Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240748

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
148 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 06Z TAFs...

Low pressure is over southern Manitoba late this evening and will
move to James Bay Friday evening while a trailing cold front
pushes across northern Illinois and northwest Indiana. Through the
day Friday, strong south-southwest winds will be in place ahead
of the approaching cold front. Warm air advection into the region
will result in poor low level lapse rates which will inhibit
effective mixing of 50-60kt winds between 015-020. Still,
anticipate being able to mix down frequent gusts into the mid to
high 20 kt range and would expect at least a few sporadic 30+ kt
wind gusts. Cold front will move across the terminals late in the
evening and overnight with winds turning northwest. There may be a
brief lull in gustiness immediately ahead of the front within the
frontal trough, but expect winds to become gusty again behind the
cold front as steep low level lapse rates develop. No
precipitation is expected with the front. There is still an off
chance for MVFR stratocu to develop behind the front but
confidence remains higher for conditions remaining VFR at this



235 PM CST

The active marine pattern continues with a gale event on Friday as
another deep low pressure moves eastward just north of the Great
Lakes. South-southwest winds will be on the increase tonight with
gales likely by sunrise over the open water. There is some
uncertainty over the nearshore areas, though gusts at and a
little above 30 kt are likely much of the afternoon. A cold front
will pass early Friday evening, and as winds turn northwest, there
could be a few hour period of occasional gale force gusts.
Otherwise 30 kt winds are likely.

The next system will influence the lake on Monday again as low
pressure passing north of the Lakes. Southwest winds on Monday
look to potentially reach gales later in the day or into Monday
night. The cold front is likely to pass sometime early Tuesday at
this point.



LM...Gale Warning...LMZ777-LMZ779...6 AM Friday to 9 PM Friday.

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

     Small Craft Advisory...IL nearshore waters until 6 PM Friday.




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