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fxus65 kgjt 032057 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
255 PM MDT Thursday Jul 3 2008 


Short term...tonight through Saturday... 
high pressure covers Utah and Colorado and this will continue 
through Independence day. Terrain and diurnally driven isolated 
storms have developed this afternoon and expect similar conditions 
for the Holiday. Water vapor reveals the air mass is drier over the 
northwest half of the forecast area...the main reason that convective 
activity has been slower to develop over the northern mountains. One 
subtle change for Friday...precipitable water in the model data 
rises a notch over The Four Corners. The source of the moisture 
increase coming from thunderstorm outflows from north central New 
Mexico this afternoon. Thunderstorm coverage may increase a notch 
Friday afternoon/evening for the southern zones...but MOS pop guidance 
does not show much of an increase. Increased the coverage of slight 
chance probability of precipitation...but did not raise any values into the chance 
category. With the warmest 700 mb temperatures so far...Independence day 
may be the hottest day so far this Summer. 


Ridge weakens on Saturday as Pacific northwest short wave skirts 
across the northern tier states. The tail end of this wave moves across 
western Colorado during the peak heating hours. As mentioned in the 
previous paragraph...precipitable water will have increased ahead of 
this short wave. Water vapor shows Boris getting entrained into the 
southwest flow ahead of this short wave...not sure if models have 
picked up on this moisture plume that is evident in the water vapor. 
But the GFS and WRF have increased convective precipitation...especially the 
San Juan Mountains...for Saturday afternoon. So have increased probability of precipitation 
over the southern and central mountains with chance probability of precipitation where moisture 
will be more readily available as compared to the northern mountains. With 
increased cloud cover...afternoon temperatures will be a little 
cooler than the Fourth of July. 


Long term...Saturday night through Thursday... 
Saturday night through Monday...still looks like westerly flow to the 
north of our County Warning Area during this period in response to a couple of 
shortwave Pacific troughs that will suppress the upper high into Arizona 
and nm. This should be a drier pattern for our County Warning Area...and not quite 
as warm as we are currently experiencing. Still may have isolated 
diurnally-driven thunderstorms over the mountains of our County Warning Area Sunday 
and Monday...though expect by Monday that they will be confined to 
western San Juan Mountains. 


Tuesday through Thursday...resurgence of strong upper ridge 
expected over the area with upper high center migrating northward. 
We should see temperatures 5-10f above normal again...generally 
around 100f each day in the climatologically warmer areas of our County Warning Area 
with some of the hottest locations in southeast Utah reaching the 105f mark. 
There are indications for a little increase in convective cloud 
development by Wednesday or Thursday. But still looks to be generally 
dry with only high-based thunderstorms. 


&& 


Aviation...isolated thunderstorms will continue into early 
evening...with most storms dissipating by 04z. A few storms will 
drift over the lower valleys. Expect local MVFR visible and ceilings near 
some storms...mainly over the mountains. Gusty thunderstorm outflow 
winds expected in the lower valleys. Otherwise...VFR conditions to 
prevail through tonight. Expect similar conditions on July 4th. 


&& 


Hydrology... 
mountain snowpack continues to dwindle and runoff will gradually 
decrease resulting in a slow lowering of river and stream flows 
through the week. Although water levels are decreasing flows remain 
cold...swift...and turbulent. Caution is urged when around rivers 
and streams. 


&& 


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


$$ 


Short term.....Pf 
long term......jrp 
aviation.......tal 
hydrology......tgjt