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Area Forecast Discussion (AFD)

Issued by Chicago, IL (LOT)

FXUS63 KLOT 240713

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

211 AM CDT

Through Tonight...

Tranquil weather is in control across the Lower Great Lakes on 
this late summer Saturday. East-northeast boundary layer winds 
off of Lake Michigan have eased slightly with a gradually 
reducing fetch over the lake. While there still is enough for 4 ft
wave observations and a high risk of rip currents early this 
morning along the Illinois shore, just enough easing is forecast 
to occur to likely take that risk down to more of a moderate 
later this morning and this afternoon (2-4 ft waves). Otherwise, 
a concentrated area of lake effect clouds early this 
morning...yes lake effect (low-mid 50s air temps over mid-upper 
70s water temps)...will ease over northeast Illinois by or shortly
after daybreak. After that just patchy cumulus and thin cirrus 
will be the rule. Highs should be near what they were yesterday 
with mid to some upper 70s prevailing.



205 PM CDT

Sunday through Friday...

Surface high pressure is expected to shift over New England on
Sunday ahead of a developing storm system over the Plains. 
Pleasant weather is expected to continue Sunday, with highs into 
the upper 70s to around 80across the area. However, cloud cover 
will increase across the area Sunday night into Monday as moisture
increases across the area in association with the approach of a 
disturbance shifting eastward across the Lower Missouri Valley. 
This system could result in some light rain potential entering far
southern portions of the area as early as later Sunday night. 

On Monday a well defined mid/upper level trough is forecast to
dig in over the Upper Midwest. As it does so, an associated 
surface low will deepen late Monday and Monday night over western
Ontario. This will will then drive a cold front eastward across 
our area Monday night into early Tuesday morning. While there will
be some chances for showers and thunderstorms during the day on
Monday, the best chance for showers and thunderstorms looks to be
Monday night into very early Tuesday morning as the cold front
shifts across the area. Severe thunderstorms do not appear to be a
big issue with these storms, but some locally heavy rainfall will
be possible.

Any lingering showers should end quickly early 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 a period of showers and storms. Since this is a week 
away, and timing is likely to chance, I have not strayed from the 
blended guidance during this period.



For the 06Z TAFs...

East-northeast winds will prevail over the Chicago area airports
for most of this TAF period. Early this morning, there is some
backed flow to due north at ORD, but that should turn northeast
before sunrise. Surprisingly for August, there are some lake
effect clouds, even some with MVFR bases near the lakefront, that
will drift over ORD and MDW mainly prior to daybreak. There is
high confidence in the wind forecast of 060-090 wind direction 
today with a speed of 10-11 kt and any gusts being very sporadic.



IL...Beach Hazards Statement...ILZ006-ILZ014 until 4 AM Saturday.

IN...Beach Hazards Statement...INZ001-INZ002 until 4 AM Saturday.