001
FXUS65 KREV 311032
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
232 AM PST Fri Jan 31 2025

.SYNOPSIS...

* An active storm pattern with deep atmospheric river moisture
  returns today through early next week, producing gusty to
  strong winds and abundant rainfall with higher elevation snow.

* Long periods of nearly continuous rainfall even into lower
  elevations will produce substantial rises on regional creeks
  and streams through this weekend.

* Dropping snow levels next week will lead to heavier snowfall
  potential and travel impacts in the Sierra.

&&

.DISCUSSION...

The quiet weather is over, time to gear up for a high impact and
prolonged storm event with deep atmospheric river moisture! During
the next several days it would be a good idea to minimize travel
especially over higher elevations, avoid outdoor activities and
have adequate supplies at home in case of power outages due to the
incoming heavy rain, wet mountain snow and periods of strong
winds.

* TODAY-TONIGHT:

Today`s initial wave of precip will start by early-mid morning
with relatively low snow levels near 4500-5000 feet for northeast
CA and around 5500 feet around the Tahoe basin due to wet bulb
effects in the pre-existing dry air mass. This could produce some
slick conditions over the Tahoe area and northeast CA passes this
morning, then as warmer air overtakes this antecedent air mass,
snow levels will push upward above 6000 feet for northeast CA and
above 7000 feet for Tahoe this afternoon-tonight. The intensity
of the precipitation will increase through tonight from Tahoe
northward to Lassen County, with lighter rain spilling into parts
of northwest/far western NV and southward to western Mono County,
where snow levels of 8000-8500 feet are expected. We`ll see an
increase in  winds mainly for the higher elevations and Tahoe
basin, start of a prolonged period of choppy to rough conditions
on Lake Tahoe from this afternoon onward.

* SATURDAY-SUNDAY NIGHT:

This weekend will be quite a washout for the eastern Sierra and
northeast CA, with the majority of the ensemble guidance bringing
peak liquid precip rates (up to 1"/6 hours) across the Tahoe
basin northward to central Plumas County Saturday morning-night.
Snow levels are looking to vary from 7500-8500 feet around Tahoe
and 5500-6500 feet for northeast CA with the greatest chances of
accumulating wet snow near and above these elevations, as noted in
our Winter Weather Advisory. The current forecast is projecting
liquid totals in the 1-3" range for most of northeast CA, with
2-4" for the Tahoe basin, and 5+" near the crest. This is in
addition to whatever falls on Friday (about 0.50-2.50"). While the
dry ground will initially be able to absorb the rain, runoff
concerns will increase as the weekend progresses with faster flows
and rises for the rivers and creeks.

Far western NV along the I-580/US-395 corridor can also expect
longer periods of steady rain, with projected totals through the
weekend around 1" for the main urban areas and up to 2" for
western foothills, but there are several more aggressive scenarios
which could double these precip totals. Ponding in urban and low
spots will become likely, while recent burn scars including the
Davis Fire area could be at higher risk for flooding and debris
flows.

Then on Sunday, the moisture feed appears to shift farther northward
into northeast CA mainly north of I-80. This will allow for winds
to become the prevailing impact for much of western NV southward
to Mono County, with potential for damaging gusts as indicated in
the High Wind Watch. Patchy blowing dust could also reduce
visibility downwind of the lake beds/sinks in west central NV.
Finally, a surge of warmer air will push into parts of western NV
especially for Churchill-Mineral-Lyon counties with projected
highs in the lower-mid 60s.

* NEXT WEEK:

Monday is looking to be a near-continuation of Sunday with the
best moisture still over north central and northeast CA, and
another mild day with potential strong winds for western NV and
the eastern Sierra. Then the first cold front passage is projected
to slowly push southward Monday night-Tuesday which would increase
snow impacts over more Sierra locations, although this might be a
slow progression with the core of the colder air mass remaining
off the west coast and the deep moisture plume becoming more SW-NE
oriented.

