High Wind in California, November 25, 2019

Area Forecast Discussion
National Weather Service Reno NV
458 AM PST Mon Nov 25 2019

.UPDATE...

We are issuing a Lake Wind Advisory for Pyramid Lake today, and
also boosting winds/waves for Tahoe with this update.

The cold front is pushing through Reno at this time, with wind
gusts up to 40 mph. While these front-enhanced winds will be short
lived, brisk winds are expected to persist on Pyramid Lake
through this afternoon, with a favorable northwest-north
direction producing rougher conditions on the lake through much of
the day. Winds will also be elevated on Tahoe, especially this
morning, but speeds look more marginal so no advisory is planned.

&&

.SYNOPSIS...

Cooler and breezy conditions arrive today, with the strongest
winds in Mono County. A cold storm system will bring significant
travel impacts from late Tuesday into Wednesday, with heavy snow
in the Sierra and accumulating snow into lower valleys, along
with gusty winds. Snow showers could linger Thursday into Friday,
with another chance of snow possible by the end of next weekend.

&&

.PREVIOUS DISCUSSION... /Issued 342 AM PST Mon Nov 25 2019/

SHORT TERM...

Bottom line up front: If you are traveling for the Thanksgiving
holiday and want to avoid major winter weather travel headaches,
finish your travels by midday Tuesday.

A few small forecast adjustments: We nudged snowfall amounts up a
bit for the Reno-Carson region on Tuesday night, and also put in
some locally higher snow totals downwind of Tahoe (and to a lesser
extent for Pyramid) for Wednesday night.

The transition to much colder and more active weather begins
today as a cold front pushes southward across western NV and far
eastern CA this morning. This system will be more of a wind
producer, especially for southern Mono and Mineral counties where
gusts of 45 mph are forecast, with stronger gusts of 50+ mph in
some wind prone areas such as US-395 near and south of KMMH
airport, the Chalfant Valley, and US-6 near Benton. While winds
along US-95 in Mineral County don't look to be quite as strong
compared to Mono County, short periods of enhanced winds could
impact travel for high profile vehicles. Precipitation with this
system will be minimal, with light snow showers mainly near the
Oregon border and east of US-95 into central NV, although some
brief non-accumulating snow flurries can't be ruled out in other
areas as the front pushes through.

After a short break tonight and Tuesday morning, the much
advertised winter storm event is still on track for later Tuesday
through Wednesday. While dry conditions are probable through
midday, conditions will worsen rapidly during the afternoon and
evening/overnight hours, with intensifying snowfall rates
(possibly near 2"/hour at times and may even be accompanied by a
few flashes of lightning) producing widespread travel impacts with
slick and snow covered roads for long distances along the main
Sierra travel routes (even down to near 2000 feet west of the
crest). The snow will be rather dry and powder-like, with gusty
winds combining to produce periods of whiteout conditions
especially near the Sierra.

For the Reno-Carson vicinity, strong forcing and jet dynamics
could produce snowfall amounts more toward the higher end of the
projected 1-5" range, with peak snow most likely Tuesday evening
between 7 pm and midnight.

As we get into Wednesday as low pressure settles into northern CA,
cold and unstable conditions will keep the chance for snow
showers going, with several more inches likely to accumulate in
the warning areas near the Sierra and lighter amounts for western
NV. For Wednesday night, a shortwave rotating around the low,
along with pre-existing unstable conditions over the lakes could
produce areas of greatly enhanced snowfall. For now we added about
2-5" in the Incline Village-Mt. Rose-Galena-Washoe Lake areas
(and lesser amounts east of Pyramid Lake), but if a strong lake-
effect snow band sets up and persists, some locations could
receive much greater amounts.

For more details on forecast snowfall amounts in the warning and
advisory areas, please see the latest Winter Weather Message
/WSWREV/. For west central NV southward to Mineral County,
snowfall totals are generally expected to be 2" or less, but
still sufficient to produce travel impacts especially during the
night and morning hours, as sub-freezing temperatures are
expected on paved surfaces. MJD

LONG TERM...Thursday through next week...

A few changes, mainly to increase the threat of precip for Sunday
into early next week along with warming temperatures and rising
snow levels then. Ensemble suite this morning shows the upper low
over California Thursday, moving through the Great Basin Friday.
A new upper low is anticipated to drop in off the coast Sunday
into early next week.

