Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 191010
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
310 AM PDT Tue Sep 19 2017

.SYNOPSIS...

A strong cold front will bring windy conditions Wednesday, with
below average temperatures continuing through the weekend.
Thursday and Friday are expected to be the coolest days, with
possible freezing conditions at night in some lower elevation
valleys. Light showers, with a dusting of snow in higher
elevations, are possible at times from Wednesday through Friday.

&&

.SHORT TERM...

The first cold front will complete its push across western NV this
morning, although it will generally become diffuse with zonal flow
aloft prevailing today. We will have a short break in winds today
with surface gusts generally 25 mph or less. Dry conditions
prevail, except near the Oregon border where a few very light
showers are possible. Temperatures will be about 10 degrees below
average with highs mainly in the lower 70s for lower elevations
and lower-mid 60s near the Sierra.

For Wednesday and Wednesday night, the next cold front will bring
windy conditions with gusts 40-45 mph in most areas. Some wind
prone areas could receive gusts above 50 mph, while Sierra ridges
are likely to exceed 80 mph.

Precipitation chances during the day Wednesday will be mainly
limited to areas north of Susanville-Gerlach, where up to 0.25
inch of rainfall is possible. Then as the cold front passes
though Wednesday night, bands of showers are more likely to
develop farther south. Current projections show the best chances
for measurable precip (up to 0.10 inch) Wednesday night in west
central NV east of US-95 (due to enhanced lift from right entrance
region of upper level jet), and near the Sierra from Tahoe
northward (due to forcing from secondary shortwave behind the main
front). Snow levels could dip below 7000 feet by early Thursday
morning, with patchy light accumulations up to 2 inches possible
above 7500 feet. A few snowflakes are even possible down to lake
level around Tahoe by early Thursday.

For Thursday and Thursday night, chilly conditions will prevail as
low pressure moves slowly across the northern Great Basin. Highs
will struggle to reach 60 degrees in lower elevations, and only
get to near 50 degrees for Sierra valleys. Cyclonic flow and weak
shortwave energy wrapping around the low will keep the shower
potential going through the afternoon and early evening, with most
activity diminishing overnight. Snow levels will likely hover
around 6500-7000 feet from US-50 northward and 7000-8000 feet
south of US-50, but little or no snow accumulation is expected.
MJD

.LONG TERM...Friday through Monday...

Minimal changes were made to the inherited long term forecast...
mainly to adjust lows down a bit for Saturday and Sunday mornings.

The upper low over the region begins to weaken Friday...but is still
in place until midday Saturday. Upper level short waves rotating
around this low will keep at least a slight chance for showers over
the region into Friday night. It is difficult this far out to try to
pinpoint locations and any amounts...so we will just keep some low
end pops over the far northern CWA and parts of the Sierra and far
western Nevada Friday.

Highs remain well below average with temperatures in the 60s for the
western Nevada valleys Friday and Saturday and 50s for the colder
Sierra Valleys. Highs warm a few degrees Sunday, then a building
ridge by late Monday should allow highs to climb to within a few
degrees of normal.

Lows in the western Nevada valleys could dip into the mid 30s
Saturday and Sunday with a few outlying locations dropping to
freezing or below. In the colder Sierra valleys lows could drop into
the mid 20s to lower 30s both days. It should go without saying that
lows of this nature can cause harm to any sensitive vegetation left
outside...and such plants should be protected from temperatures
below 40 degrees. At this point we are not planning any Freeze
Watches or Warnings as the colder valleys are in areas with limited
agricultural impacts.

Lows by Monday morning will rise a bit into the upper 30s and 40s
for the western Nevada valleys and the upper 20s to lower 30s for
the Sierra valleys.

&&

.AVIATION...

Lighter winds are expected today at the surface but there could
still be rather gusty winds over the ridges...so some turbulence
is possible aloft. A few showers may linger near the Oregon border
later today...but the better chances for showers develop
overnight and spread south through the forecast area Wednesday.
This could lead to lowered ceilings...but still mainly VFR except
in the mountainous terrain where some obscurations are likely
Wednesday into Thursday.

Winds increase significantly again Wednesday along and ahead of a
cold front that will bring the showers. Surface gusts could reach 35-
40 kt in many areas Wednesday with ridge gusts in excess of 70 kt.
This would lead to increased turbulence and low level wind shear as
well.

The winds should decrease by Thursday morning...but an upper low
settles over the region that will result in unsettled weather into
Saturday. The better chances for precipitation and moderate to poor
flying conditions with this low will be Thursday...but showers are
also possible for Friday.

&&

.FIRE WEATHER...

Gusty winds Monday were in the range of 30-40 mph and we did see
rising humidity values through the day. That said...there were a few
fires that started and were able to spread minimally in the drier
grass and brush.

A similar scenario is likely to play out Wednesday as an even
stronger cold front drops south across the region. Wind gusts along
and ahead of this front could reach 35-45 mph at times...a little
stronger than Monday. And precipitation will be somewhat limited...
although there is a better chance of showers along the front as it
is more dynamic that the front the passed through Monday.

A factor in whether to issue a Fire Weather Watch or Red Flag
Warning revolves around how fast humidity levels will increase. The
latest model soundings...and additional model data...suggest
humidity values will increase faster and reach higher levels
through the day Wednesday than they did Monday. This could limit
the time for critical conditions to only 2-4 hours...with the
best potential along and south of a line from Lovelock to
Bridgeport. Humidity may not be the overriding cause of fire
spread if any were to develop...strong gusty winds will likely
have a bigger influence. But humidity most be considered.

With all this in mind...the confidence level in critical conditions
for more than a few hours is rather low at this time so we will
refrain from issuing any watches or warnings at this time and just
headline strong gusty winds in the planning forecast.

&&


.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

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


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