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Area forecast discussion 
National Weather Service Las Vegas Nevada 
312 am PST Thursday Nov 20 2008 


Synopsis....temperatures will trend slightly cooler today through 
Saturday as a storm system passes by to our north today and another 
on Saturday. A significant pattern change is likely by the middle of 
next week...with temperatures falling closer to normal and the 
chances of rain and mountain snow increasing. 
&& 


Short term...high level moisture is increasing this morning with 
satellite showing significant leeside enhancement across central 
Nevada. High clouds will be more prominent today then thinking of 
the past two days. Model relative humidity forecasts show minor break in the high 
clouds tonight before next area presently enhancing near 30n/130w 
increases from the southwest during the day Friday. Tightly wound 
shortwave off the Oregon coast this morning still prognosticated to weaken 
as it lifts east-northeast into the northern rockies this evening. 
Another set of weak disturbances move through the northwest states 
Saturday while weak southern branch disturbance near the Southern 
California coast keeps some high clouds across the Mojave Desert. 
The combination of high clouds and lower heights will lead to 
slightly cooler temperatures today through Saturday. 


Long term...surprisingly little difference between the 00z GFS and 
European model (ecmwf) solutions throughout the extended term. Both models are 
forecasting similar strength and track of an incoming Pacific storm 
for the middle of next week. Some difference in timing remains with 
the GFS bringing precipitation to the southwestern County Warning Area as early as 
Tuesday afternoon and evening while the European model (ecmwf) is about 12 hours 
slower...remaining dry until Wednesday. Overall confidence in a 
major weather change for the area next week is increasing as models 
reach a consensus. Ramped up probability of precipitation beginning Tuesday night to slight 
chance in most areas increasing to chance on Wednesday. If models 
remain consistent...additional increases will be necessary. There 
could be some decent quantitative precipitation forecast amounts ahead of the storm with an area of 
upper divergence and low level convergence centered over the area. 
In addition...model forecasted precipitable water values of one inch reach into the 
southern regions of the forecast area which would provide sufficient 
moisture. At this time...it is too early to predict amounts. With 
the increased cloud cover and showers...temperatures will likely be 
much cooler than what has occurred recently and could actually be 
below normal for the first time in quite some time. 
&& 


Aviation...for McCarran...light and variable wind conditions under 
6kts expected through Friday. Scattered-broken cirrus at or above 25k feet expected 
by daybreak this morning and continuing through the day. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...generally light diurnal winds less than 10kts through 
Friday. Scattered-broken cirrus at or above 25k feet is expected. 
&& 




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


$$ 


Pierce/Salmen 


Http://weather.Gov/lasvegas