Area Forecast Discussion

KEY MESSAGES

- Storm system brings moderate to heavy rain and mountain snow, thunderstorms, cooler temperatures and breezy winds today through Wednesday morning. Lingering light showers and thunderstorms into Wednesday afternoon.

- Winter Storm Warning in effect through Wednesday afternoon - Mostly dry weather, with the potential for light mountain showers late this week into early next week. Isolated mountain thunderstorms possible on Saturday.

DISCUSSION

..Today through Wednesday

An upper level low will continue to move onshore today and into early Wednesday, bringing widespread showers, moderate to heavy mountain snow, gusty winds and thunderstorms to the region. Latest afternoon radar shows scattered showers across the area, with isolated thunderstorms developing across portions of the Valley. Precipitation is expected to continue through the rest of the day, with the potential for afternoon and evening thunderstorm development. WPC guidance indicates additional precipitation amounts of 0.25 to 0.60 inches in the Valley, with 0.50 to 1.50+ inches in the foothills and mountains.

As the upper low moves inland, that is where our greatest chance for thunderstorms will also be across the region. Atmospheric profiles suggest the potential for strong to severe thunderstorms this afternoon and evening, mainly across the northern San Joaquin Valley and adjacent foothills. Main threats with thunderstorms will be heavy rain, dangerous lightning, small hail, and brief funnels/weak tornadoes.

Moderate to heavy mountain snow will bring travel impacts across the northern Sierra and southern Cascades today. A Winter Storm Warning remains in effect above 5000 feet until 5 PM PDT Wednesday. Heaviest snow, with potential snowfall rates of 1-2" per hour, will be today, where some convective snow bands may develop. Any convective snow bands that develop may also lower snow levels briefly, so some brief, heavy wet snow showers may be possible below 5500 feet. Additional snowfall accumulations of up to 6-12 inches are expected above 5000 feet, with up to 18 inches at the highest peaks, and Minor accumulations of 2 inches down to 4500 feet are in the forecast today through Wednesday. Snow levels will lower to around 4500-5500 feet by early Wednesday, with mostly light lingering snow showers up to 1-3 inches expected.

Shower activity decreases after Wednesday morning, with mainly light lingering mountain showers possible through the afternoon and early evening. There is also a 10-15% chance for thunderstorms on Wednesday.

..Thursday through Monday

By Thursday, generally dry conditions will overtake the area and continue into the weekend. A trough will build in the EPAC however, which will introduce chances for light mountain rain and snow showers Friday through early next week. Latest NBM also depicts a 10-25% chance for mountain thunderstorms on Saturday, with the highest chances in Shasta County. High temperatures will fluctuate Thursday- Sunday, with gradual warming Thursday and Friday then gradual cooling by the weekend. Highs will be in the 60s to 70s in the Valley and foothills, with cooler low to mid 40s to 50s for the higher elevations.

AVIATION

A weather system is currently moving through interior NorCal, bringing Valley rain and t-storms and mountain snow. Widespread MVFR conditions due to low ceilings at all TAF sites next 12-18 hours. Occasional breaks in clouds will allow for rapid changes in visibilities, and any storm that develops will lower viz/ceilings to IFR/LIFR conditions. Best chances for t-storms through 06z Wednesday. Snow levels around 5000 feet next 24 hours. Surface wind gusts up to 25 knots in Valley; up to 35 knots in higher terrain.

STO WATCHES / WARNINGS / ADVISORIES

Winter Storm Warning until 5 PM PDT Wednesday for Lassen Volcanic NP-Sierra (Cal-Tuo) Above 5000 ft-Sierra (El Dorado- Amador) Above 5000 ft-Sierra (Sierra-Placer) Above 5000 ft- Sierra (Tehama-Plumas) Above 3000 ft.