Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 150859

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
359 AM CDT Sun Oct 15 2017

241 AM CDT

Through tonight...

The heavy rain threat has ended across the region, so the flash
flood watch will be allowed to expire. An area of many light to
occasionally moderate rain showers continues across the I-55
corridor and points east early this morning. This area of rain
will gradually shift to the southeast this morning as a surface
cold front sweeps eastward over the area. Therefore, expect the
rain to end all together by early to mid morning.

The parent surface low has deepened to right around 1000 MB early
this morning, and is currently centered near Oshkosh, WI. Expect
this surface low to continue deepening down to around 990 MB
through the day as it shifts east-northeastward into southern
Ontario by this evening. As it does so, a strong cold front, now
approaching the Mississippi River, will sweep eastward across
northern IL and northwestern IN early this morning. Winds will
turn west-northwest and become quit gusty with its passage. Due
to the fast movement of this deepening low, strong pressure rises
of 8-10 MB/6hr are expected to overspread the area following the
frontal passage. The associated isallobaric response to this will
likely drive a short 1-2 hour period of very gusty winds up to
around 40 MPH around, or shortly after daybreak. Following this,
wind gusts will remain elevated through the day, but should
settle back down around 30 MPH this afternoon.

Temperatures behind this front are expected to go nowhere today.
In fact it appears that the current temperatures will be the highs
for the day. During the daylight hours, temperatures are likely
to reside in the 50s as a cooler airmass filters in over the area.
It also appears that in spite of the fact that the rain will be
ending, the cloud cover will not. Mostly cloudy skies will persist
through much of the day, but some breaks in the clouds are
possible this afternoon.

Surface high pressure will gradually build eastward from the
Central Plains through the day. As this occurs, expect wind speeds
to begin to abate across the area this evening. A gradual decrease
in cloud cover this evening should also set the stage for a very
chilly night across the region. Low temperatures tonight look to
drop down near 40, with mid to upper 30s also a good bet over
inland areas of Illinois. While some frost may develop late
tonight, it appears that it will remain relatively patchy across
portions of northern IL.



241 AM CDT

Monday through Saturday...

High pressure will remain dominate across much of the eastern
CONUS for much of next week. Overall, this looks to set up an
extended period of dry and increasingly mild weather for the
area. Temperatures are expected to warm back into the 70s by the
middle of next week.



For the 06Z TAFs...

-Lingering SHRA with occasional TS
-Timing wind shifts and gusty WNW winds around 30 kt.
-IFR Cigs ahead of the cold front, MVFR cigs behind it

The rain is not quite done yet, but thunder coverage is lowering
considerably. There will still be some VCTS over the next few
hours largely along and south of a PNT-ORD line. Next concern will
then be timing the cold front. Still appears on track for around
11z near ORD/MDW where ceilings will rise back to MVFR from IFR.
The peak winds do not come right with the front, but likely a few
hours behind it in the more significant pressure rises behind the
front. With a lower MVFR deck, mixing will be somewhat limited,
but gusts to around 30 kt are likely for time this morning. As
ceilings lift we will mix a bit more but winds aloft will be
diminishing a bit, but we still expect gusts into the mid to upper
20s into the early to mid afternoon. MVFR cigs will eventually
lift later today. Higher pressures arrive tonight and wind gusts
will drop along with clearing skies.



356 AM CDT

Deepening low pressure will continue to strengthen as it moves
toward Quebec. With the first seasonally strong cold front behind
this low, expect a period of gale force northwesterly winds, with
the prime window being after daybreak today through mid afternoon in
the strong pressure rises in wake of the low.

Following this low, high pressure will setup across the Ohio Valley
and eventually spread to the mid Atlantic region, while a series of
low pressure systems will pass by across Canada through mid week.
The pressure gradient will tighten to support near gale force winds
along the northern tier of the lake Tuesday and Wednesday. Otherwise
modest southwest winds will prevail for much of the week.



IL...Flash Flood Watch...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     until 4 AM Sunday.

LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     Sunday to 4 PM Sunday.

     Small Craft Advisory...nearshore waters
     until 7 AM Sunday.

     Gale Warning...LMZ777-LMZ779 until 7 PM Sunday.




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