041 
fxus63 kdmx 211740 aaa 
afddmx 


Area forecast discussion...updated 
National Weather Service Des Moines Iowa 
1140 am CST Sat Nov 21 2009 


..updated 18z 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 Wednesday 
may need to be raised if the system slows even more. Turkey day 
appears to be dry and seasonal. 




&& 


Aviation... 
typical for November with fog and low ceilings lingering much of the 
morning. Will see some improvement this afternoon though some areas 
may not reach VFR conditions. Deeper low level moisture moves across 
the area this evening. Should bring a return to IFR and LIFR 
ceilings. Possible that if ceilings develop early that it could deter 
the development of dense fog where as it was the dense fog that 
developed first last night...then the ceilings. LIFR visibilities still 
possible again this evening...especially near kmcw and Kalo where 
deeper moisture arrives a little later this evening and may allow 
for fog to develop ahead of it. Some drier low level air begins to 
work in Sunday morning...but likely will take time to scour our the 
moisture. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


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