Marine Weather and Tide Forecast for Sonora, CA

DISCUSSION

Today through the Weekend

Current upper air pattern has a 500mb trough off the coast of California moving onshore today and through the weekend.
Southerly flow of instability and moisture has helped develop showers and storms within the forecast area, with continued chances for storms this afternoon and evening. Soundings indicate low LCL, CAPE indices around 800-1500 J/kg, weak low level shear, and long CAPE through the atmosphere. This type of set up brings the chance for large hail (1 inch plus), accumulating hail, strong winds, moderate rainfall rates (locally heavy), and brief weak tornadoes.

Currently this morning, we have had a few pulse/multi cellular storms develop along the foothills/valley with a report of accumulating hail east of the Orville, CA area. Latest CAMS have continued development through the remainder of the afternoon and evening, with the prime time for thunderstorm activity this afternoon and early evening when speed shear, directional shear, and instability is at its peak. Continued chances for strong to potential severe storms again Saturday and into Sunday as the upper level system moves through CA. If you are headed out, keep an eye on the skies and have a way to receive watches, warnings, and statements today and through the weekend.

As the system moves onshore and we filter in cooler air aloft, precipitation changes over to snow within the mountains. Latest NBM has kept the forecasted snow totals roughly the same, with slightly lower snow levels Sunday. A Winter Storm Warning is in effect from this evening through Sunday evening for elevations above 4500 feet. Snow levels today will be above 6000 feet and lower toward 4000-5000 feet by Sunday. Heaviest snow rates and lowest snow levels are expected to be from Saturday afternoon through Sunday where major impacts to mountain travel are anticipated. Mountain travel is discouraged this weekend. Heavy snowfall rates of 1-2 inches per hour are possible within the Sierra Saturday afternoon through Sunday.

Gusty southerly winds are also forecasted, with the strongest on Saturday. The north/central Sacramento Valley, northeast foothills and Sierra Crest will see the strongest winds of 35-45mph. We will continue to monitor the trends in the forecast to see if a product will be needed for the winds.

Next Week

A return to drier and warmer temperatures early to mid next week as a ridge of high pressure builds into the region. How amplified the ridge becomes is uncertain as latest guidance from the NBM suggests the ridge flattening out mid to late week. This would bring the chance for isolated showers and a few snow showers within the mountains. Amounts, timing, and development of any potential system mid to late next week is uncertain at this time with confidence being low.

AVIATION

MVFR conditions are expected over the next 24 hours, with periods of IFR in and around any thunderstorm activity.
Showers and storms will continue to move through the region through the weekend. Winds, in and around thunderstorms may become erratic with direction changes and quick speed changes.
Otherwise, surface winds will be out of the south for sites around Sacramento through RDD and RBL. MOD and SCK will see winds out of the NW. Surface winds will be around 10-12kts, with periodic gusts to 20kts in RDD and RBL. Winds will be on the stronger side tomorrow in the northern Sacramento Valley, with gusts up to 45mph at times.

STO WATCHES/WARNINGS/ADVISORIES
Winter Storm Warning from 5 PM this afternoon to 11 PM PDT Sunday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.