Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 211149

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
649 AM CDT SUN AUG 21 2016

223 AM CDT

Through tonight...

A cool and breezy day is on tap for the area today. While the day
will start out on the sunny side, diurnal CU will develop over the
area by early afternoon. This will result in a partly cloudy to
partly sunny afternoon over the area. We also cannot rule out a
few isolated sprinkles or light rain showers this afternoon,
particularly over northeastern Illinois and points north. These
areas will be in better proximity to an afternoon disturbance
propogating through the northwest flow aloft. However, these
should not make much of an impact to the day, with most areas
likely staying dry. High temperatures this afternoon are only
expected to warm into the middle 70s.

A surface ridge of high pressure will set up over the region
tonight. This will result in light winds and clear skies over the
area, which should set up a chilly Monday morning over the area.
The coldest areas will be outside the warming effects of the city,
where temperatures could drop near 50. This could also result in
some patchy fog late tonight into early Monday morning.



259 AM CDT

Monday through Saturday...

Temperatures will begin to warm back to near 80 on Monday, and back
into the low to mid 80s on Tuesday as the low level flow turns
back out of the south in the wake of tonight`s surface ridge of
high pressure.

The main story during the extended period will center around mid-
week (Wednesday through Thursday). Forecast model guidance
continues in good agreement with the evolution of another stout PV
anomaly, currently located near the British Columbia coast, per
the latest water vapor imagery. This feature is expected to shift
eastward across south central Canada through Wednesday morning. As
it does so, expect surface low pressure to develop over the
Northern High Plains by Monday night, then gradually shift
eastward over towards the upper Great Lakes region by Thursday.
This systems cold front then looks to push over northern IL and NW
IN by Thursday afternoon.

Deep layer Gulf Moisture (Precipitable water values near 2") will
be likely be driven back northward over the Plains and the
Mississippi valley on Tuesday as a 35+ KT southerly low-level jet
sets up in association with the developing northern Plains low.
This gulf moisture then looks to be steered towards the southern
Great Lakes region on Wednesday into Thursday. This could be
setting up another wet period local, with possibly a couple rounds
of showers and thunderstorms during this period as an active
southwesterly flow in the upper levels sets up over the central
CONUS. So heavy rain could again become an issue for some.

Following this period of stormy weather, high pressure and cooler
weather looks to make a return to the area for Friday into
Saturday. Another disturbance could produce some more storms on
late Saturday or Sunday.



For the 12Z TAFs...

While high pressure is providing an influence early this morning
with mostly clear skies, an upper level system was sliding
southeast across the Western Great Lakes and helping to develop
some low end MVFR cigs across Wisconsin and beginning to develop
over far Northern Illinois. Expect with the cold air aloft the
cloud deck will quickly develop and lower with bases around
1200-1500ft agl through late morning, then begin to rise to around
2500-3000ft agl by 18-20z. Winds will be turning from west to
northwest and increasing in speeds. Expect gusts to approach 20kt
by mid-morning and continue through this afternoon, then as sunset
approaches cloud cover will begin to thin and lift back to VFR
conds with diminishing winds. High pressure will be shifting east
and allowing winds to slowly turn southwesterly but not increase
overnight, with speeds lingering between 3-5kt to at times calm.



437 AM CDT

Gale warning will continue this morning for the far northern zones
of Lake Michigan, with frequency of gales diminishing quickly by
mid-morning. Winds will then becoming northwesterly between 20 to
25 kt later this afternoon. Further south the winds will be
strongest this morning to 30 kt from the west then shifting
northwest and diminishing slightly. With cooler air flowing over
the lake, waves will easily grow and should remain elevated
through this afternoon. Then with a diminishing gradient tonight,
winds and waves should steadily subside. Small craft conditions
will end this morning for the Illinois nearshore; however, with
the northwest/west winds the Northwest Indiana nearshore waters
will persist. High pressure will remain over the region late
tonight into Monday, then shift east with a gradient arriving and
producing stronger winds ahead of the next system for Monday night
through Wednesday. Then a low pressure will lift northeast of the
Lake Thur, with a frontal boundary passage expected for Thur aftn
and shifting southwest winds yet again to the northwest.



IN...Beach Hazards Statement...INZ001-INZ002 UNTIL 7 PM Sunday.

     10 AM Sunday.





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