Area Forecast Discussion
Issued by NWS Chicago, IL

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487
FXUS63 KLOT 221733
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1233 PM CDT Fri Sep 22 2017

.UPDATE...
1028 AM CDT

Going forecast appears to be in fine shape this morning, and no
changes are needed.

Forecast area remains on western periphery of surface high
pressure ridge, which is centered over the eastern Lakes and Ohio
Valley. Morning RAOBs from DVN and ILX both sampled +20C at H8,
and +25/24C at H9 respectively. Warm start to the morning has
allowed temps to warm into the mid-80`s already as of 10 AM CDT,
and low-mid 90`s appear on track for this afternoon. Weak
southeasterly lake breeze should hold temps down a little along
the immediate Lake Michigan shore. Record high temps of 92 at
Chicago and 93 at Rockford should be withing reach.

Going forecast has this all well in hand. Will freshen text
forecasts late morning for wording, but otherwise no changes
needed at this time.

Ratzer

&&

.SHORT TERM...
341 AM CDT

Through tonight...

Main forecast concerns/challenges are with continued warmth, as
another day of temps well into the 90s are expected today. No big
change in the air mass will support temps similar to Thursday,
with low to mid 90s expected area wide. This will be supported by
an abundance of sunshine, once early morning dense cirrus shifts
to the east. Winds do turn onshore today, but think locations near
the lake will rise to around 90 before this lake breeze cools
temps down some. Dewpoints in the upper 60s will provide another
humid day, with heat index values in the mid to upper 90s. Some
guidance showing some isolated convection developing across the
south/southeast CWA later this afternoon. However, would think
that if anything does develop during this time, that it should
stay just outside of the area.

Rodriguez

&&

.LONG TERM...
341 AM CDT

Saturday through Thursday...

Large upper level ridge and surface high will remain in place
through the weekend, with similar conditions expected to persist.
As some slight moderation to the air mass is expected, temps may
not rise as high on Saturday. Still think many locations will have
a chance at reaching the 90 degree mark though, with this a
possibility on Sunday too. By early next week, upper level ridge
shifts to the east while a trough moves through the central CONUS.
As this trough and surface low push east through the region, will
see precip chances returning late Tuesday into Wednesday. This
will also be an end to the warmth, as a much cooler air mass will
move in behind this system.

Rodriguez

&&

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

Very quiet aviation weather to continue through the next 24-36
hours. Only real concern will be a shift to east-southeast winds
Saturday afternoon, with lake breeze expected to impact Chicago
metro terminals. Only few VFR clouds expected through the period.

In the near term, south winds (generally 190-220 deg) around 10
kts are expected to persist through this afternoon, with the lake
breeze boundary not moving through the terminals.

Ratzer

&&

.MARINE...
429 AM CDT

Mainly southerly winds in place across the lake as high pressure
is situated to the east, and while low pressure is across the
central Plains. This low will lift to Ontario today through
tonight and as this occurs, expect winds to see an increase in
speeds. This will especially be the case across the north half,
with speeds dropping off the further south down the lake. With
weak gradient/winds in place over the far southern portions of the
lake, should see winds turn onshore across both the IL and IN
nearshores. No real big change in the overall pattern will support
similar wind direction/speeds through the weekend.

Rodriguez

&&

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

$$

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