Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 231713 AAA

Area Forecast Discussion
National Weather Service Las Vegas NV
1010 AM PDT SUN OCT 23 2016

.SYNOPSIS...A Pacific storm system will impact the region today
through Monday. This will bring increased winds and cloudiness as
well as chances for rain and isolated thunderstorms. More tranquil
weather is expected during the middle of next week before another
series of storms takes aim at the region late in the week through
next weekend.

.UPDATE...Quite a bit of virga occurring this morning; with some
light rain probably falling at elevation above 7500 feet. Moisture
continues to stream northward into the area today, lingers through
tonight and Monday before shifting east Monday night. Little
dynamics or forcing out there currently but that is expected to
change tonight as jet nosing into Southern California places much of
southern Nevada and the Mojave Desert under favorable left front
exit region. Most significant change in the update was to cancel the
Red Flag Warning for the Spring Mountains. With light rain starting
to fall do not see relative humidity values lowering below the 15
percent threshold. Having some reservation about the remainder of
the Red Flag Warning for Inyo, Esmeralda and southern and central
Nye Counties due to wind speeds not being met. Will monitor the
situation and make a determination to continue or cancel products
this afternoon.

.SHORT TERM...Today through Monday Night.

Busy short term period coming up as the next Pacific storm is set to
move across the region today through Monday. Dry conditions early
today will quickly give way to increasing moisture and winds by this
afternoon. There will be a few hours of overlap where critical fire
conditions will be possible across southern Nevada and southeast
California (see FIRE WEATHER for more detail). The Wind Advisory in
place for Inyo, Esmeralda, and portions of Nye county still looks
good with wind gusts of 35-45 MPH likely by this afternoon.

The bigger story remains the moisture and precipitation potential
associated with this system. Models have come into slightly better
agreement on the placement of the precipitation bands, but it`s
still not quite as good as would be expected for such a short lead
time. In any case, have made numerous adjustments to the forecast to
account for the latest guidance.

Satellite imagery shows increasing mid and upper level moisture
beginning to stream across San Bernardino early this morning. Dry
low levels and relatively weak dynamic support during the day will
likely result in gradually lowering cloud bases as well as quite a
bit of virga before precipitation eventually starts reaching the
ground. These virga showers will need to be monitored for gusty
winds as multiple high-res models indicate outflow winds emanating
from San Bernardino and Inyo counties.

One or more slow moving precipitation bands (it looks like at least
two) are likely to develop by late this afternoon or evening. Given
the slowness of the eastward movement of these bands as well as the
increasing dynamic support associated with the left exit region of a
jet streak, the lower levels should moisten enough to have steady
rain at the surface by early Monday morning. The best chances for
rain should center around a line extending from Palm Springs, CA to
Caliente, NV through Monday morning, likely impacting the Monday
morning commute in Las Vegas.

By mid-day Monday, precipitation is likely to become more scattered
and convective as weak instability develops. Isolated thunderstorms
will be possible, with gusty winds, hail, and lightning all
possible. This period will also bring the highest potential for
showers to the Sierra, falling as snow above 10k feet. Precipitation
will diminish from west to east Monday afternoon through Monday

.LONG TERM...Tuesday through Saturday.

Frustrating low confidence forecast continues. There is at least
model to model and run to run consistency in the Tuesday-Wednesday
period. The wave which affected the region during the short term
will be departing to the east Tuesday morning, with precip chances
coming to an end around that time. Ridging then builds over western
Mexico on Wednesday, with higher heights over our area keeping
things dry and pushing temps about 5-10 degrees above normal. For
Thursday, models this morning look more like they did two days ago
than yesterday, showing low pressure somewhere off the California
coast by the afternoon with precip chances just beginning to spread
into the far western fringes of our CWA. Thereafter, the models
diverge quite a bit, and felt the best choice was to make no changes
from Thursday night onward.

.FIRE WEATHER...Cancelled the Red Flag Warning for the Spring
Mountains as believe relative humidity values will not lower below
the required 15 percent threshold. Have some reservation but Red
Flag conditions appear more likely across Nye and Inyo counties,
with winds gusting 35-45 MPH by this afternoon. The rest of the area
will see breezy conditions with increasing moisture as a storm
system moves in. Chances for rain will spread across much of the
region late today through Monday. Drier conditions will return
during the middle of the week, with unsettled weather returning late
this week and next weekend.

.AVIATION...For McCarran...The next Pacific storm system will begin
to impact the region today. Light winds should continue through much
of the day today before eventually turning to the south-southwest
between 22z-00z and increasing. There is a slight chance that
showers could generate gusty/erratic winds before that time. Have
included VCSH in the TAF after 23z today. However, the best chance
for showers won`t arrive until early Monday morning and continuing
off and on through Monday evening. CIGS will lower to 10-12kft by
this evening, and could drop to around 8kft with shower activity.
Mountain obscurations will be possible this evening through Monday.
Confidence in winds and precipitation is below average.

For the rest of southern Nevada...northwest Arizona...and southeast
California...The next Pacific storm system will begin to impact the
region today. This will bring breezy south-southwest winds today,
with the strongest gusts (30-40kts) across Inyo, Esmeralda, and Nye
counties. Elsewhere expect gusts 15-30kts, especially near shower
activity. Showers will be spreading northeast across the region
today with one or more bands of precipitation forming by this
evening. The most widespread precipitation is expected Monday
morning. Isolated to scattered thunderstorms will be possible by
Monday afternoon. CIGS will drop to 10-15kft as this storm system
moves through and as low as 6-10kft near stronger precipitation.
Mountain obscurations will be possible this evening through Monday.
Confidence in winds and precipitation is below average.

.SPOTTER INFORMATION STATEMENT...Chances for rain and perhaps
isolated storms will increase on Sunday and Monday. Spotters should
report significant weather according to standard operating



Short Term/Fire/Aviation...Wolcott
Long Term..................Morgan

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