July 27, 2017 – Well above normal temperatures for the next several days. A slight chance of afternoon or evening thunderstorms over the Sierra crest Friday through next week.
Weak upper trough over NorCal now shifting into the Great Basin leaving fair skies across the CWA this morning. Upper ridge over southwest U.S. will bring well above normal temperatures over the next several days. Most locations will see only minor changes in daytime temperatures today through Saturday. Small scale shortwave troughs passing to the north into the Pacific Northwest will have minimal impact on NorCal weather. Main noticeable impact will be minor fluctuations in the delta breeze. While a slightly increased delta breeze brings a little cooling in delta influenced areas Friday and Saturday, areas outside this influence will likely see very little change in daytime highs or possibly a slight warming.
Southwest flow aloft will keep any Sierra crest thunderstorms east of the the crest today. A more southerly flow aloft Friday and Saturday will bring enough moisture and instability northward up the Sierra for a threat of afternoon or evening crest thunderstorms. Upper ridge pushes back west on Sunday bringing overall warmer temperatures. A reduced delta breeze will allow for warmer temperatures in the Sacramento and delta regions as well.
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Highs Sunday are currently forecast at around 10 degrees above normal for late July. Models generally agree on a southeast flow aloft by Sunday afternoon so Sierra thunderstorms likely to make a push farther northward.
Extended discussion (Monday through Thursday)
Strong upper high pressure forecast over the region next week with triple digit heat continuing in the Central Valley. Highs forecast to be around 10 degrees above average, but below record values. Enough of a Delta trickle expected to keep more moderate temperatures across the Sacramento region. Some moisture may be drawn northward over the higher terrain of the Sierra Nevada leading to isolated afternoon thunderstorms near the crest.