textproduct: Sacramento

KEY MESSAGES

- Winter Weather Advisory in effect through 7 AM Sunday for the Sierra elevations above 7000'

- Rain and mountain snow showers continue today into Sunday for the Sierra and surrounding areas, accompanied by isolated thunderstorm chances this afternoon and evening

- Quick moving system brings shower/isolated thunderstorm chances Tuesday-Wednesday

- Below normal temperatures continue through the weekend and into the week ahead alongside periods of breezy winds

DISCUSSION

This Weekend: A positively tilted trough system sweeps across California today into Sunday, quickly ejecting out of the region late in the day on Sunday. The associated northern trough of this system will bring the primary impacts to the region. While the bulk of any atmospheric river moisture looks to stay well south of interior NorCal with this system, ample moisture remains in place for continued rain/snow showers and isolated thunderstorm chances across the Sierra and adjacent foothills northward toward the southern Cascades and Burney Basin. Earlier this morning, embedded thunderstorms were observed across Tuolumne/Calaveras/Amador counties with indications of lingering instability across a similar area still nearing the middle of today.

As a result, moderate rainfall will be possible with any showers that develop throughout the day. While thunderstorm activity generally looks to remain more embedded owing to persistent cloud cover, an area of clearing across the northern San Joaquin Valley toward the lower foothills will likely result in a few stronger thunderstorms capable of brief heavy rain, gusty winds, near severe hail, frequent lightning, and some low potential for a brief funnel cloud or weak tornado. Highest chances for thunderstorms (up to 25%) remain confined to the Sierra/foothills along and south of Interstate through this evening.

As for winter impacts, a Winter Weather Advisory remains in effect through 7 am Sunday along the Sierra for elevations above 7000'. At this time, accumulating snowfall has remained above 7000' with snow levels around 7000'-8000' through today lowering toward 5500'-6500' into Sunday as precipitation begins to taper off. Forecast snowfall totals remain largely unchanged with accumulations up to 10" expected above 7000', up to 18" at peaks, up to 3" possible between 6000'-7000', and flurries to a dusting as low as 5500'. Minor travel delays from chain controls and slick travel conditions will be possible for mountain passes within the Winter Weather Advisory, so be sure to check quickmap.dot.ca.gov for latest road conditions this weekend.

Heaviest precipitation remains anticipated through Sunday morning, with lingering mountain showers tapering off throughout the day on Sunday as the system quickly exits the region. While increasing north to east winds are expected Sunday afternoon into Monday morning, the rapid ejection of the trough will keep the duration of favorably aligned winds aloft minimal. As a result, north winds gusting 15-20 mph are anticipated throughout the Valley Sunday afternoon, alongside downslope east winds gusting 25-35 mph along the Sierra overnight into Monday morning.

The Week Ahead: As quickly as the trough moves eastward and ridging builds in behind it into Monday, another shortwave trough will be gearing up to quickly pass through interior NorCal Tuesday into Wednesday. This will yield a briefly drier period Monday into early Tuesday ahead of the system. Ensemble guidance then remains in relatively steady agreement on increasing chances for showers and isolated thunderstorms by midday Tuesday, with mountain shower chances into early Wednesday, followed by an additional period of increasing north to east winds as the system departs. Rainfall totals look notably lighter at this time with generally a 10-25% chance of precipitation greater 0.25" Tuesday-Wednesday. Snow levels also look to remain around 6500'-7500'+, with minimal snowfall impacts anticipated.

Forecast certainty continues to diverge after this period into the end of the week. A likely drier period does look to follow the midweek ejecting trough, but exact duration of dry weather remains dependent upon any subtle shortwave systems moving through remnant west-northwest flow aloft through the end of the week as well as the exact logistics of longwave troughing building in over the Gulf of Alaska. For now, generally dry weather, near to slightly above normal temperatures, and periodically breezy offshore winds are favored late week into next weekend.

AVIATION

VFR conditions are generally expected to prevail at TAF sites across the next 24 hours, although showers/isolated thunderstorms may briefly introduce MVFR/IFR conditions through 05z Sunday. Otherwise light winds less than 12 kts persist at TAF sites as well. Across the Sierra, MVFR/IFR conditions will be likely and LIFR possible as scattered rain/snow showers and isolated thunderstorms persist through 12z Sunday, tapering off to lingering light showers the remainder of Sunday morning.

STO WATCHES/WARNINGS/ADVISORIES

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