textproduct: Reno

KEY MESSAGES

* Periods of heavy Sierra snow, significant mountain travel disruptions, and gusty winds continue through Friday.

* Snow impacts may spread into western Nevada foothills Christmas night into Friday morning.

* Dry weather returns this weekend into early next week with cold temperatures and gusty northeast winds along Sierra ridges.

DISCUSSION

Merry Christmas from your friends at NWS Reno! Many in the Sierra woke up to a white Christmas as we've received 24 hour reports of 5- 10" of snow near lake level and communities along US-395, and 1-3 feet at Tahoe and Mono County ski resorts. Rain and snow has been quite showery today with breaks in the clouds allowing for periods of sunshine in western Nevada. Gusty winds and occasional showers will continue into the evening before shower activity ramps up tonight.

A band of rain and snow along and ahead of an advancing cold front begins to overspread the region after 9-10 PM PST tonight, resulting in additional heavy snow and reinforced travel disruptions in the Sierra. Colder air behind the front will lower snow levels to near valley floors overnight, broadening snow impacts to W NV foothill communities (e.g. Virginia City) where snow totals of 2-6" (up to 10" above 6000') is possible by Friday morning.

Meanwhile, the most likely timeframe for snow down to W NV valley floors will be between 10 PM and 6 AM PST, but there is uncertainty in how much sticks on the ground -- especially on roadways that received prolonged sunshine this afternoon. A trace to 2" of snow seems like a reasonable estimate on valley floors tonight through Friday morning, particularly on elevated and grassy surfaces. The caveat to this is the potential for a narrow band of heavier snow to move through the Greater Reno-Carson City-Minden area between 11 PM and 2 AM, which may result in locally greater snowfall if/where this band materializes. Should this "boom" scenario come to fruition, be prepared for snow impacts to travel across W NV valleys Friday morning. Otherwise, S/SW winds likely increase again tonight in response to the cold frontal passage with gusty winds lingering through Friday.

One final, albeit weaker, cold front passage will maintain showers in the Sierra into Friday afternoon, but rain and snow will taper off by Saturday. While residual snow may sustain travel impacts in and across the Sierra, travel conditions will improve for the weekend into early next week. The main concern after Friday will be gusty NE winds along Sierra ridges and very chilly temperatures with lows falling into the teens and twenties (single digits for cold prone valleys) each night this weekend into early next week. Unsettled weather is becoming increasingly likely around and after New Year's Day, which may renew travel and recreation impacts to ring into the new year.

-Salas

AVIATION

* MVFR with periods of IFR conditions likely for KRNO/KCXP/KMEV through much of today. IFR conditions expected due to -RA, with possible -RASN as well. IFR/LIFR conditions expected for much of the forecast period for KTRK/KTVL/KMMH due to periods of heavy SN. Snow will be wet in character, with a 50%/80% chance of runway accumulations of 6+ inches by Thursday afternoon for KTVL/KMMH, respectively. For KTRK, there is a 40% chance of accumulations greater than 3 inches by the same time. There is a 10-20% chance for up to 3 inches at KRNO/KMEV tonight, but the forecasted amount is closer to 0-1". KCXP has a 20-30% chance to see 4 inches of snow on the runway, however the forecasted amount is closer to 0.5- 1.5".

* Mountain obscurations and LLWS will impact all TAF sites through the period. Gusts up to 30 kts expected for Sierra Front terminals, with gusts up to 25 kts for Sierra terminals. -Giralte/HRICH

AVALANCHE

Impacts from heavy, wet snow and strong gusty winds expected across all avalanche center terrain through Friday. * SWE, SLRs, and Snow Levels: For the Tahoe Basin, additional SWE up to 4" along the highest peaks, otherwise 1.5-3". SLRs will range from 9-11:1, though, those might rise to 12:1 near the end of the system (Friday afternoon) as colder, drier air moves in. Snow levels this week have been hard to predict, though they should remain around 5500' for SAC terrain, with 6000' for BAC terrain, and ~6250' for ESAC. Snow levels will drop overnight, with levels below 5000' across the Sierra.

* Snowfall Totals and Rates: At lake level, 10-20" of snow expected in the next two days, with an additional 2-4 feet possible along the highest peaks. Expect similar totals across much of the Sierra down into Mono County, with up to 1 foot along US-395. Snowfall rates of 1-2"/hr for SAC terrain, except for up to 2.5"/hr during the most intense periods.

* Ridgetop Gusts: WSW gusts of 80-100 mph today, shifting more westerly with gusts up to 75 mph Friday.

-Giralte/HRICH

HYDROLOGY

The Susan River near Susanville saw a brief rise this morning from some lingering rain showers. The river has seen a drop in level since this morning.

The current forecast guidance does not predict a third crest above flood stage this week.

In other areas, high flows are ongoing and expected to continue, especially in watershed primarily draining terrain below about 6000 feet. Minor flooding is possible with prolonged periods of heavy rain, especially in low lying and poor drainage areas this morning.

Today we should be done with new flooding concerns, but high flows will take many hours to make their way downstream through the lower reaches of main-stem rivers.

The River Forecast Center will be extending hours this week and issuing additional forecasts for rivers where flooding is expected. Check for updated river forecasts at: www.cnrfc.noaa.gov

-Tim/HRICH

REV Watches/Warnings/Advisories

NV...Wind Advisory until 10 PM PST this evening NVZ001-004-005.

Winter Storm Warning until 10 AM PST Friday NVZ002.

Winter Weather Advisory until 4 AM PST Friday NVZ003.

CA...Wind Advisory until 10 PM PST this evening CAZ070.

Winter Storm Warning until 10 AM PST Friday CAZ071>073.