Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161836
AFDLOT

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

.SHORT TERM...

Through Tuesday...

136 pm...No forecast concerns this period. High pressure centered
over MO/AR will slide east to TN/KY by morning and this will
likely allow some light southwesterly winds overnight...possibly
increasing some toward morning. So while temps will quickly fall
into the 40s this evening...they may end up holding steady in the
lower 40s overnight and then rise quickly Tuesday morning. Its
possible the usual cool spots and perhaps the southeast cwa may
dip into the upper 30s but confidence is low. Thus...no mention of
frost anywhere in the area tonight/Tuesday morning. Southwesterly
winds will steadily increase Tuesday morning and expect winds in
the 15-25 mph range with some higher gusts. Guidance highs in the
upper 60s look on track but with full sun and if low levels mix a
bit deeper...possible some areas will tag 70. cms

&&

.LONG TERM...
136 PM CDT

Tuesday night through Monday...

Quiet and seasonably mild conditions are expected for the remainder
of the week, with the next chance of precipitation coming Saturday
night into Sunday.

The broad ridge across the eastern CONUS that stretches from
Texas through the Great Lakes today will pivot slightly by early
Wednesday, aligning from east Texas into New England. This
orientation will continue to block any return of Gulf moisture into
the Midwest.  At the same time, a deep low will be moving across
Canada and creating a considerable pressure gradient against the
ridge to its southeast. This gradient appears to peak Wednesday
evening, though the strongest winds would likely be Wednesday
afternoon around the time of peak mixing. Decoupling with the loss
of diurnal heating appears likely to limit speeds later in the
evening.  If timing of the strongest gradient was a bit earlier in
the day, a wind advisory might have been worth considering.

The gradient relaxes Thursday and Friday with the passage of the
Canadian low into the eastern provinces, but the ridge to our
southeast remains in place and continues to block Gulf moisture. By
late Friday the situation begins to change as the center of the
ridge moves into the Carolinas and starts to open the western Gulf.
It will take a day or so for moisture to work its way into the upper
Midwest, but the anticipated approach of a cold front Saturday night
into early Sunday would provide a focus for this moisture advection
and the support for a wet Sunday.

Lenning

&&

.AVIATION...
For the 18Z TAFs...

1222 pm...Southwest winds 10-15kts with a few higher gusts this
afternoon will diminish under 10kts with sunset and then increase
again mid/late Tuesday morning. Gusts will likely increase to
20kts or so by midday Tuesday with speeds/gusts diminishing with
sunset Tuesday evening. Some passing thin cirrus possible
tonight...otherwise skc. cms

&&

.MARINE...
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.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IN nearshore waters until 3 PM Monday.

&&

$$

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