NWS Reno - Nov. 27, 2012 - Winter Storm Briefing

Uploaded by NWSReno on 27.11.2012

This is Shane Snyder with the National Weather Service in Reno presenting an online weather
briefing for a winter storm that will impact the Sierra and western Nevada Wednesday afternoon
through this weekend. These online presentations will be updated for major weather events as
time and staffing resources permit.
After a quiet start to the work week due to high pressure and light winds, a big pattern
change will bring stormy conditions beginning on Wednesday afternoon and last through the
weekend. The area of high pressure (shown on the left image) will break down this week
and be replaced by a strong area of low pressure off the Pacific Northwest coast (as shown
on the right image). This pattern change will drive a strong upper level jet stream and
an atmospheric river of moisture into the western United States by late week.
The first impacts from this pattern change will occur on Wednesday afternoon as a weak
weather system moves across the Sierra and western Nevada. This system will bring a burst
of rain and snow in the Sierra with light rain showers across western Nevada. Snow levels
will be at or just above Lake Tahoe Level for this event with a light slushy accumulation
possible near Lake Tahoe and up to 4 inches near the Sierra Crest. Gusty winds of 35 to
45 mph are expected Wednesday, with 90 to 100 mph possible at the windiest locations
along the Sierra crest. Winds will increase on Thursday with the strongest
winds expected late Thursday night and Friday. South to southwest winds gusting 40 to 50
mph are expected across all western Nevada valleys. More significantly, a high wind watch
is in effect for the Reno-Tahoe area and south through Mono County with gusts to 65 mph or
more possible. Near the Sierra Crest, winds could gust up to 120 mph. Travel will be difficult
for high profile vehicles on Thursday night and Friday with dangerous cross winds possibly
causing travel restrictions along highways 395 and 95.
Confidence has risen for the storm scenario late this week through the weekend. The heaviest
precipitation will come in two waves, the first Thursday night and Friday and the second
Saturday night and Sunday. This image shows the position of the upper level jet stream
and moisture pattern for the first wave Thursday night and Friday. The expected jet position
should result in high snow levels (above 7000-7500 ft) with heavy rain across northeast California
and in the northern Sierra. Across western Nevada and south into Mono County, strong
winds will be the main story along the 395 corridor with generally light precipitation
amounts. The second wave is expected to move in Saturday
night and Sunday. This image shows the position of the upper level jet stream and moisture
pattern for Sunday morning. With the jet stream remaining over far northern California and
Oregon, snow levels are expected to be considerably higher than with the first wave at 8500 feet
or greater. This will result in another round of heavy rain and very high elevation snow
for northeast California and the Sierra (including Mono County). For western Nevada, a period
of heavy rain is possible especially along the highway 395 corridor. Snow levels will
ultimately fall Sunday afternoon and Sunday night as a cold front moves through the region.
However, the heaviest precipitation looks to be along and ahead of the front when snow
levels are elevated. Here is a summary of forecaster confidence
for the different components of this storm. The models have consistently shown this pattern
change for a number of days so confidence is very high that stormy weather will return
Wednesday afternoon and continue through the weekend. Forecast confidence is also very
high for snow levels to remain above 7000-7500 feet for most of the precipitation. The Sierra
will receive a significant amount of precipitation so forecast confidence for heavy rain in the
Sierra below 7000 feet is high. The forecast certainty for western Nevada has increased
slightly to moderate. However, uncertainty still remains regarding the magnitude of gusty
winds Thursday night and Friday and a possible period of heavy rain by Sunday.
Check back at our website for updates as this storm approaches our region. An update to
this online briefing is expected by Wednesday afternoon. Thank you for listening.