Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241736

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1236 PM CDT FRI JUN 24 2016

228 AM CDT

Through tonight...

Today through tonight:
Early this morning winds have become light and variable, as high
pressure was centered north of Illinois but providing enough of an
influence with the lack of a gradient. IR satellite imagery shows
just a few pockets of mid-level clouds across Southern Lake
Michigan. Temperatures have been slow to cool early this morning,
but with dew points in the 50s to lower 60s in the far south and the
recent rainfall from Wednesday, areas of fog and perhaps patchy
dense fog will linger through daybreak.

With minimal cloud cover expected later today for the bulk of
Northern Illinois/Northwest Indiana, some thicker cirrus clouds will
skirt southern LaSalle/Livingston/Ford counties through early
afternoon. Otherwise mostly sunny skies are expected, allowing
temperatures to warm well into the lower to middle 80s. The
exception will be areas adjacent to Lake Michigan, where the
onshore/lake breeze development will maintain much cooler air
flowing inland and highs will struggle to move beyond the lower 70s.

500mb heights will steadily rise overhead this evening, with the
surface ridge axis drifting east towards the Eastern Great Lakes.
The moist channel will remain well west of the area tonight;
however, expect winds to turn slowly southeasterly to southerly and
may be enough to keep temps a little warmer in the lower 60s.



228 AM CDT

Saturday through Thursday...

Saturday through Sunday: The longwave flow should remain somewhat
progressive, with operational guidance indicating the mid-lvl ridge
axis will arrive early Saturday then shift east by the afternoon.
This will allow the moisture rich, return flow to pivot east from
the Central Plains into the Western Great Lakes. Robust shortwave
will be sliding east across Southern Alberta/Manitoba late Sat ngt,
so expect the best forcing/dynamics will be displaced well north of
the forecast area. This should keep any thunderstorms that develop
below severe limits; however, given that Td`s will be approaching
70, it`s possible that the slow moving nature of storms could lead
to flooding concerns and brief heavy downpours from storms. Despite
rising Td`s Sat, and slowly thickening cloud cover, highs should
still be able to push into the upper 80s to around 90. This will
also translate into heat indices in the lower/middle 90s.

Sat ngt will remain very mild/muggy, with temps likely remaining
around 70 to the lower 70s. Forecast guidance continues to heavily
favor Sat ngt/early Sun for the most probable timing of
rain/thunderstorms, so have adjusted POPs accordingly. The focus
continues to be along and north of a Mendota to Waukegan line.

Sun will feature a weak frontal boundary pushing east, which could
be enough to agitate the environment and allow a few thunderstorms
to develop. Nonetheless another warm/humid day is expected with
highs around 90 and heat indices into the lower/middle 90s. High
pressure will then arrive Sun ngt, pushing Td`s down with less humid

Monday through Friday: Forecast guidance continues to feature a
pattern change for much of next week, with high amplitude ridging
building into the Western CONUS/Canada. This will translate into a
quasi-northwest flow across the Upper Midwest/Great Lakes region
through at least the middle of next week. Presently surface ridging
will remain overhead with temperatures ranging from the low/mid 80s
Mon, then in the 70s both Tue/Wed. Towards the second half of next
week, the surface ridge begins to push east, allowing increased
chances for rain/thunderstorms and temperatures returning to around
80/low 80s.



For the 18Z TAFs...

A band of MVFR to low-end VFR cigs are southwest of the eastern
terminals, and expecting BKN low-end VFR clouds at RFD. Clouds
will thin tonight. East winds become southeast overnight as the
high overhead shifts east. South-southeast winds around 10 kt are
expected tomorrow with continued VFR conditions. High level clouds
will be increasing from west to east in the afternoon ahead of the
next system.



345 AM CDT

With a large area of high pressure settling over Lake Michigan
today, the lake will be dominated by on-shore lake breeze flow.
However, winds will become southerly and increase through the day
Saturday in response to a deep low pressure system and associated
cold front developing from Manitoba through the northern plains.
South winds should increase to 15 to 25 KT by Saturday afternoon.
The cold front should sweep across the lake Sunday, bringing a
wind shift from southerly to westerly. A secondary cold front or
surge of cooler air should push down the lake Monday as the
surface low moves to northern Quebec. Brisk northerly winds should
develop by Tuesday as high pressure drops into the Upper
Mississippi Valley while the low sits over northern Quebec.





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