Reno Area Technical Forecast Discussion

Technical Forecast Discussion

000
FXUS65 KREV 242315
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
315 PM PST Fri Nov 24 2017

.SYNOPSIS...

After one more warm day Saturday, a storm system will bring
strong winds Sunday, then rain and snow later Sunday through
Monday morning. Expect travel delays across the Sierra Sunday
night and early Monday due to slick driving conditions and higher
traffic volume. Cool temperatures more typical for late November
will continue through the upcoming week.

&&

.SHORT TERM...

The approaching storm is showing more of a split flow pattern,
leading to a further delay in onset of precipitation and arrival
of the cold front. Less cooling (but a better potential for
spillover precip) is anticipated behind the front for late Sunday
night/early Monday in lower elevations, with snow levels unlikely
to fall all the way to the lower valleys.

No major changes were made to the early part of the forecast as
Saturday will be quite warm with some record highs possible. Areas
south of US-50 are most likely to surpass 70 degrees but some
locations northward to I-80 where cloud cover is less widespread
could also touch 70 degrees. Saturday night is now expected to be
dry and mild as winds increase ahead of the approaching storm.
More details follow on the elements of the Sunday-Monday storm:

Precipitation/Snow Levels:

The onset of the initial rain band is targeted for northeast CA
by late Sunday morning, then edging to the Sierra during the
afternoon with snow levels still likely to remain quite high
(near or above 8000 feet). Latest guidance simulations are also
slower in bringing down snow levels during the evening, although
some snow could mix in at pass level during periods of heavier
precipitation.

The main period of cooling should reach northeast CA Sunday
evening, then push south across the Sierra and western NV
overnight. Snow levels are likely to bottom out around 5000-5500
feet for western NV, with mainly rain for the urban valley areas.
The Monday morning commute is likely to be impacted with steady
snow for the Sierra including the Tahoe basin, Mono County and
also around Virginia City. Plan on a much longer commute time
Monday morning, even in areas where the roads will be wet.

Storm total precipitation of 0.50 to 1 inch is possible across
northeast CA southward across Tahoe, Alpine and Mono counties,
with locally up to 1.5 inch near the Sierra crest. A deformation
zone could set up over western NV on Monday, leading to a more
widespread area of 0.10 to 0.25 inch of rainfall, with up to 0.50
inch for parts of west central NV.

Snow amounts Sunday night-Monday are projected to range from 6-12
inches above 7000 feet in the Sierra, but with the delay in
arrival of colder air, amounts down to lake level around Tahoe
look reduced, with up to a few inches of snowfall possible.
Higher foothills in far western NV and northeast CA (5500+ feet)
could also receive an inch or two of snow.

The precipitation is expected to end Monday morning north of US-50
and west of US-95, and taper off south and east of these highways
during Monday afternoon, with dry and chilly conditions for
Monday night. MJD

Winds:

Although Sunday will be the peak wind day, breezy winds are still
expected on Saturday, especially for the ridges. Model soundings are
indicating southerly surface winds with very strong southwest winds
aloft which will promote stronger gusts, low level wind shear for
the Reno Airport, and possible damage to outdoor decor, fences, and
trees. Some power outages will also be possible when these strong
winds materialize.

Ridge winds from Saturday through early Monday will be strong with
the upper level jet across the Sierra. Although valley winds will
taper off Saturday evening, the ridge winds will still increase
gradually from Saturday through Sunday. Wind prone locations along
the foothills and especially Washoe Valley may see those strong
winds gusts Saturday overnight into Sunday. Downsloping signatures
have been consistently present for Sunday with impressive 75 kt
700mb wind speeds.

Wind gust estimates remain around 60 mph along the Sierra Front and
Highway 395 corridor. Wind prone locations could easily gust to 70
mph. Ridge wind gusts will likely exceed 100 mph at times on Sunday.
Expect travel disruptions for aviation and for high profile
vehicles. Additionally, conditions on Lake Tahoe and Pyramid Lake
will be hazardous with waves exceeding 3 to 4 feet this weekend.
-Edan

.LONG TERM...Tuesday through Friday...
Long term models are a bit all over the place by the beginning of
next week. The timing of Monday`s trough exit looking at the GFS and
ECMWF is quite different, which leads to differences with subsequent
weather.

Generally, temperatures will be colder by next week but whether or
not we will get another round of precipitation is questionable. The
GFS shows an inside slider-like system sweeping through sometime on
Wednesday, while the ECMWF keeps that trough much farther north and
east of Nevada. Regardless of the chances for precipitation, colder
air is expected to filter into the region by midweek which will
likely result in easterly ridge winds. -Edan

&&

.AVIATION...

VFR with generally light winds are expected through tonight, then
winds begin to increase on Saturday, starting in higher elevations
in the morning then spreading to lower elevations during the
afternoon. Ridge wind gusts increase to 50-60 kt with 25-35 kt in
the valleys by Saturday afternoon and evening, producing areas of
turbulence over and downwind of the ridges.

For Saturday night into Sunday, more significant aviation-related
impacts are expected including more widespread turbulence, possible
LLWS and enhanced downslope gusts. Winds in the lower levels will
increase Sunday into Sunday night with gusts near the terminals
surpassing 40 kt at times. Rain and high elevation snow will develop
through the day from northeast California into the northern Sierra.
This will lead to lower cigs/vsbys Sunday afternoon into Sunday
evening. MVFR/IFR conditions become more widespread Sunday night
and extend into western Nevada Monday morning along a cold front
that moves through the region. MJD

&&

.REV Watches/Warnings/Advisories...
NV...High Wind Watch from Saturday evening through late Sunday night
     NVZ003-005.

     High Wind Watch from Saturday evening through Sunday morning
     NVZ002.

CA...High Wind Watch from Saturday evening through late Sunday night
     CAZ070-071-073.

     High Wind Watch from Saturday evening through Sunday morning
     CAZ072.

&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno

NWS REV Office Area Forecast Discussion