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afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
258 PM MST Thursday Nov 20 2008 


Short term...tonight through Saturday... 


Middle and high level cloud shield was moving east across the forecast 
area this afternoon and is associated with a shortwave passing to 
our north. Back edge of clouds rapidly moving int northwest Utah early this 
afternoon and should reach western Colorado this evening...so expect clearing 
trend for tonight with temperatures not that different from previous 
nights. 


Next shortwave currently entering Oregon will slide across Wyoming on 
Friday as clouds overspread mainly NE Utah/northwest Colorado. Associated weak cold 
front will reach NE Utah Friday morning...and move into northwest Colorado early Friday 
afternoon but will stay north of the book cliff and I-70. Moisture 
mainly in the middle and upper levels so little threat of any 
significant precipitation is anticipated Friday...maybe a flurry for the 
northernmost mountains clearing skies Friday night...then some more high 
clouds Sat as Pacific moisture streams in ahead of the next shortwave. 
Could be a bit breezy along the I-70 corridor and points north Friday 
and Sat as these disturbances pass. 


Long term...Saturday night through Thursday... 
model consistency continues to be fairly good through about 
Tuesday...then confidence falls as the GFS solutions continue 
to bounce around. 


At the beginning of the period a shortwave trough will move across 
the northern rockies. Energy will remain largely to our north as this 
impulse proceeds east by early Sunday. Expect we will see an increase 
in clouds/winds and a decrease in temperatures....mainly over the north. But 
any precipitation will stay well north of our forecast area. Strong ridging 
follows early in the week. This will result in a warming trend and 
continued dry conditions. 


As mentioned above...model consistency begins to falter by Wednesday. The 
European model (ecmwf) has shown much better run-to-run consistency...and the 00z GFS 
and the 12z GFS ensemble also is in fair agreement with the ec 
solution. So will generally follow the ec as it splits the Pacific 
energy with a low pressure center moving over the southwest during 
the Wednesday/Wednesday night time frame. This will be our next weather maker 
with mountain snow possible beginning Wednesday night into Thanksgiving day 
as shortwave energy ejects out of the Great Basin. Did up probability of precipitation a 
little on Thanksgiving with the southern portion favored...but still 
kept them on the low side due to the uncertainty. Temperatures will 
decrease...mainly due to clouds and any precipitation...but the moist 
southwest flow will keep them moderate through Thursday. As a note... 
the 12z GFS does not split the main trough but takes it across the 
north. This solution is very similar to the present pattern...but 
with a stronger trough. Due to the similarities to what we have been 
seeing...and will see with this weekend's shortwave...this solution 
does have a bit of credibility. 


&& 


Aviation... 
VFR conditions will predominate tonight and Friday. Some MVFR 
or even locally IFR conditions possible over the northern mountains on 
Friday. Cold frontal passage Friday morning across NE Utah and 
midday in northwest Colorado could produce locally moderate to strong 
turbulence in those areas. 


&& 


Gjt watches/warnings/advisories... 
Colorado...none. 
Utah...none. 


$$ 


Short term.....Jad 
long term......eh 
aviation.......jad