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July 30, 2017 – Heatwave persists into next week with Tuesday and Wednesday being the hottest days. Isolated afternoon and evening thunderstorms possible near the Sierra crest this week. Excessive Heat Watch from Monday afternoon through Thursday evening.

Discussion

Around 3 am, valley temperatures ranged 62 to 74. Enjoy this cooler air as you wake up this morning because it looks like the Delta Breeze is weakening and won’t bring as much overnight cooling for the next several days. Onshore pressure gradient from San Francisco to Sacramento went from 2.7 milibars yesterday morning to 2.3 at this hour. Winds at Travis Air Force Base are only 16 knots, but were blowing at 23 knots 24 hours ago.

We are still on track for an extended stint of widespread triple digit valley heat through Thursday with Tuesday and Wednesday being the peak of this heatwave. Areas north of I-80 will range 100-116 degrees during this event while areas south of I-80 will range 96-106. The Delta will range about 85-95. Even higher terrain will peak in the 90s to low 100s for Tuesday and Wednesday. Excessive Heat Watch still in effect Monday through Thursday. With several days of triple digit heat and a weakening Delta Breeze, please watch out for yourself and others, including animals. Hydration and access to shade or AC will be key to prevent heat related illness.

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The potential for afternoon/evening thunderstorms continues along the Sierra Crest, though most storms are expected to remain east of the crest in the short term forecast.

Extended discussion (Thursday through Sunday)

While still well above average, temperatures will not be as hot later in the week as the strong upper ridge weakens slightly and shifts a bit further to the east as a weak low develops off the California coast. Models continue to indicate monsoon moisture will spread northward in the southeasterly flow over the region bringing a fair amount of mid and high clouds and an increasing chance for elevated convection Thursday into Friday with the potential for a significant lightning event across the region.