Area Forecast Discussion
Issued by NWS Reno, NV

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026
FXUS65 KREV 202052
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
152 PM PDT Sun May 20 2018

.DISCUSSION...

An active pattern with chances for showers and storms continues this
week as low pressure slowly moves across the region. Periods of
heavy rainfall and small hail are possible in these storms. Showers
and storms decrease in coverage Thursday and Friday before another
low pressure system approaches and provides additional chances for
storms by the weekend.

&&

.SHORT TERM...

Chances for showers and thunderstorms continue through the first
half of the week as a cutoff low develops and slowly meanders across
California and Nevada. Ample moisture and instability will be
present each day, but the limiting factor will be the presence of a
strong lifting mechanism to trigger widespread storms each day. This
will largely be governed by the position of the low each day which
is only moderate confidence due to the inherent uncertainties with
trajectories of closed lows detached from the mean flow.

For this afternoon, showers with a isolated storms will continue
mainly across northern Lassen, Washoe and Pershing counties before
diminishing this evening. A secondary pulse of showers and isolated
storms are expected across Mineral and Mono counties due deformation
developing as the trough elongates near the southern Sierra. Most
likely looking at band of light to moderate rainfall developing
across northern Mono into the Tahoe Basin after midnight.

The character of the storms looks pretty similar through mid-week
with the main threats being periods of heavy rainfall and small hail
each day. Wednesday could may see a more elevated chance of heavy
rainfall and isolated flash flooding impacts due to slow storm
motions (<10kts) and ample moisture (high PWATS & surface dewpoints
near 50F across much of western NV. Again the main limiting factor
is a strong forcing mechanism which should keep Wednesday from
seeing widespread flash flooding concerns but isolated areas are not
out of the question.

Overall, looking for showers and storms across the Sierra Monday
with most activity expected generally south of I-80 across western
Nevada. East steering flow and the backside of the low could confine
most activity to the Sierra and west slopes Tuesday while Wednesday
has the potential to become more widespread across the Sierra and
western Nevada. Fuentes


.LONG TERM...Thursday through next weekend...

The main changes to the extended forecast include a downward trend
for precip/thunder chances Thursday-Friday and removal of
showers during the overnight periods leading into next weekend.

From Thursday through Friday, an upper level ridge is projected to
build over the Great Basin with a steady warming trend (highs rising
into the lower-mid 80s for lower elevations/lower 70s near the
Sierra). Flow aloft becomes southeast to south with some residual
moisture in place, while daytime heating will provide some
instability for afternoon showers and isolated thunderstorms. This
shower potential appears more favorable near the Sierra and
northeast CA, with a few cells possibly spreading into far western
NV each evening. However, even this activity looks to be relatively
sparse due to limited forcing, while mid level warming under the
ridge appears more likely to cap convection away from the Sierra.

For the early part of the Memorial Day weekend, there is still some
disagreement among the medium range guidance with the track of
another upper low, but the overall pattern appears to favor one more
round of showers and thunderstorms Saturday. This low still could
kick inland across northern CA/NV, or remain off the west coast with
a negative tilt trough axis swinging through the region. In either
scenario there will be a potential for mainly afternoon-evening
showers and thunderstorms, with the best chances currently favoring
northeast CA and areas near the Sierra.

For the remainder of the Memorial Day weekend, we may finally see a
more definitive drying trend as a ridge axis develops east of the
region with southwest flow aloft over the Sierra. Daytime
temperatures will be dependent on the location and amplitude of the
ridge, with the most likely scenario bringing a brief cooling to near
average Sunday, followed by warmer conditions Monday. MJD

&&

.AVIATION...

For the main terminals, VFR conditions will prevail thru this
evening. A few showers may form around KMMH thru late afternoon,
otherwise precip is unlikely around the Tahoe basin and far western
NV. The most favorable locations for showers and a few thunderstorms
through this evening include northeast CA north of KSVE, and
from US-95 eastward in west central NV.

Starting later tonight and continuing through Monday, a developing
closed low will increase shower chances with a slight chance of
thunderstorms. More widespread rain bands with lowered cigs/vsbys
and mountain obscurations are most likely from I-80 southward during
the day Monday, then spreading northward Monday evening. Conditions
could become MVFR during periods of steadier rain, especially near
the Sierra. This low persists into Tuesday with continued chances
for showers and thunderstorms. MJD

&&


.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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