Thursday will see continued snow showers across the area with
light additional snow accumulation, mainly in the mountains. Lake
effect snow is still likely in the morning, particularly off
Tahoe. Where the bands set up will have to be nailed down as we
get closer. That said, the greatest threat will be to the east and
north of the lake. Areas that could see significant lake effect
include Brockway Summit clockwise to Carson City. By afternoon,
winds aloft show significant directional shear which will put a
damper on lake effect activity. Winds will be light with the
upper low nearby.

As the upper low moves into the Great Basin Friday, snow showers
will continue but become less numerous and winds will remain
light. Cloud cover should begin to wane as well, and very cold
temperatures are possible Friday morning if cloud cover clears
enough. The greatest chance for a clear night will be Friday night
which would allow colder valleys with snow cover to go well below
zero. At this point, the forecast retains enough cloud cover for a
cold night, but not nearly as cold as it could be.

For the weekend, Saturday looks dry, but the next upper low will
drop off the coast Sunday into Monday. Where it drops, and how
quickly the flow becomes south on the east side of it will
determine precip chances. The low dropping near 130W with a less
south component would be wetter while the low dropping near 140W
would be dry for all areas. The EC deterministic is indicative of
the former, but the GEFS and EC ensemble are favoring something
farther off the coast. For now, we have a chance of snow in the
Sierra trending to dry near and east of the Highway 95 corridor
Sunday into Monday. Snow levels will eventually begin to rise with
this system too.

Looking ahead, the upper low will eventually move inland with
precip chances for all areas next week. When it occurs could be
anytime from Tuesday through Thursday, with another low behind it
in the ensembles. Bottom line is it looks wetter than average for
the first week of December. X

AVIATION...

A cold front will move through this morning around 15Z for the
Tahoe/Sierra Front terminals and 19Z for KMMH. Ahead of the front,
winds are gusting over the ridges with mtn wave turbulence and
LLWS for the Tahoe terminals and KMMH. After frontal passage, the
winds will become gusty from the north with LLWS diminishing.
Speeds of 10-20 kts with gusts to 30 kts are likely, but a bit
stronger for KMMH. Winds diminish this evening between 03 and 06Z.
Some cloud cover along with a few snow showers are possible, but
conditions are expected to remain VFR today through Tuesday
morning.

Attention then turns to the next storm for Tuesday afternoon
through Wed morning. It will be fast moving, but we will see snow
with periods of IFR to LIFR conditions, strong ridge winds and
LLWS. Times for peak IFR conditions Tuesday evening into Wednesday
and runway accumulations are listed below:

KTRK/KTVL: IFR 01-15Z with runway accum 7-10 inches.

KRNO/KCXP/KMEV: IFR 04-09Z with runway accum 2-4 inches.

KMMH: IFR 07-19Z with runway accum 5-8 inches.

Occasional snow showers will continue Wednesday afternoon through
Friday with occasional MVFR to IFR conditions, most likely in the
Sierra. Winds will generally be light during this time frame. X

FIRE WEATHER...

Gusty winds still likely behind the front today. Worst conditions
to be over southern Mono County with gusts to near 50 mph and RH
15-20%. A period of Red Flag conditions is likely for 3-4 hours
this morning for southeastern Mono, especially for the Chalfant
Valley. Winds are expected to be strongest 7 AM to noon with RH
lowest at that time. Winds gradually diminish during the afternoon
with increasing humidity as some moisture moves in. We will
headline in the forecast, but not issue a warning due to the
localized nature of the threat. X

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 1 PM Tuesday to 4 PM PST Wednesday
     NVZ005.

     Winter Storm Warning from 4 PM Tuesday to 4 PM PST Thursday
     NVZ002.

     Winter Weather Advisory from 4 PM Tuesday to 4 PM PST Wednesday
     NVZ003.

     Lake Wind Advisory until 5 PM PST this afternoon for Pyramid
     Lake in NVZ004.

CA...Winter Storm Warning from 1 PM Tuesday to 4 PM PST Wednesday
     CAZ071.

     Winter Weather Advisory from 1 PM Tuesday to 4 PM PST Wednesday
     CAZ070.

     Wind Advisory from 9 AM this morning to 6 PM PST this evening
     CAZ073.

     Winter Storm Warning from 7 PM Tuesday to 7 PM PST Thursday
     CAZ073.

     Winter Storm Warning from 4 PM Tuesday to 4 PM PST Thursday
     CAZ072.

&&

For more information from the National Weather Service visit...
http://weather.gov/reno