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Area forecast discussion 
National Weather Service Las Vegas Nevada
859 PM PDT Wednesday Aug 20 2014

Synopsis...a low pressure system over Southern California will move
toward Arizona leading to increasing thunderstorm coverage over
southeast California...southern Nevada and northwest Arizona
Thursday. Lingering storms may continue over northwest Arizona early
in the weekend then dry conditions and near normal temperatures can
be expected across the entire region through the middle of next week.

no changes needed to the overnight forecast at this time. Shower and
thunderstorm areal coverage has greatly diminished this evening. We
are keeping an eye on the convection across La Paz County and a few
isolated weak cells that continue to develop in Mohave County. The
dynamics of the upper low over southwestern California will keep a
chance of isolated showers and storms in the forecast tonight across
eastern San Bernardino...Clark...and Mohave counties. We can see via
satellite data that the socal upper low is now tapping into some middle
and high level moisture from Tropical Storm Lowell. Expect at least
some increasing clouds across our eastern County Warning Area. Still not seeing a
surge of low level moisture for a widespread flash flood threat
tomorrow...but will continue to monitor trends overnight.

Previous discussion...
350 PM PDT Wednesday Aug 20 2014

Short term...through Thursday night...the upper low along the
Southern California coast was likely aiding persistent thunderstorm
development over central Clark County and Mohave counties. Even
though dewpoints had dropped into the 40s...convection was firing
quite easily along fairly discrete lines. This activity will
continue into the evening then gradually diminish but probably not
end altogether overnight as the upper low continues to spin along
the coast. As it moves inland Thursday...much of the area from Clark
County southward will be in the favorable diffluent northeast
quadrant of the system and scattered thunderstorms can be expected.
Some middle and high level moisture from Tropical Storm Lowell will get
wrapped up into the system and may limit sunshine somewhat Thursday.
There is no indication of a deep infusion of moisture from the south
so precipitable water values are indicated to remain around 1.0-1.25
inches over the southern half of the region. This is generally a
little low for a widespread flash flood concern. Also...high res
models do not indicate excessive quantitative precipitation forecast values and coverage so
confidence is not high enough to hoist a Flash Flood Watch.
However...Thursday should be an active thunderstorm day. Convection
will diminish Thursday night as the low center pulls away to the

Long term...Friday through Tuesday...made minimal changes to the
overall forecast. The closed low off the Southern California coast
will lift northeast into Arizona Thursday night into Friday. Dry
westerly winds on the back side of the low should help to clear the
moisture out of a majority of the area. However...the added dynamics
associated with this low and some lingering moisture across the
eastern zones will allow for isolated thunderstorms to develop
mainly in Mohave and eastern Lincoln counties on Friday. This low
will merge with a deeper middle/upper level trough that is prognosticated to
drop into the intermountain west Friday night into Saturday. Winds
begin to ramp up across the western County Warning Area Friday afternoon with gusts
of 25-35 miles per hour possible in some of the favored locations.

Would not be out of the question to have a few isolated
showers/thunderstorms form over far northern Lincoln County Saturday
due to the proximity to the base of the trough and the possibility
of a weak cold front moving through the area. By Sunday drier air on
the back side of the low begins to spread into the entire County Warning Area and
will clear out any lingering moisture. Temperatures should warm a
degree or two each day from Friday through Sunday with near normal
temperatures returning early next week.

Aviation...for McCarran...isolated thunderstorms can be expected
around southern Nevada including the in the Mormon Mesa and Peach
Springs corridors through early evening. Winds will be gusty and
erratic through early evening due to storms then should become light
southerly overnight. Thunderstorm coverage will be more extensive
Thursday as a low pressure system moves inland from Southern
California. This will produce gusty and erratic winds through
Thursday evening.

For the rest of southern Nevada...northwest Arizona...and southeast
California...isolated/scattered showers and thunderstorm will affect
areas roughly east of a line from Barstow to Hiko through this
evening. Winds will favor a south-southwest direction but would
become gusty and erratic in direction due to nearby showers or
thunderstorms. Thunderstorm coverage will increase across the entire
Mohave desert region Thursday from Clark County Nevada southward.

Spotter information statement...spotters should report instances of
flash flooding...strong gusty winds...hail...and blowing dust
through Wednesday.


short term/aviation...Adair
long term...stumpf

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