781 
fxus65 kbou 042109 
afdbou 


Area forecast discussion 
National Weather Service Denver Colorado 
310 PM MDT Friday Jul 4 2008 


Short term...the upper level ridge axis will be over eastern Colorado tonight. 
Enough moisture will be trapped under the ridge to produce a few weak 
thunderstorms until around 03z. Latest RUC/NAM still keep most of the 
convection focused along the Front Range foothills and Palmer 
Divide. This already reflected in the grids so no changes there. 
On Saturday...the ridge axis get suppressed to the south as a short 
wave rides over the top of the ridge. Models show potential vorticity 
associated with short wave moving into the County warning forecast area late in the afternoon. 
Interactive soundings show high based deep convection in the afternoon 
with moisture in the 500-550 mb layer. Precipitable water values high enough that some 
of these storms will produce some light rain but gusty outflow winds 
some thunderstorms will be the main threat. Some could be could be dry so 
fire danger will be elevated. Due to the higher precipitable water values prognosticated 
for Saturday afternoon will hold off on fire weather highlights at this 
time. 


Long term...upper level ridge over the central/southern rockies continues 
to break down Saturday night with a fairly strong shortwave trough 
coming onshore in the Pacific northwest. Models show this trough 
passing over the northern intermountain/Great Basin region on Sunday... 
with strengthening southwesterly middle-level flow over Colorado transporting 
subtropical moisture generally above 500 mbs up from the Desert 
Southwest. Prior to passage of the trough late on Sunday...NAM and 
GFS show a weak ripple rounding the top of the ridge and moving down 
The East Slope of the Wyoming rockies during the day. Surface wind... 
moisture and pressure change fields also show a weak frontal boundary 
tethered to this disturbance. NAM shows this wave/frontal combo 
brushing northestern Colorado Saturday evening. System appears to lack 
low-level moisture but forecast soundings indicate a ribbon of 
600-1200j/kg convective available potential energy along the frontal boundary as it passes through the 
area. Therefore may see a narrow line of T-storms sweeping across 
the plains during the evening hours with hail and gusty winds main 
threat. 


Models show the main shortwave eventually moving east over northern 
Colorado...but models differ a bit on its arrival. General consensus 
has the 700-500mb trough axis passing over the Colorado Front Range 
around 12z/Monday. Precipitation water values steadily increase 
ahead of this wave with southerly winds on the plains advecting 
mid-50s/lower 60s dewpoints up from southeastern Colorado. The additional 
moisture and lift produced by the passing shortwave should increase 
T-storm coverage across the entire County warning forecast area...with locally heavy 
rainfall possible. Increased cloud cover and gradually cooling aloft 
should also result in cooler temperatures on Sunday. 


Monday-Wednesday...latest medium range model runs show the trough 
over eastern Colorado/western Nebraska/western Kansas on Monday and just east of 
there Tuesday and Wednesday. Weak cool air surges on the back side 
of this trough should keep temperatures near or possibly below 
normal each day. Should also see at least isolated/widely scattered 
afternoon/evening T-storms each day. 


Later in the week...upper ridge is forecast to build back over the area 
bringing with it warmer and drier conditions. 


&& 


Aviation...VFR conditions and normal diurnal wind patterns will 
prevail. Threat of convection or virga affecting the airports is 
only around 10% in the 23z-04z time period. 


&& 


Bou watches/warnings/advisories...none. 


&& 


$$ 
Cooper/Baker