385 
fxus65 kgjt 201031 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
331 am MST Thursday Nov 20 2008 


Short term...today through Friday night... 
after several days of dominance...the Great Basin upper ridge is 
under attack. Aloft...Pacific moisture is streaming across NE Utah 
and northwest Colorado. At the surface...a cold front on the Front Range is 
leaking into the northwest Colorado with surface convergence into the 
morning hours there. But at 3am this morning...temperatures and 
dewpoints showed virtually no 24hr change. 


Whatever cool air that leaks into the north this morning gets 
quickly eroded this afternoon as SW flow advects warmer air. 
Afternoon temperatures should be close to Wednesday. Increasing 
gradient winds will produce a bit better vertical mixing this 
afternoon. 


Tonight-Friday night: a trough...along the Washington coast this 
morning...will pass through the northern rockies tonight. Its cold 
front will just brush the north into Friday morning. Moisture and 
dynamics are wimpy this far south. The Park Range could see a few 
flurries mainly Friday morning but do not expect measurable snowfall. 
Otherwise better mixing is expected Friday afternoon ending quickly 
with sunset in the valleys. 


Long term...Saturday through Thursday... 


Midrange models are in fairly good agreement on the weather pattern 
for Saturday through Tuesday. The model solutions for Wednesday and 
Thursday show large differences between the models as well as poor 
run-to-run consistency. 


Sat through Tuesday...zonal flow aloft with weak troughing over the 
western U.S. On Sat should give way to strong ridging Sunday. The 
ridge should move slowly east as it will be pinned between strong low 
pressure digging into the Great Lakes states and deepening low 
pressure off the West Coast. The result should be gradual warming and 
dry conditions. 


Wednesday and Thursday...the troughing off the West Coast is the big problem in 
tonight's model solutions. The GFS and dgex create a split trough 
with significant energy over the Pacific northwest and Southern California. 
Each model moves these features inland and spreads high clouds over 
the area Wednesday. By Thursday...a surface front and scattered precipitation is 
projected into eastern Utah and western Colorado. The European model (ecmwf) creates a much 
stronger closed low off the Southern California coast Wednesday with very little 
northerly component of a split trough. It then lifts this trough NE 
and into the Great Basin Thursday...while creating a second strong closed 
low of the pacnw coast. Cannot tell which solution is better at 
present so have made only minor adjustments to the grids for Wednesday and 
Thursday. 


&& 


Aviation... 
VFR conditions continue into next week. Some moderate turbulence will 
develop today and tonight as increasing stable southwest winds aloft 
create some mountain wave affects. Cold frontal passage Friday 
morning across far NE Utah and northwest Colorado could produce local MVFR 
ceilings and strong turbulence. 


&& 


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


$$ 


Short term.....Joe 
long term......cjc 
aviation.......eh+joe