643 
fxus63 kdmx 062327 aaa 
afddmx 


Area forecast discussion...updated 
National Weather Service Des Moines Iowa 
627 PM CDT Monday Oct 6 2008 


..updated aviation discussion... 


Short term...tonight 
slow moving north-south baroclinic zone over the Central Plains will 
move east tonight as low pressure over northern Kansas moves north along 
this boundary. Surface dewpoint tongue in the lower 60s nosing north 
along front and precipitation water values close to 1.5 inches will provide 
plenty of moisture to wring out. However...best qg and 
frontogenetical forcing remain northwest of central Iowa where 
northern stream dynamics merge with northward moving closed upper 
level low. Nevertheless...showers will be on the increase this 
evening...with most places receiving a solid one half to one inch of 
rain west of Interstate 35...and up to one half inch of rain farther 
east...through 12z. Cannot rule out thunder...especially across the 
west and south...but instability and lapse rates are pretty weak. 
Cold front will likely be just pushing into the far west by 
sunrise...so will have another mild night. 


Long term...Tuesday through Monday 
first focus of the long term...centers around system from short 
term...continuing to progress through the County Warning Area Tuesday. Surface trough to 
be bisecting the state in half from west to east by 12z...with best 
lift oriented along surface boundary. As stated...abundant moisture in 
place with precipitable water values near 1... widespread amounts of a 
quarter to half an inch possible Tuesday. Some MUCAPE in place as 
well...but little surface based cape...so continue with mention of only 
isolated thunder. System should progress rather quickly through the 
County Warning Area...with widespread total rainfall amounts near an inch for many 
locations. 850 mb temperatures drop into the single digits above freezing with 
clear skies/high pressure overhead for Tuesday night. Near zonal 
flow in place Wednesday into Thursday...with dry conditions 
expected. Weak cold front to push south through the area 
Wednesday...but moisture very scarce so expect a dry frontal 
passage. Otherwise focus switches to the upper level trough prognosticated 
to dig into The Rockies by late week...with southerly flow kicking 
back in across the area Friday into the weekend. Long range models 
showing disagreement in the exact track/timing of this system...but 
with the GFS ensemble mean leaning toward the ec solution...and HPC 
guidance leaning that way as well have followed the ec for this 
forecast package. This would keep a more progressive system lifting 
out of The Rockies into southern Canada through the weekend...keeping the 
County Warning Area in the warm sector with much of the precipitation staying to the north 
of the County Warning Area. Therefore did remove probability of precipitation from Friday...and even think 
may take a little longer for moisture to get into the area and could 
eventually see Friday night dry as well. Cold front associated with 
the system to move through Sunday into Monday...so have best chances 
for precipitation during those time. Otherwise little changes made 
to the going forecast...except to warm up temperatures a bit into the 
beginning of the extended period per the ec solution. 




&& 


Aviation...07/00z 
bands of rain showers have moved into southern and western Iowa...already 
beginning to affect kdsm and approaching kfod at this time. Tafs reflect 
deteriorating conditions through the evening at these two 
terminals...and later tonight at the other three. Thunder is 
possible at all terminals during their affected times...however it 
will be so isolated and infrequent that have only included cumulonimbus 
mention in the 00z tafs. As the bulk of the rain moves in overnight 
prevailing MVFR/IFR conditions will spread over the area...with 
conditions improve during the day tomorrow as a cold front moves 
through from west to east shifting winds to northwest and clearing out the 
clouds and rain. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Short term...Moyer 
long term...albrecht 
aviation...Lee