159
FXUS63 KLOT 280807
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
307 AM CDT Tue May 28 2024

.KEY MESSAGES...

- Scattered thunderstorms expected this afternoon into early this
  evening, the strongest of which may produce locally gusty winds
  to 50 mph and hail to the size of a penny.

- Cool, but dry, weather expected Wednesday and Thursday,
  followed by moderating temperatures back into the lower 80s by
  early next week.

&&

.DISCUSSION...
Issued at 307 AM CDT Tue May 28 2024

Through Wednesday:

Water vapor imagery early this morning depicts our mid-level
impulse responsible for yesterday afternoons scattered
thunderstorms currently sliding east-southeastward right across
southeastern WI/ and far northeastern IL. The lingering showers
associated with this impulse will continue to hug the
southeastern WI shores of Lake Michigan through sunrise. Most of
our area remains dry this morning, but cannot rule out a few of
the ongoing showers in southeastern WI briefly shifting into
parts of Lake county IL during the predawn hours, before the
focus quickly moves offshore.

Following a quiet and dry morning, the focus for this afternoon
and evenings weather quickly shifts to the next impulse currently
noted in the water vapor imagery across the eastern Dakotas. This
feature will be the driver for yet another round of afternoon and
early evening thunderstorms as it digs southeastward into our
area. Similar to yesterday, low-level moisture is expected to
remain marginal through afternoon, as dewpoints remain in the
lower 50s. Accordingly, MLCAPE values will remain lackluster, with
values only peaking in the 500-800 j/kg range. Deep layer shear
is also not expected to be overly favorable for organized severe
storms as a result of the stronger mid-level flow remaining
displaced to the west and southwest of the area. Nevertheless,
unseasonably cold temperatures aloft (e.g. 500 mb temperatures
around -20C) are expected to again foster rather steep low to mid-
level lapse rates as surface temperatures warm into the low 70s
this afternoon. This may thus act to compensate for the meager
MLCAPE values and poor shear to at least support some low threat
for a few isolated pulse-type storms and loosely organized multi-
cell clusters that could become capable of producing a few
instances of locally gusty winds to 50 mph and possibly some small
hail. The threat of storms will wane shortly afternoon sunset,
though some lingering showers could persist through the evening.

The weather will quiet down for Wednesday, but temperatures will
be below average. Expect high temperatures Wednesday to only be
in the 60s to low 70s. The coolest temperatures will be near the
lake due to the persistent breezy onshore flow. Dangerous swimming
conditions are also expected along Lake Michigan beaches on
Wednesday due to enhanced wave action from the breezy northerly
flow down the lake.

KJB


Wednesday Night through Monday:

The windward side of a departing upper trough will spread
surface high pressure across the Great Lakes late Wednesday and
remain in the region into early Friday. This should keep
conditions quiet and clear Wednesday night and Thursday. We can
expect seasonably mild temperatures on Thursday with highs
forecast to reach the lower and middle 70s for most of us. Light
onshore flow will keep areas near the lake several degrees
cooler.

The high will begin moving away to the east early Friday and the
mild return flow will help pull highs into the middle and upper
70s to close out the work week. Clouds are anticipated to build
during the day as moisture is advected in aloft ahead of an
approaching shortwave disturbance. This wave is expected to
bring a push of showers across the region late Friday and
Saturday. There is spread on the timing and magnitude of the
wave with the GFS being the most aggressive with forcing. In any
case, while embedded thunderstorms look very achievable, really
no guidance is hinting at an overly supportive thunderstorm
environment. At this point, the greatest precip potential for us
here looks to be late Friday night through Saturday morning
meaning we`ll hopefully spend the bulk of Saturday rain-free.

There is rather poor agreement among medium-range guidance on
the regional synoptic pattern beginning early next week. It
does look to be a moderately unsettled one with various
disturbances floating around causing models to spit out sporadic
rain and storm chances Sunday through Tuesday. The GFS and Euro
over several runs have been bringing a cold front through the
region sometime between late Sunday and early Tuesday with an
appreciable thunderstorm environment building ahead of it. We`ll
continue to monitor this potential as model confidence for this
period builds. There is considerable agreement among
deterministic and ensemble guidance in a warmup to more early
summer-like conditions early next week just in time for the
dawn of meteorological summer!

Doom

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1236 AM CDT Tue May 28 2024

The primary aviation weather concerns through the 06Z TAF period
include:

* Showers and thunderstorms Tuesday afternoon into the evening
  with a corresponding potential for MVFR cigs/vsbys.

* A chance for additional MVFR cigs late Tuesday night into
  Wednesday morning.

Light westerly winds, at times variable, will take us through
the night underneath a SCT 3-5 kft deck moving into northern
IL from the northwest. Most of the morning will see WNW winds
below 10 kt before ramping up to around 10-12 kt for the better
part of the day.

Scattered showers and thunderstorms will move over the airfields
from the north and northwest Tuesday afternoon. The onset time
continues to trend later in model guidance, now looking like 18Z
at the earliest across all sites but could wind up being closer
to 19 or 20Z before we see rain. There is a solid potential for
some embedded thunderstorms as well, primarily through only
about 00Z. While we should remain predominantly VFR, we could
see periods of MVFR cigs or vsbys while storms are in the area.
Scattered rain showers will persist likely only through about
mid-evening, although there is a growing signal for light, non-
impactful showers to continue later into the night, especially
at the Chicagoland sites.

With the arrival of the rain, winds are expected to veer to NNW.
It`s very possible that we see brief, if not prolonged, periods
of a NNE direction during the afternoon, but overall confidence
in a NNE at any given time is shaky. Following the rain, near-
northerly winds below 10 kt can be expected through the rest of
the period. There is a moderate signal for MVFR cigs to develop
late Tuesday night into Wednesday morning, although best bet
looks like continued VFR.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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