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June 24, 2018 – Cooler in the Delta area today, while inland areas remain hot and dry. Temperatures return to near normal beginning Monday and through the rest of the week. Red Flag Warning until 8 PM this evening. Heat Advisory until 8 PM this evening.

Discussion

The northerly pressure gradients, over 10 mbs at press time, are forecast to decrease rapidly into the 3-4 mbs range by 18z today.This will occur as low pressure over the Rockys moves into the central Plains by the end of the day and high pressure moves over Norcal. This will bring an end to the desiccating Nly barrier jet winds that Staudenmaier (1994) and Mathews & Juskie (2005) have documented in WRH TA-Lites as having an impact on wind advisories and red flag warning considerations.

These winds helped the rapid spread of the Stoll, Pawnee, Land and Bascom wildfires in our CWA on Sat. The Lane and Pawnee wildfires were showing some “hot” satellite signatures through the night.

Already seeing signs of a healthy onshore gradient developing from SFO-SAC at 2.5 mbs at 09z, and a return of the Delta Breeze to SUU of 14 kts. Satellite shows a return of stratus to the SFO Bay area with the Ft Ord profiler showing the marine layer deepening to nearly 2 kft just past midnight. These are indications of some much cooler air spreading into the Srn Sac Vly today which should keep max temps below triple digits. Thus, have removed zone 17 from the heat advisory.

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Still a hot day away from the Delta as the ridge axis moves over the region today, although areas away from the Delta will finally see some cooler air spreading over their areas tonight and Mon. Expect some stratus to move towards SUU Mon and Tue mornings. Will have to watch for how much the marine layer deepens Mon/Tue mornings for a potential stratus intrusion into the Srn Sac Vly.

Seasonable wx returns to the CWA Mon as another Pac NW trof provides onshore flow and some cooling. This will be followed by slight warming on Tue as high pressure from the Desert SW builds Nwd. Then a slight cooling trend on Wed as another trof moves across the Pac NW.

Extended discussion (Thursday through Sunday)

Broad upper troughing moves through Thursday then Interior NorCal sandwiched between EPAC upper ridge and downstream trough. Ridge remains offshore through the weekend limiting amount of interior heating. At the moment, high temperatures expected to be above normal through the extended, but not excessively hot with 90s expected in the Central Valley and 70s to low 90s for the mountains and foothills. Dry weather continues with breezy northerly wind Friday into the weekend.