Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161055

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
555 AM CDT Mon Oct 16 2017

208 AM CDT

Through tonight...

It feels a bit more like autumn this morning with readings in the
upper 30s to mid 40s or so. Other than some passing mid clouds
this morning, plentiful sunshine will be rule as high pressure
becomes established across the Ohio valley. This will be the
coolest day of the week, but the southwest winds on the back side
of the high will allow temps to recover to around normal, upper
50s to lower 60s. Northwest flow aloft may bring a few passing
clouds tonight, otherwise it will be another relatively cool night
with readings back in the 40s.



208 AM CDT

Tuesday through Sunday...

We re-enter another period of dry and unseasonably warm weather
throughout most of the long term as high pressure settles over
the upper Tennessee Valley. The ridge axis will extend southwest
across Texas and thus prevent moisture from spreading into the
midwest, while southwest flow locally will allow for a gradual
warming trend to occur throughout the week as southwest winds
dominate. A weak front will graze the northern tier of counties on
Thursday which will shift winds around to northerly briefly.
Otherwise the high will strengthen and build across the eastern
third of the county, and in conjunction with low pressure across
the plains will act to reinforce the mild southerly flow across
the region. Afternoon highs are expected to rise into the upper
60s Tuesday and Wednesday, upper 60s to low 70s Thursday, low 70s
Friday, and mid 70s by Saturday. Seasonal highs are typically
around 60/low 60s for the early-latter portion of October.

An upper trough is expected to move onshore over the west coast late
in the week and spread across the Great Plains and Midwest over the
weekend. Surface ridge axis will get shunted farther east out ahead
of the wave allowing gulf moisture to flow back up across the plains
and Midwest with dew points pooling back around 60F along a cold
front. The front is expected to sweep across the local area either
late Saturday night or Sunday, with the latter time frame favored
at this distance. This still looks to be the next decent chance
for showers and possibly a few thunderstorms in the area, though
the t-storm threat appears on the low side as the system is upper
level support is rather broad. A bit more fall-like conditions
return behind this front.



For the 12Z TAFs...

Surface high pressure will dominate across the Central
Mississippi Valley through the period. This will result in quiet
weather across the region, with a westerly wind. VFR conditions
are expected through the period.



301 AM CDT

The main weather concern over Lake Michigan this week is the
increasing potential for a period of high end southerly gales over
the northern half of the lake on Wednesday.

In the near term, northwesterly winds up to 25 kt continue across
southern Lake Michigan early this morning, and as of 240 am CDT,
waves at 45170 continue to be up over 7 ft. As a result, it is
likely that the small craft advisory will have to be extended
through the morning hours over the Indiana near shore waters. The
winds are expected to ease and back westerly during the day as
surface high pressure moves over the Mid Mississippi Valley. So,
waves will subside, but it may not be until late this morning, or
early this afternoon, that they drop below 4 ft.

The surface high is expected to become extended from the Lower
Ohio Valley to the Mid-Atlantic tonight into Tuesday, and will
remain dominate here through much of the week. Meanwhile, at
least two storm systems of note will shift eastward across Canada
through mid to late week. Ultimately, this looks to set up an
optimal surface pressure gradient over the lake to support a
prolonged period of stout west-southwest winds.

The first storm system, is forecast to reach a modest strength as
it shifts towards James Bay Tuesday morning. This system will
result in an uptake in the west-southwesterly winds over the lake
later today into tonight. However, expect the strongest southwest
winds to reside over the northern half of the lake tonight, where
30 to possibly a few 35 kt gales will be likely.

The second storm system is expected to be the main story of the
week, however, as it is forecast to be a much more potent area of
low pressure. As such, this will set up a very strong gradient
over the lake on Wednesday and Wednesday night. During this period
high end south-southwesterly gales of 40 to 45 kt will be
probable, especially over the northern half of the lake. If
forecast guidance continues to advertise this strong storm
system, a gale watch will likely be needed in the near future.



LM...Small Craft Advisory...IN nearshore waters until 10 AM Monday.




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