Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 192151

Area Forecast Discussion
National Weather Service Reno NV
151 PM PST Tue Feb 19 2019


Another cold low pressure system will bring more snow and snow
showers Wednesday morning through evening, producing possible
slick road conditions for both commutes, with lake effect snow
bands again possible late Wednesday night through Thursday. Cold
conditions will continue with another chance of snow showers for
the weekend.



Changes include a slightly faster onset and southward progression
of the snow for Wednesday, then ending a little sooner for areas
north of US-50 after 4 PM. Also, we increased the lake effect
snow off Pyramid/Walker for Thursday PM, but not as much off these
lakes for Wednesday night. Wind directions were also aligned more
closely with the orientation of the potential lake effect snow
bands as needed.

The next slider system is still on track to bring periods of snow
and snow showers for much of the region, with light snow
beginning near the Oregon border by late this evening, then
spreading into much of northeast CA-northwest NV overnight into
Wednesday morning. While snow amounts won`t be very large
(generally 2" or less, with locally up to 4"), the potential for
slick and hazardous conditions looks to primarily impact the
morning commute. Therefore for the Lassen/Surprise Valley/NW and
W-Central NV, we will issue the impact-based Winter Weather
Advisory for the morning time frame. While additional snow showers
are possible in these areas through Wednesday afternoon and early
evening, snow will have a more difficult time accumulating on
paved surfaces. The only possible exception may be across a small
part of northeast CA, generally from Portola and CA-70 southward,
where a heavier snow band could set up during the afternoon and
bring an hour or two of quickly accumulating snow. Little
additional snow is expected during the evening, but depending on
when the snow ends, patches of ice are possible on roads during
the evening.

For the Reno-Carson-Minden region southward across Mineral-
southern Lyon counties, the afternoon-evening commute is more
likely to be affected by the heavier snow band (again mostly 2" or
less with locally up to 4"), with a somewhat increased potential
for road surfaces becoming icy in the evening as temperatures drop
below freezing. Therefore for Reno-Sparks-Minden/Mineral-southern
Lyon, we will issue the impact-based Winter Weather Advisory for
the Wednesday afternoon-evening time frame.

In addition, we are expecting 2-6" for the Tahoe basin Wednesday
morning-evening, and 1-4" for Alpine-Mono counties Wednesday
afternoon-evening but this is below advisory criteria for these
areas. After the intense snowfall amounts these areas received so
far this month, it`s already common sense advice to drive slowly
and allow extra travel time if heading into the Sierra. All the
snow with this Wednesday system will be powdery with low moisture
content, generally 15-18:1 snow to liquid ratios.

Late Wednesday night into Thursday, the majority of the snow
showers will be finished, but conditions then become more
favorable for the formation of lake-effect snow bands. This
initially looks more likely for the southwest Tahoe shore, then by
Thursday afternoon and evening the lake-effect looks more likely
for areas south of Pyramid/Walker Lake, when model soundings show
better instability, more aligned low level winds and better
microphysics (upward motion in the -12 to -18 C temperature layer
for optimal snow growth). An additional 2-6" of snowfall could
fall in narrow bands downwind of these lakes, with potential for
over 6" in isolated locations. For far western NV, areas which
received lake-effect snow Sunday evening (including Spanish
Springs, Palomino Valley, Sun Valley, other North Valleys and
northern portions of Reno-Sparks) could see similar conditions
Thursday afternoon-evening. Snow forming off these lakes will be
quite lightweight with very low moisture content (at least 20:1
snow to liquid ratios), easy to move around with a broom or leaf
blower. Then for the remainder of Thursday night, the lake-effect
snow is expected to end with decreasing clouds and temperatures
plunging into the single digits and teens, with sub-zero lows for
colder Sierra valleys.

For Friday-Friday night, dry and cool conditions are expected with
highs only in the 30s. Lows will remain chilly, but not as
bitter cold as this morning due to expected areas of mid-high
level cloud cover. MJD

.LONG TERM...Saturday into next week...

An upper trough across the Pacific Northwest will favor a broad
northwest flow that has the potential of producing an inland slider
type system Saturday night into Sunday. Greater uncertainty arises
heading into next week as differences arise in resolving an
amplified ridge across the eastern Pacific.

This weekend`s slider system looks to dip across northern Nevada
Saturday evening into Sunday morning bringing chances for snowfall
across the Sierra and western Nevada valleys. The main question is
how far south the cold front and associated snowfall makes it
through western Nevada. The GFS is leaning towards a stalled front
roughly near Pyramid Lake while the EC has been changing towards a
wetter and more progressive cold front making it south of Highway 50
Sunday evening. Thus, will maintain the current chances for snowfall
as advertised but due to the nature of slider systems, timing will
become better focused over the next few days.

The forecast for early next week is hinging on the amount of
amplification of the upper ridge across the eastern Pacific. The more
amplification, the better chances of moisture undercutting the
ridging and making it through to the West Coast. Based on the latest
set of deterministic and ensemble runs, have leaned a bit more
towards this potential undercut scenario. While the moisture that
makes it through does not appear to be associated with a
significant subtropical moisture source, it could be enough to
introduce additional Sierra snowfall and travel impacts early next
week. Fuentes



VFR conditions all terminals through tonight with patchy shallow
FZFG possible around KTVL/KTRK although increased cirrus should
limit extent and duration.

Snow with the slider-type system Wednesday looks to begin around
KTVL-KTRK between 12-14Z, with highest probability for IFR
conditions and accumulations on runways from 20-02Z. For KRNO-
KCXP, snow looks to begin from 18-20Z, with highest probability
for IFR conditions and possible accumulation on runways from
21-01Z. For KMMH, snow looks to begin from 18-20Z, with highest
probability for IFR conditions and accumulation on runways from
03-07Z. MJD


.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 4 AM to 11 AM PST Wednesday

     Winter Weather Advisory from 1 PM to 10 PM PST Wednesday

CA...Winter Weather Advisory from 4 AM to 11 AM PST Wednesday



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