FXUS63 KLOT 291017

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
517 AM CDT Fri May 29 2020

330 AM CDT

Through Saturday...

Light to occasionally moderate rain showers continue to drift east
southeast across the forecast area early this morning. Winds were
also quite gusty behind these showers with gusts to 25+ kts
commonplace across northeast IL. These stronger gusts have since
subsided and will continue to gradually diminish this morning.
Thanks to residual cloudiness low temps this morning will only
drop into the upper 50s to low 60s.

Temperatures will be notably cooler today beginning a stretch of
more seasonable to slightly below normal temps through the
weekend with highs in the upper 60s lakeside and far northern IL,
and low 70s elsewhere. Once lingering showers push off to the
southeast by late morning, expect mostly dry conditions across
the area. A few spotty showers/sprinkles may try to develop in
the afternoon as noted in some of the hi-res guidance, mainly SE
of I-55. Gusty northwest winds will also try to mix down to the
surface this afternoon.

By Saturday the upper level trough axis will be pushing off to
the east setting up northwest flow over the area with a mid-level
shortwave expected to move through. Currently expecting dry
conditions with this wave but a few sprinkles cannot be entirely
ruled out in the afternoon. Saturday looks to be another more
seasonable to slightly below normal day with highs in the low 70s
inland. The lake breeze will keep things cooler in the 60s near
the lake.



254 AM CDT

Saturday night through Thursday...

By Sunday, the Great Lakes will be positioned beneath the inflection
point of a high-amplitude wave as a deep upper-level ridge builds
over the central united States and troughing deepens across the
northeast. As is typically the case downstream of an upper-level
ridge, a surface high pressure system will be centered locally
Sunday afternoon leading to low humidity and light winds. Highs
should climb into the upper 60s to lower 70s before a lake breeze
surges inland through much of northeastern Illinois, dropping
temperatures into the lower 60s (50s along the immediate lakeshore).
All in all, Sunday looks like a pleasant day.

Early next week, the upper-level ridge will spread eastward leading
to warming temperatures and increasing chances for showers and
thunderstorms. In fact, deterministic model guidance suggests a
"ring of fire" pattern may become established as shortwave troughs
and associated waves of showers and thunderstorms round the top
of the ridge. Usually in such a pattern, we're treated with
repeated MCSs, each tracking a smidge further south as an
effective front is pushed away via outflow. There does seem to be
a signal the first wave will pass north of our area Monday with
another closer by sometime in the Tuesday night timeframe.
Additionally, there is a signal that the front will slip south
sometime in the Wednesday timeframe. However, signals are hardly
guarantees especially with warm season (and often wave-driven
and/or nocturnal) convection. South of the front and indeed across
our area at least early next week, highs in the mid to upper 80s
are a good bet. As the front slips south, highs should moderate
somewhat to the lower 80s. There may be a day next week where the
front stalls through northern Illinois allowing for areas to the
south to remain hot and muggy while others to the north are much
more comfortable. Nevertheless, the NBM PoPs looked fair with mid-
range chance from early next week onward. The "long" temporal
splattering of the PoPs is merely a reflection of not being able
to time or place individual waves of precipitation at this range
with the expectation that most hours will actually be dry.



For the 12Z TAFs...
517 AM CDT

There are no major aviation concerns through the next 24-36 hours.

Overcast skies this morning will clear from west to east before a
VFR stratus deck fills the skies by early afternoon. A few
sprinkles are possible through the evening hours. Northwesterly
winds will pick up by late morning with a few gusts over 20 kts
(except at GYY where a lake breeze will keep winds northeasterly
by early afternoon). Winds will slacken overnight and clouds will
scatter, with Saturday poised to be a repeat of today.





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