Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 182105 AAA
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
205 PM PDT Fri Aug 18 2017

.SYNOPSIS....Tranquil weather will continue over most of the region
through Saturday before a circulation along the southern California
Coast begins to pull moisture northward into northwest Arizona,
southern Nevada and southern California Sunday into early next week.
This will lead to a return of showers and thunderstorms to the
region.
&&

.SHORT TERM...through Saturday night

Extensive cumulus field has developed within an E-W deformation zone
draped across northern Inyo County and central Nevada. Like
yesterday, best instability will be west of the southern Sierra
Crest but can not rule out an isolated shower or thunderstorm late
this afternoon/early evening. Similar synoptic setup Saturday with
closed low off the southern California coast. The deformation zone
is progged to shift slightly further north, more along Highway 50
Saturday. Elsewhere, dry and warm with temperatures above normal.

.LONG TERM...Sunday through Thursday.

Continuing to watch the closed low system that will bring active
weather back to the southwestern US. Models still show that first
moisture push starting Sunday. During the day, precip chances should
be confined to Mohave County and possibly southern NV as moisture
slowly streams in. However, as the closed low swings more towards a
positive tilt, winds become more south and moisture will quickly
surge through much of the area. This system will have strong
dynamics associated with it, one of the better synoptic set ups we
have seen this season. An area of diffluence will push northward
into central NV Sunday night and will likely bring a wave of
scattered clouds and precipitation with it. By Monday morning, a
upper level jet will be swing around the base of the low and provide
additional support as the front left quad shifts through southern
NV. There is some disagreement on the strength and timing of the
closed low off the coast of California on Monday, which would
influence the magnitude of the lift and moisture push. Favored a
stronger, higher moisture solutions, which is supported by the NAM12
and GFS (with the ECMWF showing a slower, more broad low...though it
is stronger than yesterdays model runs). Included at least slight
chance of precipitation for much of the area Sunday night into
Monday night. Think the best timing for precip will first be with
the diffluence wave 06z-12Z Monday...and then another round Monday
afternoon with the jet and moisture surge. Increased precipitation
chances in those time periods as confidence sees to be increasing
that there will at least be scattered showers and storms around.
Will likely need to increase precipitation chance more as we get
more closer to Sunday as we are able better pinpoint when and where
the rain will fall. Where the heaviest rain does fall could bring a
flash flood threat as moisture content will be high, though storms
should be fast movers.

This of course spells bad news for the Eclipse. Models continue to
trend with more moisture from 700mb and up, especially over eastern
NV into AZ. Had to increase cloud cover again from previous
forecast...and with showers and storms around likely will have a lot
of debris cloud hanging around by 18Z monday.

After Wednesday, confidence in the forecast decreases. Models show
that low stretching out and riding through the mean flow, then
exiting the region sometime Thursday. There are differing solutions
on how this would occur and how much moisture gets pushed up with
its passage. Does look like we should dry out by the end of the week
though. Made no changes beyond midweek and kept temperatures near
normal.
&&

.AVIATION...For McCarran...A typical east-southeast wind component
can be expected into early evening followed by a light southwest
component overnight. Similar setup expected Saturday with east-
southeast wind component. For the most part wind speeds will remain
at or below 10 knots. VFR conditions can be expected in all approach
corridors.

For the rest of southern Nevada, northwest Arizona and southeast
California...A circulation near Point Conception with mid-level
moisture and instability extending from near Bishop California
across central Nevada will lead to isolated high based showers or
thunderstorms this afternoon and early evening. Cloud bases will
generally be 12-15 Kft MSL. This band of moisture/instability will
shift slight further north Saturday with storms centered within the
Highway 50 corridor across central Nevada. The rest of the region
will be mostly clear with winds generally less than 15 knots.
&&

.FIRE WEATHER...Limited mid level moisture and instability will
lead to a few showers or brief thunderstorms over the southern
Sierra and central Nevada zones today and Saturday. The rest of the
region will see mostly clear skies and generally light winds. A
circulation along the southern California Coast begins to pull
moisture from Arizona into the Mojave Desert and southern Great
Basin starting Sunday. Shower and thunderstorm chances increase
Sunday night - Tuesday due to stronger dynamics associated with the
upper low.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

$$

Short Term/Aviation/Fire Weather...Pierce
Long Term...Allen

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