Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 172134
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
234 PM PDT Sun Oct 17 2021

.SYNOPSIS...

A quick hitting storm will sweep across the Sierra and western
Nevada with strong and gusty winds continuing this evening. Sierra
snowfall can also be expected beginning this evening which will
result in several inches of snowfall along with travel impacts
mainly across the passes through Monday morning. The weather pattern
is trending more active and possibly wetter for the middle part of
next week into the next weekend.

.SHORT TERM...

A quick hitting fall storm will continue to provide widespread strong
and gusty winds with a myriad of potential impacts including
critical fire weather conditions, travel, recreation, blowing dust,
and also Sierra impacts from snowfall later this evening and Monday
morning.

Here are the latest updates:

* Wind Advisory issued through tonight for portions of southern Lyon
  and Mineral Counties.

* Snow amounts increased through portions of Alpine and Mono
  Counties. A Winter Weather Advisory has been issued for higher
  elevations of Mono County through early Monday morning.

* Blowing dust possible downwind of dry lake beds/desert sinks.

WIND:

* NE California & Western Nevada:  Southerly winds are beginning to
  surface across region with gusts currently in the 40-50 mph range.
  Winds will continue to remain elevated through the evening until
  the cold front sweeps through. No significant changes with forecast
  at this time. Areas along US-395/I580 south of Susanville into the
  North Valleys, Washoe and the Carson Valley could see enhanced
  gusts near 60 mph with downsloping enhancement.

* Mono County: A High Wind Warning remains in effect due to the
  potential for strong downsloping winds. Wind prone canyons along
  US-395 will be most at risk at seeing higher end gusts of 70-80
  mph which also include: Twin Lakes, Lundy Canyon, Convict Lake,
  Rock Creek, and higher elevations. Other areas will mostly see
  gusts in the 45-55 mph range. These winds will be most likely
  later this evening after about 7pm when winds begin to shift more
  westerly. Winds should diminish a few hours before dawn on Monday.

* Walker Lake: Localized downsloping winds will also be possible
  along US-95 particularly near Walker Lake where downsloping winds
  are also possible off the Wassuk Range. The window for the
  strongest winds looks to target the 10pm-2am timeframe. Cross-
  winds hazards are possible particularly for high profile vehicles.

PRECIPITATION:

* After our winds taper off, Sierra snowfall will be the next impact
  later this evening into Monday morning. Simulations have trended
  up a bit more with this system and in general we are looking at 4-
  8" of snowfall along the Sierra passes with some localized higher
  amounts along the crest. Snow potential at lower elevations in the
  Sierra near Lake Tahoe level and for communities along US-395
  through Mono County could see 1-3" through early Monday morning.

* Due to the dynamic nature of the incoming jet streak and negative
  tilt of the trough, localized areas with heavier snow rates are
  possible. This may also result in reduced visibility and a 5-10%
  chance of a few lightning strikes.

* Western Nevada: Plan on light rain/snow mix by early Monday
  morning down in the valleys below 5000` with some accumulations of
  an inch or so possible across foothill locations. Cold
  temperatures behind the front may cause untreated roads to freeze
  which any precipitation.

The shortwave quickly exits on Monday with a few residual snow
showers likely through the day. Model soundings remain quite
unstable, so additional snow and pellet showers will be possible
through Monday afternoon. North to northwest brisk winds will keep
it feeling pretty chilly across western Nevada through Tuesday. High
temperatures will be mostly in the low to mid 50s for the lower
valleys and 40s for Sierra valleys. Edan/Fuentes

.LONG TERM...Wednesday through next Weekend...

First Weak Storm Late Tuesday night into Late Wednesday:

* Model guidance places the base of a weakening shortwave trough
  over the Eastern Pacific between 40-45N near the SRN OR coast.
  GEFS and ECMWF-ENS simulations show a weak moisture plume
  binging drawn from the subtropical Pacific into the region with
  IVT values varying between around 250-500 kg/ms. The northern
  Sierra and southern Cascades will experience weak warm air
  advection and isentropic lift along the windward side, which
  should spread light precipitation and high elevation snow
  showers from Plumas-Eureka north into the southern Cascades of
  Oregon. Most of the stronger quasi-geostrophic ascent is still
  focused over southwestern and western OR. With the warmer
  nature of this storm, temperatures will be mild but still below
  normal for this time of year.

* Possible Impacts: (1) Increased winds along ridges mainly north of
  US Highway 50 and possible mountain wave turbulence, (2) breezy
  conditions across the Sierra and western Nevada Wednesday, (3)
  Light rain and high elevation snow showers mainly confined to
  passes north of US-50 in the Lake Tahoe Basin.

Showery or Dry on Thursday? That is the question.

* Ensemble guidance keeps wavering the timing and location of
  successive waves of moisture and warm air advection into the
  northern Sierra Thursday. Ensemble guidance is sending mixed
  messages of a brief dry period or another shot of showers over
  parts of the northern Sierra that continues to the southern
  Cascades. Although it is a few days out and forecast confidence is
  a bit low, we`ll hedge our forecast towards the middle-ground with
  chances for showers continuing into the day Thursday.  These
  showers will mainly consolidate areas north of I-80 across Plumas
  and Lassen counties. Developing showers could enhance local
  breezes for another day across the Sierra and western Nevada.
  Gusts are not expected to eclipse 25-30 mph during this particular
  forecast period.

