Tornadoes in California, August 15, 2020

Area Forecast Discussion
National Weather Service Reno NV
239 AM PDT Sat Aug 15 2020

.SYNOPSIS...

Showers and thunderstorms can be expected each afternoon through
the middle of next week. Hot temperatures are forecast for the
weekend and next week. Heat impacts are likely for sensitive
groups and those with limited cooling options for their homes.

&&

.SHORT TERM...

Lots to chat about early this morning with heat and thunderstorms
the two big concerns this weekend.

Showers and thunderstorm might be a bigger issue each day as
instability builds through the weekend. There is a decent
moisture feed from the south as the Sierra and western NV are
stuck between the ridge over central/eastern NV and a trough off
the California coast. In this pattern, thunderstorms should
initially develop over the Sierra then push off into western NV
with the light zephyr breezes each afternoon. Waves of energy may
quickly pass with each moisture surge leaving the door open to the
potential for strong thunderstorms and even some late night/early
morning activity starting Sunday night. Bottom line here is to be
prepared to change your outdoor plans. Strong storms will be able
to produce winds gusts over 50 mph, hail and periods of heavy
rain. Flash flooding and debris flow threat appears to be rather
low due to a 10-15 mph storm motion, though any slower moving
storms could easily drop a burst of heavy rain.

Heat could also lead to some health impacts for sensitive groups
and those with limited cooling options. If you have outdoor plans
also be prepared for the heat, definitely carry extra water, if
you are going to be outside for several hours. Afternoon highs
will approach 100 degrees for the NV valleys, though cloud cover
may keep temperatures below 100. Highs in the Sierra up near 90
are not of the question as well. Overnight lows in population
centers may not dip much below 70, leaving little time to cool
homes at night.

Did go with a dense smoke advisory for this morning for the
actively burning Loyalton Fire. Expect smoke to settle into the
Sierra Valley around Chilcoot, Loyalton, Vinton this morning. Some
smoke may drift into the Reno-North Valleys and perhaps as far
west as Portola and Graeagle. Waiting on the early morning VIIRS
pass to initialize the fire for the smoke dispersion models.
Expect a bit more detailed smoke forecast later today. Brong

.LONG TERM...Tuesday onward...

No major changes were made to this forecast cycle. Our focus remains
on how long the heat will stick around our area as an anomalously
strong ridge looks to remain over the Intermountain West through
most of next week.

* Heat: The major headline for the long term is how long the heat
  will endure for our region. Deterministic and ensemble model
  guidance is in consensus that Tuesday will be the hottest day
  across the Sierra and western Nevada as the 597 decameter
  contour arrives overhead at the 500 hPa level. Afternoon highs
  Tuesday through next Saturday will be in the upper 90s to low
  100s for western Nevada valleys and upper 80s to around 90 in
  Sierra valleys. Radiational cooling will be limited Tuesday and
  Wednesday morning with the presence of subtropical moisture over
  our region. This prolonged period of well above normal daytime
  highs and overnight lows will create heat-health impacts for
  vulnerable populations and those outdoors for prolonged periods.
  Make sure to limit your outdoor exposure and understand the
  symptoms of heat- related illness. The good news is that a
  strong Gulf of Alaska trough looks to near the Pacific Northwest
  and Canadian Pacific coast next weekend, which may allow
  temperatures to cool back in the direction of normal.

* Thunderstorms: Another persistent leitmotif in the forecast is
  the continued potential for thunderstorms each afternoon and
  evening through next Thursday mainly along the Sierra and Sierra
  Front. Minor changes in thunderstorm coverage could occur on one
  or more of these days as mesoscale vorticity maxima pivot around
  the periphery of the ridge allowing for cooling aloft and
  improved chances for convective initiation. Subtropical moisture
  will continue to stream into the region around the perimeter of
  the Intermountain West ridge through at least Thursday. Storms
  look to be of the hybrid variety with the increased PWAT;
  however, as we saw yesterday, lightning strikes outside of cores
  could start new fires, especially given the receptive nature of
  the very dry fuels. Report any new fires and smoke to local
  emergency personnel. As the center of the 500-hPa ridge begins
  to move south and east late next week, the associated influx of
  subtropical moisture will also move with it, causing
  thunderstorm chances to shift south and east by next weekend.
  Afternoon cumulus castellanus will still be possible over the
  High Sierra and White Mountains of southern Mono County Friday.

* Winds: Expect typical zephyr breezes through next week with
  gusts to around 20-25 mph each afternoon. We will likely see
  intensified afternoon winds and heightened fire weather concerns
  depending on when the Gulf of Alaska trough moves into the
  Pacific Northwest region, which at this time looks to be next
  weekend.

  -Johnston

&&

.AVIATION...

Showers and thunderstorms to develop daily this weekend between
20z-04z. For Today thunderstorms should be limited to areas from
roughly KRNO-KTRK southward to Mono/Lyon/Mineral Counties. Outflows
35-45 kts, small hail, and brief heavy rain are possible with the
stronger storms.

Thunderstorm chances for terminals today and tomorrow...
KRNO: 25% - 30%
KCXP: 25% - 35%
KMEV: 30% - 35%
KTRK: 20% - 30%
KTVL: 25% - 30%
KMMH: 30% - 35%

Smoke and haze from the Loyalton Fire may limit visibility around
the Sierra Valley, and Stead Airport today depending on fire
activity. Brong

&&

.FIRE WEATHER...

The combination of heat and thunderstorms are the main concern
this weekend. We're stuck between a low off the California coast
and High Pressure over eastern Nevada. This will allow moisture
to continue to move into the region with a daily trend of showers
and thunderstorms building over the Sierra by mid afternoon, then
pushing into western NV as the light zephyr breezes kick in. Storm
motion will be about 10-15 mph which will limit rainfall. Gusty
outflows of 40 mph or more area also possible this weekend.

One note for the Loyalton fire today, the heat, moisture, and
instability are a very favorable set-up for pyrocumulus and
perhaps pyrocumulonimbus development in the presence of active
fire behavior.

Simulations are starting to show some potential for overnight
showers and thunderstorms this weekend as well. Overnight
instability appears minimal tonight, so perhaps just some virga or
very light showers. Sunday and Monday nights appear more
favorable. Brong

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...Dense Smoke Advisory until noon PDT today CAZ071.

&&

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