Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 210446 AAA

Area Forecast Discussion
National Weather Service Las Vegas NV
845 PM PST Tue Nov 20 2018

.SYNOPSIS...An incoming Pacific low pressure system will bring
snow to the Sierra beginning Wednesday afternoon and a chance for
light showers over much of the region on Thanksgiving Day. Dry
conditions will return Friday, but gusty north winds will likely
develop over most of the area Saturday. Slightly cooler temperatures
can be expected Sunday.

.UPDATE...Cloudiness that lingered across the region most of the day
associated with weak trough passing to our south has dissipated.
Now, satellite showing some high clouds preceding the next trough
coming across the southern Sierra. Cold air associated with the
upstream trough clearly evident west of northern California this
evening. Precipitable water plume currently is aligned more parallel
to the West Coast. Models indicate PW plume will lose most of its
punch as it try`s to penetrate inland Wednesday night and Thursday.
Southern Sierra stand in the way while the GFS does show some higher
PW values sneaking around to the south into the Mojave Desert
Thursday morning. Will continue with our Winter Storm Watch for now
as 00z models continue the trend indicating less spillover onto the
eastern Sierra Slopes Wednesday nigh. Once east of the Sierra, the
Spring Mountains and Lincoln County should receive a quick shot of
rain/snow Thanksgiving morning before the trough quickly races east.
Chances in the valleys will be less numerous. No update needed for
the rest of tonight or Wednesday.

.PREV DISCUSSION...223 PM PST Tue Nov 20 2018
.DISCUSSION...Previous forecast looks largely on track and made only
minor changes. Low pressure spinning near 38N 137W this afternoon
will eject a shortwave trough which comes into CA Wednesday evening,
bringing precip chances into the Sierra beginning Wednesday
afternoon or evening. Models have trended slower with the precip
onset, continuing a trend that has been going on for a couple of
days already, so backed off precip chances for the afternoon and
focused more on the evening and overnight. Still not too confident
in how much snow will accumulate on the eastern slopes, as the best
window for significant precip looks like it will last less than 12
hours, so left the Winter Storm Watch in place for now. The trough
axis swings through Thanksgiving morning, leading to a "high PoP low
QPF" forecast for the southern Great Basin, and lesser precip
chances farther south. If Las Vegas proper gets any rain at all, it
would likely be just a few hundredths of an inch. Precip chances
should end areawide by Thursday evening, by which time an
atmospheric river will be setting its sights on Northern California.
Models have continued their trend from yesterday of keeping the main
effects of this feature north of our area, so expecting PoPs to be
confined to the Sierra Friday morning through Friday night, with
slight chance PoPs in northern Lincoln and northern Mohave counties
Saturday morning as the trough axis swings through. This trough will
drag a cold front through the region, bringing gusty north winds
Saturday into Sunday, with the strongest winds down the Colorado
River Valley. Temperatures will only come down a few degrees since
the airmass will be of maritime origin. Dry weather areawide is
likely Saturday night through Tuesday, although a few ensemble
perturbations bring in another storm system during the period. Will
keep an eye on it.

.AVIATION...For McCarran...Light winds generally under 6 knots
favoring typical diurnal trends are expected through Wednesday.
Ceilings will be AOA 20k feet before clearing out overnight. Clouds
will begin to increase again late Wednesday.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds favoring typical diurnal trends at most TAF
sites with the exception of KIFP and KEED where north winds up to 10-
15 mph are expected through the forecast period. KIFP can expect
gusts as high as 25 mph at times. Clouds will clear out overnight
and increase again on Wednesday.

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




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