Special Weather Statement, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
143 PM PDT Tue Jul 13 2021

.SYNOPSIS...

This evening plan on well above normal temperatures and a few
isolated thunderstorms south of Highway 50. A general cooling trend
will progress through the remainder of this week and bring some
relief to the excessive heat wave gripping the west. Near normal
temperatures are expected by Friday to last through the weekend.
Smoke and haze from multiple fires will continue to impact portions
of northeastern California and western Nevada with periods of
degraded air quality and reduced visibility this week.

&&

.SHORT TERM...

* Although some relief is on its way with the incoming cooling
  trend, Wednesday temperatures will remain hot with triple digit
  readings in most valley locations across western Nevada.

* Isolated thunderstorms mainly along Mono-Mineral convergence zone
  may still have gusty outflow winds capable of 40 mph going into
  the evening hours.

* Fire weather concerns remain. Periods of critical conditions
  possible each afternoon with gusty winds and low humidity.

Thunderstorms make a brief appearance during this short term
forecast period. The only other concern during this period will be
an enhanced Zephyr wind tomorrow and Thursday afternoon. Upper
ridging and any accompanying areas of widespread subsidence that
added to the current heat wave will back off to the southeast
through the week. More sensible weather impacts for the short term
are included below:

Heat
* Tomorrow should be the last "hot" day with temperatures still
  ranging in the low 100s for most western NV valley locations.  The
  most apparent aspect of the incoming cooling trend will be the
  noticeably cooler overnight temperatures. Radiation cooling should
  become more efficient to disperse sensible surface heating going
  into the evening and drop lows into the mid/low 60s for much
  western Nevada tomorrow morning. Lows overnight Thursday will
  lower a few degrees further into the upper 50s/low 60s. And of
  course this trend will be welcomely matched for Sierra locations.
  By Thursday, slightly above average highs will still top into the
  mid/upper 90s but register relatively cooler into the more
  seasonable range of lower 90s by Friday.

Thunderstorms
* While a few cumulus buildups will be possible, drier air related
  to a more southwesterly flow pattern will limit thunderstorm
  chances to less than 10% tomorrow and Thursday. An isolated storm
  or two may still pop-up in the late afternoon hours over complex
  terrain of Mono-Mineral Counties where pockets of moisture and
  instability contribute to their development. Otherwise, some
  flattened cumulus buildups will rise over the Lassen and
  Mono/Mineral County convergence zone during the afternoon hours.

Winds and Fire Concerns
* No change. Typically breezy afternoon winds are still expected
  tomorrow with gusts 20-30 mph in general. Flow aloft increases
  Wednesday night, but surface pressure and thermal gradients do not
  increase much. Still, there could be a marginal uptick along wind
  prone spots that could lead to slightly enhanced fire weather
  concerns. See the Fire Weather Discussion for more details.

Smoke and Haze
* Until wildfire activity noticeably decreases, the smoke and haze
  coverage should only increase proportionately with wildfire
  activity. Mono/Mineral counties will have the most notable change
  as the Henry Fire in the Yosemite area has recently flared up in
  that area which could degrade air quality even more over western
  NV locations. Locations downwind of the Beckwourth Complex will
  continue to have the most significant impact on air quality east
  of the Sierra into western NV. Mixing heights, however, should
  decrease with the coming cooling trend spreading into the region.
  With some good comes an equal measure of not-so-good, as lower
  mixing heights could lead to more acute air quality issues over
  larger areas if the wildfires remain active.

-Amanda

.LONG TERM... (Friday and beyond)...

* Monsoonal moisture possibly on the march northward early next
  week.

The latest run of ensemble cluster guidance is showing with greater
certainty the position and magnitude of the broad off-shore upper
troughing and a strengthening dome of high pressure that extends
over the Rockies and Four Corners. Simulations are hanging onto this
current synoptic pattern into the weekend which looks to continue
into next week. It is still too early to know if this is the prelude
for another period of excessive heating over western NV. This
weekend should still see more typical mid-July temperatures across
the region. Unusually dry air seen in ECMWF EPS members will yield
nice cooling at night, so leaning the low temperature forecast
Friday-Sunday under NBM 50th percentile. This will be a refreshing
change from recent warm mornings.

Dependent upon the western extension of the upper ridge, confidence
fades Monday onward. Both higher temperatures and the increasing
potential for more t-storms cannot be totally ruled out going into
next week. An increase in one factor will affect the outside chances
of the other. So uncertainty abounds.

Both the GEFS and ECMWF EPS still show a general uptick in PWAT and
QPF early next week. This is a decent signal that a northward
push of monsoon moisture into the eastern Sierra and western
Nevada is still on the table. Couple that with the possibility of
the upper ridge nosing westward into the region which will
increase the mid-level southerly upper flow into the region, and
the thunderstorm potential arises. So uncertainty is only slightly
dampened for a steady northward progression of thunderstorm
activity into the region starting Monday or Tuesday next week.

There's a bit more spread in temperature forecasts with NBM 10th
percentile in the mid to high 90s at RNO while 90th percentile is
right back into heatwave territory with low 100s. Although the safe
forecast for next week seems to be warm with chances for t-storms
each day, a return of well above average heating could be a likely
outcome as well. -Amanda

&&

.AVIATION...

