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Area forecast discussion 
National Weather Service Las Vegas Nevada 
325 PM PST Friday Nov 21 2008 


Synopsis...a pleasant weekend is in store for the region as 
temperatures remain 5 to 10 degrees above normal. A significant 
pattern change still looks likely during the middle to latter part 
of next week...with a chance for rain and mountain snow showers and 
temperatures falling below normal around Thanksgiving day. 
&& 


Short term...zonal flow will persist over the area through the 
weekend...with little change to heights or winds aloft. This will 
keep day to day change in weather very minimal. Temperatures will be 
several degrees above normal...and cloud coverage limited to high 
thin cirrus...resulting in mostly sunny to partly cloudy skies. On 
Monday...heights will begin to decrease as winds aloft increase in 
advance of the next Pacific storm system...but temperatures will remain 
above normal thanks to increased mixing. By late afternoon...upper 
and middle level clouds will have increased considerably with the 
trough just off the West Coast and moisture advection increasing 
over the area. 


Long term...a very active weather pattern is looking more likely in 
the extended period of the forecast. Although models continue to 
show run to run differences and disagree with timing...the general 
consensus is for two separate systems look to affect the area during 
this time period. 


The first of these two systems looks to affect our weather possibly 
as early as Tuesday afternoon. A longwave trough is prognosticated to move 
towards the West Coast on Monday. The main issues with this feature 
looks to be if a piece of energy can close off in the base of the 
upper trough and what sort of tropical moisture feed this system may 
be able to tap into. If a closed low forms of the socal coast and 
taps a juicy feed of moisture with precipitable waters  up near an inch than we may 
be in for a decent widespread cold season precipitation event across 
our area. Probability of precipitation were bumped up beginning Tuesday afternoon especially 
in the west and then across all areas Tuesday night into Wednesday 
afternoon. Snow levels looks to lower to around 6000 feet by 
Wednesday afternoon...and could lower locally in any convection. 
Temperatures will be below normal. As for winds...there is some 
uncertainty...but the strongest winds would likely be ahead of this 
system on Tuesday afternoon or night in areas that typically favor 
southwest winds like kdag. The European model (ecmwf) forecasts a 120kt+ jetstreak almost 
right across the I-15 corridor then...which if winds align right 
could easily help to mix stronger winds aloft down to the surface. 


Thanksgiving day have maintained slight chance probability of precipitation but we look to 
be in between the two systems then. Still it should be chilly with 
northwest flow prevailing and a good amount of clouds still 
around. 


The next system looks to drop in from the north on Friday. This 
system may initially take a more inland Route before dropping back 
closer to the coast of socal by Saturday afternoon. Due to the 
decent model consistency with this system...bumped up probability of precipitation 
significantly. Although snow levels will be between 5000 and 5500 
feet...this a strong cold upper low and the dynamics of the low 
could generate convection that locally lower snow levels further. 
Marginal instability could also support isolated thunderstorms in our County warning forecast area. 
Temperatures will fall even further with most desert valleys only in the 
50s for highs due the clouds and showers around. 
&& 


Aviation...for McCarran...light southwest winds are expected once 
again this evening and tonight...then winds are expected to become 
variable again around 09z Saturday. Winds may become southeasterly 
around 3-6 kts late Saturday afternoon for a brief time. Few-scattered 
clouds at or above 25k feet. Two separate systems are expected to impact the 
area next week. The first looks to move in as early as Tuesday 
afternoon and last through Wednesday afternoon while the second 
looks to arrive as early as Friday afternoon and last into Saturday. 
Both of these systems will bring the potential for showers...low 
ceilings and local mountain obscurations. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...overall light diurnal winds tonight and tomorrow with 
few-scattered clouds at or above 25k feet. Two separate systems are expected to 
impact the area next week. The first looks to move in as early as 
Tuesday afternoon and last through Wednesday afternoon while the 
second looks to arrive as early as Friday afternoon and last into 
Saturday. Both of these systems will bring the potential for 
showers...low ceilings and local mountain obscurations. 


&& 
Vef watches/warnings/advisories... 
Nevada...none. 
Arizona...none. 
California...none. 
&& 


$$ 


Kennedy/stachelski 


Http://weather.Gov/lasvegas