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fxus63 kdmx 211141 
afddmx 


Area forecast discussion...updated 
National Weather Service Des Moines Iowa 
539 am CST Sat Nov 21 2009 


..updated aviation discussion... 


Short term /today/... 
areas of dense fog are firmly entrenched over about three fourths 
of the County Warning Area early this morning...and plan to continue the dense fog 
advisory through 10 am. Thereafter...southerly winds will pick up 
in advance of the first of three upper level troughs to affect the 
region. Low level moisture...already manifesting itself in 
stratocu developing across Kansas/MO at this time...will progress northward 
into Iowa today...though may not result in solid cloud cover until 
after sunset. High temperatures today are somewhat tricky as they are 
dependent on how quickly fog Burns off...and how prevalent clouds 
moving north from Missouri will be this afternoon. Generally 
accepted a MOS blend. 


Long term /tonight through Friday/... 
synoptic scale lift acting on the column tonight...will deepen and 
raise the moist layer...likely resulting in areas of drizzle. As 
the cold front to our west encroaches on Iowa late 
tonight...additional convergence ahead of the front may help 
provide enough extra lift to squeeze out measurable light rain. 
For now...have kept probability of precipitation on the low end...but would not be 
surprised to see them raised by later shifts. This first upper 
level trough dampens out as next trough digs quickly in behind it. 
Consequently...the eastward momentum of the surface front ends 
before entering central Iowa...and actually pulls back to the 
west. While forcing mechanisms retreat or pull away from 
Iowa...expect chances of measurable rain to diminish Sunday into 
Sunday night temporarily. 


Heading into the Monday through Wednesday time period...there is 
still a spectrum of solutions regarding the evolution and path of 
low pressure moving through the region. The GFS/gefs/sref are 
farthest north and fastest...while the NAM is the slowest and 
farthest south. The ec and Canadian Gem models are in the middle 
with the ec closer to the NAM. From what I can tell...individual 
models have stuck close to their same tune in the last 24 hours. 
Without a clear indication of which is right...I have opted to use a 
Canadian/ec blend for this period. The result is increasing probability of precipitation 
Monday afternoon and decreasing them Tuesday night. Models are 
indicating decent elevated instability Monday night...so may need to 
add thunder mention at some point if that indication remains in the 
picture. With a slower solution preferred...will have generally 
warmer temperatures until Tuesday night when we finally get on backside of 
system. So have kept ptype as rain until Tuesday night when some 
snow could enter the picture over the western half. Probability of precipitation wednesay 
may need to be raised if the system slows even more. Turkey day 
appears to be dry and seasonal. 




&& 


Aviation /06z Sat to 06z sun/... 
visibilities in The Tank this morning east and south of kfod...with 
slow improvement by 16z. Will have better visibility and mixing late 
morning and afternoon...but could still have MVFR conditions in haze 
in the afternoon. Due to the uncertainty...kept visibility at or above 
6sm. Stratocu spreading north over Kansas/MO at this time will move over taf 
sites late this afternoon into early evening. Expect a return to low 
clouds and low to medium visibility restrictions after 00-03z. Could even 
have some drizzle around after 06z. 


&& 


Dmx watches/warnings/advisories... 
dense fog advisory until 10 am CST this morning for 
Adair-Adams-Audubon-Appanoose-Black Hawk-Boone-Bremer-Butler-Cass- 
Cerro Gordo-Clarke-Dallas-Davis-Decatur-Franklin-Greene-Grundy- 
Guthrie-Hamilton-Hancock-Hardin-Jasper-Lucas-Madison-Mahaska-Marion- 
Marshall-Monroe-Polk-Poweshiek-Ringgold-story-Tama-Taylor-Union- 
Wapello-Warren-Wayne-Winnebago-Worth-Wright. 


&& 


$$ 


Short term...Moyer/beerends 
long term...Moyer 
aviation...Moyer