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KEY MESSAGES

* Rain and snow showers will diminish this afternoon with mainly dry conditions Friday.

* A stronger storm will bring periods of heavier Sierra snow and valley rain late Friday night through early Monday, with possible flooding concerns in northeast CA.

* Additional storms could bring more snow chances to the Sierra, with rain and snow in lower elevations by mid-late next week.

DISCUSSION

Final band of snow continues to diminish as it moves across Mono County, with an area of light rain pushing across west central NV. The Sesame snow study plot (~9000 ft at Mammoth Mountain) has received about 11 inches of new snow as of 1230 PM, and patchy slick travel could linger through this afternoon for southern Mono County, but overall conditions will improve as this snow winds down. For the Tahoe basin, most of the precip today fell as rain up to 8000 feet with highway web cameras showing wet roads on the main passes including Mt. Rose Summit.

For tonight and Friday we'll see a break in the action, with patchy fog/low clouds overnight in some valley locations that received rain since early this morning. Temperatures on Friday will climb upward to a bit above average to the mid 40s for Sierra communities to lower 50s for western NV valleys.

The next storm is projected to reach northeast CA-eastern Sierra by late Friday night/early Saturday morning, with periods of valley rain and mountain snow continuing through the remainder of the weekend, and even into Monday. Sierra snowfall will pile up through this time frame, with Winter Storm Warnings now issued from Tahoe southward to Mono County. For northeast CA and western NV, mainly rain is expected Saturday, but snow levels will gradually trend downward to near 5500-6000 feet Saturday night- Sunday, then settle to 4500-5000 feet by early Monday as precip winds down. During periods of heavier precip, these snow levels over the weekend can temporarily dip by 500 or more feet. While the valley floors in the main urban areas of western NV have a less than 10% chance for 1" or more of snow, foothill locations such as Virginia City could end up with minor accumulations up to a few inches by early Monday.

We're still watching the potential for flooding concerns in northeast CA due to rain falling on existing snowpack and will keep the areal flood watch in place. However, recent trends of more intermittent precip during the milder day on Saturday followed by lowering snow levels Sunday may reduce the extent of flooding risk. This storm has shown more variance over northeast CA with precip amounts and snow levels, so it remains a good idea to have flood preparations ready if near rivers or creeks.

As for winds, Saturday looks to have the best potential in lower elevations with gusts of 30-40 mph and some gusts up to 50 mph in wind prone sites. The spilling over of precip and more limited 700 mb flow (mainly 30-40 kt) appears sufficient to prevent a significant wind event this weekend for lower elevations. However, Sierra ridge top gusts will be typically strong for a Pacific winter storm, with gusts in the 80-100 mph range.

For next week, unsettled weather is likely to continue with additional storm systems approaching the region. The timing continues to vary, although there is now an increased potential for a colder storm which could bring snow into lower elevations by next Wednesday or Thursday. MJD

AVIATION

Mainly VFR with light winds through Friday, except lingering showers will produce lower CIGS to MVFR at times for the Sierra/Tahoe terminals and terrain obscurations for western NV terminals, mainly through 03Z. Patchy FZFG could return to KTRK overnight, although advancing areas of mid-high level cloud cover reduces the probability of prevailing IFR/LIFR conditions to about 40%.

The next storm Saturday-Sunday will bring more widespread weather impacts to aviation especially for the Sierra/Tahoe terminals where periods of rain and snow transition to mainly snow by Sunday. For western NV terminals, rain will be the prevailing precip type. Increasing ridge top winds will bring periods of turbulence/shear to all terminals both days this weekend. MJD

AVALANCHE

A more potent winter storm will bring periods of more significant snow and windy conditions to all avalanche center terrain from early Saturday morning through Monday morning.

* Snow Levels: Starting around 7500-8000 ft at storm's onset before dropping slowly to below 7000 ft from Saturday night onward.

* Snow/SWE amounts: 1-3 feet with locally up to 4 feet for Mono County. SWE totals between 1.5" and 3", with a few sites receiving up to 4".

* Snow-Liquid Ratios (SLR): Higher density 8-11:1 Saturday, then becoming less dense with SLR's increasing to 10-14:1 from early Sunday morning through Monday.

* Snowfall Rates: Steady at 0.5-1"/hour with periodic bursts of up to 2"/hour through the weekend.

* Ridge top winds: Gusts 70-90 mph, with stronger gusts up to 100 mph for Sunday. MJD

REV Watches/Warnings/Advisories

NV...Winter Storm Warning from midnight Friday night to 10 AM PST Monday NVZ002.

CA...Flood Watch from Saturday morning through Monday afternoon CAZ071.

Winter Storm Warning from midnight Friday night to 10 AM PST Monday CAZ072-073.