Alta, CA 95701 Weather

Key messages

- Mostly dry weather conditions through today

- Chances of light rain and mountain snow returns late this evening through Friday for the Sierra

- A storm system will bring cooler temperatures, rain and mountain snow above 6000-7000 feet Saturday into Sunday

- Winter Weather Advisory in effect from 8 AM Saturday to 7 AM Sunday for elevations above 7000 feet in the Sierra Nevada

- High pressure will promote a drying and modest warming for Sunday and Monday

- Breezy north to east winds Sunday into Monday

Discussion

A larger upper-level trough centered over the Northeastern Pacific will continue to deepen offshore today and Friday, with embedded shortwave trough approaching the area this afternoon. High level clouds have been promoting sky obscuration across the area, but mostly dry weather conditions is expected to persist through today. The aforementioned shortwave trough will bring chances of of showers and mountain snow above 7500 feet over portions of the Sierra later this evening through Friday, and tapering off Friday evening. There is a low chance for elevated isolated thunderstorms on Friday. Elsewhere, will see mostly dry weather with mid to high clouds streaming across the area.

The aforementioned upper level trough is expected to weaken and moves across the region Saturday through Sunday. A system will moves across the area Saturday into Sunday bringing an increasing chance of rain and mountain snow above 6000-7000 feet. Precipitations amounts has been trending higher with this system, especially over the Sierra. Most likely rain total amounts range 0.5 to 1.5 inch over the mountains and 0.25 to 0.75 for the Sierra foothills. Meanwhile, lighter amounts ranging from a trace to a tenth of an inch are expected for the Valleys and Coast Range.

Colder air aloft will bring an increasing instability on Saturday, capable of produce brief heavy downpours and a chance of isolated thunderstorms. Snow levels are expected to be above 7000 feet on Saturday, lowering to 6000-7000 feet Saturday night into Sunday. The snowfall total amounts are also trending higher with this system over portions of the Sierra Nevada, with the heaviest snowfall amounts expected above 7000 feet. NBM probabilities indicates there is a 50% chances of 3 inches or more of snow for the Donner Pass, and a 25% chances for snowfall exceeding 6 inches. Total snow accumulations up to 8 inches, with up to 12 inches at the highest peaks. Minor accumulations of up to 2 inches possible down to 6000 feet. A Winter Weather Advisory is now in effect from 8 AM Saturday to 7 AM Sunday for Northern Sierra above 7000 feet, including Highway 50 and Interstate 80.

Ensemble cluster shows a ridge building in right after the trough exits on Sunday. Resulting in drying and modest warming Sunday through early next week. Breezy to east northerly winds are expected to developed across the area, with the strongest winds over the Sierra.

Aviation

VFR conditions prevail across interior NorCal next 24 hours. Surface wind gusts generally below 12 knots across Valley TAF sites next 24 hours. Mountain surface wind gusts up to 20 kts. Low to mid-level clouds will move into the Valley around 08z Friday, slightly lowering ceilings at TAF sites.

Watches, warnings and advisories

Winter Weather Advisory from 8 AM Saturday to 7 AM PDT Sunday for Sierra (Cal-Tuo) Above 5000 ft-Sierra (El Dorado-Amador) Above 5000 ft-Sierra (Sierra-Placer) Above 5000 ft.