Flash Flood and High Wind in California, January 1 to 2, 2017

Area Forecast Discussion
National Weather Service Las Vegas NV
245 AM PST Sun Jan 1 2017

.SYNOPSIS...A wet storm system will exit to the east along the US-
Mexico border this morning allowing the remaining rain showers to
end. Breezy to windy conditions are expected to develop this evening
through Monday across much of the region with a slight chance of
precipitation over the higher terrain of Lincoln and Mohave counties
and the Sierra early the week. Unsettled weather will continue into
next weekend.
&&

.SHORT TERM...Today through Monday Night.

Impressive rainfall totals have been noted across portions of San
Bernardino County, especially near Barstow where around 1 inch of rain
has fallen. The main area of precipitation will continue to spread
east along and south of the I-40 corridor for the rest of the
morning, with precipitation tapering off by mid-day. One concern
through the next 6-9 hours is snow above 6000 feet in Mohave county,
mainly over the Hualapai Mountains. A quick 3-6 inches of snow is
quite possible there, with perhaps some isolated higher amounts.

The next concern will be winds as we move into this evening. Models
are in good agreement that at least advisory level winds will
develop across the Sierra after 00z. There is less agreement about
advisory level winds elsewhere. But there is a decent chance that
widespread gusts of 35-45mph will develop across portions of San
Bernardino, Clark, and Mohave counties tonight through Monday. The
strongest winds are likely over the ridges and higher terrain of
these areas, with the potential for some downslope winds reaching
the valley floors. As a result have issued wind advisories for much
of the region from 00z Monday through 06z Tuesday.

Lingering moisture and the presence of strong jet aloft will result
in a chance of light precipitation over the higher terrain of
Lincoln and Mohave counties as well as the Sierra through the short
term period. Confidence in timing of any shower activity is very
low, however.

.LONG TERM...Tuesday through Saturday.

Another low confidence forecast for the long term as models continue
to flip-flop and show some significant differences between them.
Tuesday starts out with an elongated west-east oriented trough
across the Pacific Northwest with zonal flow over the forecast area.
The western portion of the trough is still expected to form a closed
low off shore during the day Tuesday, remaining there through
Tuesday night. This leads to ridging over the forecast area.
Although there will be a fair amount of moisture/clouds around,
chances for precipitation Tuesday through Tuesday night should be
rather low and limited to mainly the Sierra and extreme northern
portions of the southern Great Basin, namely northern portions of
Esmeralda and Lincoln Counties and possibly into the northern part
of central Nye County.

The models diverge after that with the EC and GEM opening the low
and progressing it gradually southeastward into the forecast area
Wednesday through Thursday night. The GFS and DGEX keep the low off
shore with somewhat amplified ridging over the forecast area. If the
EC/GEM verify we will see precip chances spread southeast through a
good portion of the forecast area with cooling temperatures. The
GFS/DGEX solutions would lead to warm temperatures and minimal
precipitation chances except maybe the far northern part of the area.
I basically kept what we had which is a compromise with minimal
temperature trends and a chance of precipitation across the southern
Great Basin including northern Mohave County. Friday still looked to
be mainly dry with attention then turning to a potential atmospheric
river event in a long fetch of southwesterly flow. A nice plume of
moisture is aimed at California by the weekend but there are timing
differences in the arrival of the moisture. For now we are
forecasting precipitation chances into mainly just the Sierra
Saturday. For what it is worth, the EC looks much slower than other
models with moisture arrival and appears to be aiming it mainly into
northern and central California. Stay tuned.
&&

.AVIATION...For McCarran...Rain chances have pretty much ended but
cigs 4-5kft will be likely through early this morning with sct lower
clouds. Some light fog will also be around the valley but confidence
in reduced vsby at Mccarran is low. Cigs should rise to 8-10kft
after about 15z with just scattered clouds by 20z-21z. Winds will
remain less than 7 knots through this morning and early afternoon.
Southwest winds 10-20 knots will develop late this afternoon and
continue through tonight and Monday morning. Gusts around 30 knots
will be possible.

For the rest of southern Nevada...northwest Arizona...and southeast
California...A storm system will continue to impact eastern San
Bernardino County and southern Mohave County through early this
morning before moving to the east after 15-17z. This will keep low
CIGs BKN-OVC 020-050 in the forecast for areas from Las Vegas south.
Rain is expected to impact areas primarily along and south of the I-
40 corridor. Clouds will clear late Sunday morning through the
afternoon as the system moves to the east. No significant winds are
expected this morning but southwest winds of 15-25 knots will
develop across the Mojave Desert region this afternoon and evening.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant rain, snow, or wind impacts according to standard
operating procedures.
&&

Short Term...........Wolcott
Long Term/Aviation...Harrison

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