942
FXUS63 KLOT 261935
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
235 PM CDT Wed Jun 26 2024

.KEY MESSAGES...

- Dangerous swimming conditions at Lake Michigan beaches into or
  through Thursday afternoon.

- Strong to severe thunderstorms and flash flooding are possible
  Friday night into Saturday.

&&

.DISCUSSION...
Issued at 235 PM CDT Wed Jun 26 2024

Through Thursday Night:

Following a warm and less humid afternoon behind the cold front
passage, a quiet and relatively cool night is in store, especially
by recent standards. Forecast lows tonight are generally in the
55-60F range outside of Chicago, and lower 60s in and near the
city. A secondary surge of cold air advection, strongest down
the length of Lake Michigan, will enhance northerly winds and
result in building waves. The enhanced northerly winds should
continue until high pressure centers over the lake tomorrow
(Thursday) afternoon and causes speeds to steadily ease. As a
result, high (but gradually subsiding) waves and strong currents
will persist into the afternoon. With this in mind, will be
extending the Beach Hazards Statement for northeast Illinois and
northwest Indiana beaches through the mid afternoon hours.

Aside from the dangerous swimming conditions, there are no other
concerns through Thursday night. The most comfortable daytime
conditions in weeks can be expected, with inland highs in the
mid 70s to near 80F, upper 60s to lower 70s near the lake, and
dew points in the upper (locally mid) 40s to mid 50s. Favorable
radiational cooling conditions to start Thursday evening will
allow for similar low temperatures to those of tonight, though
increasing clouds and warm advection will result in steady or
slowly rising temperatures overnight into early Friday.

Castro


Friday through Wednesday:

A chance for showers and storms will return Friday and Saturday
as multiple shortwaves propagate through the area. Convection
is expected to form across the Mid and Upper Mississippi Valley
on Friday and move towards the CWA through the day. Instability
will be quite meager across the area with MUCAPE values below
500 J/kg resulting in decaying showers and storms reaching the
area through the day on Friday. The best chances for precipitation
are in the western portion in the CWA.

Southerly flow on Friday will bring a plume of moisture into the
area in evening leading to some elevated instability building
overnight. A shortwave may provide enough lift late Friday night
for elevated showers and storms to regenerate. Continued
southerly flow overnight and diurnal heating will allow some
modest instability to build Saturday. However, a warm nose will
keep things pretty well capped despite 1000-2000 J/kg of MLCAPE.
Any storms that are able to break through this cap and form
have the potential to become strong to severe given the modest
instability and 30-35 kts of deep layer shear bringing a threat
for strong winds and hail. With PWAT values expected to be in
excess of 2", these storms Friday and Saturday also pose a risk
for flash flooding.

High pressure will build into the region on Sunday bringing
quiet weather through Monday, though seasonably cool with
highs in the mid to upper 70s. An active pattern looks poised
to return Tuesday, brining shower and storm chances through the
middle of next week.

Carothers

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1226 PM CDT Wed Jun 26 2024

A cold front has been advancing southeast through the area this
morning bringing scattered showers to all of the TAF sites. It
is currently just south of KORD, however, some scattered
showers are still hanging around on the backside of the
boundary. Thus have opted for a prevailing VCSH at KORD through
19Z, KMDW through 20Z, and KGYY through 21Z. Clouds are
expected to clear out behind this boundary with VFR conditions
expected at all five TAF sites through the end of the TAF
period.

Northwest winds will shift to northeast this afternoon at KORD,
KMDW, and KGYY as a lake breeze pushes inland. A shift to
northwesterly winds will also occur at KDPA and KRFD later in
the evening. Winds will become stronger with a few gusts
possible with the northeasterly shift. Winds will remain
northeasterly through the end of the TAF period though the
strongest winds will be confined to areas near the shore of Lake
Michigan.

Carothers

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from 10 PM CDT this evening through
     Thursday morning for ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement from 10 PM CDT this evening through
     Thursday morning for INZ001-INZ002.

LM...Small Craft Advisory from 10 PM this evening to 10 AM CDT
     Thursday for the IL and IN nearshore waters.

&&

$$

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