Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 161035

Area Forecast Discussion
National Weather Service Reno NV
335 AM PDT Wed May 16 2018


Showers and thunderstorms may produce heavy downpours with
accumulating snow or small hail possible in the higher elevations
on today. Showers and storms will decrease some this weekend
before increasing again next week.



Widespread rain with embedded thunderstorms are expected
throughout the region today. The main weather threats today will
be periods of heavy rain, possibility of accumulating small hail
(snow above ~8-8500`), and lightning. Ponding on roads, and low
visibility will likely be the biggest hazards for transportation
with the potential for isolated minor to moderate flash
flooding depending on just how much storms are able to develop.

Precipitation is expected to start in the late morning in the
Sierra and central western Nevada with a few hours of heavy rain
and high elevation snow, especially around the Tahoe Basin and
in the Reno/Carson City area. The area with the most persistent
signal for significant heavy rain potential and runoff concerns
is around Churchill and Pershing Counties during the late
afternoon and into the early evening. It`s also possible the
northern Sierra and Lassen counties could be a heavy rain threat
later in the afternoon, but clouds will have a better chance of
inhibiting convection in that area.

The cut-off low pressure that has been spinning over the region
this last week is finally being pushed north of the Nevada border
this morning as another area of low pressure is currently moving
into the central California coast. This will create a wide area of
divergence aloft over the region and bring a new round of upper
level forcing. Clouds are expected to inhibit some storm
development today, but it currently looks like there will be
enough clearing and instability to get stronger storms to form,
especially around Mono/Mineral counties where the best chance for
clear skies will be this morning.

Model simulations are pointing towards the possibility of a
mesoscale complex of storms developing around Mineral county this
afternoon and moving into Churchill and Pershing counties later
in the day. This type of convective development is very difficult
to predict but most models are simulating a similar scenario with
the potential for 1-2 inches of precipitation if this feature

One question that persists today is how much cloud cover inhibits
surface heating that could add to the instability. The band of
light showers in the region overnight moved north faster than
models had forecast with current IR satellite observations showing
good clearing in the southern part of the CWA. It is really
difficult to say how much increasing cloud cover could hamper
storm development, but the latest guidance is pointing towards
some strong thunderstorm development today.

Lighter showers are expected on Thursday with only a slight chance
of thunderstorm development. By Friday it looks like the main
area of concern will be in the central and southern Sierra where
thunderstorms could develop with potential for heavy rain and high
elevation snow. -Zach

.LONG TERM...Saturday into next week...

It is slowly becoming a bit clearer on the timing of the upper low,
with the models and ensembles in better agreement for the weekend.
They are also in better agreement with timing of the next low for
Monday into Tuesday, although the track is still hazy.

For the weekend, the GFS/EC have a weak wave moving through in light
west flow aloft between the upper lows. Instability is not overly
impressive, but will keep the slight chance to low chance for the
Sierra and adjacent eastern slopes. Sunday the low approaches, but
the southwest flow ahead of it will increase. For now, the track
appears to be toward the SF bay area which would put the best
forcing north of a KSVE-KLOL line, but this could change. With the
stronger SW flow, Sierra convection will be hard pressed to form
unless it`s early in the afternoon. Have the best chances east of
there and then where the best forcing is for Sunday. SW winds will
make a decent appearance, with peak gusts of 25-30 mph. Keep in
mind, this is the best idea for now, but with the way the models
have been changing, this forecast may be way off.

Monday into Tuesday, the area will be affected by the upper low.
Where it tracks will determine best chances. It could end up being
similar to what we see tomorrow, or just generic thunderstorms. Will
keep the chance pops going both days area-wide with a decrease
Wednesday as the low pulls away. Temperatures will be near average
through the period, although Monday could be cooler depending on
track of the low. X


FG will continue around the Tahoe terminals and Sierra Valleys this
morning with LIFR conditions. Expect it to burn off between 15=16Z.

The upper low will move in today with High chances of SHRA and
embedded TSRA for Reno-Tahoe area 17-23Z, about 80-90% for each
terminal. Some small hail is also likely to occur with MVFR to
local IFR conditions and mtn obscuration in the showers/storms.
These showers and storms will move north and east during the
evening. 70-90% chances for periods of MVFR CIGS/VIS at
KSVE/KLOL/KNFL 23-06Z this evening. KMMH/KHTH will still see storms
around, but chances of those terminals being affected are less, 40-
50% and 18-23Z. Winds will be light outside of thunderstorms, where
peak gusts could approach 35-40 kts.

More thunderstorms Thursday, but not as widespread with chances 40-
50% for any terminal. Wind gusts to 40kts and small hail primary
threats. Thunderstorm threat a little less Friday into Saturday
before possibly increasing again early next week with another upper
low. X


.REV Watches/Warnings/Advisories...


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