717 
fxus63 klot 301145 
afdlot 


Area forecast discussion 
National Weather Service Chicago/Romeoville Illinois 
645 am CDT Sat Aug 30 2008 


Discussion... 
240 am CDT 


With clear skies in all directions and high pressure building in 
from the west to secure same...there isnt much issue for discussion 
for todays scenario. Cumulus should be at a minimum if not existent under 
such strong subsidence. The high center is however shifting east 
of the area by sunset with winds veering to the southeast by 
Sunday morning. 


Gulf moisture begins working up into the plains from the Texas coast over 
the weekend with a decent 30 to 40 knots southerly low level jet pumping this 
moisture northward into the upper MS valley by Monday. This trend continues through 
Tuesday as a wave comes bearing across the upper MS valley from the 
Dakotas. Meanwhile Gustav makes landfall in Louisiana late in the 
day Monday and begins to Harbor most of that moisture over the lower MS 
valley...leaving little to pass northward through the plains by the end of the day 
on Tuesday. Viewing models with suspicion on the outcome of these 
two features...I would say that best lift from the northern short wave would 
be across the Great Lakes while most of the major storm activity 
would confine itself to gustavs influence over the lower MS valley through 
Thursday. Frontal passage from the northern system would cross through northern Illinois and 
Indiana Thursday night and Friday...while storms still rage over Texas 
and the lower MS valley. 


Am leaving extended forecast as is for now...pending more solid 
resolution on gustavs outcome. 


Temperature-wise...the extensive period of south flow through Thursday 
would permit Summer temperatures to work through the 80s during the day. These 
would be dampened only by cloud cover and increasing relative humidity values. Will 
start seeing some 90s south on Monday...threatening the north by 
Tuesday and Wednesday but not making it. Increasing clouds and 
possible rain by Thursday will limit temperature rises only into the 80s. 


Rlb 


&& 


Aviation... 
630 PM CDT 


12z tafs...no changes necessary to going tafs. The large ridge of 
high pressure continues to slowly sag south...with the axis now 
along the Kankakee River. The high pressure will remain over the 
area through the period. Skies will remain generally sky clear through 
the period with perhaps just a very few cumulus during the afternoon. 
The main concern will be wind direction this afternoon. For the 
early morning hours...expect calm winds to continue with the ridge 
axis just south of the terminals...but with a very weak pressure gradient 
in place...lake breeze development is likely again this afternoon...which 
should turn winds to more east-southeasterly or Ely at Ord/mdw/gyy. Rfd/dpa 
should remain more synoptically influenced and more southerly. Winds 
should go light/variable again at sunset. With the dry airmass in 
place...do not expect any visibility restrictions tonight. 


Krein 


&& 


Marine... 


1230 PM CDT 


High pressure centered over northern Illinois will move east 
across the southern Great Lakes Saturday. The high will continue 
east across the eastern Great Lakes Sunday and then remain there 
through Wednesday. Low pressure is expected to develop over the 
northern rockies tonight and move out over the northern plains on 
Sunday. The low will be forced to track northeast into southern 
Ontario Monday night...around the western periphery of the 
stationary high. Another low is forecast to develop over the 
central rockies Monday night and quickly track into the upper 
Mississippi Valley Tuesday. This will allow for generally 
southerly winds across Lake Michigan beginning tonight and 
continuing through midweek. 


Krein 


&& 


Lot watches/warnings/advisories... 
Illinois...none. 
In...none. 
Lm...none. 
&& 


$$