Oak Lawn, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

964
FXUS63 KLOT 180204
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
904 PM CDT Thu Apr 17 2025

.KEY MESSAGES...

- Strong thunderstorms may track near and north of I-88 after
  midnight tonight with a threat for large hail and locally
  gusty winds (30 to 60% chance).

- Friday will offer an early taste of summer-like warmth with
  highs in the lower 80s, albeit with gusty south winds (gusts 35 to
  40 mph).

- Showers and storms may develop Friday evening, especially
  along and south of I-55. A few storms may be severe with
  damaging winds and hail.

- Periods of showers and perhaps some thunderstorms are forecast
  on Sunday with widespread rain and some storms Sunday night. A
  highly conditional severe thunderstorm threat exists for
  mainly far southern portions of the forecast late Sunday
  afternoon and evening.

&&

.UPDATE...
Issued at 904 PM CDT Thu Apr 17 2025

Most of the showers have moved out over the lake. This will
allow for a period of drier conditions. Forecasted temperatures
currently/tonight were knocked down a few degrees owing to the
warm front still in eastern Iowa and down into west-central
Illinois. Temperatures should remain steady if not nose upwards
as that front moves east tonight.

A lot of attention has been paid tonight on the severe weather
around the Omaha, Nebraska area. The convection out west is
expected to move east and become more elevated through the
overnight. While most models have it arriving sometime after
midnight, they still disagree on what will happen. The forecast
kept the best threat for showers and storms around and north of
Interstate 88, with the stateline having the best chances. The
main adjustment was to slow down the arrival of the storms. With
steep mid level lapse rates and a strong low level jet, the
main risk from these storms will be strong wind gusts and large
hail. Last but not least, some of recent the high res guidance
is showing a bit of a southerly shift in the evolution so PoPs
were brought slightly farther south.

DK

&&

.DISCUSSION...
Issued at 307 PM CDT Thu Apr 17 2025

Through Friday Night:

The primary weather concerns continue to focus on the threat of
strong to severe convection, particularly late tonight and again
Friday evening.

In the near term (late this afternoon through early evening), a
batch of showers will shift east-northeastward across the area.
Severe weather is not expected with this activity, though some
instances of small hail and possibly a few lightning strikes
cannot be ruled out given some rather steep lapse rates aloft.
This activity is expected to move out of the area shortly after
sunset this evening. A few isolated to widely scattered showers
could persist for a couple hours this evening, but the coverage of
showers is expected to decrease through the evening as we await
our next period of showers and thunderstorms north of I-80 after
midnight tonight.

The thunderstorm threat overnight has increased a bit over the
previous forecast, though the best chances continue to be favored
across southern WI and far northern IL. This thunderstorm activity
overnight is expected to develop across eastern NE and far
western IA early this evening. As this activity develops in
advance of a cold front well to our west, the thermodynamic and
kinematic envionrment will be supportive of eastward moving
supercells, with an attendant very large hail threat. We will be
watching the evolution of these storms closely through the
evening, as it appears that this activity will shift eastward
across southern WI and far northern IL after midnight tonight.

There does continue to be some uncertainty as to how far south
into IL this storm threat will reach, owing largely to the
presence of a stout EML capping inversion, which is expected to
strengthen with southward extent into IL. At the present time,
areas roughly along and north of I-88 have the best shot at seeing
a few of these strong storms overnight. This is the general area
that will remain near the northern periphery of this EML capping
inversion. Accordingly, there will be a corridor across southern
WI and far northern IL in which an eastward focus will exist to
steer this evenings severe convection over IA eastward into parts
of our area overnight. The primarily threat with these storms
will be large hail (1-1.5" diameter), given the presence of very
steep mid-level lapse rates. This threat will especially be
maximized with any lingering elevated supercell structures.

