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fxus65 kvef 210542 
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Area forecast discussion 
National Weather Service Las Vegas Nevada 
942 PM PST Thursday Nov 20 2008 


Synopsis....there will be little day to day change in the weather 
through the weekend...with temperatures slightly above normal and 
mostly sunny to partly cloudy skies. A significant pattern change is 
likely by the middle of next week...with temperatures falling to 
below normal and a chance for rain and mountain snow. 
&& 


Update...forecast in good shape and no updates needed this evening. 
&& 


Previous discussion...230 PM PST Thursday Nov 20...short term...zonal flow 
will persist over the area through Saturday...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. 


Long term...models are all in decent agreement on an upper ridge 
building into the western Continental U.S. Sunday afternoon before shifting 
east on Monday. This will result in above normal temperatures once again 
across the area. Increased mixing of the lower levels should result 
in Monday being a tad warmer than Sunday. 


Starting on Tuesday there is significant model divergence. The 12z 
operational GFS and the 18z dgex have a completely different look 
than earlier runs of these models as well as the 12z runs of the 
European model (ecmwf) and the GFS ensembles in that the much talked about storm 
potential is gone on the former two models. Given the European model (ecmwf) has been 
more consistent with the idea of a pattern change and the majority 
of the GFS ensembles also support the European model (ecmwf) solution...the official 
forecast shows a cooler and wetter look for the middle to later part 
of next week. A deep trough and associated closed low is forecast to 
drop towards socal by Tuesday afternoon with upper divergence out 
ahead of it over the Mojave Desert. In addition the upper low looks 
to tap into a surge of juicy tropical moisture out ahead of it with 
forecast precipitable waters  approaching 1 inch. Based on a local study done of 
cold season heavy rains in Las Vegas...such a set-up could result in 
a decent precipitation event for our area should it unfold as the 
European model (ecmwf) shows. Our heaviest precipitation total at McCarran in the 
last year was 0.60 inches on November 30th of 2007. For now...have 
kept with the idea that showers may get into western areas by 
Tuesday afternoon...but the better chance looks to be Wednesday into 
Thursday as this system crosses the area. Snow levels are expected 
to lower to at least 7000 feet in association with this system...but 
could lower locally in heavier convective bursts. Temperatures are also 
expected to finally fall below normal by Wednesday...with highs not 
cracking 60 degrees in Las Vegas for Thanksgiving due to the 
northwest flow...clouds and precipitation. The first system looks to depart 
the area on Thanksgiving Day...Opening the door for possibly a 
second system to move down the West Coast for Friday or Saturday 
bringing the chance for another round of showers and keeping temperatures 
below normal. 
&& 


Aviation...for McCarran...light southwest winds this evening...then 
winds are expected to become variable after 15z Friday. There could 
be a few periods of easterly winds late Friday morning and in the 
afternoon. Broken clouds at or above 25k feet tonight should decrease tomorrow 
to the few range. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...overall light winds are expected across the area 
tonight and tomorrow. Winds will be southwesterly across the 
southern Great Basin tonight then shift to the northwest there 
tomorrow behind a system passing by across northern Nevada tonight. 
Scattered-broken clouds at or above 25k feet tonight are expected to decrease for 
tomorrow and thus just a few high clouds are expected then. 
&& 


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


$$ 


Harrison/Kennedy/stachelski 


Http://weather.Gov/lasvegas