458 
fxus65 kvef 210043 cca 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
341 PM PST Friday Nov 20 2009 


Synopsis...a cold front will move eastward across the area tonight 
bringing gusty winds to parts of Inyo County California and 
southern Nevada along with a few showers mainly to the higher 
elevations of the Sierra and White Mountains. Drier and slightly 
cooler weather is expected in the wake of this system for 
Saturday. Another system will graze the area with some clouds late 
Sunday. Dry weather accompanied by near to slightly above normal 
high temperatures is expected through Thanksgiving day. 
&& 


Short term...the latest storm system to impact the west has 
become more elongated with the bulk of the moisture and energy 
remaining well north of our area over the Pacific northwest and 
norcal/northern Nevada. However as this system slides eastward 
later tonight it will bring a cold front across our area that 
should be off to the east by later Saturday morning. 


As far as precipitation impacts from this system are 
concerned...the trajectory of this system will result in most of 
the area being rainshadowed. Cross sections show precipitation 
will barely spill over into the eastern Sierra but elevations 
above 10000 feet could see a few inches of snow tonight. Outside 
of that...a few showers may brush the White Mountains and higher 
elevations of Esmeralda County later tonight just ahead of the 
front...but the frontal passage will just be marked by some clouds 
and a wind shift in the rest of the area. 


Wind products presently out were left as is...as they appear to be 
working out. Cross sections from the arw model show that gusty 
winds over the Sierra may make it down into the west side of the 
Owens vally for a brief period this evening...but otherwise 
warning level winds should be felt at the crest and down to middle- 
slope. The lack of an inversion above Ridgetop should be what keeps 
the stronger winds mainly confined to the higher slopes. Elsewhere 
gusty south winds will continue this evening ahead of the front 
and we have kept in areas of blowing sand and dust where 
advisories are out further west due to the dry conditions recently 
across the area. 


For tonight...high resolution models...namely the arw...show a 
potential downslope for the Spring Mountains taking place in a 
narrow window. The nmm model was not as impressive with isentrope 
folding...but still supported advisory level gusts. So a Wind 
Advisory was issued for tonight for the Spring Mountains and the 
far west side of the Las Vegas Valley. See rnonpwvef for details. 


Behind the front...slightly cooler air moves in for tomorrow...but 
high temperatures will still be around normal. Forecast soundings show 
valley inversions setting up and weak mixing...which will limit 
warming. The next system approaches the Pacific northwest Sunday morning and 
dives southeast towards southern Idaho by Sunday night. We favored 
the European model (ecmwf) which looks to have a more consistent handling on this 
system. Thus for Sunday expect some clouds to drift in ahead of 
this...but warming looks limited as mixing is weak and valley 
inversions should have trouble getting wiped out. There will 
likely be an increase in winds by Sunday night mainly across the 
north but no headlines look needed for now. 


Long term...medium range models in good agreement Monday through 
Thanksgiving day. Strong ridge will be over the area Monday through 
Wednesday. Persistent surface high over the northern Great Basin 
will lead to mainly a late morning through afternoon north breeze 
down the Colorado River Valley. Ridge will start to break down 
Thanksgiving day as next trough approaches the northwest coast late 
Thanksgiving afternoon. There are some differences in the depth of 
trough as it moves into the Great Basin Friday. European model (ecmwf) the strongest 
bringing a shortwave across southern Nevada Friday afternoon. As for the GFS 
it brushes the system across northern Nevada. Due to difference have 
kept the forecast dry. Temperatures will be running at or slightly 
above normal all week. 
&& 


Aviation...for McCarran...an area of low pressure will move across 
the northern Great Basin tonight pushing a weak cold front through 
the Las Vegas Valley. Best estimate places the cold front through 
McCarran between 8 am - 10 am Saturday morning. Scattered-broken high clouds 
through Saturday afternoon. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...potential for strong downslope winds will continue 
through 03z this evening...along with a rotor circulation producing 
moderate to severe mechanical turbulence in the Lee of the southern 
Sierra. High clouds will be prevalent across the area...with a 
thicker veil of cloud cover across the north. Strong south-southeast 
winds up the Owens Valley and across Esmeralda and central Nye 
counties will diminish tonight as a cold front pushes southeast 
across the area 
&& 


Vef watches/warnings/advisories... 
Nevada...Wind Advisory from 10 PM this evening to 6 am PST Saturday for 
nvz019 west of Buffalo drive-020. 
Wind Advisory until 10 PM PST this evening for nvz014-017. 
Arizona...none. 
California...High Wind Warning until 10 PM PST this evening for caz519. 
Wind Advisory until 10 PM PST this evening for caz520-521. 
&& 


$$ 


Stachelski/Pierce 


Http://weather.Gov/lasvegas