Weather

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fxus65 kgjt 292058 
afdgjt 


Area forecast discussion 
National Weather Service Grand Junction Colorado 
300 PM MDT Friday Aug 29 2008 


Short term...tonight through Sunday... 
big weather changes during the short term period with Saturday being 
the transition day. For tonight...convection has fired over the 
southwestern San Juan Mountains a couple hours earlier compared to 
yesterday. This was expected as moisture returns into southwestern Colorado 
in light southerly low level flow. A few storms may pop north of 
the San Juan Mountains later today...but expect activity to wane 
with sunset. With moisture continuing to seep back into The Four 
Corners area...isolated nocturnal activity will be possible. 


Incoming trough sharpens along the Pacific northwest coast on 
Saturday. Southerly flow increases over Utah and the West Slope and 
taps the monsoonal moisture currently positioned over southern Arizona and 
western New Mexico. Convective potential will be higher over southeast Utah and 
SW Colorado. These storms will be moderately high based and outflow 
thunderstorm winds will be concern for local wildfires. The deep 
layered moisture begins to arrive Saturday night with strengthening 
gradient winds. With dynamical forcing on the rise...do not expect 
early evening convection to wane with sunset. Believe that scattered 
showers with embedded thunderstorms will persist through a good part 
of the night across the southern half. The northern half will stay mostly 
dry...but convective debris means a milder night for the northern valleys. 


Upper trough deepens over the intermountain west with q vectors 
showing increasing dynamical forcing. With speed shear in the 30 to 
40 knot range across eastern Utah...potential exist for some strong 
to locally severe thunderstorms. One big concern is the amount of 
cloud cover that limits convective potential. The GFS and WRF are 
in agreement that cape values will be puny...despite high 
precipitable water around one inch and a quarter and 700 mb specific 
humidity above 8 g/kg. However with the trough sharpening between 
115 and 120w...the deeper cloud cover could stay over western half of 
Utah and leave enough sun breaks for eastern Utah to heat the surface 
and thereby steepening lapse rates. Thunderstorms will be longer 
lived and stronger...with many of them producing hail and strong 
outflows. 


Long term...Sunday night through Friday... 
a strong storm system continues to be indicated by the models this 
weekend and into early next week...however trend has been to deepen 
and slow system a little with each new successive model run. 


Sunday night the upper low will be over the Great Basin with deep 
moisture in place over our County Warning Area with precipitable water values over 1 
inch Sunday evening. As trough approaches dynamics will increase and 
widespread showers and thunderstorms are expected Sunday night and 
Monday with locally heavy rainfall possible. Current model timing 
has the cold front in the vicinity of gjt around midnight Monday 
producing forced lift and another burst of precipitation. Conditions will 
improve from the northwest after frontal passage. 


Wednesday through Friday...a dry northwesterly flow aloft will 
prevail over the region as high pressure builds along the West 
Coast. 


&& 


Aviation... 
VFR conditions expected over the entire forecast area through 
18z Saturday. Isolated thunderstorms will again form over the San 
Juans mountains and toward the Sawatch Range between 19z and 03z 
today and this evening...with gusty winds to 40 miles per hour. Any storms that 
do form will be short-lived. 


&& 


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


$$ 


Short term.....Pf 
long term......mc 
aviation.......tgjt