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fxus65 kgjt 042050 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
250 PM MDT Friday Jul 4 2008 


Short term...tonight through Sunday... 
isolated convection and increasing cloud cover expected to continue 
across the forecast area tonight as the upper level ridge axis 
shifts east of the Continental Divide. This allows a surge of 
Pacific moisture to work into the area as flow becomes more southwesterly. 
Weak disturbances in the flow and linger outflow boundaries from 
convection this evening will provide some focus for additional 
storms to fire throughout the night. As a result...have increase 
probability of precipitation for a few nocturnal storms. In addition...increased cloud 
cover will keep temperatures very mild overnight...and have went 
above MOS guidance in several locations to account for this. 


The wetter SW flow remains in place through this weekend...so 
increased afternoon and evening convection is expected...especially 
from Interstate 70 southward where precipitable water values will 
support locally wetting rains. North of Interstate 70...conditions 
will remain drier...and potential for dry lightning will be 
increased...see the fire weather discussion below for additional 
information on fire weather concerns. With the ridge shifting east... 
lowered heights over the area...and cooling temperatures aloft...afternoon 
maximum temperatures will be backing down closer to normal seasonal values. 


Long term...Sunday through Thursday night... 
trough axis passes Sunday night with moisture in place and some 
dynamics...feel T-storm activity will linger well into the night. 
So raised pop grids to keep isolated activity over the mountains Monday 
believe the GFS over the NAM...and the GFS is consistent with the 
ec and HPC guidance. As such a drier northwesterly flow will settle 
over the region as high pressure re-centers over the Great Basin. This 
will bring a little cooler temperatures and help to taper off convection. 
This pattern will continue through Wednesday then the high will 
begin to shift back toward the 4 corners bringing a return to warmer 
temperatures as well as reintroduce middle level moisture back to the region. 


&& 


Fire weather...increasing middle level moisture and with upper level 
support across the north on Saturday...we will see increased 
thunderstorm activity. The Four Corners region will be wet enough 
for wetting rains associated with the storms. However NE Utah and 
northwest Colorado will have more high-based thunderstorms producing dry 
lightning in the lower elevations. Therefore these zones are in a red 
flag warning for Saturday afternoon. Central Colorado is more 
uncertain so will leave this zone in a watch for this forecast. 


&& 


Aviation...isolated to scattered thunderstorms will continue 
through this evening. Most storms will dissipate by 04z this 
evening...although a few storms will drift over the lower valleys 
until 09z Saturday morning. 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. Another round of thunderstorms develops on 
Saturday...with storms developing after 18z. 


&& 


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


&& 


Gjt watches/warnings/advisories... 
Colorado...red flag warning for fire weather zone 201 below 7000 feet 
from noon Saturday until 9 PM MDT Saturday evening for widely 
scattered dry lightning. 
Fire Weather Watch for fire weather zone 203 below 7500 feet 
from noon Saturday until 9 PM MDT Saturday evening for widely 
scattered dry lightning. 
Utah...red flag warning for fire weather zones 430/443/444 below 7000 
feet from noon Saturday until 9 PM MDT Saturday evening for 
widely scattered dry lightning. 


$$ 


Short term.....Jdc 
long term......mc 
fire...........Joe 
aviation.......tal 
hydrology......tgjt