Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 192110
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
210 PM PDT Fri Apr 19 2019

.SYNOPSIS...

An area of low pressure will bring cooler conditions this weekend
with a chance for showers and even a few thunderstorms. Best
chances for rain will be Saturday. Drier and warmer conditions are
expected for early next week. The warmer temperatures will lead to
increases in cold and swift water in area rivers and streams.

&&

.SHORT TERM...

Changes to the forecast:

*Added a slight chance for thunder over Mono, Mineral, and
 Churchill Counties this afternoon.

*Progression of trough through our area this weekend has
 sped up slightly.

*Increased ridge winds Sunday night into Monday and Monday
 night into Tuesday.

Today:

Temperatures are expected to climb well above normal late this
afternoon as an upper ridge begins to move eastward out of the
Great Basin. A quick-moving shortwave trough will move through south-
central California and into western Nevada this evening, which will
provide weak synoptic lift and cooling aloft. This lift, combined with
ample daytime heating/deep mixing, and some degree of moisture could
provide the ingredients for some high-based convection south of
US Highway 50 this afternoon, mainly for areas of Mono, Mineral,
and Churchill Counties. Added slight chance for thunder over these
areas due to this chance for thunderstorms.

A Zephyr wind will likely develop this afternoon bringing breezy
westerly winds (up to 25 mph) along the US Highway 395 corridor
spreading eastward into eastern Washoe and Storey Counties.

Saturday:

A deep upper-level trough will approach our area from the northwest
Saturday. The cold front associated with this weather system will
push through northeastern California and far northwest Nevada
early during the day. Areas of eastern Modoc and western Lassen
counties could see wetting rains in excess of 0.25-0.30" Saturday
morning through evening.

Rainfall over much of western Nevada will be spottier throughout the
day Saturday. Modest diurnal heating (surface temperatures in the 70s)
and height falls aloft will allow for the development of isolated-
scattered showers and thunderstorms over the Basin and Range country
during the afternoon hours Saturday. Some of the stronger cells
will be capable of producing brief heavy rainfall and small hail.
Behind the cold front, a breezy westerly wind will push through
the Sierra and western Nevada, which could lead to choppy lake
conditions, especially on Tahoe and Pyramid. Turbulence will also
be possible with this cold frontal passage. Winds could gust as
high 30-35 mph, with ridges gusting 50+ mph.

Sunday:

Lingering showers will be possible during the early morning hours
Sunday, especially over the Basin and Range country and Mono
County. Temperatures will likely stay in the low 60s in western Nevada
valleys and low-to-mid 50s in Sierra valleys. Cool and breezy northerly
winds will persist through the day. With a modest easterly gradient
set up aloft, Sierra ridges will remain breezy overnight into Monday.

Monday:

High pressure will begin to build into the region through the week
leading to warmer temperatures and dry conditions. Temperatures will
climb back into the lower 70s Monday for the lower valleys and 60s
for Sierra valleys. Winds will remain light out of the east during
the day Monday. -Johnston


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

The primary changes in the extended this cycle were made to the
Thursday/Friday time frame and mainly involved increasing areal
coverage of showers and thunderstorms each day.

The extended period opens with a flat ridge over the region. That
should allow high temperatures to climb into the upper 70s to lower
80s in the lower valleys and the 60s in the Sierra valleys.
Continued mild overnight lows in the higher elevations along with
the warmer daytime highs should drive increasing snow melt next
week.

The warming low level temperatures are also likely to lead to some
weak convection by late Wednesday along the eastern Sierra and in
far northeast California. We do not expect much coverage or much in
the way of precipitation as moisture is somewhat limited.

By late Thursday into Friday the ridge axis begins to further break
down and slide east. The GFS is a little faster with this scenario
than the ECMWF and also a bit more aggressive with precipitation
chances. Earlier simulations from the operational GFS were leaning
more toward a deeper trough that moved slower...but now the GFS has
trended toward the ECMWF and the GEFS ensembles in maintaining a
less amplified trough through Friday that is a bit more transient in
nature. Still...increased instability does support a slight increase
in convective coverage both days. The rather transitory nature of
the trough should limit its precipitation potential and and limited
upper level forcing should limit convective potential to no more
than garden variety thunderstorms and showers.

&&

.AVIATION...

Convection should develop later this afternoon and evening in areas
from Bridgeport to Mammoth Lakes and then to the northeast through
Mineral and Lyon counties. We should also see some showers and
possibly a few storms north of Susanville by this evening. This is
all ahead of an approaching upper level wave and surface trough.

To go along with the potential for convective turbulence later today
and this evening...surface winds and winds aloft will increase and
begin to develop mechanical turbulence along and downstream of the
mountain ridges.

Better convective coverage...and a better chance of thunderstorms...
is expected Saturday as an upper low drops into the region. This
will bring lower ceilings and visibilities along with some mountain
obscurations where showers are the heaviest. Turbulence is expected
from the thunderstorms and even heavier showers.

Showers linger into Sunday morning east of Highway 95. Later in the
day there should be some clearing. Gusty east winds are likely over
the ridges both Sunday night and Monday night. Ridging develops
again by Tuesday with better flying weather...but we could go
through a round of thunderstorms again later 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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