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August 28, 2019 – A Red Flag warning today for possible dry thunderstorms Sierra, foothills and northern mountains.

Zero pop forecast through the remainder of the extended forecast.

A slow cooling trend with temperatures dropping to slightly above normal by the end of the week.

Discussion

Just a few mid level clouds over the CWA this morning as a shortwave trough associated with the remnants of tropical storm IVO approaches the central coast. NAM cape progs showing significant instability this morning especially over the mountain regions.

Models all show offshore shortwave pushing northward through NorCal today which should trigger at least isolated thunderstorms. Moisture cross sections show moisture confined to the 10k through 18k foot levels so believe thunderstorm potential in the valley is limited.

Better chances over the foothills and mountains however and since lower levels are so dry, thunderstorms likely to contain very limited rainfall and Red Flag warning still in place for Sierra and foothills and northern mountains.

Slightly cooler airmass will bring down temperatures a bit today but daytime highs are still expected to come in several degrees above normal.

Upper shortwave axis shifts into far NorCal by 03z this evening so except for northern Shasta county, shower threat should end over the CWA by this evening.

A quieter weather pattern starts on Thursday as NorCal remains under southwest flow aloft between high pressure over the southwest U.S. and upper troughing off the coast.

Overall airmass cools a bit more on Thursday but highs still remain a few degrees above normal. Only minor changes in overall forecast Friday and Saturday as forecast area remains under stable southwest flow, fair skies and just slightly above normal daytime temperatures.

Extended Discussion (Sunday through Wednesday)

Sunday into early next week the prominent upper high will be located across the Four Corners region, with a compact upper trough right off the coast of the PacNW. Dry weather and near to slightly above average temperatures will continue as northern California sits between these two features. Ensemble guidance suggests the upper trough closes with the low sliding south along the coast which may bring some weather to the area by mid-week. For now have kept the prevailing dry forecast through Tuesday.