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August 24, 2020 – Smoke and haze from wildfires likely to continue to impact air quality and temperatures over interior Northern California for the next several days. Dry thunderstorms possible this morning north of Sacramento, otherwise a few late day storms will be possible over the mountains into mid-week. Slightly above average high temperatures.

Discussion

Relatively weak short-wave lifting out across NorCal early this morning resulting in scattered very light showers along with a few thunderstorms. Rainfall amounts since midnight have amounted to only a few hundredths of an inch, and a few local gusts of 20-30 mph have been reported. A light Delta Breeze continues to import smoke from the Bay Area wildfires into the southern Sacramento and northern San Joaquin Valleys where air quality is mostly in the unhealthy range.

Shower and thunderstorm threat expected to subside early this morning across the southern half of the forecast area (roughly south of I-80), and by late morning across the northern half of the Sacramento Valley, as the short-wave lifts north and shears. Diurnal late day storms will be possible across the higher terrain. Red flag warnings will be trimmed in the valley south of Sacramento, and across lower elevations after 11 AM.

Remnants of the closed low offshore forecast to move across the area tonight and early Tuesday which may support a continuing threat for isolated dry thunderstorms over the foothills and mountains, mainly along the Cascade/Sierra side of the valley. Weak trough and lingering moisture/instability will keep a slightly chance of late day thunderstorms over the northern mountains into Wednesday, then dry weather is expected the remainder of the week.

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Local afternoon and early evening breezes will be possible the next several days with a generally light to moderate Delta Breeze. Temperatures will remain slightly above average with areas of smoke and haze continuing to affect temperatures by about 5 degrees where it persists. Minimum RH`s forecast to inch up slightly into mid-week.

Extended Discussion (Friday through Monday)

Interior NorCal remains positioned between the EPAC and Desert SW high pressures through the weekend. Above normal temperatures expected with a slight downward trend Friday into Sunday. Deterministic models differ early next week with GFS/FV3 keeping the West Coast under ridging. EC and most ensemble solutions favor lowering heights as short wave troughing drops through the PacNW into the Intermountain West. Forecast follows this which implies minor synoptic cooling over the area early next week, but highs remain slightly above normal. Dry weather expected through the extended forecast period.