These overnight storms are expected to come to an end by, or
shortly after, daybreak Friday morning. In their wake, the spine
of the elongated EML capping inversion will overspread the whole
area again for the daylight hours of Friday. This will thus result
in robust capping overhead, and relative dearth of showers and
storms for much of the daylight hours of Friday. In the absence of
showers and storms, deep atmospheric mixing into increasing
southerly flow will result in gusty south winds (35-40 mph)
through the day. Temperatures will turn much warmer on these warm
southerly winds, with readings likely peaking in the lower 80s in
most locations.

Our second window of potential severe thunderstorms looks to come
as a cold front shifts into northern IL into Friday evening,
likely after 6 pm. Gradually increasing large-scale ascent is
expected as this front moves into the area in the evening, and
should thus foster sufficient low-level moistening and weakening
of the residual capping inversion to support developing storms
along the frontal boundary after 6 PM Friday evening. Still think
that the highest storm coverage into Friday night should be near
and east of I-55, where our forecast PoPs are in the categorical
range.

Thermodynamic and kinematic profiles will be supportive of
strong to severe thunderstorms developing across the frontal
zone, though it appears that most convection that develops will
either form atop the EML`s base or quickly become undercut by
the cold front. The elevated nature of the convection and
progged front-parallel storm motions, plus uncertainties
regarding lingering inhibition and how quickly storms will be
able to intensify do raise questions about the extent to which
storms will be able to fully harness the parameter space that
will be in place. That said, any robust convection that manages
to develop should possess a threat for large hail, while any
convection that manages to stay along or ahead of the cold front
will also feature a threat for damaging winds. Some potential
for flash flooding also appears evident in our southeastern CWA
given the aforementioned storm motions and potential for
training convection.

KJB


Saturday through Thursday:

On Saturday, the cold front moving across the area late Friday
through Friday night will stall out south of the CWA as surface
high pressure sets up from the northern Plains to the Great Lakes
region. The low-level baroclinic zone will also be nudged south,
but remain close enough by to present a chance for at least
scattered showers into areas well south of I-80. Can`t rule out
shower activity at times drifting northward toward the I-80
corridor, but by and large areas near and especially north of
I-80 should remain dry (albeit mostly cloudy) Saturday through
early Sunday. High temperatures Saturday afternoon are expected to
be just shy of normal for the date inland, ranging from the upper
50s to around 60F/low 60s, but only near/around 50F along the
lakefront due to onshore flow through the day.

Sunday, for those celebrating the Easter holiday, it unfortunately
will be a rather inclement (breezy, showery at times, cool) day.
The main trough responsible for the approaching surface low on
Friday will finally eject northeastward while becoming negatively
tilted over the Upper Mississippi River Valley late Sunday. The
various ensemble model suites have remained in better agreement
with the evolution of the surface low, with the favored mean track
across eastern Iowa or far northwest Illinois Sunday night. This
track will keep most of the area on the cool side of a warm front
slowly lifting northward in advance of the surface low, resulting
in highs in the 50s (mid-upper 40s IL shore) and easterly winds
gusting to 30 mph.

Mass response ahead of the aforementioned trough/low will quickly
advect the moisture-rich airmass south of the front northward
across the area on Sunday. This will result in an axis of showers
lifting northward through early afternoon and then perhaps
additional waves of showers in the mid to late afternoon. While
there`s too much uncertain in exact precip timing, there is a
signal for the guidance in some dry periods, so it doesn`t
currently look like an all day washout. As the effective warm
front slowly lifts back north toward and into the far southern CWA
during the afternoon, enough MUCAPE may build to support a chance
for isolated to scattered thunderstorms.

As impressive deep layer forcing nears from the southwest late in
the day, arcs of convection racing northeast should expand into
the CWA Sunday evening. Regarding the effective warm frontal
position, there may be a window of overlap of modest uncapped
MLCAPE in the late afternoon and early evening in parts of the
southern CWA (generally near/south of US-24). We`ll need to keep a
close eye on trends for a conditional severe storm threat in these
areas within a highly sheared environment from the late afternoon
through the early to mid evening. Right moving Bunkers motions
could result in any supercells quickly crossing the front, which
may limit the tornado threat in the CWA, even if a severe storm
risk does materialize. Can`t rule out a threat for strong storms
expanding northward with the front in the evening, though the
diurnally unfavorable timing and already minimal instability may
limit the threat farther north to localized wind gusts stronger
than the already breezy background wind field.

