262 
fxus65 kslc 221137 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
435 am MST Sat Nov 22 2008 


Synopsis...a weak cold front will sweep across northern Utah 
tonight through early Sunday. High pressure aloft will return to the 
interior west early next week...followed by a cool and moist upper 
level trough for late Wednesday through Thanksgiving day. 


&& 


Discussion...shortwave just now reaching the Pacific northwest coast will 
move east through the northern rockies/northern Great Basin tonight. This 
feature may have a little better chance of generating precipitation along 
and behind the surface front late tonight/early Sunday. Slight 
amplification of the West Coast shortwave ridge indicated in the 
guidance would dig the shortwave trough more to the southeast as it moves 
through the area tonight. Increased dynamic lift to go along with 
the surface boundary and colder middle-level air could lead to some 
light precipitation over the far northern zones in the Post-frontal environment. 


The upcoming long Holiday weekend looks to be rather sloppy as a 
pattern changes takes place across the interior west. The leading 
feature to initiate the change remains embedded in the central Pacific 
westerlies near 160w. The latest GFS and European model (ecmwf) model runs continue 
to show this feature digging hard to the southeast and closing off near 
130w by Monday. The GFS remains the faster of the two models in 
pushing this low east to the coast...though The Gap between the two 
has closed a bit the past couple of runs. In any event...both models 
bring a broad upper trough to the Great Basin midweek. 


The best period for precipitation with this first trough looks to be 
Wednesday night through Thursday...with an earlier onset in the GFS 
model solution. At this point it looks like the focus for the 
heaviest precipitation will be over SW through central Utah. The best dynamic 
lift will rotate through the trough over those areas with plenty of 
moisture and cold air aloft to generate substantial precipitation. Mountain 
locations will be all snow...but valley locations will be somewhere 
between rain and snow as near 700mb temperatures are dancing close to what 
would be a rain/snow changeover. For now it looks like the p-type 
will be primarily rain in valleys through Wednesday night...with a 
gradual changeover to snow...especially in areas of intense precipitation. 
Northern Utah will also see fairly widespread precipitation...though at this 
time not looking for anything exceptional as dynamic forcing may be 
a bit less than over the southern half of the state. 


The models still do not have a good handle on the situation for the 
end of the Holiday weekend. The latest GFS continues with the idea 
of driving shortwave energy cresting the eastern Pacific Ridge southward 
through Nevada and closing off a deep low over Southern California for Friday night 
through early Saturday. From there the low drifts SW and ends up 
producing a blocking pattern along the coast late in the weekend. 
The European model (ecmwf) in contrast has thrown what looks like an outlier into the 
mix by driving the same shortwave as the GFS due south through western 
Utah Saturday...then eventually closing off this feature somewhere 
over central Mexico. Little confidence right now as to which solution 
to follow based on run-to-run consistency issues. Base Don trends in 
the guidance the past couple of days...the feeling right now is that 
a major precipitation event this coming weekend is less likely...and if it 
does find a way to develop it will be confined to the SW quarter of 
the state. 


&& 


Aviation...VFR conditions are expected overnight at the slc 
terminal. Southeast drainage winds will prevail...but may be light 
and variable at times through the morning hours. Southeast winds 
should shift to the northwest between 19z and 21z. 


&& 


Slc watches/warnings/advisories... 
Utah...none. 
Wyoming...none. 


&& 


$$ 


Public...Conger 
aviation...Kruse 


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