Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 140459
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
858 PM PST Wed Dec 13 2017

.SYNOPSIS....Dry and mild weather will continue across the region
through the weekend with above normal temperatures expected. A
cold front will bring breezy to windy conditions to parts of the
area tonight and Thursday with breezy winds possible again on
Saturday.
&&

.UPDATE...Water vapor imagery clearly showed a well defined upper
level trough diving down the Nevada/Utah border, but upstream
surface wind response has not been too impressive so far. The latest
hires models indicate north winds will develop across Lincoln and
Clark counties somewhat in unison with an increasing surface
pressure gradient between 10Z and 15Z Thursday and some valley
locations, including Las Vegas, may not see much wind materialize
until after sunrise. The wind grids were updated through 15Z based
on the latest observed trends and hires models. It still looks like
once the north-northeast wind develops Thursday morning, speeds will
support the Wind Advisory and Red Flag Warning along and near the
Colorado River Valley. No other changes needed. -Adair
&&

.PREV DISCUSSION...
158 PM PST Wed Dec 13 2017

.SHORT TERM...Tonight through Friday Night

Main forecast issues through the end of the week center around winds
and dry air behind a passing cold front Thursday. Models continue to
show the front and associated midlevel shortwave moving through the
area overnight from north to south. A 700mb jet is expected to nudge
in behind the front and should result in increasing winds tonight.
As the sun comes out and we start to mix on Thursday, gusty north
winds can be expected through the day. Bumped up wind speeds from
previous forecast as model guidance and hires models continue to
trend stronger with winds tomorrow. The best mixing will occur as
the low level jet and system are over the SoCal and Colorado River
Valley area Thursday, so continued with current timing and area for
wind advisory and see no need to make any changes to current wind
headlines. As the system exits Thursday night, winds will diminish
in its wake and should be much lighter on Friday.

With the strong winds and extremely dry fuels as reported by local
fire partners in the area, replaced the Fire Weather Watch with a
Red Flag Warning for the Colorado River Valley on Thursday. RH
values may be borderline, however with winds gusting up to 50MPH in
this area and extremely dry and critical fuels, felt the upgrade was
necessary. Critical fire conditions should wane Thursday night as we
lose the strong winds down the River Valley. Kept same timing and
area as the fire weather watch that was previously issued.

Otherwise, quiet weather is expected with continued dry and mild
conditions through the end of the work week. Temperatures will fall
slightly behind the cold front, but will remain above normal across
the area. Clear skies should give way to high clouds overspreading
the area on Friday as a plume of high level moisture pushes into the
West Coast.

.LONG TERM...Saturday through Wednesday.

By Saturday morning the next shortwave will likely be pushing a cold
front south across the region. This feature will bring another round
of gusty winds to the region, most notably across the southern Great
Basin Saturday and down the Colorado River Valley Sunday. Wind
highlights may be needed both days. The front will also bring some
additional cooling to the region with temperatures falling both
Saturday and Sunday (but likely remaining above normal for mid-
December).

Model divergence also becomes an issue over the weekend, with the
ECMWF breaking off a closed low to our west while the GFS keeps the
energy moving east in a more progressive pattern. This doesn`t have
much of an apparent impact Monday/Tuesday next week. However, the
differences result in greater uncertainty by mid-week.
&&

.AVIATION...For McCarran...Light winds and clear skies are expected
through this evening. A cold front will sweep through the valley
between 2 am and 6 am Thursday morning with breezy north winds
developing behind the front which will linger through Thursday. Some
high clouds will accompany the north winds. Winds speeds through
Thursday are expected to be between 12-22 kts.

For the rest of southern Nevada, northwest Arizona and southeast
California...A cold front will move through the region overnight
with gusty north winds developing behind the front. Winds will
generally be in the 12-25 kt range through Thursday afternoon. The
strongest winds will develop down the Colorado River Valley with
gusts around 40 kts. Some enhanced northerly winds are also possible
over eastern Lincoln County where gusts may approach 30 mph. Other
than a few high clouds, skies will remain mostly clear.
&&

.FIRE WEATHER...Dry and locally gusty, north winds will continue
down the Colorado River Valley today before a cold front produces
more widespread stronger north winds tonight through Thursday.
North winds linger through the weekend as a series of weak
disturbances pass across the region. A Fire Weather Watch was
issued for the Colorado River Valley for Thursday due to the
expected strong winds, low humidity and dry conditions.
&&

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

$$

SHORT TERM...Wolf
LONG TERM....Wolcott
AVIATION...Gorelow

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