106 
fxus63 kdmx 182100 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
400 PM CDT Friday Jul 18 2008 


Discussion... 
short term /tonight/... 
boundary in place across the County Warning Area this afternoon with low level 
instability and enough shear for a few reports of funnels. Will see 
shortwave to southwest of Iowa move toward the state with 
thunderstorms increasing in coverage through the evening across the 
southeast. Given deep and warm atmosphere along with precipitable waters  in excess 
of 1... efficient rainfall from the storms with threat for 
flash flooding remaining...although maybe not as focus in any given 
place as it appeared in previous forecast and will continue flash flood advisory for 
tonight. 


Long term /Saturday through Friday/... 
mesoscale convective system expected to develop over sdak late tonight...moving eastward 
within zonal steering flow. Disagreement among models as to motion 
and evolution of the mesoscale convective system tomorrow...with Euro tracking it along a 
higher latitude than the other models which is inconsistent with 
initialized features...NAM taking it further south initially but 
then hooking it just north of east over Minnesota which seems unrealistic 
in this steering flow...and GFS taking it east through fsd then east 
southeast across northern and eastern Iowa tomorrow. Given likely 
locations of highest instability...believe GFS solution is the most 
reasonable as the mesoscale convective system should track slightly southward toward more 
unstable air. Have increased probability of precipitation across the north tomorrow to 
account for this...to levels Above All models except GFS. Will need 
to monitor mesoscale convective system evolution over sdak later tonight with adjustments to 
tomorrows forecast one way or another probably necessary at that 
time. 


Somewhat quieter weather Saturday night and Sunday will once again 
give way to storm chances Sunday evening and night as another weak 
boundary sags nearby and destabilization along and ahead of the 
boundary becomes supportive of further convection. 
Thereafter...significant differences between extended GFS and Euro 
models as large cyclone sets up northeast of the Great Lakes and 
impulses come down across the Midwest in northwesterly flow. Bottom 
line is this will keep rain chances in the forecast at least through 
midweek...but it is impossible to nail down which periods will be 
the most likely at this time. Have opted to stick with chance/slight chance 
probability of precipitation through this period until a clearer solution presents itself. 


&& 


Aviation...18/18z 
light surface flow will continue across Iowa through the forecast period as 
front remains nearly stationary. Scattered thunderstorms and rain activity is expected to 
become numerous across southern Iowa by late afternoon into the 
evening. Otehrwise...widespread MVFR to IFR conditions are forecast 
for late tonight into early Saturday morning in low ceilings and 
visibilities...especially in northern Iowa. 


&& 


Dmx watches/warnings/advisories...Flash Flood Watch most of Iowa 
east of Interstate 30 and south of Interstate 80 from 23z/18-11z/19. 


&& 


$$ 


Long term...Lee 
short term/aviation...cogil