Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 212053

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
253 PM CST Tue Nov 21 2017

226 PM CST

Through Wednesday...

The cold front quickly pushing across the region extends from
northern Indiana through central Illinois at 230PM CST.  A band of
pcpn along the front is filling in and some pcpn will continue invof
the front and should exit the far sern portions of the CWA by late
afternoon or early evening.  Temperatures are dropping off in the
strong cold advection behind the front and expect that temperatures
should be in the upper 20s to lower 30s by shortly after sunset.
Skies should clear out from west to east through the remainder of
the afternoon and into the evening with much of nwrn IL already
seeing scattering clouds.  with clearing skies and diminishing winds
overnight, there should be a radiative cooling component to the
downward temperature trend along with the cold advection.
Temperatures tonight should drop into the lower to middle 20s across
area, with some isolated upper teens possible in sheltered low-lying
areas.  With high pressure building in from the west tomorrow, winds
should be relatively light through the day and even with ample
sunshine, temperatures tomorrow will only reach into the lower to
middle 30s.


252 PM CST

Wednesday night through Tuesday...

Some slight warming likely early in the period, as more defined
shortwave energy drops south across the region. Associated surface
trough does push across the region on Thursday but stronger
forcing will stay just to the north/northeast of the area, along
with any precip. Right behind this system, little to no CAA,
transitioning to more pronounced WAA on Friday ahead of an
approaching system. Warmer temps, likely above normal, return
Friday along with precip chances by late Friday into the start of
the weekend. Guidance continues to vary to the extent of any
precip but as a fairly strong shortwave swings through, some
scattered development will at least be possible.



For the 18Z TAFs...

Main forecast concern for the period will be wind trends with the
passage of a cold front.

A narrow band of pcpn is moving east of the terminals at issuance
time, with only some lingering light rain likely at GYY for
another hour or so. With the pcpn, cloud bases should lower to
lower end vfr, 4-5 kft for the remainder of the afternoon. In the
strong cold advection and pressure rises following the frontal
passage, the gusty swly winds are shifting to nwly and should
remain gusty to 20-25 kt through the remainder of the afternoon.
By arnd 00z, the gradient should relax as high pressure begins to
spread across the Middle Mississippi Valley, allowing winds to
drop off overnight. As the colder, drier air filters across the
region, sky cover should diminish to mostly clear overnight with
no operationally significant cloud cover. As the high pressure
continues to spread across the region tomorrow, conditions should
be dry, with relatively light, westerly winds.


252 PM CST

The gales have ended across much of the lake this afternoon, and
have let the gale warning expire this afternoon. However, could
see a few gale force gusts continuing for a time this afternoon
and have included this mention in the forecast. Winds will remain
elevated through tonight, with winds to 30 kt expected. This will
provide continued hazardous conditions for small craft along both
the Illinois and Indiana nearshore waters tonight. However, some
diminishing trend tonight is expected along the Illinois side,
while waves remain elevated into Wednesday morning on the Indiana
side. As high pressure moves across the region Wednesday, this
diminishing trend will briefly continue for much of the lake.
Winds increase Wednesday night ahead of a trough of low pressure,
with a fairly active weather supporting another period of higher
winds Friday into the weekend when gales will once again be



LM...Small Craft Advisory...IL nearshore waters until 9 PM Tuesday.

     Small Craft Advisory...IN nearshore waters until 9 AM Wednesday.




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