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Area Forecast Discussion (AFD)

Issued by Chicago, IL (LOT)

FXUS63 KLOT 240747

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
247 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.



246 AM CDT

Sunday through Friday...

By Sunday morning, the sprawling surface high will be moving east 
off the New England coast.  The longer range guidance remains 
consistent on amplifying split flow aloft, with a southern stream 
shortwave lifting through the Lower Missouri Valley and a northern 
stream short wave dropping out of the Canadian Rockies and into the 
Northern Plains.  The dry pleasant weather is expected to continue 
through Sunday, with highs into the upper 70s to around 80 across 
the area. However, cloud cover and deep layer moisture will be on 
the increase Sunday night into Monday as this double barreled system 
approaches the region.  The south stream system will bring a period 
of showers and thunderstorms beginning by early Monday morning. 
Through the day on Monday, the initial northern stream shortwave 
will track across the Northern Plains.  Then a series of waves will 
rotate around the base of the main upper low which is expected to be 
moving slowly through south-central Canada.  The series of 
shortwaves will carve out a longwave trough over the Middle/Upper 
Mississippi Valley.  A surface cold front associated with this 
system is then expected to track across the Middle/Upper Mississippi 
Valley Monday evening and then continue east, exiting the area by 
Tuesday morning.  As the cold front approaches and sweeps across the 
CWA, pcpn coverage and intensity will likely be on the increase, 
with the bulk of the total pcpn occurring Monday night. latest 
guidance suggests areal average rainfall amounts of 1.5 to 2.0 
inches Monday night with locally higher.  While the amounts 
possible.  There may still be some lingering showers over the ern 
portions of the CWA into Tuesday morning as the main cold front 
pushes off to the east.  

Another period of dry and unseasonably cool weather will return to 
the area for midweek as a surface high settles over the lower 
Missouri Valley. Towards the end of the period, the longer range 
guidance is suggesting that another cold front could cross the 
region, but there are significant enough timing differences among 
the long range models that confidence is low on the timing of any 
potential pcpn.  With broad upper troughing setting up across the 
ern 2/3 CONUS for late next week, temperatures will likely continue 
the below normal trend, with highs likely to remain in the 70s 
through late week.


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 11 AM Saturday.

IN...Beach Hazards Statement...INZ001-INZ002 until 3 AM Saturday.