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last mo.

Offshore Low Keeps Northern California in the 70s This Week

Persistent Delta breezes lock in valley highs at least 10 degrees below normal until high pressure returns late weekend.

A wavy jet stream loops across the Northern Hemisphere. These locked-in configurations can trap heat domes over one continent while steering cooler air into others.
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A few clouds and Delta breezes are present this morning and while afternoon temperatures will be warmer than Tuesday, they will still be below seasonal normals.

Overview

  • A cutoff low-pressure system stalled off the West Coast since Monday has driven an unseasonable cool spell across Northern California.
  • Gusty Delta breezes continue to generate sustained winds of 10–20 mph in the valley and up to 35 mph in the Sierra, creating choppy lake conditions and heightened fire-weather risk.
  • Valley daytime highs have lingered in the mid-70s to low-80s, about 10 degrees below the typical mid-July average of around 93 °F.
  • Isolated thunderstorms and scattered mountain showers are forecast in the Sierra through Friday, bringing a risk of dry lightning where vegetation is driest.
  • Forecast models show high pressure rebuilding late this weekend, with valley temperatures rebounding into the 90s by next Sunday.