736 
fxus65 kgjt 182116 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
315 PM MDT Friday Jul 18 2008 


Short term...tonight through Sunday... 
light west flow remains over the forecast area early this afternoon. 
A weak middle level shortwave trough is situated over east central Utah 
and tails off to the southwest. This wave is progressing slowly 
east. Greater thunderstorm coverage today across the central and 
southern mountains out ahead of the wave. Drier air is spreading into 
the area with this wave which will limit thunderstorm coverage to 
isolated across east central and northeast Utah and and northwest 
Colorado late this afternoon and early this evening followed by 
clearing conditions overnight. Showers and thunderstorms will linger 
through the the evening across the south...especially across 
southwest Colorado. A few nocturnal showers beyond midnight possible 
across the far south. The airmass remains juicy enough and 
storm motion is slow enough for some locally heavy rainfall 
with storms through this evening...especially south. 


Drier and more stable conditions on tap for Saturday while the 
subtropical high which has been centered south of the area... 
reforms over Colorado. Warmer temperatures expected Saturday as 
subsidence under the high compresses the airmass...especially for 
the central and north. More moisture and less stable conditions 
down south will allow for a few storms to pop during the heating of 
the day. 


The drier and more stable conditions will be short lived as the high 
center is prognosticated to shift east over the High Plains Sunday. This 
will open the door for moisture advection from the south with some 
embedded shortwaves potentially adding to the thunderstorm 
potential. Thus kept temperatures on a downward trend for Sunday 
with increased probability of precipitation. 


Long term...Sunday night through Friday... 
the ridge axis continues to slide slight east allowing additional 
moisture to surge northward. Winds aloft remain weak but generally 
southwest. Upper low is slightly delayed from past model runs... 
allowing a longer time for the subtropical tap bring moisture 
northward. The low moves inland over central California late Monday or early 
Tuesday. The low ejects northeast toward the northern rockies 
helping shift the ridge slightly more to the east leaving the 
southwesterly flow aloft through the end of the week. Slightly dryer 
conditions in the upper levels early Tuesday to late Wednesday. 
Models again increase the deeper moisture late in the week. 
Increased probability of precipitation slightly Sunday night into Monday and also later in 
the week. 


&& 


Aviation... 
isolated thunderstorms will continue north of a line from Vail Pass 
to Moab until sunset. Scattered showers and thunderstorms south of 
this line will diminish between 02z-04z with isolated showers linger 
beyond midnight. Localized MVFR ceilings and/or visibilities will occur with 
some showers and storms with potential for small hail and gusty 
outflow winds of 30 to 40 miles per hour. Outside of showers and storms...VFR to 
prevail. Thunderstorms should be confined to south of a line from 
about kase to kcny and mainly isolated over the high terrain. Hotter 
temperatures Saturday will raise density altitudes. 


&& 


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


$$ 


Short term.....Tal 
long term......as 
aviation.......tal