828
FXUS65 KREV 221801 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
1001 AM PST Fri Nov 22 2024

.UPDATE...Fire Weather

Very strong winds were ongoing with gusts 40-50+ mph observed
along the Highway 395/I-580 corridor through the Eastern Sierra
of Mono County with gusts to 30+ mph farther east into the Basin
and Range south of Hwy 50 and along Hwy 95. Poor overnight
recoveries in the 25-35% range got things off to a very dry start
and current RH levels were already at critical levels. Given the
magnitude of the winds and the very dry conditions, a Red Flag
Warning was hoisted for Mono-Mineral-Churchill and S Lyon Counties
through early this evening. Wind driven fires will be the main
concern.

Winds will likely persist into Saturday afternoon sufficient to
keep lakes rough and hazardous. So we have also added Lake Wind
Advisories for Tahoe/Pyramid lakes.

Hohmann

&&

.PREVIOUS DISCUSSION... /issued 228 AM PST Fri Nov 22 2024/

.SYNOPSIS...

* Strong, potentially damaging winds expected today across the
  Sierra Front, impacting recreation and aviation travel.

* Periods of rain and heavy mountain snow will result in travel
  impacts in the Sierra this morning into Saturday.

* There will be a reprieve unsettled weather late Saturday into
  Sunday before more gusty winds, rain and snow showers arrive late
  Sunday night into Monday morning.

.DISCUSSION...

Changes:

* The wind forecast has trended up this morning with increasing
  confidence for strong wind along the Sierra Front, particularly
  the Highway 395/Interstate 580 corridor. While it will be windy
  most of the day, the peak winds (nearing 60-70 mph for wind
  prone locations) will develop between 5pm-11pm. See the latest
  High Wind Warnings, Wind Advisories, and Lake Wind products for
  details.

* As of 130AM...Sierra ridge wind gusts currently 100-115 mph with
  widespread wind gusts in the Tahoe Basin and wind prone areas of
  40-50 mph so far. Wind advisories and wind warnings start time.

* Winter storm watch for the Sunday night - Tuesday snow impacts
  where there is a 60-80% chance of an additional 2 feet of snow
  possible for the Sierra crest.

This next wave of the storm is well under way with precipitation
spreading across northeastern California and slowly working its way
southward into the Tahoe Basin. Before the rain/snow returns, we
have to contend with the strong winds first. Strong wind potential
is looking more likely as HREF simulations show a burst of winds for
Friday evening. Plan on widespread wind impacts across the region
with bumpy flight conditions, difficult or restricted travel for
high-profile vehicles, and choppy lake waters much of today. The
gusty winds will continue through Saturday as well with not much of
a taper in the conditions until Saturday night.

Back to the precipitation...Showers return to the Tahoe Basin
between 8-10a with snow above 7000-7500` and mostly rain at lake
level today. Precipitation will migrate southward through the day
into Alpine (1-3p) and Mono (2-6p) counties and snow levels still
right around 7500` with snow for Sonora and Tioga passes. The snow
levels gradually fall to 5500-6000` for the Tahoe Basin Saturday
morning with snow impacting the Sierra passes and communities near
lake level. Above 7000` snowfall totals will be between 1-2 feet
with the highest peaks nearing 3 feet. Lower elevation Sierra
locales such as Truckee, South Lake Tahoe, and Mammoth Lakes will
most likely see 1-4" with a 10-30% chance of 6+" through Saturday.

Spillover into the Greater Reno-Carson City-Minden areas isn`t
looking as great, which matches up with the wind signals being
stronger for today. Best potential for spillover into far western
Nevada will be Friday night after 9p. Probabilities for 0.5" of
rain will be limited to areas along and west of Highway 395 where
Reno-Carson have a 30% chance. Areas east of Highway 395 will see
a steep drop off in precipitation potential with only a 10%
chance of a wetting rain (0.1") for Lovelock and Fernley areas.

After the main precipitation push today into Saturday, there is a
decent break in the rain/snow from late Saturday through Sunday
afternoon. The last round of showers arrives late Sunday night and
will linger about through Tuesday. This storm will be colder which
will increase the chances for some more significant Sierra snowfall.
The Sierra crest has a 50-70% chance of another foot or two feet (20-
40% chance) of snowfall through Tuesday. There`s a 40% chance for 4"
of snow or more down to lake level as well. Snow potential for `down
here` in the lower valley areas is quite a bit lower, but not zero!
Snow levels plummet to valley floors late Tuesday allowing for a
brief 10-15% for a light bit of snow for Wednesday AM.

Ensembles favor dry conditions for Thanksgiving Day with chilly
temperatures sticking around. Bundle up, put on your stretchy pants,
and get ready for some warm tasty food!

-Edan

.AVIATION...

