Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 141755
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1155 AM CST Tue Nov 14 2017

.UPDATE...

The forecast is on track for today... mild with
increasing southerly winds and clouds. Look for showers to spread
into the area tonight. A few rumbles of thunder are possible
during the overnight hours.

Cronce

&&

.SHORT TERM...
307 AM CST

Through tonight...

Cloudiness will be on the increase today in advance of amplifying
shortwave trough approaching the region. Southerly winds in
advance of the system will push temps up several degrees over
yesterday`s high temps and actually a stone`s throw from the
average highs for the date.

Tonight, WAA strengthens as 35kt+ low level jet develops and
advects a plume of better moisture northward in advance of the
approaching front. The theta-e advection and isentropic ascent
will allow area of showers to break out tonight. Instability is
progged to be quite weak, but potentially sufficient to support an
isolated thunderstorm or two, so maintained the slight chance
thunder in the grids for tonight.

Cloud cover, moderate southerly winds, and rising dewpoints
should result in nearly steady temps tonight. Cold front will move
across the area Wednesday morning bringing an end to the showers.
Winds will shift to westerly behind the front and usher in some
drier, Pacific origin air, which should be rather mild and allow
highs to climb into the 50s for the time in over a week!

- Izzi

&&

.LONG TERM...
307 AM CST

Wednesday through Monday...

A slight cool down is expected Thursday in the wake of this
system, but WAA will begin quickly Thursday night in advance of
the next system. Medium range models continue to struggle in
delivering a consistent solution for the late week/weekend system
that we`ve been watching for days now. The latest ECMWF has backed
off considerably on the intensity of this system and now was a
weak, progressive shortwave trough, which would still bring precip
to the area followed by a fairly modest cool down. The GFS has a
much more powerful system with a much longer lasting and more
significant cold snap in its wake. Given the model uncertainties,
saw no reason to deviate from a blended model solution. Hopefully
tomorrow`s model runs will come into better agreement.

- Izzi

&&

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

Lower confidence with this set of TAFs with respect to timing of
MVFR/IFR cigs into the forecast area.

MVFR and IFR cigs well out to our west late this morning have
been slower to transition to the east. Forecast soundings
continue to suggest this slower transition to MVFR conditions
later tonight will continue with rain developing across the
region after 03z and continuing into the morning hours of
Wednesday. As the stronger lift associated with the approaching
storm sytem moves across northern Illinois Wednesday morning,
rain and IFR cigs will be the rule. Surface winds will be
southerly this afternoon with a few areas seeing gusts
approaching 20 kts at times, with a south to southeast flow
expected tonight at 10 to 15 kts. As a cold front approaches
the TAF sites Wednesday morning, we should see surface winds
veer more into a southwest direction with speeds at 10 to
15 kts.

SMITH

&&

.MARINE...
931 AM CST

No change to the marine forecast.
A very active pattern will continue for Lake Michigan for at
least the next several days. As high pressure moves east of the
Great Lakes region and low pressure develops over the western
plains, winds over the lake will become southerly and strengthen
as the low and an associated cold front quickly approach from the
west, while the high parks over the Eastern Seaboard. Winds are
expected to reach Gale Force this evening for the northern
portions of the lake where the gradient will be strongest. The
cold front will sweep across the lake on Wednesday, shifting winds
to nwly. A surge of colder air will help support and increase in
the nwly winds for a short period of gales Wednesday night.
another high will build across the lake Thursday bringing another
short period of relatively light winds, but another, stronger
system is expected to develop over the central plains on Friday
and deepen rapidly as it tracks across the Upper Mississippi
Valley Friday night. Another round of south gales will likely
develop in advance of this system. The low should continue to
deepen as it tracks across Lake Michigan Friday night, dragging
another cold front it its wake. There is a chance for higher end
nwly gales over the weekend as the low continues to deepen while
lifting int sern Canada and strong high pressure builds into the
plains.

Cronce

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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