Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 252005

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
305 PM CDT MON JUL 25 2016

201 PM CDT

Through Tuesday...

High pressure will continue to provide tranquil weather through
Tuesday. Calm to light/variable winds will be in place tonight
allowing for radiational cooling. Expect lows in the lower 60s
northwest to the mid 60s south, with around 70 in the immediate
Chicago metro. Southern areas will likely see a slower cool down
as dewpoints have hung on in the lower 70s, but should fall into
the mid 60s tonight. With the light flow, patchy fog may develop
but forecast soundings suggest that moisture will be very shallow.
Areas that received the most rainfall outside of the immediate
metro area are probably most favored and it may be that any fog
that develops is rather shallow.

The center of the high shifts east tomorrow but winds will
continue to be light. This will support a lake influence setting
up once again which will keep lakeshore areas around 80 for highs
while the rest of the area sees highs in the mid/upper 80s once



305 PM CDT

Tuesday night through Monday...

High pressure over the area Tuesday night will very gradually
weaken on Wednesday and Wednesday Night with any forcing for
precipitation in the Midwest being to our north and south. The
latter forcing is a shearing/weakening upper low presently located
in the northern Gulf of Mexico. There is uncertainty in model
solutions as to what degree this interacts with the northern
stream trough forcing. Just how far north the channel of higher
theta-e air returns will depend on this. So while a chance for
showers and thunderstorms over a 48 hour window or so at this
time, overall there still is not a signal for high impact weather.
Obviously with the moist air mass to our south, that could

Despite the difference in model solutions for Thursday-Friday,
there appears to be a quieter and drier weekend setting up than
last with northwest flow aloft and north-northeast flow in the
low-levels. Depending on the strength of this low-level flow,
that could bring a rip current threat to area beaches later
Friday/early Saturday.



For the 18Z TAFs...

High pressure will be in place through the period allowing Lake
Michigan to influence the winds at all sites but RFD. Large scale
flow remains north-northwest this afternoon with the lake having
helped turn winds north-northeast at ORD/MDW/GYY. Radar shows a
boundary moving inland and positioned over ORD/MDW at 1730z.
Wind obs at each site have shown an increase in variability and
even a westerly direction which has probably been caused by
convergence just ahead of this boundary. Expect the boundary to
slowly continue inland and winds to become easterly behind it in
the next few hours if not sooner. Recent MDW and lakefront obs
already show an east direction but some variability may occur with
the slow moving boundary still nearby.

Otherwise winds will diminish and may even be calm overnight.
Will continue with MVFR vsby mention at RFD/DPA/GYY but it may be
that shallow ground type fog develops vs. a larger scale uniform
vsby reduction. The high drifts east but keeps its influence in
place Tuesday. Light and variable winds will likely persist
through the morning so its tough to pin a direction down. By
afternoon, a east to southeast lake influence is favored at
ORD/MDW with an east to northeast direction favored at GYY.



255 PM CDT

Little in the way of concern over Lake Michigan through the first
half of this week with high pressure over the Lower Great Lakes
region. A cool front inches its way down the lake Wednesday and
Wednesday night. Low pressure is expected to develop along this
front and move over the southern part of the lake late in the
week. There is uncertainty on how strong of a low this will be,
but it appears possible for 30 kt gusts sometime behind this
during the Friday/Saturday period and Small Craft Advisory
conditions in the Illinois and Indiana nearshore.






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