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FXUS65 KVEF 172141
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
140 PM PST Sat Nov 17 2018

.SYNOPSIS...High pressure overhead will lead to continued dry
and seasonable conditions through Tuesday with occasional high
clouds. By midweek, increasing Pacific troughing will bring
precipitation opportunities to the region, especially in the Sierra
and southern Great Basin where high elevation snow will also be
possible.

&&

.SHORT TERM...through Monday night.

It's a tranquil November afternoon across the region with light
winds and just some passing high clouds, along with fairly
seasonable temperatures. As expected, light winds have limited
mixing under the surface inversion, and widespread haze is notable
on webcams in the Las Vegas valley due to trapped pollutants. A very
weak cold front is expected to slide down the backside of the ridge
tonight, shifting our winds northerly for mainly the more north wind
prone locations and along the Colorado River Valley. This may
enhance surface mixing slightly tomorrow, especially down the river,
but winds will stay fairly light in the Vegas valley so improvement
will likely be minimal in the metro area.

Similar conditions are expected Monday, though an increasingly thick
deck of cirrus will overspread the region in advance of a weakening
shortwave approaching the SoCal coast. The lower atmosphere will
remain extremely dry, so no precipitation is expected out of this
disturbance, but it will be a harbinger for a more active weather
pattern in the longer term period. Inversions will remain
problematic on Monday with temperatures slightly cooler than over
the weekend thanks to the added cloud cover.

.LONG TERM...Tuesday through Saturday.

COnfidence is increasing that the weather pattern will become more
active for the second half of next week, with potential impacts to
holiday travel.

The first system is the focus of the long term as a deepening upper
level trough swings ashore the West Coast Wednesday. Models continue
to show a deeper system than yesterday's outputs, with an impressive
300mb jet developing around the base of the trough as it comes
onshore. There will be no short of forcing with this system
Wednesday through Friday, with the strongest forcing currently
expected Wednesday night being shown on most models. However, there
is still a lot of model differences with this system , mainly with
the amount of available moisture and therefore if and how
precipitation will overspread the area. Trends have increased low
level moisture with IVT forecast plots also showing a moisture surge
pushing onshore late Wednesday and Thursday, however QPF forecast
vary significant between the GFS and ECMWF. Given the trend of
increased strength and moisture associated with this system,
increased precipitation chances and QPF from previous forecast. Best
chance for precipitation will be through the Sierras then through
the higher elevations of the Southern Great Basin. Snow is likely in
the higher terrain and this could be the first snow event for higher
elevations in the Sierra. Rain is most likely in non-mountainous
areas. Still quiet a bit of uncertainty with this system, especially
around how widespread and how heavy precipitation will be, and
updates to the current forecast are likely.

After Friday, the models diverge and confidence significantly
decreases. The general pattern will remain unsettled and amplified,
with a few waves moving through at times for the weekend. However
there is too much disagreement between models on the details and
timing at the moment so didnt make significant changes past Friday.
Temperatures should cool off slightly towards the end of the week,
however a significant change in temperatures is not expected.

&&

.AVIATION...For McCarran...Periods of SCT-BKN high clouds can be
expected through the period, with very light winds favoring diurnal
trends. No operationally significant weather is expected through
the remainder of the weekend.

For the rest of southern Nevada, northwest Arizona and southeast
California...Light winds under a veil of SCT-BKN high clouds can be
expected through the period. Only exception will be along the
Colorado River Valley near KIFP and KEED where a renewed round of
north winds are expected Sunday, with gusts up to 20 knots possible.

&&

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

$$

SHORT TERM/AVIATION...Outler
LONG TERM...Wolf

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