Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241133

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
533 AM CST Fri Nov 24 2017

147 AM CST

Through tonight...

The main weather story for today will be the very mild, but windy
conditions across the area today.

With the main storm track residing well north of the area, across
southern Canada, a potent area of low pressure will be driven
eastward today across Ontario. As this occurs, an associated
surface frontal trough will shift eastward across the Upper
Midwest towards the western Great Lakes later today into this
evening. Ahead of this approaching cold frontal trough
southwesterly winds are expected to increase and become gusty up
to 35 mph during the day. This in return will advect a lower-
level thermal ridge (featuring 925 mb temperatures up around
12-13C) east-northeastward across the region through the day.
Considering the magnitude of this warm air, and the fact that good
mixing should occur with the increasing wind field, I see no
reason why temperatures today should not top out around 60.
Therefore, no big changes have been made to the inhered
temperature forecast for today.

The approaching surface frontal boundary is expected to push
eastward across the area this evening. With this boundary there is
a small chance of a few light showers or sprinkles, but any
activity should be short lived. Otherwise, expect the winds to
turn northwesterly in the wake of this front tonight.



147 AM CST

Saturday through Thursday...

Following the passage of the cold front tonight, cooler conditions
are expected for Saturday. However, the heart of the cold air
following this front will remain to our east-northeast. Therefore,
we are expected a quick return to mild weather by Sunday, when
temperatures could top out around 50. Even warmer weather is
likely on Monday into Tuesday as another potent area of low
pressure shifts eastward across Canada. This again looks to result
in an increasing southerly wind, with the associated
north-northeastward advection of a warmer airmass over the region.
Temperatures both Monday and Tuesday could end up well into the
50s to near 60.

For the later half of next week it appears that above average
conditions will prevail. A weather disturbance could take aim on
the area later Wednesday into early Thursday, but at this time
this only looks to result in the possibility of a period of light
precipitation for the area.



For the 12Z TAFs...

No big changes to the TAFs, with VFR conditions and windy
conditions expected. VFR conditions in place will likely remain
through the entire period. Although a brief light shower or
sprinkle may occur this evening, it would not provide any lower
vis. Also, still a possibility for some lower stratus later
tonight into early Saturday morning. However, this chance is
appearing low at this time. Winds will increase through the
morning, with gusts reaching the upper 20 kt range by midday and
continuing into the afteroon. Still can`t rule out a few gusts in
the lower 30 kt range this afternoon. Cold front will then move
through the area later tonight, with winds turning to the



417 AM CST

As low pressure continues to move through Ontario while deepening
this morning, gradient across the lake has tightened. This is
helping for winds to increase all across the lake, with this trend
expected to continue this morning into the afternoon. Over the
open waters, this will support a period of gales to 40 kt
primarily during the day today but likely also extending for a
brief period later this evening. Across the nearshore waters,
these higher speeds will likely also be observed, but with the
higher gale potential remaining over the Indiana nearshore. Still
am monitoring the possibility for more prevailing gales over the
Illinois nearshore, but at this time, it is still appearing that
only a small window of gales will be possible this afternoon. Over
this area, this period should be small before a slight
diminishing trend that allow speeds to fall below gales occurs
this evening. A brief lull in winds may occur but expect speeds to
remain elevated out of the northwest tonight into Saturday, and
provide continued hazardous conditions for small craft.



LM...Gale Warning...LMZ777-LMZ779 until 9 PM Friday.

     Gale Warning...LMZ743-LMZ744-LMZ745...9 AM Friday to 6 PM Friday.

     Small Craft Advisory...IL nearshore waters until 3 PM Saturday.




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