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August 29, 2020 – Smoke and haze from wildfires will continue to impact air quality and temperatures over interior Northern California for the next several days. Overall dry weather this week but a few late day storms possible over the high Sierra today. Hot temperatures continue through next week with some local northerly wind early in the week.

Discussion

Closed upper low continues to meander off the Central California today as EPAC surface high nudges along the West Coast. Onshore flow has increased and the Delta Breeze is blowing at a moderately strong level. Marine layer depth is around 1300 feet per the Fort Ord Profiler attm. Fog product showing extensive coastal stratus along the coast, extending inland into the Carquinez Strait. Delta Breeze expected to remain strong today providing some limited low level CAA inland, and also drawing smoke from wild fires to the west into the Central Valley. 850 mb temps lower about 1 to 2 degrees over a large portion of interior NorCal today.

Southeasterly mid level flow and upper level diffluence setup over the Sierra Nevada this afternoon, as differential heating increases instability, to lead to a slight chance of showers and thunderstorms over the higher terrain.
EPAC surface high continues to build inland over the PacNW tonight into Sunday. N-S surface pressure gradient increases with some northerly wind of 10 to 15 mph developing over Shasta county.

Delta Breeze weakens Sunday allowing influenced area temperatures to trend up. Highs tomorrow expected to be near to several degrees warmer across the CWA. Closed upper low forecast to drift farther south along the CA coast Sunday allowing more stable conditions over our portion of the Sierra Nevada.

Northerly flow aloft Sunday into Monday as upper troughing digs into the Intermountain West. At same time, EPAC surface high continues to build through Oregon into the Great Basin. This will continue some northerly surface wind around 10 to 15 mph mainly over Shasta county.

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N-S low level pressure gradient continues similar wind speeds Monday into early Tuesday. Heights/thicknesses trend up Mon/Tue as upper high in EPAC builds inland over NorCal. Triple digit heat expected in the Northern Sacramento Valley Monday, expanding into the Central Sacramento Valley Tuesday. 90s forecast elsewhere in the Delta, Central Valley, and lower foothills, with mostly 80s for the mountains.

Extended Discussion (Wednesday through Saturday)

Anonymously hot and dry wx forecast over Norcal in the EFP. An anonymously strong ridge from the NErn Pac will build into Norcal in the wake of a progressive and splitting trof over the Rockies and Srn Plains, before establishing residency over the Desert SW, and west of its usual 4-Corners position. This ridge will continue into next weekend with the GFS forecasting the ridge to strengthen to 598-600 dam over Labor Day weekend.

The initial 5H height rises building into Norcal from the NW Sun nite and Mon could bring a period of Nly winds up to 20 kts to the Shasta Co mtns and down the W side of the Sac Vly and surrounding foothills before weakening Mon afternoon, and quantitatively half of this wind lingering Mon nite into Tue morning. Appears there is at least a 9-12 hr window of elevated fire wx concerns Sun nite and Mon, but less Mon nite and Tue.

Temperatures will assuredly be well above normal during the EFP with max temps some 5-15 degrees above normal during the period and likely exceeding the upper bounds of the NBM forecast. The strong subsidence inversion will also result in strong thermal belts in the foothills and mountains.