Area Forecast Discussion
Issued by NWS Reno, NV

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
FXUS65 KREV 182223

Area Forecast Discussion
National Weather Service Reno NV
323 PM PDT Sun Mar 18 2018


Dry weather is expected through early Tuesday with light valley
rain and higher elevation snow Tuesday afternoon and evening. A
much stronger system for Wednesday night through Thursday night
will bring periods of valley rain and heavy Sierra snow along with
gusty winds. Conditions will turn colder late week for northeast
California and western Nevada, with lower valley snow possible.



Through Monday night, precipitation-free conditions are expected
as a ridge of high pressure moves over northeast California and
western Nevada. Lower valley areas that saw fog and low clouds/stratus
this morning (including Reno-Sparks) are most likely off the hook
for Monday morning as a thick high cloud deck is expected to hold
off radiational cooling sufficiently to preclude fog formation.
Patchy fog is still possible between 5-9 AM in the Martis Valley
near Truckee as simulations begin to move the cloud decks out
Monday morning.

Tuesday afternoon and evening, simulations continue to show a
period of warm air advection (WAA) focused over northeast
California and western Nevada, roughly north of Highway 50. The
Sierra will also have some orographic enhancement which may allow
light precipitation amounts to spread down the Sierra to Mono
County, generally along/west of Highway 395, despite less WAA
there. Impact-wise, a relatively light snowfall is expected for
Sierra and northeast California passes, with the Tahoe Basin
likely to see a mix or changeover to rain Tuesday night as the WAA
ends and mixing down of warmer air aloft ensues.

For the lower elevations of northeast California and far northwest
Nevada, some simulations show a heavier band of precipitation
(perhaps up to 0.20" - 0.35" of liquid) developing there with the
best WAA Tuesday night. This shouldn`t be an issue on valley
floors; however, some models hint at an isothermal layer (common
with warm air advection) which could keep snow levels depressed to
as low as 5000 feet...and bring the potential for a few inches of
slushy accumulations above the valley floors. Motorists traveling
in northeast California and far northwest Nevada Tuesday night
should be prepared for slick road conditions above 5000 feet. Late
Tuesday night, the WAA will break for an end to most showers in
the lower valleys of northeast CA and western NV, and Mono County
east of Highway 395. -Snyder

.LONG TERM...Wednesday through Friday...

Welp, here we go again. Looks like winter is going to stick around
for another week. Another moderate to potentially strong (depending
on your definition) storm is forecast to impact the region during
the second half of the week. Confidence continues to increase that
we will add another significant amount of snow to the Sierra
snowpack, at least at upper elevations, with the highest amounts in
Alpine and Mono Counties.

A moderate to strong atmospheric river (AR) is forecast to move into
southern California on Tuesday and persist through around Thursday.
This will provide a robust tap of subtropical moisture for the the
southern Sierra. Cold air is forecast to drop into the region from
the Gulf of Alaska, phasing in some fashion with the warm moist air
from the south. The HOW and WHEN of this phasing is where most of
the forecast uncertainty lies.

Recent model simulations continue to slow the onset of the arrival
of cold air and thus the biggest change today was to continue to
slow the drop in snow levels on Thursday and raise snow levels
during the onset of the storm. Current forecast is for snow levels
to hover in the 7000-8000 foot range Wednesday into Thursday morning
in the central Sierra (~500 feet lower in NE California, ~500 feet
higher in Mono County). Snow levels are expected to come crashing
down at some point on Thursday, but this is where small differences
in model simulations make huge differences on the ground. The
biggest boom/bust potential is for snow in the mid elevations (6000-
7000 feet in the central Sierra). This makes forecasts for areas
like the Tahoe Basin and Mammoth Lakes very uncertain for snow

Total QPF amounts Wednesday through Thursday along the Sierra crest
look to be in the 2-3" range with the highest confidence and biggest
upward potential in Mono County.

In the lee of the Sierra the biggest impacts will likely be from
wind and rain showers Wednesday into Thursday. But as of now there
aren`t indications of strong damaging winds. By Friday it looks cold
enough that snow levels would be down to all valley floors, but how
much precipitation is left by then remains uncertain.

For the weekend, models are coming into a little better agreement
that we could see a second and maybe third wave of snow as a
disturbances drops into the back side of the trough Friday into the
weekend. Any precipitation we do receive after Friday would likely
be snow at all elevations with the best chance to see snow `down
here` in western Nevada. -Zach



Light winds with VFR conditions (mainly high clouds) are expected
through Monday night under a "dirty" ridge of high pressure. Fog
and stratus are not expected tonight for the KRNO/KRTS area with
copious high clouds expected to mitigate fog formation.

A minor system may bring terrain obscuration with light rain and
above-lower valley light snow Tuesday afternoon and evening. A
stronger system is expected to bring widespread turbulence,
mountain snows, valley rain, and breezy surface conditions
Wednesday and Thursday. -Snyder


.REV Watches/Warnings/Advisories...


For more information from the National Weather Service visit... is the U.S. government's official web portal to all federal, state and local government web resources and services.