Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 011138

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
638 AM CDT Fri Jul 1 2022

Issued at 347 AM CDT Fri Jul 1 2022

Through Saturday...

There are a couple of systems that will impact today`s weather,
one being a weak cold front moving into the northwestern portion
of our CWA (Winnebago/Ogle Counties) as of this writing. The other
is a mesoscale convective system (MCS) presently located on the
border of central Nebraska/Kansas. These two systems will provide
a couple of opportunities for showers and possible thunderstorms
today into this evening.

Regarding the above mentioned cold front, southerly winds ahead of
this front will pump up higher dewpoints in the low to mid 60s,
providing fuel for scattered showers ahead and along the front
during the pre-dawn morning. A thunderstorm or two cannot be ruled
out, with a few hundred J/kg of CAPE forecasted early this morning
along the front. The front will continue to move towards the
southeast, and is expected to be around I-80 by mid-morning. The
addition of heat from the sun, the right-entry region of 110 kt jet
max, and dewpoints increasing into the upper 60s will add to an
unstable atmosphere, mainly along and south of I-80. Models show a
jump in CAPE up to 1000+ J/kg by mid to late morning, while even
higher CAPE (1200-1300 J/kg) are forecast further south. As the
front moves further into this more unstable atmosphere southeast of
I-55, the chances for thunderstorms will increase. There is the
possibility of some storms reaching severe criteria, with the main
threat being strong winds and possible hail. The front is expected
to exit to the southeast by mid to late afternoon, with winds
shifting to the northwest behind the front.

It is during the late morning/early afternoon that the MCS is
modeled to move into the CWA from the west. There is a bit of
disagreement on the exact path of this system, with some models
keeping the precipitation south of I-80 (HRRR, NSSL-WRFARW), while
other models has precipitation coverage up to the
Wisconsin/Illinois state line (RAP). All of the tracks indicate
some heavy showers at least from I-88 south this afternoon into the
early evening from this system. Chances for thunderstorms are
expected to drop after sunset as the MCS moves along the same path
as the cold front, with precipitation expected to end by early
evening to the north, and mid evening to the south.

Cloud cover and the eventual cold front passage will keep
temperatures into the low to mid 80s today, but it will be a little
muggy thanks to the high dewpoints. Dewpoints will drop near 60,
with mid 50s towards the northwest Friday night. Winds will be light
and possible even variable as high pressure moves in behind the
front on Saturday. Temperatures should reach into the mid 80s for
most of the CWA, although locations near Lake Michigan will see
temperatures in the mid to upper 70s. There is a slight chance for
some showers in the far southwestern section of the CWA from a weak
upper wave, but most of the CWA will be dry Saturday.



Issued at 250 AM CDT Fri Jul 1 2022

Saturday night through Thursday...

Potentially more active west-northwest flow pattern will develop
over the region next week, with multiple chances for showers and

Prior to the more active pattern becoming established, we will eek
another day of tranquil and warm summer weather Sunday with
comfortable humidity. Skies should be mostly sunny Sunday with
highs well into the 80s, except only in the 70s during the
afternoon near Lake Michigan.

Monday through Thursday next week, medium range guidance is in
pretty good agreement on the overall large scale pattern which
will feature a gradually strengthening upper level ridge over the
central and western CONUS. That looks to leave the Midwest and
lower Great Lakes region in a potentially active west-northwest
flow pattern with periodic bouts of showers and thunderstorms
through the period.

Operational runs of the GFS and ECMWF both suggest a convectively
enhanced shortwave trough will move across the region Monday with
showers and thunderstorms developing during the afternoon. A look
under the hood at the ensembles shows much greater variability
precip potential for Monday, so opted to stick with the chance
pops offered up by the NBM. Between Sunday and Monday, Sunday
looks to be a much safer bet for any outdoor activities, while
Monday afternoon and evening look iffy. Certainly possible all or
portions of the area could dodge rain Monday afternoon and
evening, but also entirely possible that it could be pretty
rainy/stormy during the afternoon and evening if the 00z
operational runs of the ECMWF and GFS were to verify.

Unfortunately, there is little skill in attempting to resolve
these small scale disturbances that become convectively often
become enhanced and traverse the edges of the upper ridge. Given
the lack of model skill in handling these type of features, left
with no choice to carry chance pops each period Monday afternoon
through Thursday. Ultimately, there will likely be far more dry
hours than rainy hours during this period, but one or more bouts
of showers and storms are possible. Also, worth noting that any
more robust convective cluster could push the effective boundary
and convective wave train farther south than currently indicated
by medium range guidance, which could ultimately result in a
sizable period of dry weather during this time frame. Ultimately,
anyone with outdoor plans should monitor later forecasts. Even
though there are technically rain chances each day, eventually
there will likely be some sizable periods of dry weather that
get carved out in later forecasts.

With the heart of the upper ridge likely to remain to our west and
southwest, temperatures should generally be seasonable this
upcoming week. Afternoon high temps could be cooler than indicated
in the forecast anywhere impacted by any daytime/afternoon rain
or thick debris cloudiness.

- Izzi


For the 12Z TAFs...

* Wind shift to NE expected late this morning for Chicago
* Chance of SHRA, perhaps ISOLD TSRA, especially south of Chicago
  late morning through mid afternoon

Lake enhanced cold front will blow in off the lake late this
morning resulting in a wind shift to northeast late this morning.
An upper level disturbance over Iowa will track east toward the
area this morning. Starting to see signs that the better chance of
SCTD SHRA/ISOLD TSRA will stay south of Chicago terminals, but it
could be close and confidence is not high enough to remove the
TEMPO SHRA. The chance of TSRA in the VC of ORD and MDW isn`t
zero, but appears low (20-30% chance) late morning into early this
afternoon. Outside of any SHRA, VFR conditions will prevail through
the TAF cycle.

- Izzi




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