449 
fxus63 kdvn 071936 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
236 PM CDT Thursday Aug 7 2008 


Synopsis... 
high pressure over eastern ND and northwest Minnesota will slide southeast across Iowa on 
Friday...providing continued pleasant and dry weather across the 
region. Upper level northwest flow to continue into the weekend...but 
gradually become more active as the surface high pressure slides 
east and monsoon moisture out west and south edges toward the area. 


&& 


Short term...tonight and Friday... 
temperatures are the main focus. Widespread cumulus over the area this 
afternoon not expected to evolve into showers. Unlike last night... 
have no significant surface boundaries or upper shortwaves in the 
region and radars showing no precipitation within a 250 mile radius. 
Cumulus will give way to clear skies around sunset. Airmass with 
dewpoints in the 50s across WI and Minnesota will continue to modify some 
as it builds south into the County warning forecast area. With center of high closer than 
last night...conditions will be more ideal for radiational cooling 
and have gone near low end of guidance with mins in middle 50s 
north...to around 60 south. Friday...under similar airmass... 
persistence forecast looks good...except have gone with slightly 
cooler highs than today due to shallower mixing under the high 
pressure center. 
.Sheets.. 


Long term...Friday night through next Thursday... 
northwest flow should bring down a weak short wave across Iowa and 
Illinois late Friday night and Saturday. This wave may have enough 
elevated cape to fire off a mesoscale convective system over Minnesota...which would move into the 
County Warning Area after dark. We will have chance probability of precipitation in the northwest...with 
slights elsewhere...and this can be bumped up to higher levels 
should the next shift see the same signals in the data. 


Otherwise...the Saturday through Thursday portion of the forecast 
contains unusually low confidence as model data is very 
inconsistent...even in synoptic patterns. However...the main theme 
is that our northwest flow flattens as a wave over tops...and then a 
very strong upper low will develop by middle week...sending the area 
into another long period of below normal temperatures. Our forecast 
contains numerous periods of slight chance probability of precipitation...as instability 
showers are likely given this pattern...and any wave interaction in 
the pattern change will likely bring some scattered activity as 
well. ... 
&& 


Aviation... 
high pressure over the upper MS valley will provide VFR conditions 
tonight and Friday. Scattered cumulus around 5 kft will dissipate around 
sunset...followed by clear skies tonight. Patchy MVFR fog will be 
possible around sunrise at Cid. On Friday...scattered cumulus will again 
develop 5 kft by late morning across the area. ..sheets.. 


&& 


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


&& 


$$ 


Sheets/Ervin