Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 190947
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
247 AM PDT Sat May 19 2018

.SYNOPSIS...

Another low pressure area will settle over northern California
and western Nevada, bringing an increased chance for storms this
weekend through the middle of next week. Some of these storms will
produce locally heavy rainfall, especially Monday and Tuesday.


&&

.SHORT TERM...

The overall message remains unchanged as a low pressure system
moves to the west coast today and persists into next week. Showers
and thunderstorms are a good bet with some storms producing
locally heavy rain, small hail and lightning. Temperatures will be
close to seasonal levels except for much cooler temperatures that
result from showers and thunderstorms. Keep adequate clothing
handy if you have outdoor plans. Also have an action plan to take
shelter indoors as lightning will be a hazard to boating, hiking
and other outdoor activities.

Upper level divergence was already increasing this morning as
high based showers were developing over western NV. An isolated
thunderstorm is possible there so we added the mention to the
morning. Skies had cleared along the Sierra and this will be the
focus for storm development later this morning as daytime heating
promotes increasing instability and lift along the terrain. Storms
will move off the Sierra during the afternoon with a few stronger
storms likely as they move into western NV. These storms may
persist overnight as they lift northeast across the Basin and
Range and northwest parts of NV/Surprise Valley where upper level
forcing will persist.

On Sunday the upper low will begin to move southeast into CA with
a bit more southwest flow in advance of it. This increase in flow
will act to push convection more into western NV with some model
scenarios keeping Tahoe and the Sierra Front convection-free. We
dried out the Tahoe Basin Sunday but kept a slight chance mention
for the Sierra Front in the afternoon as storms could develop
there before the westerlies become more entrenched. The best areas
for storms will be from Mono/Alpine Counties into western NV from
Highway 50 south as well as across northern Lassen County into
far northwest NV.

The upper low closes off near the southern Sierra Monday and the
focus turns to more widespread rain bands and embedded thunder
across the eastern Sierra and western NV, especially south of
I-80. Widespread moderate QPF is possible based on the projected
track of this low. There is still some uncertainty as to where the
heaviest rain will fall. But Monday is looking cloudy, cool and
wet for many areas south of I-80. Temperatures were kept at
slightly below normal levels, but they could be considerably
cooler where persistent rain bands set up. Hohmann

.LONG TERM...Tuesday through Friday...

Very minimal changes were made to the long term portion of the
forecast this morning. The forecast models persist in holding a
broad upper low over the region Tuesday...then slowly filling the
low and lifting it to the northeast Tuesday night into Wednesday.

Even with the low lifting out...there should continue to be a chance
for showers and thunderstorms through Wednesday as there is no
substantial scouring flow that develops to push any residual
moisture out of the area. Daytime heating Wednesday should act on
this residual moisture to develop convection in the afternoon and
evening.

By Thursday the operational model solutions begin to diverge and the
GEFS ensemble members solutions are split between the GFS and ECMWF.
The GFS tries to build a short wave ridge Thursday and Friday with
increasing highs and decreasing chances for convection. Meanwhile...
the ECMWF is much more aggressive with another low lifting into the
region from offshore...driving the low into central California by
late Friday. This would support more diffluence aloft and increased
chances for convection.

A compromise solution is to keep slight chance to low end chance
POPs over much of the region both Thursday and Friday with daytime
thunderstorms and nighttime showers.

&&

.AVIATION...

A wave of low pressure aloft will bring a renewed chance for showers
and thunderstorms today. A few of the storms may be rather strong
and all will be slow moving. As is typical with most
thunderstorms...expect localized strong gusty winds and turbulence
and brief periods of lowered cigs and vsbys. Otherwise...VFR
conditions will prevail for most areas today...although fog has
formed in the Martis Valley producing vsbys below 1 mile at KTRK.
This fog will burn off after sunrise.

Convective coverage may be slightly less Sunday...then increase again
Monday and Tuesday. Thunderstorms are likely to be present in the
forecast area each day through at least Thursday or Friday.

&&

.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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