Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 170958
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
258 AM PDT Sun Sep 17 2017

.SYNOPSIS...

Seasonable temperatures and dry conditions will prevail through
Monday. A series of cold fronts will produce strong gusty winds
on Monday and again Wednesday. Below average temperatures are
expected from Tuesday through early next weekend, with potential
for freezing in some colder valleys. Light showers are possible
at times from Wednesday through Friday.

&&

.SHORT TERM...

After a relatively quiet Sunday with moderate afternoon breezes,
the main weather highlight for the early portion of the upcoming
week will be in the form of stronger winds Monday as a large area
of low pressure moves into the Pacific Northwest. Surface wind
gusts on Monday are projected to range from 35-45 mph, with Sierra
ridge gusts up to 75 mph. Lake wind advisories will be issued
across both Tahoe and Pyramid for Monday. Fire Weather concerns
will also increase with these stronger winds--see the Fire Weather
segment below for more details.

Most of the moisture associated with this storm system will remain
north of the Oregon border for the next few days. A few very
light sprinkles (measurable rain unlikely) may brush across parts
of northwest NV Monday night behind the surface cold front.
Isolated showers are also possible by late Tuesday and Tuesday
night in far northeast CA and northwest NV ahead of the next
shortwave trough and reinforcing cold front.

Temperatures will remain near seasonal averages today with highs
around 80 degrees for lower elevations and around 70 near the
Sierra, then start to drop on Monday, especially north of I-80.
By Tuesday, cooler temperatures filter into most areas with highs
mainly in the lower-mid 70s for lower elevations, except 60s north
of Susanville-Gerlach and near the Sierra. MJD

.LONG TERM...Wednesday through Saturday...

The only substantial changes made to the extended forecast this
morning were to increase winds a bit more for the Wednesday time
frame. Otherwise...the model solutions are similar to the most
recent cycles and support low end pops and cooling temperatures for
Thursday and Friday with a little warming for Saturday.

The leading edge of a vigorous upper level trough and its associated
surface front move into the northern part of the forecast area
during the day Wednesday. These features move through the forecast
area by Thursday morning. The presence of a strong jet core aloft
(in excess of 120 kt) along with increased mid level flow (700 hPa
winds in excess of 40 kt) and increasing thermal and pressure
surface gradients point to Wednesday being the windiest day of the
forecast period. Gusts in some valley and wind prone locations could
exceed 50 mph while ridge gusts top 75 mph.

As the broad upper trough settles over the region Thursday and
Friday the winds should be lighter...but breezy easterly winds are
possible over the Sierra ridges late Friday night into Saturday
morning.

Precipitation chances with the trough and front Wednesday look best
over areas well north of I-80...but even these chances are no better
than 30%. With the surface front Wednesday evening and overnight
there could be a brief period of showers that progress through the
forecast area from north to south. The ECMWF is a bit more
aggressive with the possibility of precipitation at this time.
Showers could linger in Mono County Thursday in upslope flow...but
the chances are not very high.

Temperatures will be below normal Wednesday then drop even further
Thursday and Friday. Highs may not rise out of the upper 60s to
lower 70s in the warmer valleys while lows dip into the upper 30s to
lower 40s for the lower valleys, while the Sierra valleys see
lows in the upper 20s to lower 30s.

By Saturday the trough is filling and sliding east as a ridge begins
to build to the west. Clouds should decrease and temperatures begin
to rise.

Bottom line for this forecast cycle: Confidence is moderate to high
that Wednesday will be quite windy and could pose some fire weather
issues. The confidence in any precipitation is on the low end of the
scale...both in terms of location and amount.

&&

.AVIATION...

Another pleasant day with VFR conditions and relative light winds is
in the offing today. But those conditions begin to change Monday as
a surface front makes it way toward the region. Gusty surface winds
develop by midday with areas north of I-80 seeing gusts approaching
30-35 kt. Ridge gusts could top 50 kt. So turbulence and LLWS are
likely for Monday. VFR conditions should continue. There is a small
chance for a few very light showers north of a line from Susanville
to Gerlach by Monday night.

The chances for showers increase from late Tuesday into Wednesday as
another front makes its way south. This one is likely to bring even
stronger winds to the region for the Wednesday/Wednesday night time
frame with gusts approaching 35-40 kt in the valleys and better than
65 kt at the ridges.

&&

.FIRE WEATHER...

An approaching upper level trough and surface front bring strong
gusty winds to the region Monday with a second trough bringing even
stronger winds Wednesday.

While relative humidity values Monday are not expected to drop much
below 15%...wind gusts approaching 45 mph north of I-80 will still
create the potential for critical fire weather conditions as fuels
remain dry and could easily carry fire.

We will issue a Red Flag Warning for zones 278...450...453 and the
southern half of zone 458 for Monday and Monday evening. These
locations will see the strongest wind gusts with minimum humidity
values in the 12-24% range. Zone 270 and the northern part of
zone 458 will also see strong wind gusts but the minimum humidity
values there are likely to be in excess of 25%. Elsewhere wind
gusts will top out at 35-40 mph. Minimum humidity values in zone
459 could reach as low as 11%...but wind gusts are likely to be
less than 40 mph except for a few wind prone areas along Highway
95.

We will address the need for additional Red Flag Warnings for the
Wednesday time frame after the Monday event ends...but wind gusts
could top out above 50 mph in some areas Wednesday.

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning from 11 AM to 10 PM PDT Monday NVZ450-453-458.

     Lake Wind Advisory from 10 AM to 10 PM PDT Monday for Lake Tahoe
     in NVZ002.

     Lake Wind Advisory from noon to 10 PM PDT Monday for Pyramid
     Lake in NVZ004.

CA...Red Flag Warning from 11 AM to 10 PM PDT Monday CAZ278.

     Lake Wind Advisory from 10 AM to 10 PM PDT Monday for Lake Tahoe
     in CAZ072.

&&

$$

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


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