Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 141605 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
905 AM PDT Mon Aug 14 2017

.UPDATE...
Quick update to add smoke and haze to Mono County and parts of
Mineral County. Smoke from the fires on the west slope of the
Sierra, primarily the South Fork Fire in Yosemite NP will continue
to impact the area today. It is already rather active this morning
based on satellite imagery so it will likely be an issue into
Tuesday as well. Will investigate this more late this morning.
Wallmann

&&

.PREVIOUS DISCUSSION... /Issued 246 AM PDT Mon Aug 14 2017/

SYNOPSIS...

Weak low pressure will produce cooler temperatures Monday with a
chance for showers and a few thunderstorms in northeast California
and northwest Nevada. High pressure off the West coast will keep a
progressive shortwave pattern over California and Nevada through the
 week. Slight warming trend possible with high pressure
strengthening  by Thursday or Friday.

SHORT TERM...

Some slight adjustments were made to the previous forecast.
Scattered showers were removed from the Surprise Valley this
morning leaving only isolated thunderstorms; the instability axis
is forming a little farther east than models projected. With
troughing the predominant feature over the region, afternoon
instability should be sufficient by Wednesday to warrant the
mention of isolated thunderstorms over the higher Sierra of Mono
County. Storms could form as early as Tuesday afternoon, but left
mention out for now.

Otherwise, the forecast remains on track. There is a wave moving
through extreme northern California this morning which has been
the focal point for some isolated showers mainly in Oregon
this morning. Expect coverage of showers to blossom later this
morning with enough instability to produce a few isolated
thunderstorms mainly along and just behind the 700mb trough.
Timing remains on track for around 4/5am through about 8am from
best forcing in the Surprise Valley and northern Washoe County
areas. Instability lingers into the afternoon, but the primary
forcing shifts eastward. Still, a few isolated storms could fire
into the early afternoon hours towards the Oregon border.

This wave will also increase winds marginally across the region.
Afternoon gusts will be in the 20-30 mph range resulting in
isolated pockets of critical fire weather conditions mainly north
of Interstate 80, but south of the primary cloud shield associated
with the passing wave where RH will be higher. These winds will
be somewhat disrupted Tuesday and Wednesday as the wave passes and
as the thermal gradient weakens from the Sierra to central
Nevada. Afternoon winds will generally only gust to around 20 mph
into mid-week. Instability will be on the rise Tuesday and
Wednesday over the higher Sierra in Mono County. We could see a
few isolated thunderstorms, but Wednesday is currently the more
favorable day right now. Boyd

LONG TERM...Thursday through Sunday...

Modest changes were made to the extended forecast this cycle to
account for the possibility of increased convective chances for
Saturday and Sunday. Confidence is low to moderate in any solution
next weekend as previous model cycles have shown less chance of
convection. But now the operational models are in a little better
agreement that a broad trough develops by the weekend.

Weak flow aloft Thursday and Friday could lead could lead to
isolated storms both days. Thursday looks less favorable so any
mention was kept out of the at day. Low level instability increases
Friday and the overall light flow and differential heating should
allow for the development of more cumulus cloud that could grow to
storms along the Sierra.

Both the GFS and ECMWF are shifting to a pattern dominated by a
broad weak trough Saturday into Sunday. The GFS is a bit more
aggressive with storms than the ECMWF. The best coverage day would
be Saturday as models show a weak wave lifting through the region.
This would allow storms to develop into the basin and range and not
just along the Sierra. Any activity Sunday would be more isolated
and confined to areas mainly south of Highway 50.

AVIATION...

A cool front slides through the northern half of the forecast area
today. Clouds increase this morning before thinning late this
afternoon. Mainly VFR conditions are expected...but there could be a
few showers...and possibly even a few stray thunderstorms...north of
a line from Susanville to Lovelock today. Gusty surface winds are
likely south of the front. Maximum gusts could reach 20-25 kt.

Drier air pushes in tonight and Tuesday with northwest flow aloft
and at the surface. The next chance for any aviation hazards is late
in the week when thunderstorms could start developing along the
Sierra into the weekend.

&&

.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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