Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251910

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
210 PM CDT MON JUL 25 2016

201 PM CDT

Through Tuesday...

High pressure will continue to provide tranquil weather through
Tuesday. Calm to light/variable winds will be in place tonight
allowing for radiational cooling. Expect lows in the lower 60s
northwest to the mid 60s south, with around 70 in the immediate
Chicago metro. Southern areas will likely see a slower cool down
as dewpoints have hung on in the lower 70s, but should fall into
the mid 60s tonight. With the light flow, patchy fog may develop
but forecast soundings suggest that moisture will be very shallow.
Areas that received the most rainfall outside of the immediate
metro area are probably most favored and it may be that any fog
that develops is rather shallow.

The center of the high shifts east tomorrow but winds will
continue to be light. This will support a lake influence setting
up once again which will keep lakeshore areas around 80 for highs
while the rest of the area sees highs in the mid/upper 80s once



259 AM CDT

Wednesday night through Sunday...

An upper level disturbance generally emanating from the Pacific
Northwest will approach the Mississippi River Wednesday night. The
leading shortwave bring increased chances of precipitation
Thursday. The main shortwave moves overhead around Friday, which
would bring continues chances for rain showers, possibly a few
thunderstorms and slightly below normal temperatures in the upper
70s to low 80s. The low will pull east late in the weekend
decreasing precipitation chances.



For the 18Z TAFs...

High pressure will be in place through the period allowing Lake
Michigan to influence the winds at all sites but RFD. Large scale
flow remains north-northwest this afternoon with the lake having
helped turn winds north-northeast at ORD/MDW/GYY. Radar shows a
boundary moving inland and positioned over ORD/MDW at 1730z.
Wind obs at each site have shown an increase in variability and
even a westerly direction which has probably been caused by
convergence just ahead of this boundary. Expect the boundary to
slowly continue inland and winds to become easterly behind it in
the next few hours if not sooner. Recent MDW and lakefront obs
already show an east direction but some variability may occur with
the slow moving boundary still nearby.

Otherwise winds will diminish and may even be calm overnight.
Will continue with MVFR vsby mention at RFD/DPA/GYY but it may be
that shallow ground type fog develops vs. a larger scale uniform
vsby reduction. The high drifts east but keeps its influence in
place Tuesday. Light and variable winds will likely persist
through the morning so its tough to pin a direction down. By
afternoon, a east to southeast lake influence is favored at
ORD/MDW with an east to northeast direction favored at GYY.



205 AM CDT

The cold front associated with the low over Ontario shifts southeast
of the lake early this morning.  West to northwest winds diminish as
the gradient weakens today and a lake breeze is expected.  High
pressure moves over the lake early Tuesday morning. Winds become
light and variable over the southern end of the lake and southwest
10-20 kt over the northern half.  Winds will be light and variable
Wednesday, but then become north to northeast Wednesday night as the
high shifts east.  Winds remain northeast through the end of the
week as a weak low moves over northern IL Thursday night.






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