July 4, 2018 – Dry with the cooling trend continuing today. Smoke near wildfires and hazy conditions elsewhere. Warmer temperatures by the end of the week.
Clear skies continue across interior Northern California this morning under dry southwest flow aloft. A low pressure system off the Pacific Northwest coast is bringing an enhanced Delta Breeze and substantial marine layer along the coast, it is now deeper than 3000 feet at Fort Ord.
Temperatures across the forecast area are running around to a few degrees cooler than 24 hours ago. Look for south to west winds to increase during the day today, and will be occasionally breezy at times. This may push the wildfire smoke farther north than what we’ve seen the last few days.
Temperatures will peak in the 80s to lower 90s across the Valley and foothills today, with 60s to 70s over the mountains. These forecast high temperatures will be locally up to 10 degrees cooler than normal for this time of year.
Temperatures will nudge upward Thursday into Friday as high pressure centered over the central US begins to retrograde toward the Rockies. The Delta Breeze will also slacken somewhat. Look for temperatures to be in the upper 80s to mid 90s, around to slightly cooler than normal.
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Mid to high level clouds will increase on Friday as moisture originating from Fabio moves through the region. At this stage, elevated instability looks too low to generate any thunderstorms – but it wouldn’t be too surprising if we see a few sprinkles fall.
The upper ridge will continue to strengthen into the weekend, and triple digit will be possible across portions of the Valley.
Extended discussion (Sunday through Wednesday)
Ridge of high pressure will build westward into NorCal resulting in above normal temperatures during the extended period. Valley highs will peak in the upper 90s to low 100s with mid 70s to 90s over the foothills/mountains. Therefore, long outdoor exposures could increase chances for heat-related illness among sensitive groups early next week.
Models are suggesting a surge of moisture from the south, which combined with instability, could lead to afternoon thunderstorm activity over the Sierra next week. Slightly cooler temperatures expected by the end of the forecast period.