640 
fxus65 kslc 212331 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
430 PM MST Friday Nov 21 2008 


Synopsis...a stalled cold front across southern Utah will weaken 
tonight. Another weak disturbance will move through the northern 
intermountain region on Saturday. This system will bring 
primarily increasing clouds to northern Utah Saturday and Saturday 
night as a weak cold front moves through the area. High pressure 
aloft will return for early next week although unsettled weather my 
return by the middle of the week. 


&& 


Discussion...shortwave ridge moves over the state tonight behind 
upper level trough which moved rapidly into the northern plains this 
afternoon. Under upper level ridge tonight anticipate mostly clear 
skies and terrain driven winds. Another weak shortwave will move 
quickly across the northern intermountain region on Saturday which 
will nudge a cold front and a reinforcing shot of cold air into 
northern Utah on Saturday night. Ahead of this front we should see 
an increase in south winds during the day on Saturday along with 
increasing middle and high clouds. The cold front does not look as if 
it will drop as far south into the state as the front that moved 
through last night. The cold air behind this system is also much 
more moderate with 700 mb temperatures only anticipated to dip to around 
-2c over slc on Saturday night. This system does have some modest 
divergence-q forcing...largely associated with differential vorticity 
advection...but the core of the forcing should remain largely north 
of Utah. System also has limited moisture available to it and at 
this time only anticipate a band of cloud cover...and possibly some 
isolated mountain snow showers in the far north...to accompany the 
middle level baroclinic zone as it drops into the state. 


A strong upper level ridge builds quickly into the state on Sunday 
and 500 mb heights rise to 576 dam by Monday afternoon resulting in a 
couple of of days of relatively quiescent weather. The forecast then 
becomes much messier toward the middle and latter portion of next 
week as significant uncertainty remains with respect to the details 
of an anticipated pattern shift. There has been quite a bit of 
run-to-run variability as well model-to-model variability for the 
transition that appears likely by middle week. The 1200 UTC GFS is 
slower bringing the closed inland in the Tuesday-Wednesday time frame compared 
to majority of GFS ensemble members...while the European model (ecmwf) indicates a 
two part system with the initial wave ejecting faster than the 1200 
UTC GFS solution. Meanwhile the Canadian ensembles are much 
shallower and more progressive with this middle-week system. At this 
time prefer the faster solution of the European model (ecmwf) given the weight of the 
ensemble members and European model (ecmwf) performance. Either way a significant 
pattern change appears imminent. Anticipate that the threat of 
precipitation across the state to substantially increase by Tuesday. 
This trough does not appear to be particularly cold yielding a 
mountain snow and valley rain event for middle week. Will continue 
with well above climatology probability of precipitation across the state in the middle week time 
frame. 


Even less certainty with another system toward the end of the week 
which closes off and drops down the West Coast. The ec quickly 
settles the closed low in Baja California California by Saturday morning while 
the GFS is further north and west off of the central California 
coast. With this system dropping south there is certainly a 
continued chance of precipitation through the end of the week. There 
is also the potential for this storm to dig too far west or south to 
have a significant impact on Utah...particularly the north. 
However...if the storm maintains a more easterly track...it 
appears to have the potential to be much colder possibly bringing 
snow to the valleys of Utah. At this time will continue with above 
climatology probability of precipitation given the insistence on a developing trough but will not 
hit too hard given the significant model spread and uncertainty 
present at this time. 


&& 


Aviation...light northwest winds will continue at kslc terminal 
into early this evening. Southeast drainage winds expected to 
develop around 03 UTC. VFR conditions expected through the overnight 
hours. 




&& 


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


&& 


$$ 


Graham/Myrick 


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