textproduct: Reno

KEY MESSAGES

* Heavy rains that could lead to localized flooding, and heavy wet snow in the Sierra above 8000 feet continues into the late evening. * Following the beginning week system, there will be a brief lull in precipitation on Tuesday with gusty ridge winds.

* Another round of stormy conditions could bring significant rain and snow along with enhanced winds late Tuesday through Christmas Day into the weekend.

DISCUSSION

For today, precipitation continues for northern Mono County north into Lassen County. Meanwhile for western NV, light rain showers will persist mainly west of US-95 and north of I-80 into the late morning. Other areas in the inner-basins and east of the crests in Mono County will remain dry. Snow levels which have been around 8,000 ft on Sunday will remain steady around 8,000 ft today. High-resolution models and ensembles are all in agreement that the primary band of precipitation affecting the eastern Sierra will slowly move north as the day progresses. Precipitation will first end in northern Mono County by around 11 AM to 2 PM, then eventually in the Tahoe basin by 4-7 PM. Meanwhile, precipitation will become less intense for eastern Plumas and Lassen County, but models show these areas may keep light showers into early Tuesday. As for wind, some of the wind prone areas and ridges are still showing gusts to 50-70 mph (as of 1 AM). Winds will stay elevated along the ridges today with gusts of 40-60 mph, but the remainder of the region will have much calmer winds with gusts between 20-30 mph. As such, there will not be the need for additional wind-related products.

As the primary upper level trough moves closer to the coast on Tuesday, the aforementioned band of precipitation will continue to shift west, allowing for a mostly clear day across the region. But, by late Tuesday evening into early Wednesday the first in a series of multiple short-wave troughs that are rotating around the larger parent low will begin to impact the region. This will lead to multiple days of rain, snow, and strong winds. In addition, each short-wave that moves through will be colder than the previous, allowing for snow levels to drop through Christmas Day into the 26th.

To start with late Tuesday into Wednesday, the first short-wave moves into the area with more heavy rain, and heavy snow above around 6,000-6,500 ft. One thing to note from prior guidance is that models are starting to hint that the surface low and upper short-wave trough may break off from the cold front and move north into the Pacific Northwest. If this occurs, we may see clearing in Lassen, eastern Plumas, and possibly the Tahoe area longer than what we are currently forecasting. This will be watched as we get closer. By late Wednesday into early Friday, the next piece of short-wave energy moves into the area. This feature will be much colder, allowing for snow levels to drop below all pass levels (<5,500ft) in the eastern Sierra by Thursday afternoon and even as low as the valley floors (~4,500ft) in western NV by Friday. For this region, a Winter Storm Watch will remain in effect from late Tuesday evening until Friday morning for the Sierra. -McKellar

For details about the Winter Storm Watch, please visit www.weather.gov/rev/winter

If you're planning on going out to the back country in the eastern Sierra, please visit www.weather.gov/rev/Avalanche

AVIATION

* Moderate to at times heavy rain is likely at KTRK and KTVL through at least Tues 00z, with scattered showers through around Tues 06z. This will cause visibilities to decrease to IFR/LIFR with terrain obscurations in areas of heavy precipitation. Higher elevations generally above 8,000 ft in the Sierra may see snow today. Western NV TAF sites may occasionally drop to MVFR visibility when rain occurs through around 20z.

* Area-wide LLWS, mountain wave turbulence, and ridgetop winds gusting up to 40-60 mph are also to be expected this afternoon. Surface winds are lighter today, with sustained winds of 10-15 kts with gusts up to 25 kts. -McKellar

HYDROLOGY

Ongoing moderate to heavy rains are resulting in significant rises on rivers and streams today into Monday most notably from Alpine County north through Lassen County.

Minor flooding of small streams, urban and poor drainage areas and rockfall in steep terrain are possible during any prolonged periods of high intensity rainfall.

While no mainstem river flooding is currently forecast, the Susan River near Susanville is currently expected to exceed action stage and minor flooding can not be ruled out. Remain aware of the potential for additional river and stream rises near Christmas Eve in large mountain drainages below about 6000 feet, like the Susan River. In these areas additional rain and saturated conditions could lead to rapid rises and renewed flooding concerns. In most other areas, lowering snow levels will reduce flooding concerns into next week.

Enhanced runoff and sediment transport including rock fall are likely within and below recent burn areas, including, but not limited to the Davis and Bear burn areas. Post-Fire debris flows are not expected.

You can find river forecasts updated Sunday at ~3PM and ~9PM, then ~ 9am and ~3PM Monday and Tuesday at: www.cnrfc.noaa.gov

-Tim

REV Watches/Warnings/Advisories

NV...Flood Watch through this afternoon NVZ002.

Winter Storm Watch from Tuesday evening through Friday morning NVZ002.

Winter Weather Advisory until 1 PM PST this afternoon NVZ002.

CA...Flood Watch through this afternoon CAZ071-072.

Winter Storm Watch from Tuesday evening through Friday morning CAZ071>073.

Winter Weather Advisory until 1 PM PST this afternoon CAZ072.