Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 111942

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
242 PM CDT Wed Oct 11 2017

1259 PM CDT

Through Thursday...

The system responsible for last night`s rain is lifting away from
the region.  Any lingering showers should come to an end through the
afternoon today, but an expansive area of low stratus will remain in
place through tonight and likely, through tomorrow as well.  Latest
forecast sounding suggest that some drier air will overspread the
nearly saturated lower levels late tonight and tomorrow, bring a
chance for some patchy drizzle and for for the late night into early
morning hours.  The blanket of stratus will also limit the diurnal
temperature trends with temps topping out today in the low 60s. Lows
tonight are expected to be in the low to middle 50s, but highs
tomorrow should only be a couple degrees higher than today, reaching
only the low 60s.


241 PM CDT

Thursday night through Wednesday...

Main concern in the extended is multiple rounds of rain Friday
night into Sunday. After an above average end to this week, next
week starts with more seasonal temperatures and a slow warm up
through mid week.

Dry weather is expected Friday as the upper level ridge hangs
over the region. Warm air advection will also result in high
temps in the low to mid 70s. Cloud cover will play a big part in
how efficiently we warm Friday with more cloud cover leading to
cooler temps. Precip forms to our north and west along an upper
level vorticity streamer Friday evening. Showers and a couple of
embedded thunderstorms spread across the region Friday night.

A surface low surges from northwest Missouri to Quebec Saturday
afternoon to Sunday afternoon. The low`s warm front lifts through
the region Saturday bringing another surge of warm air. High
temps will range from the low 70s along the IL/WI state line to
around 80 south of I-80.

Morning showers dissipate, but I`m expecting scattered afternoon
showers to form within the  warm sector. GFS suggests CAPE and
shear values that could support strong to maybe severe storms.
Similar to many systems lately, CAPE will be the limiting factor
for severe storms. PWATs will be well above average at around 2
inches, and this much liquid could lead to heavy rain. The line
of showers and storms pushes east of the forecast area Sunday
morning or early afternoon along with the low`s cold front.

Northwest winds and a push of cooler air follow the front with
highs Sunday in the 60s. Sunday night looks particularly blustery
as a secondary upper level trough and cold pool spread across the
region. Wind gusts around 25 MPH are possible. Lows in the low to
mid 40s are expected. The upper level trough should only produce
precip over the lake early next week.

The dry period continues through mid next week under high pressure.
Temps also climb into the upper 60s by mid week as well.



For the 18Z TAFs...

Main forecast concerns for the period are cigs, any lingering shra
and the potential for fog late tonight into early tomorrow

A widespread deck of ifr-mvfr cigs will remain over the region as
nely flow on the swrn periphery of a slowly lifting upper low
persists through tonight and tomorrow. There has been some diurnal
improvement to cigs this afternoon, with many locations lifting to
lower end mvfr, but expect that this improvement will be brief and
cigs should lower again to widespread ifr toward sunset. Latest
cig guidance suggests that cigs in some locations could lower to
lifr, but expect that ORD/MDW will likely remain at 500 ft or
above, with DPA/RFD/GYY possibly seeing cigs lower to less than
500 ft. Latest radar imagery indicates some sct shra lingering
over nern IL/nwrn IN in nely-enely flow. Any lingering shra should
end early this afternoon as the main upper low continues to lift
to the northeast. A ridge of high pressure building across the
region overnight tonight should allow winds to drop off the
generally lgt/vrbl. With the diminishing winds will come a chance
for fog development in the very moist air mass in place. Drier air
spreading in aloft over the nearly saturated lower levels could
bring some patchy drizzle overnight as well. As the high moves to
the east tomorrow and a trough of low pressure moves out across
the nrn/cntrl Plains, winds will trend to more sely tomorrow and
cigs should improve to mvfr through the day, though a bkn-ovc cig
should persist through the day.


241 PM CDT

Kept current Small Craft Advisory as is as winds and waves will
slowly subside through tonight.

Low pressure over Ohio weakens as it continues east, and high
pressure spreads over the Great Lakes this evening. East winds
diminish this evening and veer to southwest by Thursday night. A
stationary front over the southern end of the lake Friday night
will lead to north winds to the north of the front and southerly
winds to the south of the front.

The next surface low forms over northwest Missouri Saturday
afternoon. The low`s warm front surges two thirds up the lake
before the low passes over the lake Saturday evening/night. Wind
gusts up to 30 kt are expected. Winds become north to northwest
behind the cold front and gales are expected Sunday.

High pressure spreads over the Great Lakes Sunday night and then
passes south of the lakes Monday night. West to southwest winds
10-20 kt are expected early to mid next week.



LM...Small Craft Advisory...IL nearshore waters until 5 AM Thursday.

     Small Craft Advisory...IN nearshore waters until 11 PM




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