Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 121056
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
556 AM CDT Sat Aug 12 2017

.SHORT TERM...
230 AM CDT

Through tonight...

A broad upper trough is currently in place over much of the Great
Lakes region. This is helping to spark off some lake effect
showers over Lake Michigan early this morning as a colder airmass
shifts into the region. Expect isolated to widely scattered
showers to continue this morning over southern Lake Michigan, and
onto the southern shores of the lake. Much of this activity may
remain east of my area, but I cant rule out a few stray showers
impacted portions of Porter county early this morning.

Otherwise, surface high pressure will be gradually building
eastward towards the area through the day. This feature will
continue to help drive a northerly wind again for most areas.
However, areas near Lake Michigan in northeastern Illinois will
likely have the winds shift off the lake during the afternoon as a
lake breeze develops. These northerly winds down Lake Michigan
will also produce waves in excess of 4 feet into the shores of
Porter county Indiana, making for dangerous swimming conditions
through the day.

High temperatures this afternoon will be seasonally cool, but
pleasant, in the mid to upper 70s under partly cloudy skies. Skies
will then become mostly clear and winds will becoming nearly calm
across the area this evening. This will set the stage for a
rather chilly (low 50s) night across the region, with the
possibility for some radiation fog, especially outside the main
Chicago area.

KJB

&&

.LONG TERM...
235 AM CDT

Sunday through Friday...

Primary forecast concerns this period are rain/thunderstorms
Wednesday into Thursday with fairly vigorous upper trough...
with potentially another period of showers/thunderstorms
Friday/Friday night with a second upper trough.

Otherwise much of early next week will see continued dry
conditions with cooler then average max temps... and daily
lake breezes keeping lakefront regions somewhat cooler then
inland temps... albeit not significantly given warm lake water.
Upper flow exhibiting somewhat of an omega blocking pattern
over North America helping bring extended period of pleasant
conditions.  Ridge breaks down by Wednesday however with fairly
vigorous short wave energy moving across the area... bringing
next chances of rain/thunderstorms.

After a brief break Thursday evening... unsettled conditions
are poised to return Friday as another upper level trough
follows quickly on the heels of the previous.  Ridging/building
heights aloft return to the area later Saturday into next Sunday...
bringing a return of dry conditions with warmer temps.

Ed F

&&

.AVIATION...
For the 12Z TAFs...

Surface high pressure will gradually build in over the region
today and become centered over the area tonight into Sunday.
This will result in another day of northerly winds up around 10
KT across the terminals. Wind directions will likely trend more
northeasterly during the afternoon at the main Chicago area
terminals as lake breeze influences try to shift the flow off of
the lake. Otherwise, expect the winds to become light and variable
tonight as the surface high becomes centered overhead. VFR
conditions should persist through much of the period. However,
some patchy fog may develop late tonight near KRFD and KDPA, and
this could result in some MVFR, to possibly a brief period of IFR,
visibilities.


KJB

&&

.MARINE...
305 AM CDT

Low pressure near Georgian Bay early this morning will maintain a
brisk northerly flow across Lake Michigan into much of the day
today... with the pressure gradient gradually relaxing from the
west. Small craft advisory conditions will be felt along the
Indiana nearshore from around Burns Harbor eastward through this
evening.

High pressure over the upper Mississippi Valley will slowly build
east into the western Great Lakes later tonight and Sunday...
causing winds to diminish. Winds will further ease Monday into
Tuesday as a sprawling ridge of high pressure at the surface
dominates the area. South flow will increase Wednesday ahead of
low pressure moving east out of the northern Plains.

Ed F

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement...INZ002 until 10 PM Saturday.

LM...Small Craft Advisory...Burns Harbor to Michigan City IN until 10 PM Saturday.

&&

$$

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