894 
fxus65 kgjt 081048 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
348 am MST Thursday Jan 8 2009 


..another winter weather system to affect the northern and 
portions of the central mountains... 


Short term...today through Friday night... 


Currently northern and central valleys running about 5-10 degrees 
cooler than last night at the same time under clear skies. While the 
southern valleys are a little warmer. 


High pressure over the region this morning gets flattened by this 
afternoon as short wave energy drops into the northern Great Basin. 
Other than increasing high clouds this afternoon little in the way of 
significant weather other than high temperatures remain problematic. Grand 
Valley one of the exceptions as it did not mix out yesterday...and 
with temperatures running cooler tonight undercut guidance again today. 


A surface cold front will work its way into the region from the 
northwest tonight preceding the upper level trough. Looks like it 
will make it through the northwestern zones by midnight...then punch through 
the remainder of the County Warning Area by sunrise Friday. Peak forcing looks like 
it will occur between 06z tonight and midday Friday. Overall 
dynamics and moisture moderate at best. Some jet support as we are 
under the right entrance region of 80kt jet...also some Omega and 
q-g forcing. Orographic component also a player. Trough passage is 
expected Friday with continued instability. Temperatures start out 
fairly mild but drop quickly after frontal passage with more 
favorable snow production characteristics. Generally expect 6-12 
inches over the northern and portions of the central mountains ending 
Friday evening. A few snow showers will linger over the northern mountains 
Friday night in upslope nwrly flow...otherwise precipitation will generally 
be over with cooling nighttime temperatures. 


Long term...Saturday through Wednesday... 
high pressure will build over the area Saturday under dry northwest 
flow. Northwest flow is prognosticated to remain over the forecast area the 
remainder of the period with weak waves and enough moisture present 
to potentially bring occasional light snow to orographically favored 
mountains across western Colorado mainly near the Continental Divide. 
Otherwise...mainly dry conditions expected with no major storm 
systems expected through the period. Valley inversions will reform 
over the weekend making the temperature forecast a bit of a 
challenge. 


&& 


Aviation... 
areas of haze and fog in some valleys will produce local MVFR visibility 
this morning. Otherwise VFR to prevail today. Areas of MVFR to 
local IFR ceilings and visibility to develop between 01z and 06z in snow this 
evening generally north of Interstate 70 ahead of a cold front. As 
the cold front pushes into the area...widespread MVFR and IFR 
expected to develop from 06z to 12z tonight over the mountains north 
of a line from kguc to kgjt...and north of Interstate 70 in eastern 
Utah. Cold front will reach kvel near 06z tonight...and extend from 
near The Four Corners to kgjt to ksbs by 12z Friday. 


&& 


Gjt watches/warnings/advisories... 
Colorado...Winter Weather Advisory for the northern mountains and the 
central mountains zones 4...10 and 13 from midnight tonight until 
6 PM Friday. 
Utah...none. 


$$ 




Short term.....Mc 
long term......tal 
aviation.......tal