200 
fxus63 kdmx 072315 aaa 
afddmx 


Area forecast discussion...udpated 
National Weather Service Des Moines Iowa 
614 PM CDT Thursday Aug 7 2008 


Updated aviation discussion 


Short term...tonight through Sat night 
high pressure remains over the area...with northerly surface winds 
becoming light overnight. Diurnally driven cumulus field expected to 
dissipate through the early evening hours...with skies becoming 
clear overnight. Warm air advection kicking in as Theta-E ridge builds eastward 
into the western County Warning Area late tonight...may result in some middle/high 
clouds into the early morning hours. Otherwise with cooler air/about 
2 to 4 celsius cooler/ than the past few nights and high pressure 
overhead stuck with the cooler overnight lows that were in place. 
Therefore have 50s going for entire forecast area...with the coolest 
spots across the northern/northeastern County Warning Area. 


Surface high pressure should remain in place over Iowa Friday keeping our 
fair and relatively cool weather in place. However by Friday night 
several short waves currently traversing or/Washington into the southwestern 
Canadian provinces will top the ridge into the upper MS River 
Valley. Philosophy from yesterday discounting the NAM was 
apparently in error as other models and ensembles are certainly more 
bullish with their precipitation potential into Sat morning. In 
hindsight...favoring the dry solution in often pesky northwesterly flow was 
likely not the best idea. Only weak elevated instability is in 
place...and moisture transport is nothing noteworthy in 300-310k or 
305-315k isent layers. However GFS/NAM both depict at least 
moderate kinematic forcing and uvm in these layers with the short 
wave. Strengthening upper level jet and increasing model trends are 
supported by the sref so have boosted probability of precipitation further into the chance 
category. 


The synoptic scale forcing diminishes with the passage of this wave 
Sat and Sat night...however have continued low end chances through 
this period. Instability increases...with a more surface based 
potential...and may be able to generate peak heating convection as a 
lingering boundary associated with the aforementioned wave extends 
across mainly northern Iowa. 


Guidance seems to be capturing our airmass change so see no reason 
to deviate from a blend of that...although did favor the lower end 
Sat with lingering precipitation and clouds possibly holding things down. 


Long term...sun through Thursday 
forecast is essentially unchanged in this period with dwindling 
confidence over the past several days and model runs. Low chances 
remain on sun with potential for short waves topping the ridge into 
the MO valley. Situation beyond this point becomes even more 
muddled with deterministic runs and ensembles all having different 
ideas how aggressive next round of short waves will be breaking down 
central Continental U.S. Ridge. Similar discrepancies appear regarding fate of 
Canadian prairie trough...and fate of any ejecting short waves and 
their ultimate magnitude by the time they reach the Great Lakes. 
Regardless of the solutions...Iowa will be influenced by northwesterly flow to 
some degree so see no reason to change from prolonged period of low 
chances. This would also keep temperatures seasonal with no extremes in 
either direction. 


&& 


Aviation...08/00z 
VFR conditions through the taf period with generally scattered clouds 
or less and winds less than 10 kts. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Public...small/albrecht 
aviation...Moyer