084 
fxus63 kdmx 080013 aaa 
afddmx 


Area forecast discussion...update 
National Weather Service Des Moines Iowa 
700 PM CDT sun Sep 7 2008 


Updated for aviation discussion... 
short term /tonight/... 
currently sh/thunderstorms and rain activity should move out of the area by 00z as weak frontal 
boundary passes and heating GOES way. Fnt will stall by late tonight in 
response to strong shortwave approaching from the northwest. Expect to see some 
partly cloudy conds tonight...especially northwestern zones and went for some upper 40s 
there. Ran likely to move into the far west after 09z with approaching shortwave. 


Long term /Monday through Sunday/... 
forecast continue to be on track for a decent rain event beginning 
late tonight or early Monday and lasting through the day. Upper 
trough sharpens as a strong vorticity maximum rounds the base of the trough 
by 18z. Current RUC analysis overlaid on water vapor showing a 27 
unit vorticity maximum and the models are only slightly stronger which is 
possible as it ejects from the base of the trough. In 
addition...there is a good push of cold air aloft coming down. 
Models have been consistent in forecasting good upper level 
divergence over central Iowa during the day Monday and shear 
increases to around 50 kts along and north of a frontal boundary 
across northern Missouri/southern Iowa. This will be sufficient for 
thunderstorms and may be enough for even an isolated severe 
storm...mainly across far southeast Iowa. The system pulls out late 
Monday with clearing behind it and good subsidence. This should 
produce some very cold temperatures across the County Warning Area Monday night. Likewise 
with lack of good temperature advection for Tuesday...I dropped highs a 
little. Surface flow then becomes southerly late Wednesday and 
Thursday ahead of the next system. A little change in thinking here 
as Ike becomes a player. Ike is now forecast to move across the 
northern Gulf Wednesday through Thursday. This will create a more 
easterly wind flow thus limiting the Gulf moisture instead of before 
when the Gulf was open. Still good dynamics so thunderstorms still 
expected but they will be more isolated than previously thought...at 
least initially. The concern now is more of a heavy rain threat 
than a severe threat. Quantitative precipitation forecast values for tomorrow across central Iowa 
are around 1-2 inches which may again be repeated Thursday and 
Thursday night. Temperatures were put a bit cooler Monday and Tuesday then 
again on Thursday due to extensive cloud cover with only minor 
adjustments other periods. 


Aviation...08/00z 
isolated showers this evening should produced just VFR conditions. 
Widespread rain and isolated thunderstorms south looks very likely for Monday 
with unseasonably strong dynamics over taf/S. Onset of -ra should 
saturate initial dry low-levels resulting in IFR conditions by late 
morning. Conditions should improve as precipitation area and associated 
forcing move east. Surface high over taf points Monday night with large 
scale subsidence and weak boundary winds should result in fog late Monday 
night beyond the taf forecast period. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Short term/aviation...Johnson 
long term...fab