Regardless of how the potential conditional severe threat pans out
or not, the dynamic system will still bring widespread showers and
scattered embedded storms over the area through part of the
overnight, with thunderstorm coverage diminishing as instability
further wanes into the pre-dawn hours of Monday.

After Sunday`s system departs across the Great Lakes region
early Monday, a mostly zonal regime will prevail across much of
North America for several days. This will bring a period of
seasonable (Monday) to seasonably warm (Tuesday-Thursday) weather
to the region, with locally cooler conditions from daily lake
breezes around the Lake Michigan shore. Monday`s main weather of
note will likely be gusty westerly winds, with gusts up to 35 mph
in the official forecast and advisory (45+ mph gusts) criteria
upside per the ECMWF/EPS ensemble. Can`t rule out a few light
showers in the morning, though suspect most areas will be dry.

The one notable perturbation in the zonal pattern next work week
will be a low-amplitude wave tracking along the U.S./Canadian
border Tuesday into Wednesday. An associated weak cold front may
slow or stall across the area Tuesday night into Wednesday, with
marginal moisture profiles resulting in perhaps isolated to
scattered showers near the front.

Castro/Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 640 PM CDT Thu Apr 17 2025

Aviation forecast concerns for the 00Z TAFs:

- Period of LLWS overnight with 50-60 kt low level jet.

- Breezy SE-SSE winds this evening become SSW-SW Friday, with
  gusts 30+ kts. Winds turn westerly late Friday evening.

- Couple of periods of SHRA/TSRA potential. First after midnight
  through around sunrise, and again late Friday/Friday evening
  ahead of a cold front. A few strong storms possible.

Early evening surface analysis depicts a cold front stretching
from the upper MS valley southwest into CO. A weak surface wave
was noted along the front near the IA/MN border, with a warm
front extending south-southeast into far western IL. A couple
areas of SHRA were evident in regional radars from southern WI
into northern IL/LM/IN, associated with moist ascent along the
the elevated warm frontal slope. These should lift northeast of
the terminals early this evening, with the greatest coverage
likely around KRFD for the first hour or so of the TAF. Farther
west and northwest, TSRA were occurring closer to the cold front
from MN southwest into western IA/eastern NE. Some of the
western IA activity will likely move into far northern IL after
07-08Z overnight on the nose of a southwesterly 50-60 kt low
level jet, and may linger through sunrise before exiting.
Coverage and timing is of somewhat lower confidence, thus have
maintained a prob30 mention for this at this time. Some of these
storms would have the potential to be strong to severe, with
hail and gusty winds.

The surface warm front is expected to lift northeast of the
terminals after sunrise Friday, with gusty south-southwest to
southwest winds developing. Gusts will likely exceed 30 kts at
times from mid-morning onward. An elevated plume of very steep
lapse rates is expected to provide a "cap" against thunderstorm
development through most of the day, though the combination of
the approaching cold front and strengthening ascent/cooling
aloft late in the day into Friday evening is expected to
eventually allow for the development of thunderstorms along the
cold front. Again, some timing differences exist within various
model guidance, though have indicated a tempo period for TSRA
during the most likely time frame. Some of these late Friday
storms may also be strong/severe.

As for winds, breezy southeast winds gusting 25-30 kt will
gradually turn more south-southwest late tonight, before
becoming southwest Friday and strengthening to 30-35 kt gusts.
Despite lingering surface gusts tonight, southwest winds of
50-60 kts around 2 kft AGL will present LLWS conditions from
mid-evening into the predawn hours. The cold front is expected
to move through the area mid-late Friday evening, shifting winds
to the west.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT Friday for the IL and IN
     nearshore waters.

&&

$$

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