Damaging Winds in California, August 16 to 18, 2020

Area Forecast Discussion
National Weather Service Las Vegas NV
107 PM PDT Sun Aug 16 2020

.SYNOPSIS...Record breaking heat continues through at least mid-week as
exceptionally strong high pressure builds across the region.
Pockets of afternoon showers and storms will be possible each
afternoon on the higher terrain.
&&

.DISCUSSION...Through Next Sunday.

Forecast concerns change very little over the next week, with heat
and thunderstorms remaining concerns.

First the heat. The region now in the heart of recording-breaking
heatwave, despite some moisture and clouds around, as the upper-
level ridge of high pressure continues to strengthen. The ridge is
forecast to maintain and remain nearly stationary through at least
midweek, before potentially slightly weakening and wobbling
southeast. The slight decrease in heights bring only minimal
relief, with HeatRisk still forecast to be high and very high
across the region through the week - highs currently not forecast
to dip below 110 in Las Vegas, 120 in Death Valley, and 115 in the
Colorado River Valley this week. Thus, there will likely be a need
to extend the Excessive Heat Warning. Will hold off for now,
because a number of factors erode confidence beyond current
warning, including increasing moisture and potential cloud cover.

That makes for a good transition to convective concerns. An area
of moisture with PWATs of three-quarters to one inch current sits
across the southern third of the CWA, then extending up the Sierra
Nevada. This moisture is not expected to really go anywhere in the
next week, so it will just sort of slosh around the area. This
presents the opportunity for afternoon thunderstorms across
portions of the area just about every afternoon. A lack of
organized forcing really limits predictability on these, and will
be driven by cloud cover, outflow boundaries, and local turnover
with previous days' activity. So far, indications are that rain
has been making it to the ground with this activity, but flooding
has yet to emerge as a concern just yet without any organization.
Gusty outflow winds have been the primary issue.

There may be gradual upticks in thunderstorm activity towards mid
and late week as a few things happen that could tip the scales.
The stage-setter is a potent upper-level trough coming into the
Pacific Northwest. This will make the upper-level ridge overhead
"flinch" a bit, and wobble eastward. This will allow moisture from
the still rather active tropics to begin moving into the region,
with slightly less subsidence suppressing activity across the
region. Still hard to pick out an organized feature to trigger
storms, so still the lack of predictability and confidence we have
in the short term. But given that we have already seen increasing
activity the last few days, these trends will continue through
the week, with activity potentially inching northward each day. &&

.FIRE WEATHER...Elevated fire weather conditions continue. There
is enough moisture in the region to trigger afternoon showers and
storms on higher terrain, but not enough to keep surface humidity
from falling below 15 percent each afternoon. While widespread
gusty winds are not expected, gusty outflow winds can be expected
with potential isolated fire starts from lightning through the
week.
&&

.CLIMATE...
DAILY RECORD HIGH MAXIMUM TEMPERATURES

               SUN 8/16     MON 8/17     TUE 8/18     WED 8/19
Las Vegas, NV  113 (1939)*  111 (1939)*  111 (1992)*  111 (1992)*
Bishop, CA     106 (1994)   106 (2015)   105 (2001)   106 (1950)
Barstow, CA    114 (1994)*  111 (2015)*  111 (1992)*  111 (2018)*
Needles, CA    118 (2015)*  117 (1892)*  115 (2015)*  117 (2018)*
Kingman, AZ    110 (1933)*  106 (2001)*  109 (1915)*  111 (1915)
Death Valley   125 (1994)*  124 (2001)*  125 (2001)*  124 (1992)*

DAILY RECORD HIGH MINIMUM TEMPERATURES

               SUN 8/16    MON 8/17    TUE 8/18    WED 8/19
Las Vegas, NV  88 (2008)*  89 (2015)*  86 (2018)*  90 (2018)
Bishop, CA     67 (1992)   65 (1992)*  67 (1970)   67 (1961)
Barstow, CA    81 (1994)*  82 (2012)*  80 (2001)*  80 (1973)*
Needles, CA    93 (1892)*  94 (1903)   91 (2018)*  93 (2018)*
Kingman, AZ    77 (1917)*  81 (1903)*  80 (2001)   76 (1999)*
Death Valley   98 (2008)*  99 (2013)*  98 (2013)*  99 (2003)*

*-Current forecast may be close to current record values.
&&

.AVIATION...For McCarran...Light winds favoring typical diurnal
patterns are expected today. A few afternoon cumulus build ups may
occur across the mountainous terrain around the valley, but no
thunderstorm activity is expected in the valley vicinity. Very hot
temperatures will result in high density altitude through the period.

For the rest of southern Nevada, northwest Arizona and southeast
California...Another hot day with scattered afternoon cloud build
ups and generally light winds.  However, thunderstorm outflow could
result in locally strong wind gusts near KDAG, KBIH, and possibly
KIFP in the afternoon and evening.  Most numerous shower and storm
activity will be near the Sierra and KBIH, with activity tapering
off in the evening and returning to VFR conditions overnight into
tomorrow morning.
&&

.SPOTTER INFORMATION STATEMENT...Extreme heat will continue as
pockets of isolated thunderstorms are possible across the higher
terrain each afternoon. Spotter activation may be necessary later
in the week as thunderstorm activity increases. Otherwise, spotters
are encouraged to report any significant weather, such as
rainfall, outflow wind impacts, or blowing dust according to
standard operating procedures.
&&

DISCUSSION...Steele
AVIATION....TB3/Outler

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