Precipitation: Precipitation will begin around 18z for KTRK/KTVL.
Snow levels will be around 7000-7500` through Sat 0z with rain
expected. Lower snow levels after 0z Sat will allow for accumulating
snow at Sierra terminals. KTRK/KTVL/KMMH will most likely see 1-4"
with a 10-30% chance of 6+" through Saturday. KRNO/KCXP/KMEV will
remain shadowed by the mountains and not receive any rain through
22z today. Between 0-3z Saturday some rain may finally make it over
the mountains and into the vicinity of KRNO/KCXP/KMEV. Showers will
taper off in all areas by 21z Saturday with a brief break through
Sunday evening.

Winds: FL100 winds around 45-55 kt through Saturday morning. Expect
mountain wave turbulence and 40-55kt LLWS along the Sierra and
eastern Sierra through Saturday. Sfc winds for Sierra terminals will
hover around 30-45kt through Saturday. Western NV terminals will see
stronger winds today with gusts of 30-45kt out of the south through
Saturday. Expect to see Sierra ridgetop gusts near 75-90kt through
at least Friday.

-Edan

.AVALANCHE...

Periods of gusty winds, rain, and mountain snow will impact the
Sierra through early next week. The main weather highlights through
Tuesday are:

* Snow levels will hover around 7000-7500` through today before
  falling to near 5500-6000` on Saturday morning.

* Upcoming round of snow totals (Friday-Saturday): 18-24" along the
  Sierra crest. For Mono County, there is a 15-30% chance of the
  highest peaks reaching 3 feet of snow. There`s a greater than 60%
  chance of 1" of SWE over a 24 hour period for elevations above
  7000`.

* Final round of snow totals (Sunday through Tuesday): Colder storm
  with a 30-40% chance of 4+" of snow at lake level, 50-70% chance
  of an additional foot or more along the Sierra crest.

* Strong ridgetop gusts of 60-90 mph, sometimes in excess of 100
  mph, will continue into the weekend before subsiding late
  Tuesday into Wednesday.

-Salas/Edan

.FIRE WEATHER...

Winds have trended upwards in latest guidance across the Sierra
Front into Mono County, Mineral County, and portions of Churchill
County Friday afternoon and evening. Southwest winds of 15-20 mph
with gusts of 30-35 mph will prevail during the afternoon,
increasing to 20-25 mph with gusts of 45-55 mph after 7 PM PST.
These winds continue through midnight before subsiding early
Saturday.

The extent of Friday`s fire threat is uncertain given: 1) the timing
of strongest winds (late in the evening) are temporally offset from
the period of lowest humidity (mid-afternoon) and 2) minimum RH will
only fall to 15-20% Friday afternoon. However, there may be a 1 to 3-
hour period of critical conditions in the late afternoon across the
portions of the Sierra Front and western Nevada Basin and Range
before humidity rises and light rain showers arrive in the
evening/overnight. Overnight humidity will be good (widespread RH >
50%) Friday night into Saturday AM, but the main concern will be
strong SW winds in the evening into Saturday AM that may compensate
for the rising humidity, especially if there are any ignitions in
this area before Friday evening.

Otherwise, periods of rain and heavy mountain snow are expected
through early next week, which will limit fire concerns through
the middle of next week

-Salas (11/21 230PM)

.HYDROLOGY...

An atmospheric river is bringing heavy rainfall across northern CA.
This will result in water ponding in poor drainage areas and rapidly
increasing flows along rivers and streams throughout the area today
through late Friday or early Saturday.

Flooding is of the greatest concern in areas of Lassen and Plumas
counties, where the combination of longer duration rainfall and
lower elevation watersheds may lead to minor flooding of the Susan
River as well as small creeks and streams in the area. Stream
response on the Susan River has been slow so far, but may still
respond quickly to additional rainfall Friday and Saturday morning.

Flooding concerns diminish somewhat to the south, and no other
mainstem rivers are forecast to approach flood levels, but minor
flooding of small creeks and streams can`t be ruled out from Lake
Tahoe north.

Recent burn areas, especially north of Lake Tahoe, are 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 to
(1) range in the precipitation forecast and (2) snow levels with
varying precipitation type and transitions from snow to rain and
back to snow again from today 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. These forecasts will be updated by 9pm
Thursday evening and again by 3am and 9am Friday.

-Bardsley (11/21 230PM)

&&

.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning until 10 PM PST Saturday NVZ002.

     Winter Storm Watch from late Sunday night through Tuesday
     afternoon NVZ002.

     Red Flag Warning until 7 PM PST this evening NVZ421-429.

     High Wind Warning until 1 AM PST Saturday NVZ001-003.

     Lake Wind Advisory until 4 PM PST Saturday NVZ002-004.

CA...Winter Storm Warning until 10 PM PST Saturday CAZ071-072.

     Winter Storm Watch from late Sunday night through Tuesday
     afternoon CAZ071>073.

     Red Flag Warning until 7 PM PST this evening CAZ274.

     Lake Wind Advisory until 4 PM PST Saturday CAZ072.

     High Wind Warning until 4 PM PST this afternoon CAZ073.

     Winter Storm Warning from 4 PM this afternoon to 10 PM PST
     Saturday CAZ073.

     Flood Advisory until 12 PM PST Saturday CAZ071.

&&

$$