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Area forecast discussion 
National Weather Service Las Vegas Nevada
810 PM PDT Friday Sep 19 2014

Synopsis...southwest flow ahead of a low pressure system will keep
most of the area dry through tonight. Southeast flow will then pull
moisture back into the area over the weekend leading to a chance of
showers and thunderstorms as the area of low pressure moves through
the region. Dry conditions and above normal temperatures are then
expected through the first half of next week.

Update...a couple lingering minute thunderstorms in extreme
northeastern Mohave County this evening. I updated the forecast to
keep thunderstorms in the forecast for the rest of the evening in
northeastern Mohave County. Clouds were increased there as
well...but reduced everywhere else. I also removed thunderstorms
from the forecast in the Sierra this evening. Southwest flow will
become more southeast overnight...bringing a return of moisture into
Mohave County and southern Nevada. The rest of the forecast is on

Previous discussion...
145 PM PDT Friday Sep 19 2014

Short term /through Sunday night/...
the upper low sitting over the central California coast will control
our weather through the short term period. Currently it is providing
a dry southwest flow across much of the forecast area. Enough
moisture and diurnal destabilization across northern Mohave and
perhaps eastern Lincoln County will provide a chance of isolated
thunderstorms through the afternoon and early evening. The same is
true for the Sierra...being closer to the upper low dynamics. Once
heating wanes so too will any shower/storm.

Expect a dry overnight...the only thing we will be watching is
potentially the return of some smoke to the Owens Valley area during
the early morning hours...similar to this morning. Smoke west and
north of the region may advect into the area once the typical
northwest diurnal winds kick in overnight. Have added patchy smoke
to the forecast for now...but will continue to monitor trends

The upper low will start to lift northeast Saturday with the flow
becoming south/southeast over the forecast area. Moisture /although
not particularly deep/ will be pulled north and west ahead of the
low. The atmosphere will destabilize through the day Saturday...with
lifted indices projected to be around -2 to -4 from Mohave to
Lincoln. Some portions of Clark...Nye...and the Sierra will
destabilize as well. This will lead to isolated to scattered showers
and thunderstorms over much of the area Saturday afternoon with the
best chances over Lincoln and Mohave counties. With the presence of
some dry air...particularly across Lincoln...Nye...and northern
Mohave counties...some of the initial convection Saturday afternoon
could produce stronger wind gusts and perhaps some small hail.

The low will continue a northeast track across California and Nevada
Saturday night and Sunday. Shower and thunderstorm chances will
continue mainly for southern Nevada and northwest drier
air will start working into our California areas...especially by
Sunday afternoon. The low will exit the region by Sunday night with
dry air pushing across the rest of the area...bringing an end to
shower and storm chances.

Being under the influence of this upper low...temperatures will
trend cooler and be close to normal tomorrow and at or slightly
below normal Sunday. Below normal reading are likely for areas that
receive precipitation and/or are under thicker cloud cover.

Long term...went with a blend of the GFS and European model (ecmwf) model solutions
Monday through Wednesday night then trended closer to the GFS for
Thursday and Friday.

Monday through Wednesday...models are in real good agreement with
shortwave ridging over the southwest Monday behind a departing low
lifting through The Rockies. The ridge axis shifts east of the area
Tuesday with increasing southwest flow aloft by middle week in response
to a Pacific trough approaching the West Coast. This pattern will
support a warming trend through middle week...sending temperatures 5-8
degrees above normal by Wednesday. This would put high temperatures in
Vegas either side of 100 degrees. Winds should be generally light
Monday-Tuesday with breezy conditions over the northwest County Warning Area Wednesday.

Thursday and Friday...the GFS/European model (ecmwf) bring shortwave energy to
northern California Thursday morning but then their respective
solutions diverge. The latest GFS remained consistent if not a bit
slower than its previous runs in sending the shortwave off to the
northeast and digging a broad trough down across the area by Friday.
This would result in breezy to windy conditions across the region
Thursday into Thursday night with cooler temperatures areawide and a
slight chance of showers in Mohave County Friday. The 12z European model (ecmwf) had
a progressive solution that would result in less wind and little to
no cooling for County Warning Area. Opted to discount the European model (ecmwf) solution for now
primarily to remain consistent with the inherited forecast but also
because it is offering a new look to the end of the week pattern
evolution that features an anomalous Pacific northwest low...which is, in
part, responsible for the progressiveness of the pattern. Looking at
a couple of degrees cooler Thursday with decreasing heights and
several more degrees of cooling Friday as a slightly cooler airmass
settles into the area.

Aviation...for McCarran...generally clear skies through tonight.
Moisture will increase over the weekend leading to a slight chance
of showers and thunderstorms. Southeast winds 5-10 kts this
afternoon will transition to south/southwest after 04z this evening.
Showers and storms around the area Saturday may produce gusty and
erratic winds through the afternoon and early evening.

For the rest of southern Nevada...northwest Arizona...and southeast
California...isolated thunderstorms possible this afternoon in the
Sierra and eastern Lincoln and northern Mohave counties. Otherwise
mostly clear skies through tonight. Smoke and reduced visibility may
return to the Bishop area overnight...once northwest winds commence.
Moisture will increase over the weekend leading to a slight chance
of showers and thunderstorms. Mostly south winds 10-15 kts this
afternoon becoming light diurnal overnight.

Spotter information statement...
spotter activation is not expected at this time. However....spotters
are encouraged to report any significant weather conditions
according to Standard operating procedures.


short term/aviation...paddock
long term...Salmen

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