Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 231910

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
210 PM CDT Sat Sep 23 2017

209 PM CDT

Through Sunday...

Very warm temperatures continue to be the weather focus through
the near term forecast period this afternoon. Record temps
occurring again this afternoon, though with more pronounced lake
breeze now providing some relief locations near Lake Michigan.

Chicago O`Hare set another record high this afternoon in this
string of 90+ degree days in late September, reaching 95 degrees.
Lake breeze is about to push through both ORD and MDW as of 2 pm
CDT, which should allow temps to cool a bit, with current temps
along the lake shore in the upper 70`s and lower 80`s. Rockford
has also set a new record high temp for the 23rd, reaching 83
degrees this afternoon. Most other inland locations were
reporting temps in the lower 90`s.

While the upper pattern will remain similar across the CONUS
through Sunday, the core of the upper level ridge will shift a bit
to the east, with slightly lower thickness values across the
forecast area. 850 mb temps, which were +20C per DVN`s 12Z RAOB
this morning, are progged to cool slightly into the +16/18C range
Sunday, with correspondingly slightly lower daytime high temps.
Highs Sunday are still expected to be unusually warm (and near
records, which are 91 and 92 for CHI and RFD respectively) for
the time of year, ranging from 88-92 degrees based on low level
thermal progs. Light southeast low level wind field will again
support development of a cooling lake breeze across parts of the
Chicago area by afternoon, with winds becoming more easterly off
the lake.

Otherwise, cumulus field across western cwa could still produce an
isolated stray shower late this afternoon, though probability and
coverage are expected to be too low to carry pops.



328 AM CDT

Sunday through Friday...

Large upper level ridge and surface high will remain in place
late in the weekend, with similar conditions expected to persist.
As some slight moderation to the air mass is expected, temps will
not be as warm Sunday. Still think many locations will have a
chance at reaching the 90 degree mark though. 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 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 18Z TAFs...

Aviation weather concerns remain minimal this afternoon, with lake
breeze passage and shift to a more solid east-southeast wind at
ORD and MDW the only real issue. Extrapolation of current lake
breeze boundary would indicate a timing of about 19Z or so at MDW
and 20Z or so for ORD. Light southeast winds should prevail
overnight into Sunday, with another east-southeast lake breeze
push Sunday afternoon.

Otherwise, VFR conditions to prevail, except for potential for
some light MVFR fog again for DPA toward sunrise Sunday.



438 AM CDT

Southerly winds in place across the lake as high pressure is
still situated to the east, and while low pressure is over
Ontario. This low will continue to the northeast, with this high
not really making much movement to the east through the weekend
into early next week. As this high remains in place, additional
trough of low pressure will be in place to the west, helping to
maintain a southerly direction for much of the period.






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