Area Forecast Discussion
Issued by NWS Las Vegas, NV

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020
FXUS65 KVEF 270234
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
734 PM PDT MON SEP 26 2016

.SYNOPSIS...An unsettled weather pattern will begin developing as
low pressure moves in from the south. Expect scattered shower
chances and increased cloud cover for much of the week. Dryer
conditions are expected over the weekend.
&&

.UPDATE...Most of the forecast area will remain basically clear
tonight but we will see high and some mid clouds increase across the
far southern part of the area. Winds will remain fairly light
tonight across the area. The forecast is in good shape and no
updates are anticipated this evening. -Harrison-
&&

.PREV DISCUSSION...
244 PM PDT MON SEP 262016

.SHORT TERM...through Wednesday Night.

The focus for much of this week continues to be the low that has cut
off from a departing trough and sunk southward around the Baja
Peninsula. This low continues to entrain moisture which is being
pulled up into the Southwest US.

Most mesoscale models bring in a push of moisture from the southeast
this evening. However, without much northward progress by the low,
the atmosphere looks to remain fairly stable through the overnight,
thus only clouds and perhaps even some brief breezes are expected
tonight. The low really begins its northward progression tomorrow.
With continued moisture advection and height falls, at least some
instability is likely to develop, mainly across Mohave county, where
forcing for ascent will also be the best. Cloud cover will likely
inhibit coverage and limit activity to showers with just a few
thunderstorms, however, any reduction in cloud cover will likely
yield an environment favorable of a few more organized
thunderstorms with 20 to 30 knots of easterly shear in central
Mohave county between the easterly jet streak to the north and
southwesterly jet streak to the south. Wind gusts and small hail
would be the main threats under that scenario.

As the low continues its trek up the Colorado River Valley,
moisture, instability, and lift will all expand in coverage over
most of the area. Once again, cloud cover will likely limit
instability and keep most activity as isolated to scattered showers
with a few lightning strikes here and there. Plenty of wildcards
exist that could enhance or inhibit thunderstorm chances. Areas of
clearing could enhance instability, as could any shortwaves rotating
around the low. Tropical Storm Roslyn might be worth watching, as
it could direct more moisture into the low, even without a favorable
track for a gulf surge.


.LONG TERM...Thursday through Sunday Night.

We will continue to deal with a pesky upper level low as well as the
remnant moisture from Tropical Storm Roslyn that will be moving up
the Colorado River Valley on Thursday. PW values increase fairly
substantially on Thursday in the southern half of Mohave County and
southeast portion of San Bernardino County with values increasing
from around one inch to values of 1.5 inches. I have increased PoPs
modestly in those areas on Thursday. The main trough will begin to
move onshore in the Pacific Northwest on Friday and provide drier
westerly flow to the western two thirds of the area, but moisture
and sufficient instability will remain in Lincoln, Clark and Mohave
Counties and continue to provide the chance of showers and
thunderstorms. By Saturday the trough will begin to move into the
Great Basin enabling additional drying. At this point kept a slight
chance of showers in the far eastern portions of Lincoln County and
northern Mohave County on Saturday as models continue to linger
moisture a bit longer. The trough axis will move across the forecast
area on Sunday and Sunday night and will provide a few degrees of
cooling, bringing temperatures back to near their seasonal normals.
&&

.FIRE WEATHER... A low pressure system moving in from the south
will increase moisture for most of the area by the middle of the
week. Shower and thunderstorm chances will initially enter northwest
Arizona Tuesday...overspread the area Wednesday...then decrease as
the area dries out from west to east through the end of the week.
Some easterly breezes remain possible across the far western Mojave
Desert...otherwise expect lighter winds for the rest of the week.
&&

.AVIATION...For McCarran...Northeast gusts could persist until
sunset, then light and variable winds overnight favoring a west or
northwest direction. Tomorrow will bring light winds, increasing
clouds, with dry weather for the Las Vegas Valley but a chance of a
showers and thunderstorms along the Peach Springs corridor.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Generally light winds expected area-wide. Some
exceptions may be across the western Mojave Desert where east
breezes may prevail. Increasing clouds and shower/thunderstorm
chances will enter northwest Arizona tomorrow.
&&

.SPOTTER INFORMATION STATEMENT...Shower and thunderstorm chances
will increase in Mohave County tomorrow, overspread most of the area
Wednesday and begin decreasing the rest of the week. Spotters are
encouraged to report rainfall amounts and any other significant
local weather.
&&

$$

Short Term/Aviation/Fire...Steele
Long Term..................Czyzyk

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