514 
fxus63 kilx 060147 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
847 PM CDT Sat Jul 5 2008 


Discussion... 
issued 843 PM CDT Sat Jul 5 2008 


High pressure over the eastern lakes will continue to dominate our 
weather through most of the day on Sunday. Clear skies and light winds 
tonight should allow temperatures to drop into the upper 50s to lower 60s. 
Dew points are a bit higher across the south and east this evening 
suggesting the potential for some patchy fog again by morning but 
not enough to include in forecast at this time. Light winds 
overnight should become south on Sunday bringing warmer and more 
humid air back into the region. Current zones in good shape 
early this evening...as a result...no update will be needed. 


Smith 
&& 


Aviation... 
issued 626 PM CDT Sat Jul 5 2008 


Other than the possiblity of some patchy ground fog before dawn 
Sunday...VFR conditions will prevail through most of this period. 
High pressure will shift slowly away from the region over the 
next 24 hours resulting in a light wind regime tonight with surface 
winds veering into the south on Sunday. Convection is expctd 
to develop across northwest Iowa late tonight and track southeast across east central 
Iowa before dissipating Sun afternoon. Addl storms may fire along 
residual outflow boundaries across Iowa but it appears any affect 
from the Iowa storms will not be felt across our area until 
late Sun night or Monday morning. Until then...aftr our clear 
skies tonight...some cirrus from the storms to our northwest will filter 
into the area during the day Sunday. 


Smith 
&& 


Previous discussion... 
issued 300 PM CDT Sat Jul 5 2008 


Short term...tonight through Tuesday... 
surface ridge will begin to let go of the area Sunday as the next 
weather system moves into the northern plains. Convection expected 
to fire up over western or central Iowa along the front late Sunday 
or Sunday night then move southeast with the mean flow into Illinois 
after midnight Sunday night and Monday. Prefer the GFS with its 
position/timing of convective initiation...but the NAM has a better 
handle on which way the storms will travel. Will have some slight 
chance probability of precipitation Sunday evening in the northwest half...then raise them 
to chance after midnight. Will keep probability of precipitation in the 30-40 percent range 
for Monday...but these may need to go up if the above scenario ends 
up playing out. Will also keep chance/slight chance probability of precipitation for Monday 
night...but by then the next round of thunderstorms will be 
developing further west again along the front which by 12z Tuesday 
will have progressed into central Iowa. 


Starting Monday night...both the 12z NAM and GFS models begin 
suffering from convective feedback which adversely affects their 
mass fields and especially quantitative precipitation forecast forecasts through Tuesday and 
Wednesday. With the 12z GFS low pressure center over central Iowa 
likely way overdone 12z Tuesday...will side with the European model (ecmwf) which 
looks better with its quantitative precipitation forecast and surface pressures. The cold front 
should therefore only make slow progress into the area on Tuesday 
with thunderstorms continuing. At this time the greatest coverage of 
precipitation looks to be Tuesday night in the central and south. 
Will keep probability of precipitation in the healthy chance range for now due to timing 
uncertainties... but likely probability of precipitation may become warranted as that 
timeframe grows closer. 


Long term...Wednesday through Saturday... 
how far south the Tuesday night cold front penetrates will be the 
main forecast issue for the long term as well. The old 00z/06z GFS 
runs backed off on the depth of the eastern Continental U.S. Upper trough from 
the previous couple of runs and trended toward the flatter and more 
Summer-like European model (ecmwf). This means that the front should not get that far 
to our south...so will hold on to chance probability of precipitation in the central and 
southern areas Wednesday. Even the flatter European model (ecmwf) keeps the northern 
fringe of the precipitation shield out of the area Wednesday night 
and Thursday as cooler high pressure begins to take control. 


By Friday and Saturday...the surface ridge moves east and warmer 
temperatures begin to return to the Midwest. With the upper flow 
perpendicular to The Rockies...Lee-side troughing out west will aid 
in bringing up increasing amounts of moisture. Initially...the 
strongest moisture return will be to the west of the Mississippi 
River until the next storm system moves across the plains...which 
will be beyond this forecast period. With increasing upper ridging 
building westward from the southeastern states and little in the way 
of surface forcing...any storms that develop will be isolated and 
transitory. The warm temperatures aloft should also provide an 
effective cap to any deep moist convection that tries to develop 
this far east. Will therefore keep Friday and Saturday dry with a 
warming trend. 


&& 


Ilx watches/warnings/advisories... 
none. 
&& 


$$