Mainly VFR conditions are expected this week except for areas closer
to the ongoing wildfires in Mono County and the Beckwourth Complex
in northeastern California where near-surface smoke may drop flight
conditions into MVFR.

We'll see typical west-southwest afternoon breezes with gusts around
25 kts for the next few days. As is typical for these summer
afternoons, mixing will promote some turbulence, especially downwind
of the Sierra.

Thunderstorms as of writing this are currently ongoing across
southern Lyon and Mineral counties. These storms could produce
erratic outflow winds to 40 kts with blowing dust and mountain
obscurations possible.

-Johnston

&&

.FIRE WEATHER...

The area of high pressure over the region weakens and moves east
Wednesday into Thursday as a trough moves just off the Pacific
Northwest coast. This pattern will slightly enhance afternoon
breezes and lead to drier conditions through the weekend.

Breezes: We will continue to be on the verge of near-critical winds
today through Friday with an enhanced zephyr occurring each
afternoon. Wind gusts in most areas will be in the 25-30 mph range
with a few wind-prone areas possibly seeing 30+ mph winds,
especially east of the Sierra Front. With the trough moving into the
northeastern Pacific, ridge winds will likely stay up this evening
through Wednesday.

Dry Conditions: Southwesterly flow will bring drier air to the
region beginning Wednesday into this weekend. Minimum RHs in valleys
could possibly dip into the single digits in valleys and low-teens
in mountain locations. Overnight recoveries will remain poor,
notably on the mid-slopes and ridges.

Isolated Thunderstorms this afternoon: Thunderstorms as of this
writing are ongoing across Mineral and southern Lyon counties. These
storms may produce outflows to 50 mph and given their rather quick
movement and the dry low-level environment, any lightning outside of
cores could spark new fires. These thunderstorms will move east into
central Nevada through the evening hours.

-Johnston

&&

.REV Watches/Warnings/Advisories...
NV...Excessive Heat Warning until 9 PM PDT this evening
     NVZ001-003>005.

CA...Excessive Heat Warning until 9 PM PDT this evening CAZ070-071.

&&

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

Special Weather Statement
National Weather Service Reno NV
1147 AM PDT Tue Jul 13 2021

CAZ073-NVZ001-003-004-132015-
Mono CA-Western Nevada Basin and Range including Pyramid Lake NV-
Greater Reno-Carson City-Minden Area NV-
Mineral and Southern Lyon Counties NV-
1147 AM PDT Tue Jul 13 2021

...SIGNIFICANT WEATHER ADVISORY FOR MONO...ALPINE...SOUTHEASTERN
CHURCHILL...MINERAL...DOUGLAS AND SOUTHERN LYON COUNTIES UNTIL 115
PM PDT...

Thunderstorms have started to develop across the Eastern Sierra in
Mono County and also in Mineral County. Primary threats with these
storms will be gusty and erratic outflow winds, frequent lightning,
localized heavy rain, and a few stronger storms could produce small
hail.

Outflow winds will likely produce areas of blowing dust for
locations east of Highway 395 this afternoon and into the evening.
The gusty and erratic outflow winds may also redirect the fire front
of wildfires in the area.

Monitor your favorite radar app or check weather conditions
frequently if you are outdoors.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud-to-ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm and produce
new fire starts. Seek a safe shelter inside a building or vehicle.

Persons in campgrounds should consider seeking sturdy shelter until
the thunderstorms dissipate.

&&

LAT...LON 3748 11885 3786 11917 3861 11939 3919 11894
      3955 11749 3938 11776 3922 11772 3914 11781
      3910 11778 3900 11819 3889 11817 3847 11770
      3790 11834 3789 11842 3747 11783
TIME...MOT...LOC 1846Z 240DEG 49KT 3845 11876

EW

Special Weather Statement
National Weather Service Reno NV
145 PM PDT Tue Jul 13 2021

CAZ073-NVZ001-003-004-132215-
Mono CA-Western Nevada Basin and Range including Pyramid Lake NV-
Greater Reno-Carson City-Minden Area NV-
Mineral and Southern Lyon Counties NV-
145 PM PDT Tue Jul 13 2021

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL MONO...SOUTHEASTERN
CHURCHILL...MINERAL...DOUGLAS AND SOUTHERN LYON COUNTIES UNTIL 315 PM
PDT...

At 141 PM PDT, Doppler radar was tracking strong thunderstorms over
the region that are moving northeast at 15 mph.

Winds in excess of 40 mph will be possible with this storm. Stronger
storms could have outflows capable of producing areas of blowing
dust with lowered visibility.

Locations impacted include...
Hawthorne, Yerington, Luning, Mina, Middlegate, Wellington, Smith,
Mason, Walker Lake, Weed Heights, Mina Airport, Junction U.S 50 And
Nv 121 (Dixie Valley Rd), Junction U.S 50 And NV 839, Junction Nv 339
And Nv 208, Schurz, Nv 361 At Mineral-Nye Co Line South Of Gabbs),
Junction NV 338 And CA 182, Rawhide, Junction U.S 6 And NV 360 and
Hawthorne Industrial Airport.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3790 11834 3789 11843 3853 11933 3873 11940
      3897 11941 3908 11932 3938 11776 3922 11772
      3914 11781 3909 11778 3900 11818 3892 11819
      3847 11769
TIME...MOT...LOC 2041Z 242DEG 11KT 3883 11902

AY