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May 25, 2020 – High pressure will continue to build over the region with dangerous heat this week. The hottest days will be Tuesday through Thursday with moderate to high heat risk expected. A pattern change is expected on Friday, which will lead to cooler temperatures and chances of mountain showers and thunderstorms over the weekend.

Discussion

Clear skies cover the region early this morning. Winds are generally light and temperatures are already running considerably milder (5-10 degrees in many areas) compared to 24 hours ago. Current readings range from the mid to upper 30s in the colder mountain valleys, to the 60s to lower 70s across the Central Valley.

High pressure will build/amplify over CA this week resulting in a prolonged period of very hot (if not dangerous heat for sensitive groups) for interior NorCal. As a result, the excessive heat watch was upgraded to an Excessive Heat Warning for elevations below 3500 feet over most of our CWA.

Highs across the Central Valley will range from about 101 to 107 during the hottest portion of the week, Tuesday through Thursday, with the hottest readings currently forecast for Thursday.

With the upcoming heat wave, 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 this holiday, 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.

Extended Discussion (Friday through Monday)

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563 DM closed upper low centered about 550 NM west of KSAN 12z Fri deepens as it approaches the Central CA coast. Mid level southerly flow and PWS increase over interior NorCal Friday into Saturday. Pattern is favorable for widespread thunderstorm development over interior NorCal, including nocturnal storms. Models keep main threat of precip over the foothills and mountains on Friday. However as low nears and AMS moistens, threat includes portions of the Sacramento Valley Saturday. Cooling trend begins Friday with triple digits replaced by 90s throughout much of the Central Valley. Widespread cloudiness Saturday results in more significant cooling with highs upwards of 10 to 20 degrees lower than Friday, i.e., returning to near normal.

Closed upper low forecast to continue to lift northward up the PacNW coast Sunday as secondary weaker low develops off the Central CA. This will continue a threat of mountain showers Sunday and Monday. High temperatures during this period expected to be near to slightly below normal.