Winter Storm Watch 1, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
918 AM PST Wed Feb 15 2017

.SYNOPSIS...Mainly dry conditions with above normal temperatures
can be expected through Thursday. A Pacific storm approaching
California Thursday will result in an increase in southerly winds
with light snow likely developing in the Sierra during the
afternoon. This storm will weaken as it moves across the area
Thursday night but a stronger system will bring valley rain and
mountain snow to the region Friday through Sunday.
&&

.UPDATE...High, dry and warm today under ridge aloft. Some high
clouds presently over the western zones will gradually spread
southeast. Time heights indicate more substantial layer of high
level moisture tonight with some mid level moisture working in
Thursday morning. The north wind around Laughlin/Bullhead City will
weaken during the day with little wind expected elsewhere. No update
necessary as forecast look good.
&&

.PREV DISCUSSION...248 AM PST Wed Feb 15 2017
.SHORT TERM...through Thursday night.

High pressure over the area today with clear skies and light winds.
The ridge axis will shift east a bit tonight as a shortwave trough
approaches the California coast. The bulk of the moisture associated
with this feature will remain west of the Sierra but increasing high
clouds can be expected across the western half of the CWA. The
shortwave trough will move into California Thursday with
precipitation moving into the east side of the Sierra with a slight
chance of precipitation spilling over into the Owens Valley and
White Mountains. Many areas will be seeing an increase in south to
southwest winds Thursday afternoon with the strongest winds along
the Sierra where we will have to keep an eye on the potential for
strong downslope winds. At this time it looks like winds will remain
below high wind warning levels there. Nye County also looks to
become windy but probably below advisory levels. This shortwave
trough will weaken substantially Thursday night with minimal
precipitation across the CWA but all models do show some spotty
precipitation here and there with little agreement in exact
placement. For now I kept slight chance pops Thursday night across
the southern Great Basin and mainly western portions of Inyo and San
Bernardino Counties. Temperatures today and Thursday will be running
5 to 8 degrees above normal.

.LONG TERM...Friday through Tuesday.

Active weather still on tap through the weekend, although some model
discrepancies persist.  Tonight the models still seem to agree on a
more southerly track with the storm system moving through the region
Friday into Saturday, however, both the GFS and ECMWF now keep the
closed system move elongated from north to south.  This orientation
would bode more favorable for keeping our forecast area wet and
active, than if all the energy dug south as was previously
advertised. With the more elongated orientation, we maintain
stronger divergence aloft and more favorable dynamics to maintain a
band of moderate precipitation wrapping around the north side of the
closed system on Saturday.   Unfortunately, tough to have a lot of
confidence in the forecast details as the models are still
inconsistent, but the trend tonight seems to favor a wetter outlook
than it was appearing last night.   As such, Ive maintained fairly
high POPs through the Friday and Saturday period, with the highest
chances across Inyo and San Bernardino counties.  Precipitation
could potentially be significant across Inyo county where as much of
an inch of rain could fall by Saturday afternoon in parts of Death
Valley. If this continues to look possible, a flood watch may be
required down the road.   Precipitation in the Las Vegas valley and
points east and north will be more dependent on the details of the
storm system, but 0.25-0.75" of  will be possible in the lower
elevations and deserts through Saturday evening.

Snow levels will be fairly high in general but should hover around
6,000 feet in the Spring Mountains and Sierra where 1-2 feet of snow
will be possible above that level. Winter highlights will likely be
coming in the next shift or two. With fairly heavy precipitation
rates possible at times, will need to be mindful of wet bulb cooling
potential and the possibility of locally lower snow levels,
especially across Inyo county.

Sunday onward, weak ridging will try building in allowing for a
gradual drying trend but with the Pacific jet still aimed at
California, periods of precipitation will remain possible especially
north of I-15.  Breezy conditions with periods of cloud cover can be
expected as well.
&&

.AVIATION...For McCarran...Typical diurnal wind pattern expected
through Thursday morning. We will likely see an increase in
southwest winds Thursday afternoon. Clear skies today will be
followed by mid/high clouds tonight and Thursday.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Typical diurnal wind patterns expected through Thursday
morning. Most areas will see increasing southerly winds Thursday
afternoon with gusts 25-35 knots in many areas. VFR conditions
areawide through tonight. Snow and lower clouds are expected in the
Sierra Thursday afternoon.
&&

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

Update...Pierce

Short Term/Aviation...Harrison
Long Term...Outler

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