Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 220842

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

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.



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.



For the 06Z TAFs...

No real big changes to the TAFs, as not anticipating any
significant weather at the terminals. Patchy mvfr/fog this
morning, mainly affecting DPA, will make way for just some
scattered high clouds through the period. Continued similar
thoughts with lake breeze potential later this afternoon, and not
include a wind shift at the terminals.




218 pm...A weak cold front has stalled over south/central
portions of Lake Michigan this afternoon. This front will lift
back north as a warm front tonight...shifting light winds back
southerly. A large trough of low pressure will remain nearly
stationary over the plains through early next week maintaining
southerly winds over the lake. This trough/front will move across
the Great Lakes region Tuesday night into Wednesday shifting winds
northwest with a period of 15-25 kts expected. cms





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