684 
fxus65 kgjt 231113 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
405 am MST Monday Nov 23 2009 


Short term...today through Tuesday night... 
upper trough has moved over western Colorado early this morning with 
snow developing over the northern half of the forecast area as 
expected. Associated cold front has moved over the western San Juan 
Mountains and is bringing a quick shot of snow there. Snowfall there 
should wind down rather quickly as the frontal zone moves on. 


Models now show a reinforcing impulse bringing the -30c cold core at 
500 mb over northwest Colorado around midday today. This additional 
energy is supported by infrared satellite imagery and will keep activity 
going over our favored northern Colorado mountains through the day. 
Will let present Winter Weather Advisory stand through midnight as 
light orographic snow will continue over the northwest facing slopes 
through this evening. An additional 2 to 6 inches are expected by 
midnight...with most falling early today. Other mountains areas and 
the northern valleys...will continue to see areas of snow mainly 
through the morning before rapidly diminishing this afternoon. 
Temperatures will be cooler today...and much colder tonight as skies 
clear behind this latest storm. 


A drier and weaker northwest flow will dominate through the remainder 
of the short term period as high pressure builds to our west. 
Temperatures on Tuesday will have a hard time warming above monday's 
highs due to a cold morning start. But lows will moderate Tuesday 
night...especially on the slopes as a result of warming aloft. 


Long term...Wednesday through Sunday... 
building high pressure over the western Continental U.S. Will translate across 
Colorado Thursday night...keeping the skies clear Wednesday and 
Thanksgiving day with the exception of the northern Divide. With the 
amplifying ridge...the models hint at orographic flurries from warm 
advective lift along the far northern Divide. Inserted low probability of precipitation for the 
elkheads and park/Gore ranges to account for this. This may be 
overdone but not unusual for this to occur as northwest gradient 
flow briefly strengthens as a closed low digs into the upper Midwest. 


The real forecast question regards the latter half of the Holiday 
weekend. The GFS and ec are beginning to converge to a solution... 
but not good enough to provide any detail for Saturday and Sunday. 
The GFS and ec do show a progressive short wave will move across 
Utah and Colorado Saturday morning. Most lead waves weaken as they 
encounter an amplified ridge...so prefer the ec at this point over 
the wetter GFS. Confidence in the models erodes even further on 
Sunday...both GFS and ec indicate that a closed low circulation will 
form over the Desert Southwest. How this pattern evolves is 
considerably different on each model. Either way the models show a 
change from sunny and dry to more clouds and the threat of weather. 
Low Mountain probability of precipitation are needed for Saturday and Sunday as pieces of 
energy slosh around the four corner states. 


&& 


Aviation... 
occasional MVFR conditions can be expected at mountain airports 
today...but gradual improvement can be expected tonight. Valley 
airports will continue to have VFR conditions...although brief 
periods of MVFR will occur with a passing snow shower. Clearing 
conditions from the northwest can be expected late this afternoon 
and tonight. 


&& 


Gjt watches/warnings/advisories... 


Colorado...Winter Weather Advisory until midnight MST tonight for zones 
4/10/13. 
Utah...none. 


&& 


$$ 


Short term.....Eh 
long term......pf 
aviation.......pf