531 
fxus65 kgjt 072100 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
300 PM MDT Thursday Aug 7 2008 


Short term...tonight through Saturday... 
precipitable water on the morning kgjt sounding was 200 percent of 
normal...or above one and half inches...and rarely do values get 
this high. Showers that have developed have produced significant 
rainfall in a short period of time. The culprit is the small closed 
low circulation trapped in the subtropical high over northwest 
Colorado. This feature is a slow mover but the models do show it 
moving east and weakening in time. This circulation is still with 
US on Friday...but its impact should be reduced as it begins to 
depart our forecast area. 


Friday...high precipitable water will still remain over the forecast 
area and expect more heavy showers. At this time...tough to 
pinpoint where the heaviest showers will occur. The highest threat 
could be northwest Colorado in the wake of the aforementioned 
departing circulation. 


Saturday...the flow aloft becomes northwest...but not strong enough 
to get rid of the low level moisture. However...specific humidity 
at the 700 mb level drop to the 6 to 8 g/kg range. While heavy 
showers will continue to be a concern...the number of heavy rainers 
will be less. With more sun...temperatures will trend upward. 


Long term...Sunday through Thursday... 
monsoonal flow will continue to stream into the region as we start 
off the weekend. However...a passing wave to our north will shift 
the ridge axis slightly eastward and suppress heights somewhat... 
allowing for a little drier air to work in Saturday afternoon. This 
drying is short-lived with another surge lifting back over the area 
Sunday. Stronger system moving across British Columbia Sunday and 
Sunday night will finally suppress the ridge enough as it works 
east across southern Canada. This will bring in drier westerly flow 
to start off the new work week. Still enough residual moisture to 
keep low probability of precipitation running...but conditions will be much drier through 
about mid-week. Ridge re-builds across the western states by 
Thursday...with moisture once again sneaking northward into the 
forecast area by the end of the week. Will start ramping probability of precipitation up as 
another surge of monsoonal moisture appears likely. 


Temperatures through the period will start off on the cool side due 
to all the moisture and cloud cover across the region. Conditions 
warm as we move into the new work week with drier air and less 
cloud cover...with little change then expected through the rest of 
the week. 


&& 


Aviation... 
expect scattered to numerous showers and thunderstorms across the 
region tonight and Friday. Storms will likely bring MVFR ceilings and 
visibility with an isolated few resulting in brief IFR conditions. 


&& 


Hydrology...very moist conditions will persist across eastern Utah 
and western Colorado for the next few days. A weak upper level 
disturbance will remain nearly stationary across the area this 
through Thursday...aiding in the development of widespread showers 
and thunderstorms. Heavy rainfall is possible across southeast Utah 
and southwest Colorado. 


&& 


Gjt watches/warnings/advisories... 
Colorado...Flash Flood Watch until 9 PM MDT for northwest...west central 
and southwest Colorado...including zones 
01/02/03/06/07/09/11/14/17/18/19/20/21/22/23. 
Utah...Flash Flood Watch until 9 PM MDT for all but the eastern Uinta 
Mountains...including zones 22/24/25/27/28/29. 


$$ 


Short term.....Pf 
long term......jdc 
aviation.......jdc 
hydrology......tgjt