Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 181756
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
955 AM PST Tue Dec 18 2018

.SYNOPSIS...Fair weather with above normal temperatures can be
expected through the weekend with afternoon highs nearing record
territory on Wednesday. By early next week, the weather pattern
looks to turn cooler and more active, as stronger weather systems
impact the western US.
&&

.UPDATE...Mostly transparent cirrus clouds streaming overhead
today on the front side of the ridge which will move inland and
amplify over the next 48 hours. This will lead to mostly sunny and
relatively mild daytime conditions as mentioned in the previous
discussion and no immediate changes are needed.
&&

.PREV DISCUSSION...225 AM PST

.SHORT TERM...through Friday night.

High pressure will begin to build back over the region today, with
the ridge axis amplifying overhead on Wednesday. The end result
will be gradually warming temperatures, perhaps to near daily
records on Wednesday afternoon. For today, light winds and mostly
sunny skies are expected area wide. Valley inversions will
encourage some light haze across the Vegas valley as pollutants
stay trapped beneath the warm layer aloft.

On Wednesday, surface gradients will tighten a bit in response to
short wave energy sliding into the Central Plains states,
increasing the northerly winds over our region. These winds will
play a big role in how warm temperatures climb Wednesday
afternoon. High resolution model guidance has backed off a notch
on the strength of north winds in the Las Vegas valley, but winds
remain fairly breezy down the Colorado River Valley. As such,
maintained a middle ground forecast high in Las Vegas, topping out
a couple degrees shy of the daily record, but boosted
temperatures by a couple degrees near Laughlin, Needles, and Lake
Havasu where I have greater confidence on stronger mixing being
achieved.

Similar (though perhaps a degree or two cooler) temperatures are
expected Thursday and Friday as the ridge begins to break down and
the flow aloft turns more southwesterly. As this occurs, periods
of high clouds can be expected. In addition, we will need to watch
for the potential of gusty downslope winds in the Sierra as short
wave troughs begin impacting northern California Thursday night
into Friday.

&&

.LONG TERM...Saturday through Tuesday.

The weekend weather should be quiet as dry northwest flow persists
through Monday. Occasional high clouds is likely, though it was
difficult to pinpoint the cloudier vs sunnier periods due to model
differences. It will remain warm, with high temperatures running 10
degrees above average in many locations.

The forecast then becomes much more complicated for next week. Long
range models show a more active pattern with numerous systems
pushing through the mean  cyclonic flow. Some of these systems
become more amplified and dig significant low pressure systems into
the desert southwest, which could bring widespread precipitation,
colder temperatures, and gusty winds to the area. Timing and details
of these stronger, more impactful systems through out next week is
not consistent from model to model or even run to run, so confidence
in the forecast is very low. However, anyone with travel plans for
the holidays should pay close attention the forecast as it could
impact the area during peak travel times around Christmas.

&&

.AVIATION...For McCarran...Light winds at 8kts or less are expected
through Wednesday. Expect typical diurnal wind direction patterns,
with a brief period of light east winds this afternoon.
Occasional high clouds around 25kft are possible.


For the rest of southern Nevada, northwest Arizona and southeast
California...Dry conditions are expected today across the area.
Expect diurnal winds at 10kts or less through tonight.

&&

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

$$

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

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