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Area Forecast Discussion (AFD)

Issued by Chicago, IL (LOT)

FXUS63 KLOT 241915

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
215 PM CDT Sat Aug 24 2019

213 PM CDT

Through Sunday night...

Fairly quiet weather will continue across the area through at least 
Sunday morning as sprawling high pressure over the Upper Great Lakes 
slowly moves east. Expect continued winds from the NE to SE quadrant 
under some passing upper-level clouds through tonight.

Winds have diminished over water this afternoon and waves have 
responded accordingly. Therefore, the current ending time of 3pm
CT for the Beach Hazards Statement looks on track. However, another
increase in onshore winds late tonight into Sunday morning may 
result in an increased swim risk with 2-4 foot waves during this 

A fairly pronounced trough currently over the central Great Plains 
will track NE, reaching the CWA by late Sunday night. Upper-level 
clouds will gradually thicken and lower through the day Sunday ahead 
of this trough. Though some guidance is attempting to bring a few 
showers into the south half of the CWA by late Saturday afternoon, a 
substantially dry layer should lead to only virga. The dry layer 
will continue to limit the northward extent of showers Sunday 
evening. As the trough arrives late Sunday night, notable moisture 
advection in the low to mid-levels will finally allow for isolated 
to scattered shower coverage, especially farther east in the CWA. 
Poor mid-level lapse rates will limit thunderstorm potential, but 
enough instability exists within this WAA regime to support at least 
a slight chance mention of thunder.



215 PM CDT

Monday through Saturday...

The period is expected to begin Monday on the unsettled side as an
upper level trough digs over the north central CONUS. However, by
Tuesday another few day period of mainly dry and cool weather is 

Showers, and possibly a few thunderstorms, may be ongoing across 
eastern IL and northern IN Monday morning in response to an 
lead mid-level disturbance shifting northeastward over the area.
While skies will remain cloudy through the day Monday, it does 
appear that we could have a period of rain-free time from the 
late morning and into the afternoon following the passage of this 
initial disturbance. However, the chances for showers and 
thunderstorms will increase across the area again by Monday 

A well defined mid/upper level trough will set up over the Upper 
Midwest later Monday and Monday night. As it does so, an 
associated sub 996 MB surface low is expected to develop late Monday
and Monday night over far western Ontario. It will be this storm
systems cold front that we will be focusing on for our next chance
for shower and thunderstorm activity over the area Monday night
through early Tuesday. Currently it appears that this cold front
will shift over north central IL by late Monday evening, then over
northeastern IL during the overnight hours and then exiting my
southeast Tuesday morning. For this reason, our best chances for
decent rainfall amounts will be Monday night. Severe weather is
not expected with this activity. 

Any lingering showers should end quickly Tuesday morning 
following the passage of this cold front. Dry and pleasant 
conditions should return to the area for midweek as a surface high
settles over the lower Missouri Valley. High temperatures are 
likely to remain in the 70s through late week.

Overall, mainly dry conditions are expected mid to late week.
However, forecast guidance suggests that another cold front could
move over the area sometime later in the week, and this could 
result in another small chance for showers and storms. However,
given that this is several days away, I have not strayed from the
blended guidance during this period.



For the 18Z TAFs...

VFR conditions expected through the period with persistent winds
from the NE to SE quadrant. Some virga will be possible late
Sunday afternoon as approaching -SHRA from the SW dissipate in a
substantially deep dry layer.



IL...Beach Hazards Statement...ILZ006-ILZ014 until 3 PM Saturday.

LM...Small Craft Advisory...IL nearshore waters until 3 PM Saturday.