992 
fxus63 kdmx 240740 
afddmx 


Area forecast discussion 
National Weather Service Des Moines Iowa 
240 am CDT Thursday Jul 24 2008 


Short term...today 
evolution of current mesoscale convective system is obviously primary forecast concern this 
morning which lines up quite well with decent moisture convergence 
associated with 30-40kt low level jet noted on 305/310k isent sfcs. This 
convergence reaches S central/southeast sections by 12z-15z so have boosted 
probability of precipitation to categorical in those locations and diminished northern portions. 
Convection should have no problem sustaining itself and will likely 
increase somewhat. Lifting parcels from various elevated levels on 
the RUC depict steady 1500-2000 j/kg convective available potential energy with decreasing cin and 
convection being rooted lower. Effective srh and especially 
effective shear sufficient for organization as well...especially if 
storms become rooted lower as cins suggest so may see a gradual 
increase in severe threat toward daybreak. Heavy rains will be a 
concern as well with precipitable waters  around two inches...13kft wcds...and cells 
tracking over same locations. 


Airmass should stabilize somewhat during the afternoon with no real 
forcing mechanism noted so have slights/chances lingering by 
then...mainly southern portions. Sref and especially NAM raw temperatures are 
not too bullish on temperatures with NAM suggesting areas of Post-precipitation 
stratus so went at or just below guidance...lower end NE. 


Long term...tonight through Wednesday 
frontal boundary to be in place from northeast to southwest across 
the County Warning Area by this evening...with much of County Warning Area in the warm sector. Fair 
amount of instability with best surface based cape situated across the 
southwestern County Warning Area. May see some isolated storms initially with 
daytime heating...but expect majority of convection with approaching 
shortwave through into the later evening/overnight hours as low level jet 
strengthens. Moisture expected to pool ahead of approaching weak 
cool front situated across eastern NE/wc Iowa...with precipitable waters  approaching 
two inches. Main activity still expected along the frontal boundary 
through the early evening...with everything pushing eastward 
overnight. Friday into Saturday...main frontal boundary to be 
somewhat washed out...but in vicinity of the southern County Warning Area. Northwest flow 
pattern continues...with main weak disturbances dropping southeast 
out of the northern rockies into the area. Hard to nail down timing 
and placement...but instability to remain greatest across the 
southern half of the County Warning Area into Friday night and Saturday...as surface 
high pressure/drier air begins to build southeastward into northern 
Iowa. Little changes made into the extended range...as 
western/central US upper ridging flattens some. However still looks 
like trend for weak waves to traverse the ridge...and impact the 
area allowing for unsettled conditions to continue through the 
weekend into the middle of next week. 


&& 


Aviation...24/06z 
light showers continue move over central Iowa though is falling with 
VFR conditions. Thunderstorms developing west of the Missouri River 
and will move into western Iowa later tonight. Main sites affected will be 
dsm then later otm. MVFR ceilings expected for a period all sites as 
this system passes. Additional MVFR ceilings mainly north expected 
after 00z. 


&& 


Dmx watches/warnings/advisories...none. 


&& 


$$ 


Short term...bss 
long term...mja 
aviation...donavon