176 
fxus63 kdmx 212014 aaa 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
313 PM CDT Thursday Aug 21 2008 


Discussion... 
middle level low pressure system moving northward is currently centered 
somewhere over far southern Iowa. Large low cloud and drizzle field 
continues to affect the area...but is slowly breaking up in the far 
southern counties. Temperatures have been held in check to say the 
least...with many locations not making it out of the upper 60s today 
and the rest stalling in the lower 70s. Given ample low level and 
surface moisture in veering southeast to south flow 
overnight...expect redevelopment of stratus deck after sunset with 
areas of fog likely. Given the persistent if light surface 
flow...dense fog appears unlikely at this time. Have added a lot of 
drizzle and fog wording to forecast tonight with very low probability of precipitation 
mainly in the evening. Temperatures will likely only drop by a few 
degrees in this regime...and min temperatures forecast to reflect this. If 
clouds break up in the far south and it takes a while after dark for 
the stratus to reassemble...it is possible temperatures could 
radiate down more than a few degrees. However...The Breaks in this 
area late this afternoon will also allow solar heating to increase 
temperatures...which should offset the subsequent radiative 
effects. Looking into Friday...expect gradient to tighten up and any fog 
and St should break up with decent mixing. The real question will be 
how far we will destabilize. Feeling is that with decent moisture 
in place and frontal convergence...combined with decent heading ahead 
of cold front...we will see some sort of squall line form. Shear is very 
meager and dynamics weak so don't expected to see a widespread event, 
but also would not be surprised to see an isolated hailer or wind gust. 
The genl thunderstorms and rain will likely continue through the night. Not much change in the 
longer term other than the cold front is likly to pass a bit quicker than 
thinking was yesterday...so precipitation should exit the state before midnight Sat night. 
Generally quite under high pressure sun through Tuesday with next frontal system 
likely to affect the area about Wednesday. Speed of progression is 
somewhat dictated by where "fay" eventually GOES as it appears likely 
that "fay" will build the upper high into the central and eastern U.S. 
Tending to keep the surface high in place longer than would otherwise be expeceted 
as well. 




&& 


Aviation...21/18z 
aviation forecast is complex to say the least. Large slug of 
low-level moisture and clouds will continue to advance from the 
south and is already impacting kdsm and kotm with IFR ceilings...LIFR 
visibilities...and steady light rain. More of the same will be the rule 
through the afternoon...with the IFR ceilings spreading into the 
northern sites by around 20z and the rain tapering off at the 
southern sites later this afternoon. The mist and low ceilings/visibilities 
appear likely to persist at least into the evening and quite 
possibly right through the night. While the higher clouds will move 
out overnight...the low stratus deck with IFR ceilings may linger just 
above the saturated surface into tomorrow morning. Once the sun 
comes up tomorrow low clouds and br will burn off by around 
14z...with southerly winds increasing beneath partly cloudy skies by 
midday. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Short term...Lee 
long term...MS Aug 08 
aviation...Lee