Excessive Heat in Nevada, July 15, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
830 AM PDT Sat Jul 15 2017

.SYNOPSIS...High pressure overhead through the weekend will result
in hot temperatures over the next couple days with limited monsoon
moisture mainly focused across northwest Arizona. By next week...a
more favorable pattern for widespread monsoonal moisture will set up
with daily thunderstorm chances and increased potential for locally
heavy rainfall.
&&

.UPDATE...Hot day in store as temperatures this morning are already
running 2-4 degrees above yesterdays values.. Expecting Las Vegas to
top out near 112 today, though creeping up a degree or two beyond
that can't be completely discounted. Elsewhere temperatures well
into the 110s expected across the lower deserts and River zones,
with 120+ expected across Death Valley. Intense heat will be
relatively short lived with slight cooling expected tomorrow
followed by decreasing temperatures next week as clouds and moisture
start increasing. This has precluded the issuance of an excessive
heat product today, but the heat will still be dangerous if not
properly prepared for. Stay hydrated, and limit outdoor activities
to the cooler parts of the day.

Convection today will again be suppressed due to the strong high
pressure ridge overhead, however, leading edge of deeper moisture
will be hanging across Northwest Arizona which will be the focus of
some isolated activity this afternoon. Easterly flow developing on
the southern periphery of the high will also tend to steer this
activity westward towards the Colorado River valley, so slight
chances for storms in that area look good this evening. Given the
very hot boundary layer conditions, strong downburst winds will be
the main threat.

-Outler-

&&

.SHORT TERM...Thru Monday Night.

Mostly clear sky conditions across the area this morning with
satellite imagery showing a very large decaying MCS moving west
across northern Mexico. High pressure to the north of this feature
will stop any northward progress towards our area and instead, keep
it moving west or southwest away from the area.

Deeper monsoon moisture will lie at our southern doorstep today then
slowly move north into our southern regions on Sunday and linger
through Tuesday. Today should be mostly a down day convection wise
with warm air aloft creating stable conditions in most areas. The
main concern will be hot temperatures today and possibly Sunday.
Based on forecasted temperatures, records seem unreachable with this
current heat and widespread excessive heat is not anticipated.
Moisture increases and the high center migrates east on Sunday,
thunderstorm chances increase with increasing instability across
Mohave County and the Colorado River Valley. Chances spread a little
further west and north on Monday to potentially include more of San
Bernardino County, as well as Nye, Clark and Lincoln counties.
Temperatures for Sunday through Tuesday trend down as moisture
becomes a key ingredient.
&&

.LONG TERM...Tuesday through Friday. Still dealing with model
differences which are significant enough to call forecast confidence
below average. High pressure overhead today is forecast to drift
eastward to the Plains by Thursday and Friday. The main concerns for
thunderstorm chances are whether or not there will be enough
westward extension of the ridge to keep monsoon moisture suppressed
to the southeast, and the timing of any easterly waves/inverted
troughs which might move west across the Gulf of California and
potentially send a surge of moisture our way. Highest confidence is
in delaying the greatest chance of a significant moisture push from
Tuesday to Wednesday, but even that could change if a strong
convective complex in the right place pushes moisture into our area
Monday or Tuesday. With the uncertainty, chose to make only minor
changes to the previous grids.
&&

.AVIATION...For McCarran...West to southwest winds should persist
through 14Z then become light. Typical diurnal summertime winds
continue again this afternoon with a very light easterly component
between 15-20Z. Some upticks in southeasterly wind cannot be ruled
out between 20-01Z. Thereafter, winds should become more southerly
before becoming southwesterly by 03-04Z tomorrow evening. FEW to SCT
above 15 kft through the forecast period.

For the rest of southern Nevada, northwest Arizona and southeast
California...Typical summertime diurnal winds continue through
today. Thunderstorm activity will mainly be across higher terrain of
Lincoln, Mohave and Inyo counties. Though, isolated thunderstorms
may drift into surrounding valleys creating variable and gusty
winds. Storms should dissipate by 04-06Z tonight. FEW to SCT above
10 kft through the forecast period. &&

&&

.FIRE WEATHER...Hot conditions expected through the weekend as
strong high pressure sits overhead. Monsoon moisture today will be
mainly limited to Northwest Arizona but will begin to expand
westward Sunday. Next week looks cooler with clouds and thunderstorm
chances each day as the monsoon turns more active across the region.
&&

.HYDROLOGY...Creeks, streams and rivers in northern Inyo County
continue to run high and fast from snow melt. Some road closures
continue in the area. Bishop Creek Bypass and Big Pine Creek Bypass
continue to be utilized to minimize flows through Bishop and Big
Pine. Isolated thunderstorms over the mountains may aid snowmelt
runoff and keep some drainages elevated over the coming days as
well. 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...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

UPDATE...Outler
SHORT TERM/AVIATION...Salmen
LONG TERM...Morgan

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