Two potential Atmospheric Rivers (AR) early next Weekend:

* A couple decent AR events look to take aim at the Sierra next
  weekend. The first weaker AR event should push warmer sub-
  tropical moisture into the Sierra by Friday into Saturday. Some
  light precipitation could spill-over into far western NV but
  leaning rather on the light side of the scale. The second
  stronger system could possibly bring another shot of increased
  precipitation chances over the region Sunday into early next
  week. Breezy to windy conditions look probable for much of next
  weekend into the next week. Due to the wide variability in
  ensemble members of both the ECMWF-ENS and GEFS, it is uncertain
  which dynamical process will dominate this particular AR event.
  At this time, the second potential AR is driven by a strongly
  zonal jet, with ensemble AR tools showing a 30-50% probability
  of IVT >250 kg/ms reaching the lee of the Sierra into western
  Nevada. Snow levels would be sharp, and warm air advection
  processes strong. The weather pattern looks to remain active
  into week two with AR events mainly north of 40 degrees north
  latitude. -Johnston/Amanda

&&

.AVIATION...

* The fast-moving low pressure system entering the region this
  evening is still on track to bring chances for rain and snow
  showers to the Sierra and western Nevada later tonight into
  Monday morning. Gusty winds will continue into the evening at
  all terminals today with gusts ranging 25-35kts. Most Sierra
  terminals and westernmost Nevada terminals will be contending
  with turbulence and LLWS overnight into Monday morning.

* Local Sierra terminals KTRK and KTVL could still see MVFR VIS/CIG
  conditions with possible brief periods of IFR conditions during
  heavier snow showers between 06-12Z. There is uncertainly with
  exact timing of IFR VIS/CIG condition so extra caution is advised
  for any flight planning into Sierra terminals later this evening
  through the early morning hours. Light  accumulations are also
  forecast at lake level for Lake Tahoe early Monday morning.

* Western NV terminals will likely only see a mix of rain/snow. It
  is within the realm of possibility that additional colder air
  mixing into the surface layer during the early morning hours
  Monday will produce condition to produce a brief period of light
  snow. Accumulations will only range from a trace to half an inch.

* Eastern Sierra terminals will see winds later this afternoon and
  evening with increasing potential for wind gusts 30-40kts by
  this evening. For KMMH, there are similar weather signatures
  from the Feb 2020 wind event. There is a 1/5 chance of wind
  gusts exceeding 50 kts this evening if downslope conditions
  materialize into the area. Light snow is a possibility during
  the early morning hours with VIS/CIG conditions lowering to MVFR
  between 06-12Z. Heavier showers could bring brief period of IFR
  conditions in both VIS/CIG, -Amanda

&&

.FIRE WEATHER...

* Strong and gusty winds continue through early evening. Gusts
  currently in the 40-50 mph range with wind prone locations around
  55 mph. Winds will continue to ramp up through early evening.

* Wind prone locations may see wind gusts 60+ mph, especially for
  south-north oriented valleys. A couple areas at higher risk for
  strong wind gusts will be the North Valleys (downwind of Peavine
  mountain), South Lake Tahoe, and wind prone areas along US-395/I-
  580.

* Eastern Sierra mainly through the Sierra Front and into Mono,
  County will see the most critical conditions as downsloping winds
  are possible. There is roughly a 20% chance of wind gusts
  exceeding 70+ MPH for wind prone locations. Downsloping winds
  further exacerbate conditions by drying out as they descend.

* Strong, gusty winds may blow down damaged or burned trees in
  recent burn areas.

* Current humidity is dipping into the 10-15% range along the Sierra
  Front and into Mono County. While the winds look to peak late
  afternoon into early evening, RH will quickly being to increase to
  over 30% during this window and will continue to rise through the
  evening.  Fuentes


&&

.REV Watches/Warnings/Advisories...
NV...Lake Wind Advisory until 8 PM PDT this evening for Pyramid Lake
     in NVZ004.

     Wind Advisory until 5 AM PDT Monday NVZ001.

     Wind Advisory until 11 PM PDT this evening NVZ002-003-005.

     Red Flag Warning until 5 AM PDT Monday NVZ421.

     Winter Weather Advisory from 7 PM this evening to 5 AM PDT
     Monday NVZ002.

CA...     Winter Weather Advisory until 5 AM PDT Monday above 5500 feet in
     CAZ071.

     Wind Advisory until 11 PM PDT this evening CAZ070>072.

     Winter Weather Advisory from 11 PM this evening to noon PDT
     Monday CAZ070.

     High Wind Warning until 5 AM PDT Monday CAZ073.

     Red Flag Warning until 5 AM PDT Monday CAZ274.

     Winter Weather Advisory from 10 PM this evening to 5 AM PDT
     Monday above 8000 feet in CAZ073.

     Winter Weather Advisory from 7 PM this evening to 5 AM PDT
     Monday CAZ072.

&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno


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