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fxus65 kgjt 050954 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
354 am MDT Sat Jul 5 2008 


Short term...today through Sunday night... 
analysis this morning shows the Ridgeline moving east of the area 
allowing a bit more unstable SW flow move into western Colorado and eastern 
Utah. Quite a bit of middle-level clouds stretches from southern Arizona 
through Utah to western Wyoming. Time heights using NAM data over the area show 
a moderate about of middle level moisture with so low level convergence 
beneath upper level divergence this afternoon and very weak shortwave 
troughs. Forecast soundings get moderately unstable this afternoon 
but remain very dry in the lower level with moisture confined to 
altitudes above 600 mb. A good setup for high-based dry 
thunderstorms. Forcing mechanisms present are not very impressive... 
so believe the dry thunderstorms areal coverage for a red flag 
warning will just reach criteria over central and northwest Colorado and 
portions of northeast Utah. The big question will be how much the cloud 
cover this morning will inhibit convective development. Believe thunderstorms 
will begin first along the periphery of the cloud cover then fill in 
the middle as outflows develop and spread. See fire weather section 
below. 


Southwest Colorado and southeast Utah will see wetter thunderstorms dew to 
more available moisture. 


Sunday and Sunday night will see a repeat of Saturday...except 
moisture plume from the SW appears to increase a bit allowing 
thunderstorms to produce more rain. Have decreased temperatures a bit the 
next to days to reflect more clouds and precipitation. 


Long term...Monday through Friday night... 
trough axis is east of western Colorado and eastern Utah by Monday morning 
leaving northwesterly flow aloft. The ridge builds over the western 
USA during the first portion of the week and then starts to shift 
slowly to the east and to The Four Corners by Friday night. A few 
disturbances are indicated by the GFS to skirt just north of the 
forecast area in the later part of the week. Limited middle level 
moisture slides northward under the ridge in the extended. Kept the 
current forecast trend with only minor tweaks. 


&& 


Fire weather...increasing middle level moisture and with weak upper 
level troughs will move across the western Colorado and eastern Utah 
today...causing increased thunderstorm activity. The Four Corners 
region will be wet enough for wetting rain associated with the 
storms. However NE Utah and northwest Colorado will have more high-based 
thunderstorms producing dry lightning in the lower elevations. 
Therefore fire weather zones 201 and Utah 430...443 and 444 below 
7000 feet...and fire zone 203 below 7500 feet will have a red flag 
warning in effect from noon to 9 PM. 


&& 


Aviation...isolated to widely scattered thunderstorms will develop 
across eastern Utah and western Colorado this afternoon and evening. Expect 
local MVFR visible and ceilings near some storms...mainly over the mountains 
..with gusty thunderstorm outflow winds expected in the lower 
valleys. 


&& 


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 until to 9 PM MDT this evening for widely scattered 
dry lightning. 
Red flag warning for fire weather zone 203 below 7500 feet 
from noon until 9 PM MDT this evening for widely scattered dry 
lightning. 
Utah...red flag warning for fire weather zones 430/443/444 below 7000 
feet from noon until 9 PM MDT this evening for widely 
scattered dry lightning. 


$$ 


Short term.....Cjc 
long term......as 
fire...........cjc 
aviation.......cjc 
hydrology......tgjt