Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 190512
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
1012 PM PDT Mon Sep 18 2017

.UPDATE...

Breezy conditions continue across much of the region this
evening, though wind speeds are decreasing compared to the peak
earlier today. The one exception are Sierra ridges which remain
strong and gusty with 40 kts at 700 mb draped across the region
through approximately 2 am, before weakening. Have gone ahead and
expired both the Red Flag Warning and Lake Wind Advisories on time
this evening due to overall decreasing winds. Most locations will
not fully decouple overnight with lighter winds anticipated
during the day Tuesday. Otherwise, the forecast remains on track.
-Dawn


&&

.PREVIOUS DISCUSSION... /Issued 309 PM PDT Mon Sep 18 2017/

SYNOPSIS...

A series of cold fronts will produce gusty winds today and again
Wednesday. Below average high temperatures are expected through
the weekend. Light showers, with a dusting of snow in high
elevations, are possible at times from Wednesday through Friday.
Near or below freezing temperatures are possible for normally
colder lower valleys by Friday and Saturday morning.

SHORT TERM...

A cold front extends through southeast Oregon and into extreme
northern California this afternoon. Ahead of the front, wind
gusts have reached 30-40 mph near and north of Highway 50, and
could reach up to 45 mph for a time late this afternoon and into
the evening before diminishing overnight. The increased winds have
brought some heightening of fire weather concerns (and a few
local fires!) so see the fire discussion below for more details.

The cold front will move through far northeast California and
into the northern third of Nevada tonight as an upper low moves
over the interior Northwest CONUS. The front/cooler air will
filter through western and west-central Nevada on Tuesday for some
cooling; however, the front will be running out of gas as the
main chunk of colder air moves into northeast NV so some areas of
the eastern Sierra and northeast CA may not see much cooling over
today. With the main forcing remaining well north of the region,
precipitation with the front looks very anemic and restricted to
well north of Susanville and Gerlach tonight.

Wednesday and Wednesday night, the next front will move through
the region. The best forcing with that front will also reside
north of the area over Oregon and the moisture is looking
disjointed with the front in current simulations (at least until
you go over into central/eastern NV). Therefore, precipitation
looks meek with Wednesday`s front, at least from Susanville and
Gerlach south where at best a couple hundredths is expected (most
likely in northern Sierra and in the Basin and Range north of I-80).

As far as wind with Wednesday`s front, gusts 35-50 mph will be
possible especially within a few hours on either side of FROPA.
The winds will bring a sharp drop in wind chills (teens and 20s)
by later Wednesday night into Thursday morning for the Sierra and
higher elevations of northeast CA. Take precautions for cold and
wind if you will be venturing in the Sierra for mid-late week.
-Snyder

LONG TERM...Thursday through Monday...

The main concerns in the long term will be freezing low
temperatures in colder western NV valleys and late fall/winter-
like temperatures in the high Sierra as a trough remains over the
region through most of the weekend. By Friday or Saturday morning,
colder western Nevada and northeast California valleys (Cold
Springs, Stead, Carson Valley, Sierra valley to name a few) could
see their first freezing temperatures since spring. As a rule of
thumb, if the forecast low is below 40 degrees you may want to
take precautions for sensitive vegetation.

Isolated to scattered showers are possible from time to time
through Friday, although placement is very uncertain at this time
and will be based on subtle smaller-scale waves dropping into the
trough. -Snyder

AVIATION...

Surface gusts are generally in the 25-35 kt range this afternoon
across northeast CA and western NV, with higher ridge gusts 45-65
kts. Turbulence is expected downwind of the Sierra well into this
evening, with turbulence above valley floors downwind of the
Sierra continuing into Tuesday morning as flow aloft remains
elevated. Shower chances are rather slim with this front...but a
few areas north of a line from Susanville to Gerlach could see
slightly lower ceilings.

The next system impacts the region starting Tuesday night and
Wednesday. Initially there will be an increase in clouds and a
lowering of ceilings near the Oregon border Tuesday night with a
few more showers. This will expand south during the day Wednesday
into the overnight hours. Showers with some reduction in ceiling
will be possible north of I-80 and down into the northern Sierra
by Wednesday evening. The more impactful feature will be increased
winds with widespread surface gusts reaching 35-40 kt with ridge
gusts closer 70 kt. This is likely to result in more widespread
turbulence than today. Snyder

FIRE WEATHER...

Widespread winds 15 to 25 mph with gusts 30 to 40/45 mph are expected
through the evening. Relative humidity values are around 15-25%
for areas near and south of Highway 50 in west-central Nevada and
for Mono County, but have risen above 30% for most areas north of
Interstate 80 and in the far northern Sierra. Peak winds will
occur through 7pm. The Red Flag Warning itself remains unchanged
and is in effect for zones 278, 450, 453, and the southern half of
458.

Wind gusts will be between 30 to 35 mph for localized areas in
Mono and Mineral counties into this evening, but it should be
relatively sparse in coverage and the duration shorter than for
the areas in the Red Flag Warning. So just be aware that there
could be some very localized critical fire conditions due to gusty
winds and low humidity for Mono and Mineral Counties.

Another round of gusty winds is likely for Wednesday as the next
cold front moves through northern California and Nevada. Relative
humidity values still appear to remain above the critical (~15%)
threshold, but there could still be a period of critical conditions
from late Wednesday morning into the afternoon. The wind gusts
for this next cold front appear to be in the 35 to 50 mph range
which could mean that even with higher humidity values, it could
still warrant critical fire conditions. We will keep an eye on it
and hold off issuing any watches or warnings for this event for
now. -Edan

&&

.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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