875 
fxus65 kslc 231122 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
420 am MST sun Nov 23 2008 


Synopsis...a weak cold front will drift south across northern Utah 
today. Strong high pressure aloft will return to the interior west 
for early next week. A cool and moist upper level trough will follow 
for Wednesday through Thanksgiving day. 


&& 


Discussion...shortwave currently over western Wyoming will push a weak 
cold front south across the northern half of Utah today. Only threat of 
any light precipitation will remain behind the front this morning near the 
middle-level cold pool near the Idaho border through SW Wyoming. Strong 
high pressure aloft will bounce back beginning late today. This 
ridge will remain centered across the Great Basin through Monday 
night. 


Elongated trough axis currently along 145w will see the southern end of 
the trough close off near 35/130 early Monday...and then remain off 
the California coast through at least Tuesday evening. The European model (ecmwf) and GFS 
have been consistent for several runs now developing the closed low 
Monday. The difference that did exist with the GFS pressing this 
feature east much faster than the European model (ecmwf) has all but disappeared in 
the latest runs of the models. Both models now take this low east 
through Arizona Thursday...with the European model (ecmwf) a bit further north with the 
center closer to the Utah/Arizona border. 


Moisture will begin to increase across the basin ahead of the upper 
low late Tuesday. The initial surge of moisture does not look all 
that productive as thermal advection and dynamic lift weak at best 
late in the day. Have introduced some precipitation over the higher terrain 
with snow levels still quite high into Tuesday evening. The areal 
coverage and intensity of precipitation will increase as the low tracks 
closer to the area. Clearly the more northern track of the European model (ecmwf) offers 
up much higher qpfs and the attendant snow at the high elevations. 
The peak precipitation period looks to be Wednesday night through at least 
the daytime hours on Thanksgiving. Near 700mb temperatures suggests snow 
levels will remain relatively high...though the more intense precipitation 
across southern Utah could drive snows down to the valleys during the 
overnight hours. 


Northern Utah will see fairly widespread precipitation as the low passes to the 
east through Arizona. Significantly weaker dynamic lift will keep qpfs on 
the lower side with only modest snow accumulations at the higher 
elevations. One caveat would be if the upper low maintains a tighter 
circulation as it moves into northwest Arizona. If this comes to pass...then the 
potential for an heavy wrap around precipitation band developing over the 
north becomes a real possibility Wednesday night/early Thursday. 


Still no real agreement between the medium range guidance on the 
evolution of the pattern next weekend. The latest GFS still holding 
on to the idea of a deep closed low forming over the far western Great 
Basin then dropping south-southwest off the Southern California coast late Saturday. The 
result blocking pattern along the coast will bring an end to most 
precipitation by Sunday...with colder temperatures settling into the area. The 
European model (ecmwf) solution of bulging the eastern Pacific Ridge inland leaves Utah 
under a long northerly fetch through the weekend. This pattern will 
leave the basin open to the possibility of very cold Canadian air 
dropping into the area early the following week. Very hard to pick 
which model has the best chance right now...though both suggest that 
the threat of widespread substantial precipitation has decreased from what 
earlier model runs would have indicated. Will not make any notable 
changes to the previous extended forecast in the morning package. 


&& 


Aviation...a weak cold front moved across the slc terminal 
overnight. Light and variable winds are expected to become 
predominately north to northwest between 16-18z this morning. There 
is a 10 percent chance winds will shift as early as 15z. 


&& 


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


&& 


$$ 


Public...Conger 
aviation...Kruse 


For more information from National oceanic and atmospheric administration/S National Weather Service visit... 
http://weather.Gov/saltlakecity (all lower case)