Tinley Park, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

758
FXUS63 KLOT 302343
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
643 PM CDT Fri May 30 2025

.KEY MESSAGES...

- Isolated to widely scattered showers and thunderstorms are
  expected over primarily northeast Illinois and northwest
  Indiana this evening. A couple of storms may produce
  marginally damaging winds and small hail.

- Smoke from wildfires over central Canada will filter over the
  area this afternoon and tonight, with some smoke potentially
  reaching the surface.

- Above average temperatures, the warmest since mid May, are
  expected early to middle part of next week.

&&

.DISCUSSION...
Issued at 303 PM CDT Fri May 30 2025

Through Saturday:

Early this afternoon, a zonally-oriented cold front is draped
across northern WI and upper Lake Michigan. It will continue
working southward down the lake until it spreads inland across
northern IL and northwest IN late this evening and tonight. A
potential for showers and thunderstorms exists near and ahead of
this front for late this afternoon and evening, including the
possibility of a couple of stronger storms later in the evening.

A swath of showers is moving across southeast WI as of around 2
PM, but a big majority of this activity is on a trajectory to
move out over the lake before crossing the stateline. Guidance
was formerly highlighting this afternoon and early evening for
the best rain and storm potential, including any severe threat,
as the nose of a strengthening low level jet moves over northern
IL. However, dry boundary layer air and a lack of forcing
elsewhere should keep the rest of our afternoon largely dry,
although certainly can`t rule out a few isolated showers here
and there, primarily around the Chicago metro area. At this
point, it appears that any thunderstorms should hold off until
at least around dusk when we can get some better forcing and
layer moisture in here with the best chances during the mid and
late evening just ahead of the boundary.

The drier RAP and HRRR solutions won out today as dewpoints
this afternoon have successfully mixed out into the upper 40s
around the area where just about every other piece of guidance
held onto 50s, some even in the middle and upper 50s.
Temperatures have also been a few degrees cooler around most of
the area than expected due to a thick mid level cloud deck.
Consequentially, the near to over 1,000 Joules of MUCAPE that a
handful of camps were resolving for later now look out of reach.
I`d imagine then that thermo profiles this evening will be
better matched with the RAP and HRRR than just about anything
else, and this means a couple hundred to, at most, 500 Joules of
MUCAPE to work with, LFCs up between 800 and 700mb, and tons of
dry air (and therefore CIN) off the surface. Forced ascent just
ahead of the front doesn`t look bad and low level forcing will
be ramped up further by that LLJ and an appreciable isallobaric
component ahead of the front, but deep layer forcing is meager.
At least some showers and a couple of weaker thunderstorms look
likely ahead of the front, but strong/severe storm coverage
should be very isolated, if any.

If a stronger storm or two does manage to go up, marginally
damaging winds would be the biggest concern. But, with upwards
of 40 kt of 900mb flow amid (likely) very dry low level air, any
thunderstorm or appreciable shower will be capable of producing
gusty winds to around 40 mph or so. Some small hail might be
possible as well, but anything severe is beginning to look like
a stretch. The favored timeframe for a couple of stronger storms
would be roughly 8PM to midnight. The potential will move from
north to south and should be primarily focused around the
Chicago metro area, or namely areas east of the Fox Valley and
north of I-80.

The precip will be shunted to the south by the cold front once
it passes over later tonight and skies should clear up pretty
nicely behind it. Expect mostly sunny skies during the day
tomorrow. Following the cold frontal passage, temperatures will
be cooler around most of the area. Highs are forecast in the 60s
and lower 70s around much of the metro and middle 70s around
outlying areas. Highs look to be in the lower 60s around the
lakeshore and downtown.

Doom

Saturday Night through Thursday:

High pressure over the western Great Lakes should lead to
plenty of sunshine Sunday with warmer temperatures than
Saturday, especially away from the lake. Sunday should be the
last day of lake breezes and cooler conditions near the lake for
a few days as high pressure moves east of the region and south
to southwesterly winds develop Monday. The southerly winds and
upper ridging shifting east into the region should set the stage
for very warm, above average temperatures early next week.
Highs should climb well into the 80s with highs potentially
nearing 90 in spots by Tuesday. High pressure ridging across the
lower Mississippi Valley and southeast should prevent
appreciable moisture return, leading to rather comfortable
humidity levels with the increased warmth.

Medium range guidance is in pretty good agreement on upper
trough gradually moving eastward across Canada and the northern
tier of the U.S. during the early-middle part of next week.
Tightening pressure gradient in advance of this system should
result in gusty southerly winds Tuesday, possibly over 30 mph at
times in the afternoon.

Eventually, a cold front associated with the approaching upper
trough will approach the area bringing increasing chances of
showers and thunderstorms, likely holding off until Tuesday
night into Wednesday. Rain chances should end as cold front
passes by with drier and slightly cooler conditions expected
behind the front Wednesday night into Thursday.

- Izzi

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 643 PM CDT Fri May 30 2025

Main aviation forecast concerns for 00Z TAFs:

- Scattered gusty SHRA/isolated TS this evening ahead of an
  approaching cold front. TS potential likely greatest along LM
  shore eastward.

- Surface winds turn NNE behind cold front overnight, and
  remain NE Saturday.

Latest surface analysis places a sharp "back-door" cold front
stretching from central lower MI into northwest WI, moving
southward along the Lake Michigan shore just south of KMTW as of
23Z. Scattered SHRA/TSRA were occurring along the front, though
radar/lightning trends indicate these have been decreasing in
intensity and coverage with diurnally weakening low-level
instability. Farther south into our forecast area, thick mid-
level cloud cover has resulted in cooler surface temps and a
lack of low-level instability. Expectation is that these showers
and storms will continue to move south into our area by mid-
evening, though likely with a decrease in overall coverage and a
lower TS threat. High-res CAM guidance appears to favor areas
along the LM shore and east-southeastward for the greater TS
threat area, though confidence remains low for direct TS impacts
to TAF sites (with chances decreasing westward from KGYY). Looks
like a 2-3 hour period of SHRA/isol TS between roughly 02-06Z.
Even outside of TS, SHRA may produce northerly wind gusts into
the 25-30 kt range as they briefly mix down stronger winds
aloft. Otherwise, may see some scattered MVFR bases behind the
front during the predawn hours, but VFR conditions are expected
to prevail.

The dense cloud cover has also minimized winds especially across
the Chicago metro this afternoon/early evening, though sporadic
gusts in the upper teens/low 20 kt range remain possible. Winds
are expected to become north-northeast in the 10-15 kt range
behind the front after midnight, persisting through the day
Saturday.

Ratzer

&&

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

&&

$$

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