256 
fxus65 kgjt 072025 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
225 PM MDT sun Sep 7 2008 


Short term...tonight through Tuesday... 
another cloudless night expected tonight. Then a relatively Flat 
Ridge will pass south of the area Monday and Monday night...with west-northwest 
flow aloft over the northern half of the forecast area. As the ridge 
moves further east...a bit of moisture begins to rotate northward 
from souther Arizona and nm into southeast Utah and SW Colorado Monday night...and then 
spread north and east Tuesday. After another dry and warm day 
Monday...clouds will increase from SW to NE Tuesday. Have kept the 
low probability of precipitation for that were introduced earlier. Low temperatures should warm up 
Monday night over SW Colorado and southeast Utah due to cloud cover and increased 
moisture. Maximum temperatures Tuesday should drop a few degrees for the same 
reasons. Have stayed closer to GFS guidance numbers as GFS MOS has 
done better the last few days. Best chance for precipitation Tuesday will be over 
the mountains of SW Colorado and southeast Utah. 


Long term...Tuesday night through Sunday... 
models show good agreement/continuity initially...then confidence 
drops significantly by later in the work week. Southwest flow that 
will have developed over the area by the beginning of the period...as 
result of a trough along the West Coast...will continue to carry 
moisture moisture over the forecast area. This southwest flow will 
continue as long as the trough remains to our west. The main concern 
is that the later runs of the GFS are less progressive than we have 
been seeing...which is more in line with the early European model (ecmwf) solution. A 
few days ago the ec showed a closed low forming in the Great Basin. 
Subsequent runs of the ec have gone back and forth between the closed 
low and a more progressive open wave. While todays 12z ec still shows 
the closed low...it is now faster then the 12z GFS. So with some 
skepticism...feel that the relatively wet period that is just getting 
underway at the beginning of the period will extend into Friday...and 
possibly even Saturday. By Sunday...both the ec and GFS indicate the 
trough will have passed to the east for a drier northwest flow over 
the region. 


For this forecast have modestly upped probability of precipitation through Friday. If the models 
trend continues...then probability of precipitation will need to be increased some more... 
with hopefully better timing resolution. For now though...a broad 
brushed approach seems best. Have also decreased temperatures to a hair 
below normal for highs...and a hair above normal for lows...with 
most cooking over the north. 




&& 


Aviation... 
VFR conditions will prevail through Tuesday. 


&& 


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


$$ 


Short term.....Cjc 
long term......eh 
aviation.......cjc