Red Flag Warning 24, NWS Reno, NV

525 
WWUS85 KREV 150239
RFWREV

URGENT - FIRE WEATHER MESSAGE
National Weather Service Reno NV
739 PM PDT Mon Sep 14 2020

CAZ270-271-278-NVZ458-150345-
/O.EXP.KREV.FW.W.0024.000000T0000Z-200915T0300Z/
Surprise Valley California-
Western Lassen, Eastern Plumas, Eastern Sierra, and Eastern
Nevada Counties-Eastern Lassen County-Northern Washoe County-
739 PM PDT Mon Sep 14 2020

...RED FLAG WARNING WILL EXPIRE AT 8 PM PDT THIS EVENING FOR
GUSTY WINDS AND LOW HUMIDITY FOR NORTHEAST CALIFORNIA AND
NORTHERN WASHOE COUNTY...

The gusty southwest winds across the region have decreased below
criteria this evening. Therefore, we will let the Red Flag Warning
expire on time. Winds are expected to remain breezy during the
overnight hours for more wind prone areas and along ridges with
poor humidity recoveries. Breezy winds and low humidity are 
forecast for Tuesday and Wednesday afternoons with localized 
critical fire conditions likely during this time. 

$$

http://weather.gov/reno

Area Forecast Discussion
National Weather Service Reno NV
201 PM PDT Sun Sep 13 2020

.SYNOPSIS...

Widespread smoke and haze issues will continue much of this week.
Warm temperatures are expected through Thursday then a cold front
will drop readings back to near or even below normal for the
upcoming weekend. Increased winds could bring fire weather
concerns especially Thursday and Friday. A few light showers
possible in NE California Friday and Saturday.

&&

.DISCUSSION...

Most of the forecast hinges on the progression of quasi-cutoff
low currently over NE Pacific Ocean and it’s progression inland
by mid to late week.

* Smoke: Well today sure started out nasty with hazardous air
  quality in many areas. Smoke has been slow to clear from valleys
  thus far relying mainly on vertical mixing. However, a little
  bit more SW wind into the evening could allow for more
  appreciable clearing, at least away from ongoing fires. Smoke
  models are changing up the scenario some Monday-Tuesday versus
  the last couple days with increased SW transport winds. We’re
  seeing two distinct plume areas in the models where smoke
  concentrations are heaviest: one into NE California and far NW
  Nevada (e.g. Susanville) and another from the E Sierra up into
  parts of W Nevada (e.g. Mammoth, Carson Valley, Yerington,
  Fallon). Elsewhere likely to still be somewhat hazy with periods
  of smoke - low confidence scenario on where boundaries between
  denser smoke and haze will be.

* Wind: Winds will be a little stronger the next few afternoons
  compared to this past weekend, but where we’re really watching
  is Thursday and Friday. Guidance projecting a cold front into
  the area with stronger S-SW winds for most areas. An appreciable
  number of ECMWF EPS members showing gusts 30-40 MPH from NE
  California south along the Sierra Front into the Eastern Sierra
  both days. Could see localized travel and recreation impacts,
  along with critical fire weather (see below). The stronger winds
  could either make the smoke situation in our area worse via
  long range transport and increasing fire activity - or those
  winds could thin it out alot. We shall see. Smoke models are
  only reliable out to 24-36 hours.

* Rain: Sorry, but not much luck happening here next 1-2 weeks.
  The best we can muster: ECMWF/GFS ensemble guidance brings the
  remnants of a weak-moderate atmospheric river into N California
  late this week. This could yield a few showers down into parts
  of NE California Friday-Saturday but precip amounts look to be
  0.1” at best. Only 3 out of 52 ECMWF members showing anything
  above 0.25”. Could be a good soaking rain further north into
  Oregon which would help the fire situation up there.

-Chris

&&

.AVIATION...

* Areas of dense smoke will continue to impact aviation interests
  in the region through at least Monday. Based on the latest HRRR
  Smoke model two major plumes will affect the east side of the
  Sierra tonight into Monday - Quincy to Susanville (SVE) and
  Mammoth (MMH) to Yerington and Carson City (CXP). Conditions
  likely to get into IFR or even LIFR levels in smoke in these
  areas.

* Elsewhere including Reno (RNO) and Tahoe (TRK, TVL) smoke and
  haze are likely however concentrations do not appear as severe
  as they were this morning. Probably still a good bet to expect
  some periods of MVFR in these areas.

* The slight increase in SW winds we’ve seen today will
  continue into Monday with slightly higher gusts but nothing too
  impactful. Generally at or below 25 knots for most areas. This
  could be enough to really mix out the smoke in most areas except
  near and downwind on ongoing large fires.

-Chris

&&

.FIRE WEATHER...

***Increased Confidence in Widespread Critical Fire Conditions
 This Thursday/Friday***

Changes this forecast cycle:

*Cancelled the Fire Weather Watch for the northern Sierra Front
 for Monday. The Watch for northeast California and northern
 Washoe County still remains.

*Increased winds for Friday, especially along the Sierra ridges.

Today through Wednesday will most likely see an uptick in the
southwest flow with low humidity and poor overnight recoveries.
Recent model guidance shows weaker winds overall during this time
and that could be the result due to the smoke impacts. With thick
smoke present, thermal gradients will be weaker which in return
would dampen the strength of the afternoon winds. With this in
mind, we have decided to cancel the Fire Weather Watch for NV zone
420, the northern Sierra Front, for Monday. There could be some
localized gusts of up to 30 mph with Sierra ridges remaining gusty
into the overnight hours, but widespread critical fire conditions
throughout the area is less likely at this time.

The Fire Weather Watch remains for CA zones 270, 271, & 278 and NV
zone 458 (northeast California and northern Washoe County) for
Monday afternoon through the evening thanks to gusty southwest
winds and low humidity. These areas look to be the best shot at
widespread critical conditions, however, confidence is medium at
this time which is why we have left the Watch versus upgrading to
a Warning. Expect southwest winds 10-20 mph with possible gusts of
up to 30 mph. Higher gusts of up to 35 mph are more likely for
wind prone locations as well as for the ridges.

Tuesday and Wednesday look similar with zephyr-like breezes each
afternoon/evening. Localized critical conditions are possible each
day with emphasis on the ridges, northeast California, and
northern Washoe County.

Forecaster confidence continues to increase in the potential for a
widespread critical condition event sometime during the
Thursday/Friday timeframe of this week. It's still early and
things could change, for example the overall timing of the gusty
southwest winds, but for the most part it looks to be windy thanks
to more upper-level support rather than just thermal gradient
driven. Therefore, we have increased winds on Friday with the
strongest winds along the Sierra Crest (emphasis on Mono and
Alpine counties). Even though humidity both daytime and overnight
look to increase during this time, the presence of the gusty winds
could essentially negate the higher RH. Unfortunately, chances for
wetting rains (>0.10") across the region are unlikely at this
time. -LaGuardia

&&

.REV Watches/Warnings/Advisories...

NV...Dense Smoke Advisory until 11 AM PDT Monday NVZ001>005.

     Fire Weather Watch from Monday afternoon through Monday evening
     NVZ458.

CA...Dense Smoke Advisory until 11 AM PDT Monday CAZ070>073.

     Fire Weather Watch from Monday afternoon through Monday evening
     CAZ270-271-278.

&&

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