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fxus65 kgjt 092218 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
318 PM MST Friday Jan 9 2009 


Short term...tonight through Sunday... 


Middle-level trough will continue dropping south across the forecast the 
area for the remainder of today. Secondary surface cold front 
oriented northwest to southeast across Wyoming was becoming stationary...and the 
majority of the quite cold air behind it will stay east of The 
Divide. Batch of clouds and precipitation in south-central Wyoming associated 
with the cold pool and 300 mb deformation zone aloft will also move S 
over our area late today. Clouds tops warming with the feature... 
so expect only light snow amts from it but enough to keep likely 
wording in the forecast for the western Colorado mountains and part of the northwest 
plateau into evening. Upslope north flow into the Uncompahgre Gorge 
area S of Ouray will keep snow there into the evening. Silverton 
avalanche center passed along a report of an estimated 6-8 inches in 
The Gorge as of 100 PM. Will keep current winter highlights in place 
until their normal expiration time of 600 PM /01z/ this evening. 


As the upper trough moves across...models indicate weak 700 mb low 
trying to form over south-central Colorado this evening. The 700 mb 
convergence maximum on the RUC model is located to our east at 00z 
but close enough to bring some light snow to the southwest San Juans 
to Sawatch Range...with a chance of snow for Durango and pagosa this 
evening. With temperatures near or above freezing in snow covered valleys of 
eastern Utah and far western Colorado...could see a bit of fog develop tonight in 
those areas where some melting occurred. 


An upper level ridge builds northward along the West Coast on 
Saturday and stays on Sunday. This will allow energy currently 
moving into SW Canada and the Pacific northwest dip southeastward. Nose of 
upper jet reaches our northern forecast area Sat afternoon...and 
small embedded disturbances combined with west-northwest orographic flow will 
keep a chance of snow around for the northern Colorado mountains this weekend. 


Valley inversions will redevelop tonight and as limited mixing of 
valley air takes hold again this weekend. 


Long term...Sunday night through Friday... 
northwesterly flow aloft will be the dominate feature through next 
week. Weak shortwaves track through the flow along with a couple of 
troughs skirting the northeastern portion of the County Warning Area will increase 
precipitation chances over the northern mountains of western Colorado. The 
far western part of a trough skirts the northeastern portion of 
the County Warning Area Sunday night and exits early Monday. Snow showers will 
increase slightly over the northern mountains and then decrease again 
early Monday. Weak waves continue to move through the flow from 
Monday to Tuesday night. Showers will linger over the northern 
mountains with limited moisture although the latest GFS model 
run indicated more moisture...will have to keep an eye on this 
trend. Next main trough axis skirts the area on Wednesday. Increased 
probability of precipitation for Wednesday over the northern mountains. The western flank of 
the trough exits western Colorado by early Thursday. Temperatures will 
warm through middle week especially middle slopes with valleys having a 
harder time under low level inversions. 


&& 


Aviation... 


IFR to occasionally MVFR conditions in widespread snow will continue 
for most western Colorado mountains until 04z this evening...then gradually 
improve. VFR conditions in eastern Utah. Local to areas of fog expected 
in parts of northwest Colorado and eastern Utah overnight...potentially affecting 
kvel...kgjt...kril...kcny..kmtj. 


&& 


Gjt watches/warnings/advisories... 
Colorado...Winter Weather Advisory remains in effect until 6 PM this 
evening for the northern...central and a portion of the 
northwest San Juan Mountains...zones 4/10/13/18. 
Utah...none. 


$$ 


Short term.....Jad 
long term......as 
aviation.......jad