Excessive Heat in Nevada, July 6 to 8, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
341 AM PDT Thu Jul 6 2017

.SYNOPSIS...High pressure intensifying over the region will
produce excessive heat through the end of the week before more
monsoon moisture looks to begin to push into the area for next
week, bringing cooler temperatures and thunderstorm chances.
&&

.SHORT TERM...through Saturday Night.

The focus for the short term is an intensifying ridge over the
region as well as modest moisture around the Sierra Nevada.

Models are showing better agreement surrounding the heat over the
next few days, with guidance coming in with higher temperatures
once again. Upper level high over the four corners region is
forecast to strengthen and expand westward beginning today and
persisting through the end of the week. Strong subsidence from the
intense high should keep any monsoon activity at bay, outside of
the Sierra Nevada, which will likely have sufficient moisture and
be far enough removed from the center of the high for a few
afternoon thunderstorms each day. For most the area, some shallow,
low-grade moisture may continue to seep into the area, even some
outflow is possible from Arizona complexes, however, the high
should keep any activity in check. A few afternoon cumulus or weak
showers are possible over the Spring Mountains, but impacts should
be limited.

The main story will be the rising mercury with temperatures,
likely to near record levels once again for many locations. With
the warmer guidance, opted to upgrade excessive heat watch to a
warning, expand areal extend to cover most the Mojave desert, and
begin the warning this morning.
&&

.LONG TERM...Sunday through Wednesday.

Models are in decent agreement indicating high pressure moving
eastward during this period. Initially, this should lead to an
increase in moisture and thunderstorm chances along with a drop in
temperatures, out of the excessive heat territory. So, for Sunday I
am going with a slight chance of thunderstorms across the entire
forecast area with somewhat higher pops over some mountainous areas.
Model instability is still not that impressive, therefore the pops
were kept on the low side but high enough to mention thunderstorm
chances. High temperatures are forecast to be about 4 or 5 degrees
lower than Saturday. Not looking for any huge changes for Monday
although it does look like some drying beginning in the far western
CWA and some additional minor cooling. The models are forecasting a
bit more of a southwest flow for Tuesday and Wednesday with drier
air pushing in across San Bernardino and southern Inyo Counties and
to some extent into southern Nevada and western Mohave County. So, I
trimmed pops back somewhat in those areas, enough to remove mention
of thunderstorms. Temperatures Tuesday and Wednesday look to be
fairly similar to Monday, a couple of degrees above normal.
&&

.AVIATION...For McCarran...Light winds will follow typical diurnal
trends through the period. East winds may reach 8-10 kts at times
this afternoon. Temperatures exceeding 110F will create density
altitudes approaching 6000 ft in the afternoon. Scattered high
clouds in the morning will likely shift westward during the day,
but no operationally significant ceilings are forecast.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds will mainly follow typical summer
diurnal trends for most terminals with periods of SCT to BKN
clouds above 10 kft over the region. A few thunderstorms are
possible over the Sierra Nevada.
&&

.FIRE WEATHER...The big story through Saturday will be excessive heat
across much of the area as high pressure expands over the region.
This will limit instability and thunderstorm chances to mainly the
Sierra and Spring Mountains but chances even there do not look all
that high. The high shifts east beginning Sunday, opening the door
for moisture and thunderstorm chances in most of the area Sunday and
Monday. A somewhat drier southwest flow may push in Tuesday and
Wednesday.
&&

.CLIMATE...Temperatures will once again soar across the region,
and may peak at near-records.

Records for today, Thursday, July 8, 2017

Location		Forecast High	 Record High (year)
----------------------------------------------------
Las Vegas, NV		112 			115 (2007)
Kingman, AZ 		107 			108 (1905)
Barstow, CA 		110 			115 (2007)
Bishop, CA 			100 			105 (1989)
Death Valley, CA 	123 			129 (2007)
&&

.HYDROLOGY...Ongoing minor flooding may continue in the eastern
Sierra as temperatures continue to climb once again. Afternoon
thunderstorms over the mountains may aid snowmelt runoff to keep
some drainages elevated over the next few days. Remember, never
drive through flooded roadways or around barricades. Also,
pastureland or farmland adjacent to creeks, streams or rivers
could experience areas of standing water.
&&

.SPOTTER INFORMATION STATEMENT...Strengthening high pressure is
expected to keep monsoon activity at bay through the end of the
week, therefore, spotter activation is not anticipated. However, spotters
are encouraged to report any significant weather or impacts
according to standard operating procedures.
&&

Short Term/Aviation/Climate...Steele
Long Term/Fire................Harrison

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