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January 18, 2020 – Areas of dense Valley fog will impact travel this morning and tomorrow morning. Dry and quiet weather will continue into Sunday and Monday. Our next system starts to push in later Monday night and will bring the return of mountain snow and valley rain.

The heaviest precip is expected Tuesday morning into the afternoon. Mountain travel delays and chain controls are expected with snow levels 4500 to 5500 feet. Showers diminish early Wednesday morning with dry weather into early Thursday.

Discussion

Weak upper ridging moving through Interior NorCal at the moment with considerable overrunning higher cloudiness. Patchy fog is trying to develop in portions of the Central Sacramento valley southward but cloudiness is hindering it. Under this type of pattern we typically see visibilities bounce around considerably as variable cloudiness moves overhead. Weak Pacific frontal system is evident on satellite approaching the NorCal coast. Models suggest baroclinic zone weakening as it moves inland today. A few light showers may be possible over western portions of Shasta county and Coastal range, but most of the CWA forecast to remain dry today. Despite higher cloud cover, AMS expected to warm with afternoon high temperatures upwards of around 5 to 10 degrees warmer than Friday.

Upper ridging amplifies behind fropa with axis shifting into the Great Basin tonight. Some valley fog possible again tonight into Sunday morning in the Central Valley and favorable mountain valleys. Warming continues Sunday under variable high cloudiness with highs slightly above normal.

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Series of Pacific waves forecast to move through Interior NorCal next week. First tracks through Monday and weakens as it pushes inland. Main impact appears to be some associated cloudiness and slight cooling. Significantly stronger Pacific storm follows on its heels Monday night through Wednesday morning. Models suggest the potential for significant snow over the higher elevations of Western Plumas and Northern Sierra Nevada with 1 to 2 feet possible. Snow levels expected around 4000 to 5500 feet late Monday, lowering to 3500 to 4500 feet Tuesday night into Wed. Up to around an inch of rain is possible in portions of the foothills. Storm totals in the Central Valley increase from a few tenths in southern portions to approaching an inch in the Northern Sacramento Valley. Breezy to windy conditions possible Monday night through Tuesday night.

Extended Discussion (Wednesday through Saturday)

Upper level ridging builds in by the middle of next week behind the departing system. This should bring drier conditions, although a few showers could still linger over higher terrain on Wednesday. A weak system could bring some light precipitation late next week, mainly over the mountains.

Uncertainty arises late in the period as some model solutions suggest more widespread precipitation returning next weekend, but confidence is low. Daytime temperatures are expected to remain near average through the period.