138 
fxus63 kdvn 240754 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
254 am CDT Thursday Jul 24 2008 


Synopsis... 
the endlessly active warm frontal boundary which has brought 
thunderstorms to some portion of the Midwest each of the last six 
nights is again targeting Iowa early this morning. Strong warm 
advection and a weak short wave has helped elevated storms 
organize into an mesoscale convective system over southeast South Dakota and and western 
Iowa. Other weak...but none the less rather widespread coverage 
showers are over eastern Iowa and adjacent northeast MO and western 
Illinois. These are forming on the nose of 700mb moist warm 
advection. 
... 
&& 


Short term...today and tonight... 
today...showers will be ongoing early in the northwest and possibly 
central areas. Otherwise...the mesoscale convective system to the west will have reached 
southern and western portions...or will be poised to move in around 
12z. This activity should impact the south today with 0.5 to 1.0 
inches of rain...with lesser amounts northeast. By late morning...it 
should have moved southeast into Illinois and eastern MO...ending 
the rain threat temporarily. Clouds should limit highs today to the 
upper 70s...to near 80 in all sites. 


Tonight...mesoscale convective system parameters again show the south 1/2 to 2/3rds getting 
hit. Rainfall potential of 1 to 2 inches or more is possible. A few 
counties that get hit hard this morning will need to be watched 
again tonight. If storms are surface based...they may miss all but 
the far south tonight...but looking at capping potential...it seems 
tonights storms should be displaced north...roughly from Des Moines 
to Burlington at the edge of the 12c 700mb temperature contour. Humidity 
will increase through the day today...with lows tonight only falling 
to the middle to upper 60s west..and lower 60s northeast. 
... 


Long term...Friday through next Wednesday... 
mesoscale convective system that develops in the plains Thursday night should move across 
the County warning forecast area during the morning. Boundaries left over from this mesoscale convective system will 
provide the focus for additional convection in the afternoon/evening 
hours. Late Friday night becomes more questionable as model 
solutions diverge on what will happen. Since the frontal boundary 
has been a focus for nightly nocturnal mesoscale convective system development...will go 
with the idea that another mesoscale convective system will develop Friday night. Said mesoscale convective system 
may or may not reach the County warning forecast area prior to sunrise Saturday. 


Saturday/Saturday night...going on the Assumption that an mesoscale convective system will 
form Friday night...a decaying mesoscale convective system should make its way across the 
County warning forecast area on Saturday. Most likely area to see said mesoscale convective system would be the 
southern half. Boundaries left over from this mesoscale convective system may result in 
additional development Saturday afternoon/evening. 


Sunday on...made no changes to current forecast. Model solutions diverge 
significantly on details. However...all seem to indicate a continued 
active weather pattern in northwest flow. Monsoonal moisture with 
added moisture from the remnants of Dolly will provide the fuel for 
additional mesoscale convective system development. However...smoothing of model solutions 
make it difficult to key in on any shortwave to provide a sense of 
timing for precipitation. ... 


&& 
aviation... 
mainly VFR conditions are expected today...despite occasional 
showers at all sites but dbq. The afternoon should be free of 
rain...but this potential should return again after 00z. 
Tonight...MVFR ceilings of 2000 feet or so...will be possible at all 
sites...with IFR conditions likely at brl where thunderstorms will 
likely also affect the terminal. 
... 


&& 


Dvn watches/warnings/advisories... 
Iowa...none. 
Illinois...none. 
MO...none. 


&& 


$$ 


Ervin/08/Ervin