688
FXUS63 KLOT 071110
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
610 AM CDT Sat Jun 7 2025

.KEY MESSAGES...

- Showers will develop this afternoon through the evening,
  mainly south of I-80 where a few isolated thunderstorms may
  occur.

- Sunday afternoon will have a better chance of scattered
  thunderstorms, particularly near and northwest of I-55, with a
  corresponding threat for strong to damaging winds.

- Following another chance for scattered showers and storms
  Monday afternoon, a period of drier and warmer weather is
  expected by the middle of next week.

&&

.DISCUSSION...
Issued at 321 AM CDT Sat Jun 7 2025

Through Sunday Night:

The weak surface high that brought us the tranquil weather
overnight will begin to get shoved east as the shortwave trough
currently over the central Plains propagates into the
Mississippi Valley and southern Great Lakes later today. While
recent forecast tends continue to show the core of the wave and
developing surface low tracking across central IL and IN, an
area of scattered showers is expected to develop across portions
of northern IL and northwest IN this afternoon. The highest
coverage of any showers will be south of I-80 where the
combination of better forcing and moisture overlap, but an
isolated shower or two cannot be ruled out for the rest of the
area. As for the thunder potential, the bulk of the instability
this afternoon is expected to develop south of our area in
central IL but some modest instability is still forecast for the
southern portions of our area. Therefore, think that an
isolated storm or two remains possible (20% chance) south of
I-80 as well.

Despite the showers and much more cloud cover than yesterday,
temperatures are still expected to warm into the upper 70s this
afternoon. However, persistent onshore winds will keep highs
near the lake only in the mid-60s.

The shortwave will continue to move east into IN and OH this
evening thus allowing showers to gradually taper from west to
east overnight. While most of the area should be rain-free
shortly after midnight, isolated showers may persist east of
I-57 into the predawn hours of our Sunday. As we enjoy a brief
hiatus from the rain Sunday morning, another upper trough will
be digging into the Upper Midwest and pushing a cold front
towards our area. Ahead of the front temperatures will warm
quickly into the upper 70s and low 80s under mostly sunny skies
with dew points climbing into the upper 50s to around 60. These
conditions are forecast to result in a few hundred joules of
CAPE developing across northern IL which should be sufficient to
generate scattered showers and thunderstorms Sunday afternoon
along the front especially northwest of I-55.

Furthermore, a stout 500 mb jet streak is expected to pivot
around the base of aforementioned trough on Sunday resulting in
30-35 kts of bulk shear across the area. While shear of this
magnitude is sufficient for severe weather, the veering winds
ahead of the front and modest mid-level lapse rates suggest that
forcing along the front and deeper instability may be a
limiting factor. That said, still think an isolated strong to
severe storm is possible Sunday afternoon, mainly across
northwest IL, with damaging winds being the primary threat.

Regardless, thunderstorm coverage is expected to wane with
eastward extent as the front outruns the upper trough and better
instability. However, showers will prevail through Sunday
evening before tapering overnight though most should be rain-free
by midnight Sunday night. Otherwise, expect clearing skies with
lows in the mid-50s heading into Monday.

Yack

Monday through Friday:

The upper-level low will shift into the western Great Lakes on
Monday. As it does, an embedded impulse rotating around it`s
southern periphery is slatted to foster a period of scattered
afternoon showers and thunderstorms as it tracks across southern
WI and northern IL during peak heating on Monday. Low-level
moisture is not expected to be overly impressive as this impulse
tracks overhead (dewpoints only around 50). However, steepening
low to mid-level lapse rates during peak afternoon heating beneath
of a pool of unseasonably cold temperatures aloft (500 mb temps
of -18 to -20C) look to support ample destabilization (MLCAPE
values of 500 to 800 j/Kg) supportive of thunderstorm chances. We
will have to also keep an eye on the potential for a few stronger
storms capable of producing strong gusty winds across far
northern IL given what looks to be rather well sheared
environment. This threat should wane quickly early Monday evening.

Even outside of the shower and storm chances Monday afternoon,
conditions look to be rather breezy during the day, with WSW to
west winds gusting up to 30 mph. Thereafter, a deamplifying mid-
level ridge is expected to cross the region for the second half of
next week. Accordingly, this will support a period of drier and
warmer weather. Thus, after a cooler start to the work week, with
highs in the low to mid 70s, temperatures are expected to rebound
back into the 80s mid to late week away from any lake cooling.
Shower and some thunderstorm chances may then return to close out
next work week.

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 610 AM CDT Sat Jun 7 2025

There are currently no significant aviation weather forecast
concerns through the period.

Our area will remain along the southern periphery of an area of
surface high pressure over the Upper Great Lakes today. This
will continue to foster east-northeasterly winds up around 10
kt during the daylight hours of today.

A mid-level weather disturbance will track eastward into IL late
this afternoon and evening, with an associated area of showers
expected to develop eastward across much of central and portions
of northern IL. As mentioned in the previous discussion, it
appears a majority of the rain, and any lower CIGs will largely
pass south of the terminals into this evening. However, with the
main Chicago area terminals likely to reside right along the
northern periphery of the rain showers, it appears a period of
light showers may impact the Chicago area terminals for a
period this evening. Accordingly, we have opted to continue this
mention in the latest TAFs for the Chicago area terminals from
02-06Z this evening.

Otherwise, expect winds to become light and variable overnight,
before settling into a westerly direction later Sunday morning.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Air Quality Alert until midnight CDT tonight for INZ001-INZ002-
     INZ010-INZ011.

LM...None.

&&

$$

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