Area Forecast Discussion
Issued by NWS Reno, NV

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738
FXUS65 KREV 192245
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
245 PM PST Fri Jan 19 2018

.SYNOPSIS...

Bands of snow showers will develop through this evening producing
patchy slick road conditions mainly from Plumas County through
northern Mono County. Light accumulations will be possible up to 2
inches for localized areas west of Highway 395. After a dry and
cool Saturday, weak low pressure will bring light snow late Sunday
into Monday, with a stronger cold storm possible by midweek.

&&

.SHORT TERM...

The surface cold front has swept through the region ending
widespread chances of snow. Meanwhile, the upper trough is current
swinging through northern California and will be the focal point
for shower development from Lassen County through Mono County this
evening.

The main change for the forecast was to expand coverage of snow
and snow showers as the upper trough moves through the region.
Short range models are beginning to feature a weak deformation
area, and potential lake enhancement, as the upper low dips
southeast. This upward lift coupled with upslope flow will promote
chances of snow from the Tahoe Basin through at least northern
Mono County this evening. Accumulations will generally be light
this evening and overnight, up to 2 inches, but could be higher if
persistent bands develop. The flow pattern supports these chances
into the overnight hours before the upper low ejects into
southern Nevada.

Saturday and most of Sunday will be rather quiet with transient
high pressure over the region. Then, a weak low pressure system
will move through the Pacific Northwest trailing a boundary into
the northern and central Sierra. The primary mechanism for
precipitation east of the Sierra crest will be weakly forced
boundary dynamics and some limited warm air advection. As such,
totals expected with this system will be generally light, but
could be a nuisance for trans-Sierra travel. Current estimates
are: Up to 4 inches below 7000 feet and 4 to 8 above 7000 feet.
There could be some very light accumulation for western Nevada,
but signals are not very promising at this time. Showers will
linger through the day on Monday. Boyd

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

Some simulations still show a period of light warm air advection
precipitation (mainly snow) across northeast California and
northwest Nevada on Tuesday. By Wednesday and Wednesday night, there
is medium-high confidence for a significant system to round the base
of a large-scale northeast Pacific trough and push a strong cold
front through the region. The system currently looks better
organized than the system that moved through today as next week`s
system is simulated to have the axis of the upper low more
coincident to the surface front. Also, the last couple runs of the
GFS and EC show a better moisture feed with increasing precipitation
amounts simulated. All this points to higher precipitation amounts
as compared to the current system, especially in the Sierra.

Right now, either solution would keep precipitation mainly in the
form of snow for the Sierra (a chance for a brief rain-snow mix at
Lake Tahoe level Wednesday). The system is progressive and this will
be a limiting factor for precipitation totals. Still, the Sierra
could see a moderate snowfall. For western Nevada valleys, it seems
likely that precipitation will start as rain before changing over to
snow behind the cold front later on Wednesday or Wednesday night.
Snowfall amounts for western Nevada are too uncertain to predict yet
as it will depend on if snow showers can be maintained for a time
post-frontal (as the cold front is expected to be quite progressive).

Temperature-wise, there is high confidence that colder air will
filter into northeast CA and western NV for Thursday and Friday with
temperatures below normal. Snyder

&&

.AVIATION...

As a trough axis moves over the area this evening, the airmass will
remain unstable for isolated-scattered snow showers. Simulations
continue to show snow showers developing this evening in the Sierra
and possibly out into far western Nevada; however, the potential for
more widespread and heavier snow showers has shifted to south of
Lake Tahoe (possible lake effect) and into Mono County in recent
high resolution model runs. Occasional terrain obscuration and IFR
conditions will be possible through evening in the northern Sierra.
Farther south into Alpine and Mono Counties, more widespread and
longer-lived terrain obscuration will be possible with snow showers.

Snowfall accumulations in the Sierra this evening look generally
less than 2 inches north of Highway 50, with locally higher amounts
for Mono County terminals possible (including KBAN/KO57/KMMH). There
is low confidence on where exactly the higher snowfall totals will
wind up in Mono County. For western Nevada, little or no
accumulation is expected for terminals.

High pressure builds overhead Saturday for VFR conditions with light
northerly flow. Snyder/Hohmann

&&

.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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