Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 151039
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
339 AM PDT Tue Aug 15 2017

.SYNOPSIS...

Weak low pressure will develop off the coast during the week with
overall light winds. This low will increase the instability with a
few thunderstorms possible Wednesday and Thursday in Mono County.
Thunderstorms chances will affect most of the Eastern Sierra and
Western Nevada for the weekend. Temperatures will be near to
slightly above average for the next 7 days.

&&

.SHORT TERM...

There were no large adjustments made to the forecast through
Thursday night. We could see a few showers along the Lassen
convergence zone in north-central Lassen County this afternoon as
a weak wave moves through the region. NAM highlights this weak
wave pushing through that could aid in providing forcing along the
convergence zone. Current estimations of forcing are on the lower
end of the scale and should not be able to overcome a moderate
mid-level cap that is present over the region, so only a mention
of low chances of showers is prudent at this time. The wave will
continue to produce very low chances of showers overnight, around
10% in the Basin and Range, but capping should keep thunderstorms
out of the equation.

A few isolated showers over the higher Sierra of Mono County may
also occur as surface heating provides lift. Expect haze and some
smoke in Mono County from nearby wildfires today, and possibly
into Wednesday. Air quality will decrease, so you may need to
limit your exposure outdoors if you are sensitive to smoke.

The capping mechanism largely erodes Wednesday and Thursday allowing
for slightly higher chances, around 15%, of thunderstorms over
the higher Sierra of Mono County. Westerly flow in the afternoon
could spread these chances into central and eastern Mono County. A
few build-ups may be present in Alpine County and the very
southern reaches of the Tahoe Basin by late Thursday afternoon.
Boyd

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

Minor changes were made to the extended forecast this cycle. These
changes mainly involved expanding areas of slight chance pops to
account for uncertainty in the placement of convective activity each
day starting Friday.

The medium range models are coming into better agreement with the
overall evolution of the primary pattern. Both the ECMWF and GFS
depict weak flow aloft with the GFS a bit more aggressive showing a
minor wave Friday which could aid the development of storms in the
Sierra.

Beyond Friday a more amplified trough develops in each model for the
weekend and the early part of next week. The main difference is the
GFS is faster to develop a closed low along the CA coast by late
Sunday. It takes the ECMWF until later Monday for this to happen.

The GFS is more aggressive with convective development each day as
well. The presence of this upper low to the west could lead to less
in the way of a thermal gradient over the region and that means a
limited zephyr each day. That would support more convection north
along the Sierra into northeast CA along with the typical
development east into western NV and the basin and range. So slight
chance pops were expended each day through Monday...but Saturday
still looks like the greatest coverage day. The presence of the
upper low and its induced instability could lead to overnight
activity Saturday night and Sunday night...but this was not added
yet.

&&

.AVIATION...

VFR today through Wednesday for most terminals. KMMH could possibly
experience MVFR conditions today due to smoke from the South Fork
Fire. Visibility still looks to be VFR overall, but could be
reduced to 4-5SM 09-18Z depending on smoke production. Slant-wise
visibility will likely be poor. A few showers may pop over the
higher terrain today, but thunderstorms are unlikely today.

Better chances of higher terrain thunderstorms, mainly in Mono
County, will occur Wednesday into the weekend. Wallmann/Boyd

&&


.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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