High Wind in California, October 11, 2021

Area Forecast Discussion
National Weather Service Reno NV
302 PM PDT Sun Oct 10 2021

.SYNOPSIS...

A cold low pressure system is slated to bring breezy winds and
chances for snow showers across the Sierra and western Nevada
later this evening into Monday. A hard freeze is expected for much
of the region overnight Monday and Tuesday. Dry and warmer
conditions gradually return later next week.

&&

.SHORT TERM...

Get ready for that first taste of winter! A strong cold front
will continue to push through the region later tonight through
Monday morning. It will be cold enough for snow at all elevations
and don't be surprised if you see some flakes of the frozen
variety during the Monday morning commute. Here are the
highlights:

* SNOW:

Hi-Res CAMS and ensembles still paint the highest snow potential
for areas near and south of US-50, with the highest possible
totals into eastern Nevada. There may be a bit of enhancement in
the Sierra south of Tahoe late Monday morning due to upslope flow
and frontal forcing. Eastern margins along the Sierra in Mono
County could see the highest snowfall totals. These locations
could pick up several inches of snow above 7000’, but
probabilities are less than 15% for reaching 6" or greater. The
other area to watch is near the Oregon border tonight where a
brief burst of snow or a rain/snow mix could occur.

Elsewhere, a quick dusting of snow up to possibly 1" (for
foothill locations) is most likely. Given the warm road surfaces
of late, what little snow that does accumulate on road surfaces
Monday morning it will either likely melt quickly or remain as a
slushy mess till later in the morning. Mountain roads could hold
the accumulations longer since those roadways were relatively cold
at the start of this event. The timing of the snow looks to
coincide with the morning commute, so allow extra time and
remember that even wet roads have been contributing to accidents
in recent days.

The other wildcard is the potential for lake effect snow with very
cold northerly flow across the relatively warm lake surfaces
ranging within 50-60F. Unstable lapse rates in the colder, drier
airmass certainly suggest this possibility. But this too may be
limited due to the excessive wind shearing developing updraft at
and downwind of the larger lakes in the region.

* WIND:

Westerly winds will begin to increase tonight, sharply turning north
as the front spreads south and east through the overnight hours.
Post-frontal wind gusts ranging 20-30 mph or even to 35 mph will
be fairly widespread across the region. High-Res CAM guidance
forecasts areas in southern Mono and Mineral Counties could see
localized gusts exceeding 45 mph Monday afternoon due to the
strengthening thermal gradient and strong upper level wind
support. Therefore a wind advisory was issued for those areas from
21-03Z. The strongest winds still appear to be farther south into
Esmeralda, Inyo, and Nye Counties. Rather strong northeast-east
winds will continue into Monday evening through Tuesday with gusts
possibly exceeding 50-60 mph along the Sierra crest.

Anticipate choppy conditions on area lakes, particularly Pyramid
Lake on Monday, which orientates well to the nearly streamlined
northerly flow. Lake Tahoe will be choppy late on Monday and will
continue to see gusty winds into Monday night with the easterly flow
ranging 60-70 mph over Sierra ridgelines.

* COLD TEMPERATURES:

Highs on Monday will struggling to reach 50 degrees, even in the
warmest valleys. For Sierra sites, valleys are likely to only reach
into the low 40s with mountains predominately in the 20s. The fairly
strong north wind will further drive wind chills lower and make it
feel even colder. The cold will linger into Tuesday as a northeast
flow continues to bring in colder temperatures.

Widespread freezes are still on tap for Monday night and again
Tuesday night. So, many more locations will complement those colder
sites that have already experienced hard freezes. NBM probability
for low temps less than 30 degrees exceed 90% in even the warmest
urban valleys. -Amanda/Dawn

.Long Term (Wednesday Onward)...

* WEDNESDAY FRONT: A reinforcing shot of cool air associated with
  a short wave diving into the Great Basin will keep temps from
  warming much or at all Wednesday into Thursday. A few showers are
  expected across far N Nevada on Wednesday, but limited moisture
  will keep precip amounts rather meager. NBM 90th percentile QPF
  under 0.05" in far N Washoe County, though temps are cold enough
  where most of it would be in the form of light snow showers.

* PLEASANT FRIDAY-MONDAY: Ridging aloft overspreads the region
  leading to gradually warming temperatures with dry conditions.
  Best warming probably won't happen until Sunday when low level
  flow switches from cool easterly to a light downslope westerly.
  Great weekend to do outdoor projects ahead of what might be an
  active weather week.

* STORM POTENTIAL NEXT WEEK: We continue to see signs in the
  ensemble guidance of a large scale trough developing off the west
  coast, which could steer storm(s) into the region next week. The
  main unknown is how far south and closer to our latitude the storm
  track would get. ECMWF ensemble is more aggressive with that and
  shows decent potential for meaningful precip, even into W Nevada,
  and/or high wind scenarios. GFS and Canadian ensemble members are
  less robust with a further north storm track, as seen clearly in
  the atmospheric river landfall probability charts. Overall
  definitely a week to monitor if you have travel or outdoor
  activities planned.

-Chris

&&

.AVIATION...

Winds will begin to increase overnight and turn northerly as a
strong cold front quickly sweeps south and east through the region.
Anticipate gusty winds, rough air, and low level wind shear,
particularly along the frontal boundary late tonight into early
Monday morning. Gusty northeast-east winds will continue across
Sierra Monday night into Tuesday, with mountain wave activity
largely west of the Sierra crest.

Colder air spreading behind the front will drop snow levels down to
all valley floors. A quick burst of snow showers are also possible
along the front as its pushes south, starting first along areas near
the Oregon border later tonight and continuing to near and south of
US-50 later Monday morning. Therefore, light snow showers are
possible for all terminals, but snow-fall amounts will range only
from a trace to half an inch. Periods of terrain obscuration, and
lower CIG/VIS will remain a concern tonight through Monday. -Amanda

&&

.Fire Weather...

While we are not expecting widespread nor prolonged critical
conditions with this incoming front tonight and Monday, there are
some localized fire weather concerns mainly in the Eastern Sierra
and Mineral County regions. These are areas that tend to blow
strongly in frontal passage northerly wind scenarios such as this.
While humidity values won't be super low, periods of wind gusts over
40 mph are likely along Hwy 395 in Mono County pre-dawn Monday and
into the Owens/Chalfant Valleys during the day Monday. This could
create localized fire weather concerns with dry fuels persisting.

Elsewhere in the forecast area, light rain and snow showers are
expected along the front Monday morning, with a more general brisk
N/NW wind through the day Monday. Humidity levels will drop with dry
air working in behind the showers but likely remaining above 25%
most areas.

-Chris

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 8 AM to 9 PM PDT Monday for Pyramid Lake
     in NVZ004.

     Freeze Warning from 11 PM Monday to 11 AM PDT Wednesday
     NVZ001-003>005.

     Wind Advisory from 2 PM to 8 PM PDT Monday NVZ001.

     Lake Wind Advisory from 2 PM Monday to 8 AM PDT Tuesday for Lake
     Tahoe in NVZ002.

CA...Freeze Warning from 11 PM Monday to 11 AM PDT Wednesday
     CAZ070-071.

     Wind Advisory from 2 PM to 8 PM PDT Monday CAZ073.

     Lake Wind Advisory from 2 PM Monday to 8 AM PDT Tuesday for Lake
     Tahoe in CAZ072.

&&

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