As we get to mid-late week, additional waves of moisture and
colder air will spread across eastern CA-western NV. These storms
are less likely to have the persistent high precip rates and less
wind in comparison to this weekend`s event, but snow impacts
could spread down into lower elevations, with periods of heavier
Sierra snow reaching down to lake level around the Tahoe basin and
into the US-395 corridor of Mono County. There`s still some
variance in how these storms play out, but in general expect a
continuation of adverse weather for the majority of next week. MJD

&&

.AVIATION...

Widespread weather impacts to aviation will prevail for the next
several days. Expect flight delays, cancellations or diversions
especially with the strongest wind days Sunday-Monday.

* WINDS: Turbulence and/or shear will be widespread from today
  through Monday, including mountain wave and rotor conditions.
  Ridge top/FL100 winds will increase to 50-65 kt with gusts
  80-100+ kt. SW-W surface winds increase at the main terminals
  with gusts 20-25 kt this afternoon, 25-35 kt Saturday afternoon,
  and 35-45+ kt Sunday afternoon which may also occur on Monday.

* RAIN/SNOW: Other than 13-20Z today when light snow may bring
  accumulations up to 1" (20-40% chance) to KTVL/KTRK, this will
  largely be a rain event at all the terminals, with long periods
  of continuous rain especially for the Tahoe area this afternoon
  thru Sun AM. Rain will most likely extend into the western NV
  terminals from Saturday morning thru Sat night, and KMMH from
  late tonight thru Sat afternoon. Expect MVFR/IFR conditions with
  mountain obscurations, and even some LIFR cigs/vis during the
  heaviest rain with ponding on runways. MJD

&&

.AVALANCHE...

Widespread wind with heavy wet snow or rain impacts across all
avalanche center terrain from Yuba Pass southward to Bishop Creek
ramping up today and continuing through this weekend. Additional
rounds of snow are likely for next week.

* SWE totals today-Sunday night: 5-8" for the Sierra Avalanche
  Center terrain, then 2-5" for the Bridgeport Avalanche Center
  terrain and 1-3" for the Eastern Sierra Avalanche Center
  terrain. 90-100% probability of at least 1" SWE in a 24 hour
  period.

* Snow-Liquid Ratios: Mainly wet character from 7:1 to 10:1 where
  snow falls.

* Snow levels: Rising to 7000-8000 feet by this afternoon for
  Sierra Avalanche Center terrain and remaining around these
  levels through Sunday night. Rising to 8000-9000 feet for
  Bridgeport Avalanche Center terrain and 8500-9500 feet for
  Eastern Sierra Avalanche Center terrain by this evening and
  remaining around these levels through Sunday morning, then
  dropping to 7500-8500 feet Sunday-Sunday night.

* Snowfall totals today-Sunday night: 2-4 feet for highest terrain
  (above 8000 feet from Ebbetts Pass northward and above 10,000
  feet south of Ebbetts Pass), then dropping off to 1-2 feet down
  to 7000 feet from Ebbetts Pass northward and between 8000-10,000
  feet south of Ebbetts Pass. 90-100% probability of at least
  1"/hour snowfall rates for all terrain.

* Ridge top gusts: Increasing to 80-100 mph by late this afternoon
  or evening, continuing through much of the weekend. Occasional
  gusts to 125 mph at times Saturday-Sunday. MJD

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 4 AM Friday to 10 PM PST Saturday
     NVZ002.

     Winter Storm Watch from late Saturday night through Monday
     evening NVZ002.

     Lake Wind Advisory from noon Friday to 7 PM PST Saturday NVZ002.

     High Wind Watch from Sunday morning through Sunday evening
     NVZ001-003.

CA...Winter Weather Advisory from 4 AM Friday to 10 PM PST Saturday
     CAZ071-072.

     Winter Storm Watch from late Saturday night through Monday
     evening CAZ071-072.

     Lake Wind Advisory from noon Friday to 7 PM PST Saturday CAZ072.

     High Wind Watch from Sunday morning through Sunday evening
     CAZ073.

&&

$$