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Area forecast discussion 
National Weather Service Las Vegas Nevada 
302 am PST Sat Nov 22 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...satellite shows thin cirrus covering much of the 
County warning forecast area...compliments of the southern stream weakness spinning off the 
Baja California peninsula. Per GFS 300 mb moisture forecasts...the cirrus will 
stick around today before being suppressed to the south tonight as a 
northern stream shortwave trough passes by...and eventually pushed 
away on Sunday as anticyclonic flow develops in the wake of the 
shortwave. The next problem will be the deepening system seen near 
43n 161w early this morning. The models show quite a range of 
solutions with this storm as it digs down off the California coast. 
The NAM swings it into California as an open wave Monday night...and 
then through central Nevada Tuesday. This is much faster than any of 
the other solutions...and is discarded. The GFS depicts a deeper 
more closed off system nearing the California coast early Tuesday 
morning...with a plume of moisture affecting roughly the western 
half of our County warning forecast area by that time. The European model (ecmwf) is similar to the GFS...but 
about 6-12 hours slower. Current forecast leans toward the GFS...and 
breaks out slight chance probability of precipitation over the western half of the County warning forecast area as 
the short term draws to a close early Tuesday morning...but will 
need to monitor run to run trends...as they frequently support the 
slowest solution in this type of pattern. Until the storm reaches 
our area...temperatures will remain above normal for late November. 
Little day to day temperature change is expected today through 
Monday. 


Long term...Tuesday through Friday...the extended period is going 
to be active. Still have differences in model depictions of how 
things will unfold next week and lower confidence comes into the 
picture late next week. Still look for two systems to move through 
the area. 


First system makes its presence felt Tuesday afternoon as a major 
trough approaches the coast. Decent model agreement at the start 
with a low forming in the trough base. European model (ecmwf) is much slower in 
moving the trough/low inland versus the GFS and Gem. Went with the 
slower European model (ecmwf) since downstream ridging will be an impediment. There 
will be a widespread chance of precipitation late Tuesday but the 
best chances come Wednesday and Thursday as the low passes overhead. 
For now there is no evidence for a subtropical fetch of moisture to 
be entrained in the flow ahead of trough/low. It appears the system 
has to mainly work with moisture it brings with it. 


European model (ecmwf) does not really show well the second system sliding into the 
West Coast late Friday while the GFS really emphasizes this one. As 
the weekend progresses the European model (ecmwf) builds a strong ridge off the 
coast. Prefer the GFS solution of a second system on the heels of 
the first as it is a more consistent solution. Again no moisture 
tap expected. However first system brings in colder air and thus 
second one will have lower snow levels as a result. Hard to say this 
far out but thickness forecasts are indicating snow levels down to 4000 
feet in southern Nevada Friday. Further the second system sticks 
around for a while over the Great Basin next weekend and could bring 
some significant snow to the Sierra due to strong dynamics...despite 
a lack of significant moisture being pulled in. 
&& 


Aviation...for McCarran...cloud cover for today and into Sunday 
will be primarily high level cirrus. Winds will be light southwest 
this morning becoming light and variable late morning onwards. 
Sunday the will southeast the same winds. Looking further out Tuesday will 
see the first of two systems impact the area. Wednesday ND Thursday 
will see widespread cloud cover...rain showers in the valley and the 
local mountains obscured by cloud and snow showers. Next Friday and 
into next weekend will see a second system bring another round of 
sub 10kt feet ceiling and wide spread precipitation. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...light diurnal wind pattern today and Sunday with 
primarily high cirrus clouds. Looking further out Tuesday will see 
the first of two systems impact the area. Wednesday ND Thursday will 
see widespread cloud cover...rain showers in the valley locations 
and the mountain areas obscured by cloud and snow showers. Next 
Friday and into next weekend will see a second system bring another 
round of sub 10kt feet ceiling and widespread precipitation. 
&& 


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


$$ 


Morgan/Jacques 


Http://weather.Gov/lasvegas