Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 181148

Area Forecast Discussion
National Weather Service Las Vegas NV
348 AM PST Wed Jan 18 2017

.SYNOPSIS...Our brief stretch of dry weather will end this evening
and Thursday as the first in a series of wet storm systems pushes
across the region. This will be quickly followed by a second system
Friday into Saturday and yet another Sunday into Monday. These
storms will bring significant snowfall to the mountains and rain to
the deserts.

.SHORT TERM...Today through Thursday Night.

Shortwave ridging that has brought us clear and dry conditions for
the past couple days will exit to the east today as a sharp trough
pushes in from the west. This will result is rapidly deteriorating
conditions this evening and overnight. Precipitation will begin to
spread across the Sierra late this afternoon and into the desert
regions this evening. This timing is 3-6 hours faster than what was
shown 24 hours ago and this is now reflected in the forecast. This
means the precipitation is expected to reach Clark County sometime
this evening and the Colorado River Valley around midnight. Gave a
slight boost to precipitation amounts due to the prolonged nature of
this system. This resulted in slightly higher snowfall estimates for
the Sierra and Spring Mountains which has prompted an upgrade to
Winter Storm Warnings for both those zones.

* A note about the Winter Storm Warnings/Winter Weather Advisories:
  In an attempt to limit confusion we opted to issue products that
  cover both the first and second system despite a short break
  between systems. We did this instead of having a mix of
  Advisories, Warnings, and Watches for the same zones.

For the desert areas, expect most locations to receive 0.20-0.50
inches of rain, with locally higher amounts possible under heavier
showers and across Mohave County. Please see the winter weather
products for more details about snowfall, snow levels, and timing.
Precipitation is expected to taper off from west to east during the
day Thursday, but again, this will be followed quickly by a second
system Friday.

.LONG TERM...Friday through Tuesday night.

The second storm will begin to impact the area Friday by afternoon.
This trough is progged to have a much better moisture tap, with the
bulk of moisture transport in a southwest to northeast trajectory,
which should help avoid interception by the Sierra for most the
area. The storm has evolved a bit in the models with a perhaps
slightly longer precipitation duration than previously thought, as
the wave widens over the area. With the moisture tap and moisture
trajectory, along with consistent model signals, the heaviest
precipitation will likely occur from the Spring Mountains and Sheep
Range in Clark County eastward into Mohave county. Liquid/equivalent
amounts in these areas are favored to be around either side of a
half-inch for valleys/deserts, with amounts just above an inch for
the mountains and southeast Mohave county. This would yield
significant snows above 5000 ft. The heaviest precipitation will
likely occur over a shorter period Friday evening with perhaps some
embedded convection helping precipitation rates a bit. Snow levels
look to start around 4000 feet in the Southern Great Basin, and
around 5000 feet in southern portions of the area.

Breezy to gusty southerly winds are expected with this system on
Friday with speeds around 20 mph and gusts in the 30s mph; locally
higher gusts are possible. Very windy conditions are expected across
western San Bernardino county early Saturday as the system exits
with gusts on the plus side of 40 mph.

After a brief break on Saturday, the third trough takes aim at the
region for later Sunday through Monday. Quite a few of the details
have yet to be worked out by models, but there is general agreement
it will be a potent and cold system, with a healthy moisture tap,
yielding more chances of decent precipitation along with gusty

.AVIATION...For McCarran...VFR conditions along with light winds
favoring typical diurnal trends are expected through Wednesday. East
winds at 5-10 kts with occasional gusts cannot be ruled out this
afternoon. The next series of storm begins to impact the area
tonight bringing precipitation and CIGs rapidly lowering to around
5k feet between 03z-09z. Precipitation and low CIGs are expected to
persist through much of Thursday before improving. Additional storm
system will impact the region into early next week.

For the rest of southern Nevada...northwest Arizona...and southeast
California...VFR conditions are expected across most of the region
through the day. Precipitation and rapidly lowering CIGs to 5-10k
feet are expected to push west across the region this evening.
Winds of 8-15 kts and gusts 20-25 kts favoring a southerly direction
are expected at most terminals by this afternoon. Precipitation and
low CIGs are expected to persist through much of Thursday before
improving. Additional storm system will impact the region into early
next week.

.SPOTTER INFORMATION STATEMENT...Spotter activation is not expected
today. A series of storm systems will impact the region tonight
through early next week. Spotters are encouraged to report rain and
snow amounts as well as any weather-related impacts/damage.


Short Term/Aviation...Wolcott
Long Term.............Steele

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