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Area forecast discussion 
National Weather Service Las Vegas Nevada
210 PM PDT Tuesday Jul 7 2015

Synopsis...showers and thunderstorms with locally heavy rainfall
expected this evening across much of the region. Drier conditions
are expected Wednesday before a powerful Pacific system brings
breezy conditions and chances for showers and thunderstorms to
mainly mountain areas north of i40 on Thursday. Cooler conditions
will arrive Thursday as well with temperatures slowly rebounding to
near normal over the weekend.

&&

Short term...today through Thursday night.

Convection has materialized across the higher terrain this afternoon
as anticipated. With a broadly diffluent flow aloft and nearly full
surface heating today...expect things to continue developing through
the evening hours and progress into the lower elevations with time
and along outflow boundaries. Steering flow is a little stronger
today which will help mitigate the flash flood threat slightly but
any training storms or particulary strong downbursts will carry the
risk of flash flooding. Thus...the Flash Flood Watch through the
evening looks good. Slightly stronger shear is present as well
especially across Mohave County...so a pulse severe storm or two
will be possible.

Drier conditions are expected Wednesday as dry stable air pushes in
off the Pacific in advance of an incoming Pacific trough. Some
isolated activity will remain possible across northern Inyo County
which will be in closer proximity to the approaching low and may
benefit from vorticity maxima rotating around the low.

On Thursday the approaching Pacific trough will crash into the West
Coast and push eastward across Nevada by Thursday evening. This is a
rather unusual situation for middle Summer and will bring much cooler
temperatures to the area as well as breezy conditions. More
interestingly...there may be just enough moisture advected northward
to initiate some shower and thunderstorm activity across mainly the
more mountainous terrain of Inyo County and southern Nevada. The
closed low looks to move right over the Sierra on Thursday so I
increased probability of precipitation further for that area. Father east...ive increased
probability of precipitation mainly north of Interstate 40 as the trough moves across the
region Thursday afternoon and evening. Instability will be rather
limited but should be sufficient for mountain convection. In the
lower elevations of southern Nevada and Inyo County...instability
looks marginal and the wind shear may overwhelm weaker
updrafts...but with strong forcing associated with low and the wind
shear in place...a few stronger storms moving into lower terrain
cannot be completely outruled. So slight chances for these areas are
justified.



Long term...Friday through Tuesday (from previous afd).

It appears we will see the first break in the monsoon pattern across
most of our forecast area by Friday as a dry southwest flow develops
behind a short wave trough lifting over the northern intermountain
region. A mean trough is forecast to hold along the West Coast
through early next week which will keep the majority of our forecast
area under a dry southwest flow. The southern Sierra and Esmeralda
County will still see a slight chance of thunderstorms Friday as
some moisture lingers in proximity to the center of the West Coast
trough.

The medium range models indicate the middle level high will become
centered near around New Mexico which will bring southeast to
southerly flow and limited moisture spreading back into northwest
Arizona as early as Sunday. A slight chance of thunderstorms was
added accordingly. This pattern will lead to well below normal
temperatures Friday followed by a gradual climb back to normal
readings through the weekend and early next week.

&&

Aviation...for McCarran...low confidence forecast once again due to
thunderstorm development and their associated outflows. Expect a
general southerly wind at 8-12 kts unless distured by outflows from
nearby thunderstorms. Thunderstorms will be possible at the airfield
through 4z before chances begin to diminish. Thunderstorms may
produce brief heavy rainfall and gusty winds exceeding 30kts. Drier
conditions are expected Wednesday with a breezy southerly winds
expected in the afternoon in the 10-15kt range with gusts to 25kts.

For the rest of southern Nevada...northwest Arizona...and southeast
California...showers and thunderstorms the main concern again this
evening...mainly north of a kbih-keed-kigm line. Gusty surface winds
exceeding 30kts...convective turbulence...and ceilings near 10k feet mean sea level
expected along with locally heavy rain. Rain showers/thunderstorms and rain will diminish
between 3z and 7z. Otherwise expect winds favoring typical diurnal
directional trends. Gusts of 20-25 kts in the afternoon and evening
in the Owens Valley and in and near kdag.

&&

Spotter information statement...spotters are encouraged to report
any significant weather conditions according to Standard operating
procedures.

&&

$$

Short term/aviation...outler
long term...Adair

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