Red Flag Warning 4, NWS Reno, NV

589 
WWUS85 KREV 050248
RFWREV

URGENT - FIRE WEATHER MESSAGE
National Weather Service Reno NV
748 PM PDT Sun Sep 4 2022

CAZ270-278-NVZ458-050400-
/O.EXP.KREV.FW.W.0004.000000T0000Z-220905T0300Z/
Surprise Valley California-Eastern Lassen County-
Northern Washoe County-
748 PM PDT Sun Sep 4 2022

...RED FLAG WARNING WILL EXPIRE AT 8 PM PDT THIS EVENING FOR
GUSTY WINDS AND LOW HUMIDITY FOR PORTIONS OF NORTHEAST CALIFORNIA
AND FAR NORTHWESTERN NEVADA...

Winds have decreased below critical level criteria over the past
hour. Therefore, the Red Flag Warning will be allowed to expire.

$$

http://weather.gov/reno

Area Forecast Discussion
National Weather Service Reno NV
1224 PM PDT Sat Sep 3 2022

.SYNOPSIS...

The current heat wave will continue through the middle of next
week, bringing moderate to high heat-health impacts. Gusty winds
will bring areas of critical fire weather conditions along with
choppy lakes and pockets of blowing dust today. A few
thunderstorms may return next week along with some cooling later
in the week, with additional moisture possible next weekend.

&&

.SHORT TERM...through Sunday Night...

The heat goes on with triple digit highs again on tap for most
lower elevations through Sunday and into the middle of next week.
The slight dent in the ridge over far northeast CA-northwest NV
due to the overnight shortwave passage across Oregon will push
highs down a few degrees in those areas, but rebound again Sunday
as the Great Basin ridge re-expands north and west. Afternoon flat
cumulus mainly south of US-50 today are expected to expand farther
north to near I-80 on Sunday. High resolution guidance indicates
the flatter cumulus extending northward to around I-80 on Sunday,
and possibly a little more vertical cumulus growth near the
Sierra crest in Mono County, but probability for a brief
thunderstorm is 10% or less.

Gusty winds will keep dusty conditions around the Black Rock
Desert through the remainder of today, then winds ease back to
more typical zephyr-type breezes on Sunday. See the fire weather
section for more details on wind speeds and impacts.

Record highs continue to be established for Reno after yesterday's
observed 102 degrees at the airport tied the overall September
record for warmest day. This morning's low of 67 degrees also
stands as the warmest minimum temperature for any September day in
Reno's climate history (previous record 66 degrees on 9/2/2013).
Lows will continue to be well above average for the next couple of
nights, although with more areas having lighter winds overnight
it isn't likely to be quite as warm compared to last night. MJD

.LONG TERM...Tuesday onward...

Expansive area of high pressure remains over the west with
continuing record or near record temperatures across the region.
The current forecast of 103 for KRNO on Tuesday would be the
latest 100 or greater degree on record AND the hottest September
day on record. Latest guidance is showing the ridge remaining
strong for another day, with 100+ degree temps for lower valleys
once again Wednesday, per the NBM. So Wednesday may end up being
the new latest 100 degree day on record for KRNO. Who is ready for
fall?

Some remnant monsoonal moisture may work its way north, with
ensemble data hinting at a 10-15% chance for thunderstorm
development Tuesday through Thursday. This is definitely a concern
given the recent very hot and dry conditions and little indication
that the low levels will moisten enough for meaningful rainfall.
This is a critical fire weather set up for dry lightning, and at
this point something to be aware of, but also remains lower
probability.

The spread in model/ensemble solutions is rather large for the end
of the week and into next weekend due to a variety of factors.
First, there is the question of a potential trough moving through
the northwest, finally flattening the ridge Thursday into Friday.
This is showing up in 30-40% of the cluster analysis 500 mb
solutions, while the rest bring a much weaker wave through British
Columbia. Either way, we should finally see the end of the triple
digit heat, and an uptick in afternoon winds from the middle into
the end of the week. We're getting into the season where we're
transitioning from summer ridges to Pacific troughs--something
models always struggle with.

Then, there is the real wildcard - a potential hurricane and how
the remnants may interact with weather in the mid-latitudes. The
big kicker is the fact this storm hasn't even formed yet, but the
National Hurricane Center is indicating a 90% chance for this
current disturbance off the coast of southern Mexico to become a
tropical system within the next 48 hours. Global forecast models
have an excellent handle on this part, but again, it's the
transition as it becomes an extratropical cyclone that tends to
bring wildly different model solutions. This is exactly what we're
seeing in the 6-10 day outlooks.

At this point, there are a handful of ensembles (roughly 20% of
the GEFS/EPS members) and low end chances in the NBM (10-20%) for
this moisture to absorb into the flow and actually make it as rain
into the Eastern Sierra and Nevada next weekend. The way this
evolves will yield wildly different forecast results, so stay
tuned! -Dawn

&&

.AVIATION...

Breezy winds along with continued very hot conditions are the main
concerns for aviators.

Southwest FL100 winds are sustained around 30-40 kts for areas
near and north of I-80 and will remain rather breezy, though
decrease 5-10 kts, into Sunday. This is leading to a bumpy ride
across and downwind of the Sierra. Winds are mixing down into
valley locations this afternoon with terminals expected to see
gusts 20-30 kts through around sunset. While this is not a set-up
for widespread wind shear, anticipate pockets of shear to develop
due to flow interaction with the terrain. Breezy winds to continue
Sunday, but most terminals will peak out with afternoon gusts
15-20 kts. Winds may bring areas of blowing dust, especially
downwind of deserts and sinks near and north of I-80.

Otherwise, the continued record high temperatures will bring midday
density altitude concerns through at least Wednesday next week.

There is a 10-15% chance for thunderstorm development next week,
initiating along the eastern Sierra, then potentially pushing
eastward into the late afternoon hours. -Dawn

&&

.FIRE WEATHER...

A Red Flag Warning remains in effect through early this evening
across northeast CA and northwest-far western NV. Ridge-level
winds have backed off from the peak gusts of 50-60 mph earlier
this morning, but should still allow for 30-40 mph gusts to mix
down for 5+ hours in the warning areas. Meanwhile, RH values
which only recovered to 20-30% last night in thermal belts/ridge
tops will drop into the 6-12% range across most elevations this
afternoon.

For Sunday, lingering 700 mb flow of 30-35 kt in the morning could
mix down with a short period of 25-30 mph gusts along with low
humidity again for northeast CA-northwest NV. Isolated sites may
reach critical levels for a short duration, but isn't expected to
be widespread enough for issuing any additional fire weather-
related watches or warnings. MJD

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...Heat Advisory until 9 PM PDT Tuesday for NVZ001-003>005.

     Red Flag Warning until 8 PM PDT this evening for NVZ420-423-458.

     Lake Wind Advisory until 8 PM PDT this evening for NVZ003.

     Lake Wind Advisory until 8 PM PDT this evening for NVZ004.

CA...Heat Advisory until 9 PM PDT Tuesday for CAZ070-071.

     Red Flag Warning until 8 PM PDT this evening for CAZ270-278.

&&