cloudy skies cover the region early this morning. Satellite imagery shows the marine layer cloudiness mostly confined to areas near the coast, and profiler data indicate that it has become more shallow (around 1k ft in depth at Ft Ord), so not looking promising for a stratus intrusion into the Sacramento area this morning. Current temperatures range from the mid 30s in the mountain valleys to mostly the mid 50s to mid 60s elsewhere.

Upper ridge expected to continue dry and mild weather across the region today and most of Tuesday as it gradually shifts eastward ahead of more active flow developing across the eastern Pacific. Highs today will be down a few degrees compared to Sunday with more substantial cooling forecast Tuesday as the ridge retreats.

Models have come into agreement with unseasonable strong storm system affecting the region Wednesday into Thursday bringing precipitation, gusty winds and cooler temperatures.

Operational models and ensemble suite continue to lend increasing confidence in what would be an unusually wet late season storm system for NorCal. Current forecasts indicate potential for 1/2 to 1 inch of rain for the valley with 1 to 2 inches for the foothills and mountains. The higher elevations of the northern Sierra Nevada and the Mt Lassen area will have the potential for seeing a foot of more of snowfall accumulation.

Extended Discussion (Friday through Monday)

Cool wet weather is going to continue into the extended period as we remain in a troughing pattern. Deep upper level trough will be pushing east Thursday night and we will see short wave ridging for Friday. This will bring mainly dry weather but some light showers look to linger in the higher elevations. Both GFS and EC ensembles agree on falling heights on Saturday with another trough axis moving through NorCal Sunday. This will bring increasing shower chances for Sunday. Wet weather looks to continue into early next week as both ensembles indicate another short wave trough but are not in agreement with the timing. Snow levels throughout the period look to be between 5500 and 6500 feet. High temperatures will continue to run well below normal, 10-20 degrees.