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May 27, 2020 – High pressure will continue hot weather with moderate to high heat risk through Thursday. A pattern change begins Friday which will lead to cooler temperatures and chances of showers and thunderstorms over the weekend.

Discussion

Clear skies and generally light winds continue across the region early this morning. Current temperatures are very mild and are several degrees warmer across most of the region compared to 24 hours ago. Readings range from the mid 40s in the mountain valleys to the upper 60s to around 80 across the Central Valley.

Hot temperatures will continue today and Thursday as strong high pressure remains over NorCal. We will see a gradual return of stronger onshore flow later today and Thursday which may begin to cool the Delta a few degrees.

With the prolonged heat in the forecast, the general population should take precautions to prevent heat related illnesses given the potential for moderate to very high heat risk. Stay hydrated, limit outdoor activities, and check on sensitive groups. If you plan on enjoying the outdoors, be sure to practice heat safety and a cold water safety if visiting area waterways. Area waterways continue to run very cold and fast, and precautions should be taken if heading to the water.

A cutoff low continuing to spin well off the coast of SoCal and Baja will bring changes to our weather on Friday as it pushes toward NorCal. We will see the start of a cooling trend with valley highs falling back into the 90s. The forcing will be on the weak side for Friday but we do see some instability build in generally above 500 mb. This will bring a slight chance for t-storms in the higher elevations during the afternoon and evening.

Better shower and thunderstorm chances develop Saturday, especially to the north of Sacramento as moisture and vertical motion increase ahead of the low as it lifts northward. Temperatures will cool significantly on Saturday due to the increase in clouds and showers, stronger onshore flow and major synoptic cooling.

Extended Discussion (Sunday through Wednesday)

Long wave trough sets up off the West Coast Sunday with a series of embedded waves moving through interior NorCal. This will keep unsettled weather through the extended forecast period. Best chances for showers will be over the foothills and mountains. High temperatures will be near to slightly below normal through Tuesday, warming to slightly above normal Wednesday.