654 
fxus65 kgjt 210937 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
337 am MDT Thursday Aug 21 2008 


Short term...today through Friday night... 
dry westerly flow aloft through the period. Upper low will be 
passing by to our north during the period with associated cold 
front sagging close to our northern border. Gradient winds should 
pick up this afternoon in response to the upper low...generally 
sustained 10-15 miles per hour at the surface with gusts in the 20s. 
Local red flag conditions possible NE Utah and portions of northwest Colorado 
this afternoon. But in general...winds not likely to meet criteria 
in most locations...and single digit relative humidity values expected to be 
localized. 


May have a significant amount of middle level clouds on Friday along 
the baroclinic boundary over the far northern zones. In addition to 
the clouds...slightly cooler air could seep into the far northern 
zones on Friday for maximum temperatures a tad lower than today. Otherwise... 
little change in maximum and min temperatures in our County Warning Area through the period. 
Slight chance for isolated dry thunderstorms mainly far northern 
mountains of NE Utah and northwest Colorado on Friday. 


Long term...Saturday through Thursday... 
a little better moisture will creep northward from the south during 
the first half of the forecast period as high pressure sits over the 
central rockies. The best activity will be on Sunday and Monday with 
the southern slopes of the San Juans favored. However...low chance 
probability of precipitation looks like the best we can do...with a slight chance over the 
other mountains and the high eastern valleys. A drier westerly flow 
then sets up for the remainder of the period as another Pacific wave 
moves across the northern tier states. One item of note...by the end 
of the period the 00z GFS shows another...and much stronger Pacific 
trough moving across the west. This disagrees with the 18z run...and 
the 12z European model (ecmwf). The 00z GFS shows the trough moving into the Great 
Basin Wednesday and a low forming on our doorstep by Thursday. The European model (ecmwf) and the 
18z runs indicate the flow will remain westerly through the period. 
Have chosen to keep the persistent dry forecast for this forecast and 
discount the latest GFS for now. Have made only minor tweaks to the 
forecast. 


Temperatures will remain above normal through the period. 




&& 


Aviation... 
isolated high-based diurnal thunderstorms possible over the mountains 
Friday and Saturday...then increasing some in aerial coverage Sunday 
and Monday. Otherwise...VFR conditions to prevail over the area 
through Friday as a generally dry westerly flow will persist. 


&& 


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


$$ 


Short term.....Jrp 
long term......elh 
aviation.......jrp