Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 202148

Area Forecast Discussion
National Weather Service Reno NV
148 PM PST Mon Nov 20 2017


A weak disturbance will bring light rain to portions of northeast
California and northern Nevada through tonight, then drier
conditions will prevail through midweek with temperatures well
above average into next weekend. Light rain may return later in
the week, mainly over northeast California and far western Nevada.
A colder storm system is possible by early next week.



Areas of light rain will continue mainly over the Tahoe basin and
northeast CA, with a few sprinkles possibly spreading into
western NV through this evening. The weak disturbance producing
this rain will exit to the east later this evening, bringing an
end to this precip. Rainfall rates have been light, generally
0.05"/hour or less, with the final push of moisture bringing
additional rainfall generally 0.10" or less, except local amounts
up to 0.25" possible near the crest west of Tahoe and into
western Lassen/central Plumas counties. Snow levels will remain
very high, above 10,000 feet as warmer air mass expands over the
region. Locally breezy conditions over far northeast CA/northwest
NV will wind down this evening with generally light winds over
lower elevations, but Sierra ridge winds will remain gusty as 700
mb flow of 25-30 kt continues.

For Tuesday-Wednesday, ridge will build over the southwest US with
axis over central-eastern NV and moderate southwest flow over the
Sierra leading to continued gusty ridge winds. This will push the
moisture feed farther north and bring drier conditions to the
region, except possibly some very light rain thru Tuesday night
near the Oregon border. Cloud cover will remain extensive through
Tuesday, (although higher cloud bases are expected compared to
today), then retreat a bit farther north on Wednesday. This will
lead to a gradual warming trend with highs in the 60s for most
lower elevations Tuesday, with some valleys possibly reaching 70
degrees by Wednesday.

On Thanksgiving Day, a weak disturbance is projected to ride over
the top of the ridge, accompanied by a narrow band of Pacific
moisture. Similar to today`s light rain event, the forcing will be
limited so rainfall amounts again will be light, with best rain
chances north of I-80. The expanded cloud cover and the flatter
ridge will lead to a bit of cooling compared to Wednesday for
areas north of US-50, but highs will remain about 10-15 degrees
above average. MJD

.LONG TERM...Friday through Monday...

There were only a few minor adjustments made to the existing
forecast primarily concerning the potential system early next week.

The upper ridge is projected to retreat Friday through the holiday
weekend allowing for zonal flow aloft. A weak jet feature is
expected to continue to arc over the northern periphery of the
ridge, funneling moisture into the Cascades and the extreme northern
Sierra while providing sufficient forcing for light precipitation.
As a result, periods of weakly forced precipitation will occur
mainly north of Interstate 80 in central Plumas and Lassen county.
With snow levels above 9000 ft, precipitation will be in the form of
rain with low accumulation rates.

Models favor a more dynamic, colder system to move into the region
as early as Monday. The largest change was to increase precipitation
chances in the Sierra and increase ridge winds. The extent of
precipitation chances was also expanded through Mono County since
models show more of a frontal push through the region. Snow levels
will drop, but current estimations only show a dip to around 6500
feet since the parent low is projected to lift into the Canadian
Rockies. So far, indications are pointing to low-end to moderate
storm if cold air phases with moisture for the Sierra. Still, this
system may have impacts for higher Sierra passes and bears watching
for post-holiday travel. As of now, Friday through Sunday will be
decent travel days, with Monday and Tuesday showing the potential
to have slick conditions in the higher Sierra. Boyd



Areas of -RA will bring MVFR cigs/vsby at times to KTRK/KTVL with
mountain obscurations extending into western NV until precip
diminishes after 04Z this evening. If a steady period of light
rain occurs early this evening around the Tahoe basin, areas of
fog with IFR/LIFR conditions could form by late evening and
continue overnight even with only partial clearing of the cloud
deck. Otherwise, VFR conditions will prevail through much of the
upcoming week.

Mountain wave turbulence will continue thru midweek as southwest
flow over the Sierra produces ridge gusts up to 50 kt at times.
Lighter winds are expected for lower elevations but the speed
difference from the ridges down to the valleys is likely to be
gradual enough to minimize the threat for LLWS. MJD


.REV Watches/Warnings/Advisories...


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