Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 180908
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
208 AM PDT Fri May 18 2018

.DISCUSSION...
Showers and thunderstorms will be confined mainly to the Sierra
today except for a few storms pushing off the mountains into the
Highway 395 corridor by evening. Another low pressure area will
set up this weekend and bring increasing chances for storms this
weekend and early next week.

&&

.SHORT TERM...

No significant changes to previous thinking as the area will be in
a relative lull today before another trough sets up over the west
coast this weekend. Temperatures will warm to slightly above
normal levels through the weekend with mid-upper 60s Sierra
valleys and 70s lower elevations.

For today, a mid level cap will exist across much of western NV
with the best area for isold-scattered thunderstorms expected to
be along the Sierra. Some storms may push out to the Highway 395
corridor by late afternoon/early evening but overall storm motions
will be slow and erratic. Sufficient moisture and instability
remain present for locally heavy rain and accumulating small hail
with stronger storms.

For Saturday and Sunday, upper level divergence increases and
temperatures aloft cool ahead of incoming trough which will
increase shower and thunderstorm coverage. The potential for
stronger storm development also increases, especially along
preferred surface convergence zones including the Sierra Front
south into Mono-Mineral Counties as well as northern Lassen
County. Daytime heating/instability will combine with increasing
shear aloft to support decent long-lived updrafts. Heavy rain
could lead to some flash flooding issues where storms anchor to
stationary outflow/terrain induced surface boundaries. We also
added a mention of thunder Saturday night and Sunday night as
general large scale forcing and mid level instability remained in
place. If you have outdoor plans, have an action plan to take
shelter indoors as lightning will be a hazard to boating, hiking
and other outdoor activities. Hohmann

.LONG TERM...Monday through Thursday...

There were not many changes made to the extended forecast this
cycle. The deterministic models...and most of the ensemble
members...persist in keeping an upper low entrenched over the region
through at least early Thursday. This results in periods of showers
and thunderstorms each day with near normal temperatures.

The difficulty with these upper lows is trying to pinpoint the areas
with the best chance of convection. This far out that can be largely
impossible in the extended portion of the forecast as the situation
may not evolve as advertised at this time.

We have left the broad brushed higher chance POPs for the daytime
with lower end chance POPs overnight. While we did not mention
thunderstorms during the overnight hours...it is possible there
will be enough instability associated with the upper low to
generate deep convection overnight.

Thursday the model agreement breaks down with the GFS trying to
build a weak short wave ridge while the ECMWF shows the next upper
low moving from well offshore to close to the coast. The ECMWF would
support more coverage...but we will keep Thursday to a relative
minimum compared to the previous days in deference to the GFS
solution for now.

&&

.AVIATION...

The exiting of the low over the region the past few days will mean
less coverage of showers and thunderstorms today...but not the
complete end of all activity. Localized turbulence will be possible
near any storms that develop along with small hail and brief
gusty winds. Outside of the lowered cigs/vsbys near any stronger
storms...most areas will be VFR today. There could be fog in areas
that received rain yesterday and overnight...but that should burn
off quickly after sunrise.

Another wave will bring increased chances for showers and
thunderstorms Saturday...then an upper low starts to dig in later
Sunday. This low will persist into the middle of next week with
periods of showers and thunderstorms. Overall...an active pattern is
expected to continue through at least the middle of next week.

&&


.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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