Red Flag Warning 18, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
158 AM PST Tue Nov 19 2024

.SYNOPSIS...

* The next storm arrives late tonight into Wednesday with
  increasing snow/rain chances across NE CA and widespread gusty
  winds.

* A potentially more significant storm arrives late Friday into
  Saturday bringing gusty strong winds, and chances for rain and
  snow.

* The wet and stormy conditions may continue as another round of
  wind and rain/snow chances arrives for Sunday into Monday.

&&

.DISCUSSION...

As we gear up for a fairly active, wet pattern kicking off
midweek, let's be sure to be prepared for the adverse weather
conditions. It will not only be fairly wet with the valley rain
and Sierra snow potential, but the winds will pick up again late
Tuesday into Wednesday. Plan on choppy lake conditions and
backcountry recreational impacts for much of the day Wednesday
with the strong wind's arrival. See details about flying
conditions in the aviation section. In preparation for the
potentially heavy rainfall en route, be sure to clear storm drains
and gutters to allow for efficient water runoff. Leaves, dirt, or
any other obstructions may result in ponding of water in
undesired areas.

An atmospheric river (AR) making landfall along the northern CA
coast will be the primary culprit in all of the weather impacts
popping up this week. The initial wave of moisture arrives
Wednesday into Thursday with enough to warrant a winter weather
advisory for portions of NE CA tonight into Wednesday. Then with the
next storm Friday into Saturday we see a jump in the projected
liquid storm totals with 2.5-3.0 inches for the Sierra crest,
0.75-1.00 inch for the foothills, and 0.10-0.75 from the Basin and
Range into far western Nevada. Forecaster confidence is medium to
high for the QPF totals across the region, with potential for
higher liquid totals in stronger shower activity considering the
CAPE/CAPE Shear signals present in the ECMWFI EFI.

The lower confidence factor in all of this is the snow levels. Of
course. With the initial wave pushing in on Wednesday, the snow
levels will start quite low (near 5000 feet), but then are
projected to rapidly climb (near 9000 feet) late Wednesday with
the arrival of the mild, subtropical moisture associated with the
AR. Following that initial rise in the snow levels, blended
guidance shows them holding rather steady around 7000-7500 feet
for much of the next wave from Friday-Sunday. Initial projections
show the potential for 1-2 feet of wet, heavy Sierra cement for
areas above 7000 feet this weekend with this storm.

-Edan

&&

.AVIATION...
Light and variable winds along with VFR conditions for all TAF
sites. KTRK is the only exception, where some FZFG may form
through 19/17Z. Stronger northwesterly FL100 winds may produce
bouts of turbulence along the Sierra through 19/05Z.

Two storms will impact the airspace this week with a storm on
Wednesday and another storm on Friday into the weekend. Plan on
low chances for a rain/snow mix Wednesday into Thursday as an
atmospheric river pushes into northern CA. Winds will be a larger
concern with W/SW surface winds 20-30 kts and FL100 winds
approaching 50-60 kts for KTRK, KTVL, KRNO, and KRTS.

The next storm wave for Friday into the weekend holds a higher
potential for wetting rains and high elevation snowfall. Liquid
water storm totals are nearing 1-2" for along the Sierra crest,
with a 50-60% chance of 2+ inches of snow for KTRK, KMMH, and
KTVL.

-Edan

&&

.HYDROLOGY...

Heavy rainfall due to an atmospheric river making landfall in
northern CA will likely cause ponding in poor drainage areas and
increasing flows along rivers and stream throughout the area late
Wednesday through Friday. If storm waves end up being on the
wetter and warmer side of the forecast, minor flooding will be
possible along small creeks and streams in northeastern
California and the Susan River. Recent burn areas will also be a
concern for minor flooding exacerbated by the transport of ash,
sediment, and debris that may obstruct drainage areas.

There is considerable uncertainty in the hydrologic response due,
not only to the range in the precipitation forecast, but also
uncertainty in the varying precipitation type with transitions
from snow to rain and back to snow again from Wednesday into the
weekend. Additional consideration should be given to the fact that
at storm onset soils will be dry with generally low streamflows,
which will delay and mute streamflow responses initially. Keep an
eye on river forecast updates at cnrfc.noaa.gov.

-Bardsley

&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory from 10 PM Tuesday to 7 PM PST Wednesday
     NVZ002.

CA...Winter Weather Advisory from 10 PM Tuesday to 10 PM PST
     Wednesday CAZ071.
     Lake Wind Advisory from 10 PM Tuesday to 7 PM PST Wednesday
     CAZ072.

&&