Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 210532

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1132 PM CST Mon Nov 20 2017

155 PM CST

Through Tuesday...

Strong high pressure centered over the Tennessee Valley and low
pressure moving through south-central Canada has set up strong
swly winds across the region. Along with broad warm advection,
temperatures across the region should top out in the low 50s this
afternoon with winds gusting to arnd 30 mph. Winds should remain
rather gusty through the night as well. As the low continues to
track east, just north of the Great Lakes, an associated cold
front will push into nwrn IL by daybreak tomorrow and quickly push
east through the CWA durg the morning hours. latest guidance
still suggests that the front should push east of the CWA by 18z,
with winds shifting from swly to brisk nwly. Temperatures should
reach the daytime high just in advance of the front and drop off
through the afternoon as strong cold advection sets up.
Temperatures should top out around 40 F across ncntrl IL and then
drop into the upper 20s to near 30 F shortly after sunset. Some
guidance is suggesting that there may be some light showers or
sprinkles with the fropa, but given a relatively dry airmass in
place ahead of the front, with sfc dewpoints on in the low 30s,
any pcpn would more likely be virga. So, will keep a dry forecast.


215 PM CST

Tuesday night through Monday...

After frontal passage on Tuesday, conditions look to be cooler
and dry through mid week. Some slight warming on Thursday will
transition 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. This warmth is brief as colder air returns for the
remainder of the weekend.



For the 06Z TAFs...

The gustiness of the south to southwest winds will likely grow
less frequent with time leading up to sunrise. Recent ACARS
soundings show winds around 2000ft have increased to around 50 kt
and while these winds will slowly ease overnight and veer more
westerly, the corresponding easing of the sfc winds will likely
result in a continued threat of LLWS. The LLWS threat should
diminish after sunrise and end altogether with cold frontal
passage Tuesday morning. Behind the front, winds will shift to
northwest and likely become gusty again as colder air spills into
the area. VFR cigs will likely persist through the period,
gradually lowering, especially behind the front Tuesday afternoon.


215 PM CST

Speeds have initially picked up over the southern portions of the
lake today, but with this increasing trend to continue across the
south and north portions for the remainder of the day. Still
anticipate gales developing over the entire open waters this
afternoon, with the current Gale Warning still on track. Gales to
40 kt still likely, and still am monitoring the possibility for
gales to 45 kt for a time tonight. Hazardous conditions for small
craft which are occurring along the nearshore will likely continue
into mid week. As was previously thought, the possibility for
gales to be observed for a time tonight into Tuesday morning
across portions of the nearshore is looking to likely occur and
have included the Indiana nearshore water in the Gale Warning late
this afternoon into Tuesday morning. Still monitoring the end
time for the gales on Tuesday, mainly for the open waters. Some
variability continues to be noted, and may need to adjust the end
time of the warning in place.



LM...Gale Warning...IL nearshore waters until 6 AM Tuesday.

     Small Craft Advisory...LMZ740-LMZ741-LMZ742...6 AM Tuesday to 6
     PM Tuesday.

     Gale Warning...LMZ777-LMZ779 until 3 PM Tuesday.

     Gale Warning...IN nearshore waters until 10 AM Tuesday.




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