Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 062123
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
223 PM PDT FRI MAY 6 2016

.SYNOPSIS...

Widespread showers and scattered thunderstorms this afternoon
could once again produce small hail and brief moderate to heavy
rain. Locally heavy rainfall is expected across portions of
northeast California, the northern Sierra, and northwest Nevada
tonight into Saturday with isolated thunderstorms. Showers will
linger into Sunday before drier, warmer weather returns next
week.

&&

.SHORT TERM...

Only minor tweaks were made to the ongoing forecast to track the
most likely locations of heavy rainfall banding due to a
deformation axis tonight into Saturday. There are multiple events
and festivals that may be affected by the heavy rain and isolated
thunderstorms on Saturday, so be sure to have a back-up plan.

Thunderstorms this afternoon have initiated across central Nevada,
and with east to west storm motions, will spread into western
Nevada as the afternoon progresses. Storms could once again
produce frequent lightning and small hail in addition to brief
moderate to heavy rain. Storms will be moving fairly fast,
especially north of Interstate 80, due to a jet segment across
the region. This will lessen flooding risks, but flooding is still
possible if storms train or heavy enough rain falls on the already
saturated ground. Although slower storm motions are expected to
the south, the also coincides with lesser chances for heavier
rainfall. For more details regarding flood risks, please see the
hydrology section below.

For tonight into Saturday, the development of a deformation axis
should provide the forcing necessary for heavy rainfall.
Instability isn`t as favorable, but deep moisture is present.
Therefore, am expecting more in the way of rain with only isolated
thunderstorms. Have trended the forecast closest to the GFS as far
as positioning of the highest precipitation chances, which has had
the most consistency and model support over the past several days.
The position of these bands also matches up well with the location
of the jet and warmer air wrapping into the low, almost a TROWAL-
like feature, which can also bring heavier precipitation. At this
point it appears the heaviest rain tonight will be over northern
Washoe County into northeast California, spreading to around the
I-80/ US-50 corridor by Saturday morning. Under these bands a half
inch or more rainfall is likely, on top of what has already fallen
over the past 2 days.

Snow levels will be on the rise through much of the Sierra due to
warmer air wrapping around the northern side of the low. Expect
snow levels around 8500-9500 feet Saturday, with only the highest
passes potentially affected. With the higher snow levels, it`s
also likely the rain will help to melt the snowpack, only adding
to the runoff. At this point, will refrain from issuing a flash
flood watch due to less thunderstorm coverage anticipated
Saturday and more steady rainfall. Best chances for localized
flooding will be along small creeks and streams in addition to
burn scars.

The area of low pressure causing this long period of wet weather
will slowly shift eastward Sunday into Monday. Expect decreasing
storm coverage Sunday, with dry conditions by Monday and a slow
warming trend. -Dawn

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

No significant change to the long term forecast.

A ridge of high pressure will slowly build over the Sierra and
western Nevada for the middle to latter portion of next week. The
00Z/12Z GFS and the EC and their ensembles are in good agreement on
the general pattern. The 06Z GFS is an outlier for Thursday night
and Friday with digging a stronger upper low farther west into the
northern Rockies and eastern Great Basin. It is typical for the
06Z/18Z GFS to veer away from the 00Z/12Z runs at longer ranges and
will discard it for now given consistency in other runs.

As far as highlights next week, we currently expect temperatures to
slowly warm to around 10 degrees above average for late next week.
Showers were left in place for Thursday and Friday in Mono and
extreme western Mineral County with well above average temperatures
and relatively light winds aloft allowing for some more summer-like
cumulus bubbling. Snyder

&&

.AVIATION...

Showers and thunderstorms have developed over central Nevada and
are currently working their way west in the upper level flow
around the low pressure trough over California. A few of the
storms could last longer than the more typical pulse (short-
lived) storms and produce GS and gusty winds to 30-40 kts. MVFR
CIGS in SHRA with IFR VIS again in +SHRA/TSRAGS. While all
terminals should see at least a couple showers during the day, the
chance of a heavier shower/storm will be about 30% for each
individual terminal. These worst case conditions would last for
about an hour.

Expect the showers and storms to weaken after 7-9PM/02Z-04Z tonight.
However, models indicate a broad swath of rain with possible
embedded thunderstorms developing late tonight and persisting into
Saturday morning. Simulations disagree with where it will form, with
some placing it mainly north of a KTRK-Gerlach line while others put
it between the highway 50 and I-80 corridors. We are currently
leaning towards the farther south solution as it has been
consistently shown for many days and lift looks best there. The band
will bring widespread MVFR CIGS/IFR VIS and terrain obscuration...
with freezing levels generally 9000-10000 ft msl. Snyder

HYDROLOGY...

Additional widespread moderate to heavy rain tonight into
Saturday will fall on already moist soil and likely causes more
snow to melt in the mid/high elevation snowpack as snow levels
rise above 9000 feet in the northern Sierra and above 8500 feet in
Mono County. Small streams around the Tahoe Basin...across
northeast California...along the eastern flanks of the Carson
Range and south into Mono County could overflow their banks
Saturday afternoon and evening causing minor flooding. Poor
drainage areas and areas of steep terrain in recent burn scars
could also experience flooding by Saturday afternoon due to
moderate to heavy rain. No main stem river flooding is expected at
this time...but area rivers will start running quite high by late
Saturday.

As of now we will not issue a Flash Flood Watch as a widespread
thunderstorm event is not anticipated and rainfall rates will be
more steady. For now be aware that minor flooding is possible for
Saturday. Anyone camping or hiking near small streams...or driving
near or otherwise making use of areas that are prone to flooding
due to poor drainage or steep terrain should be alert to the
possibility of flooding for Saturday. 20/Dawn

&&

.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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