Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 300756

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
256 AM CDT Fri Sep 30 2016

240 PM CDT

Through Tonight...

Similar to the past couple days, and upcoming ones for that
matter, tonight will continue to be dominated by the large
closed upper low centered over Kentucky this afternoon. Mid-
afternoon visible satellite imagery has indicated some breaks with
more cumuliform clouds across northern Indiana into far eastern
Illinois. Isolated showers are likely to fill in there and cannot
100% rule out a lightning strike or two. Further to the north, a
ribbon of scattered to numerous showers will continue within the
wraparound moist conveyor belt of the occluded system. This axis
will persist into this evening with likely an uptick in showers
later this evening from lift of a left entrance region of the
upper jet wrapping around the low center.

Clouds overall will continue tonight, even if some areas see a
break late in the day into early evening. This along with the
continued winds will prevent temperatures from falling much at all
with lows in the mid to upper 50s, and likely around or above 60
near the lake shore.

Speaking of the lake shore, continued battering waves of 7 to 11
ft through tonight will probably cause some minor flooding in
typical vulnerable areas immediately along the lake front. The
upstream mid-lake south buoy has been steady around 7 ft today,
and would expect to see around 115-125% of that within our
northeast Illinois nearshore given the flow pattern. The Wilmette
buoy has been near that, with 8-9 ft a good part of today and
webcams and pictures supporting that. While that is borderline
for what usually causes flooding, have seen around a 15 inch
increase in lake levels the past 48 hours from the constant
northeast flow and that could inch up the next 12-18 hours.



317 PM CDT

Friday through Thursday...

Friday will be another blustery fall day as the upper level low
pushes north.  Occasional rain showers as we`ve been seeing for the
past few days will continue, and the best chance of showers will be
east of a McHenry to Pontiac line closer to the main low.
However, showers are possible across the warning area. Models
feature minimal CAPE along and south of I-55, but think a couple
embedded thunderstorms will be possible Fri afternoon. Severe
weather is not expected.

The tight pressure gradient will result in gusty winds. Gusts will
vary from up to 25 mph away from the lake to up to 30 mph along the
lakeshore.  The winds and damp conditions will likely make it feel
cooler than the mid to upper 60 degree high temps.

The low continues it slow path north resulting in much of the same
Saturday.  Periodic showers are once again expected, but winds will
be lighter and high temps will be slightly warmer.  The low shifts
northeast Saturday night. Guidance suggests lake effect showers will
be possible over northwest Indiana into early Sunday morning.
Guidance differs on how strong of a vort streamer will shift south
through the region Sunday. Decided to go dry but damp conditions and
perhaps a few sprinkles are possible. Sunday will be drier than it
has been lately.

An upper level ridge and surface high move overhead Monday leading
to much drier and warmer conditions. Highs should be in the low to
mid 70s by Tuesday.  The next system arrives mid to late next week
with the ECMWF having a faster solution than the GFS.  Kept thunder
out of the forecast for now since the cold front precip looks to
arrive Wednesday night. If the cold front arrives at a more
favorable time, we could see more thunder than currently



For the 06Z TAFs...

Not much change in guidance for the 6z set of TAFs. A batch of
rain showers will continue to drift westward as a multitude of
shortwaves on the north end of deep low pressure to our southeast
shift through the area. Cigs continue to fall early this morning,
and the axis of IFR cigs getting closer, and expect at least
occasional IFR cigs and at minimum low MVFR cigs overnight into
early Friday. It is possible to have a mix of MVFR and IFR during
the day but the propensity is to remain MVFR as there will be
break in the shower activity. Several compact shortwaves look to
increase shower coverage in the afternoon time frame, though
showers can really occur at any time in this pattern. Gusty NE
winds continue. Guidance is hitting IFR and even LIFR hard again
tonight. Will leave the return of IFR Friday night in place,
though confidence is low on this time frame to see if we keep the
IFR cigs around today or not.



255 AM CDT

Strong northeast winds will continue across the lake through
today before easing. Waves have eased a little but still hold near 5 ft at the
south buoy and around 7 ft at the Wilmette and Michigan City
buoys. Would expect these to hold steady or undulate slightly.
Winds to 30 kt remain a good bet today, especially for the south
half, and occasional gale force gusts also cannot be ruled out
this morning but 25-30 should generally rule. The threat for
waterspouts appears slightly lower today, but we may have a better
chance on Saturday. This is due to colder air aloft arriving as
the main low pressure system moves northwestward and we get some
additional wind convergence across the southern tier of Lake
Michigan from a surface low currently across the Ohio Valley that
will drift northwest as well. Waves may be slow to subside into
Saturday in spite of the wind field weakening, and it is possible
the current Small Craft Advisory for Illinois and Indiana needs to
be extended through Saturday morning. Much quieter conditions
arrive Sunday into early next week as the low will finally kick
eastward and high pressure will approach from the northwest.



IL...Lakeshore Flood Advisory...ILZ006-ILZ014 UNTIL NOON Friday.

IN...Lakeshore Flood Advisory...INZ001 UNTIL NOON Friday.

LM...Small Craft Advisory...NEARSHORE WATERS
     UNTIL 4 AM Saturday.




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