Tinley Park, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

409
FXUS63 KLOT 150851
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
351 AM CDT Thu May 15 2025

.KEY MESSAGES...

- Summer-like warmth continues through Friday, with record
  breaking heat possible this afternoon.

- A threat of severe thunderstorms exists this afternoon and
  evening from ~3-10 PM CDT (Threat level 3 out of 5).

- A threat of rapid fire spread exists today and especially
  Friday due to a combination of strong winds and dry
  conditions.

&&

.DISCUSSION...
Issued at 351 AM CDT Thu May 15 2025

Through this morning:

Dense fog continues across far northeast Illinois due to marine fog
over Lake Michigan having drifted inland once again. This is
expected to gradually improve after sunrise as the fog bank lifts
north of the area by mid morning as southerly flow develops ahead of
the deepening low pressure system over the north central Plains.

Only other item of note is the very narrow axis of spotty showers
that developed within a region of warm advection and isentropic
ascent ahead of the aforementioned surface low. This activity
continues to struggle to persist more than a few radar scans and
suspect only a few more showers are possible through daybreak this
morning.

Petr


This afternoon through Friday night:

Quite an interesting and potentially impactful close to the work
week is on the way with multi-faceted hazards. Today will offer
record/near record mid-summer-like heat, followed by a threat for
higher end severe weather late this afternoon into this evening.
Then on Friday, some weather whiplash. Right on the heels of very
warm, windy, and dry conditions, another threat for high based
storms, some possibly strong to severe, may materialize late in
the day through mid evening.

Here are some summary thoughts on the key points regarding the
forecast today through Friday evening:

Heat and Wind Today: Temperatures appear on track to soar into
the 90s in many locations away from the Illinois shore, so no big
changes were made to this part of the forecast. These temps will
be accompanied by dew points surging well into the 60s, so peak
heat indices should top out in the mid to upper 90s in spots,
offset somewhat by the winds. South to southwesterly gusts up to
35-40 mph are expected this afternoon and early evening. We still
need to keep an eye on a short burst of wind and sudden dew
point/RH drop behind the Pacific front/dryline expected to serve
as a key impetus for convective initiation (CI) later today.

Severe Threat Today: The 00z CAM guidance, with some exceptions,
did come in much more aggressive with thunderstorm coverage,
particularly east of I-39 this afternoon and early this evening.
In addition, the ECMWF/EPS remained consistent in its
parameterized depiction of at least scattered CI in the mid to
late afternoon. With this in mind, we adjusted PoPs upward some
(40-50% peak east of I-39) and included thunderstorm coverage
wording in the gridded forecast.

This still remains a conditional setup with competing factors
that may suppress coverage and delay CI in parts of the CWA,
especially farther west. However, it`s also a conditionally higher
end in magnitude setup regarding the severe threat, supporting
SPC`s level 3 of 5 threat probs for the northeast 2/3 of the CWA.
Any storms able to sustain themselves will in all likelihood
become severe (intense supercells) given the parameter space in
play. Damaging to destructive hail (up to 2-3" in diameter) and
damaging to destructive winds (some 75+ mph gusts) appear to be
the primary hazards. With that said, given expectation of
supercellular mode and large instability, and increasing low-level
shear towards and after sunset, there may be a localized strong
tornado threat if LCLs are not too prohibitively high.

Timing wise, thunderstorms may develop near/just west of the I-39
corridor during the 3-4pm window. This should place the main
severe threat timing window in the 4pm to 10pm timeframe, latest
far east/southeast. The day shift will need to closely assess the
signal on some of the CAMs for a secondary round right after
initial supercells around sunset until ~10pm CDT.

Castro

Meteorological synopsis for today through this evening:

A strong sub-985 mb surface low will track northeastward while
occluding across eastern South Dakota and the Upper Midwest late
today into tonight. Our area will become oriented solidly within
the warm sector of this cyclone following a warm frontal passage
early this morning. Breezy south winds (gusting up around 30 mph)
in the wake of this warm front will drive a thermal ridge
northeastward into the Lower Great Lakes, with 925 mb temperatures
progged to increase to around +25C. Locally climatology suggests
that this will support lower (to perhaps locally mid 90s) high
temperatures for the area, which is right around the record high`s
for May 15th.

The warm sector airmass is expected to remain capped through
most of the day by an EML. Accordingly, the threat for storms
through at least 3 PM this afternoon will remain very low.
However, the chances for at least isolated storm development will
begin to ramp up after 3 PM as a cold frontal/dry line feature
shifts eastward into northern IL. There continues to be
uncertainty with the overall storm coverage with southward extent
into northern IL later in the afternoon, owing to lingering
capping and rather weak large scale forcing. However, there are
signs in the guidance that the exit region of an upper-level jet
will try to nose into northeastern IL towards the early evening
period just as modest mid-level height falls/cooling spread into
the area. This is should thus foster a gradual uptick in storm
coverage along and ahead of the surface boundary into Thursday
evening as cap weakens.

While it`s uncertain how quickly an uptick in storm coverage will
occur, the 00z CAM solutions (and 06z HRRR) at least gave more
credence towards the idea of explosive CI indeed occurring within
our area. Still can`t rule out the possibility that the
front/dryline surges east quickly enough (with winds veering to
southwesterly prior to fropa and limiting convergence) for the
higher storm coverage ends up largely east-northeast of our area
(and also up across WI). But perhaps this scenario (little/no
storms in our area) has become a less likely outcome. Regardless
and needless to say, satellite and observational trends will be
monitored very closely. Assuming storms do occur, the
thermodynamic and kinematic environment in which they develop
will be very supportive of organized severe storms, particularly
supercells. Expect the the threat of storms to quickly end from
west-to-east following the frontal passage into early Thursday
evening.

KJB/Castro

Friday`s Potentially Significant Fire Danger and Strong Winds:

A substantial mid-level dry layer atop a residual EML just above
the surface will advect across the area Thursday night into
Friday. Meanwhile, near-record low MSLP values for May of
potentially sub-980hPa over Minnesota on Friday will generate
anomalously strong synoptic winds over the forecast area. The
combination of RH values lowering to 25% or less and southwest
winds gusting to around or over 40 mph amid deep diurnal mixing
into the dry air mass will support the potential for critical fire
weather conditions Friday afternoon. Per forecast soundings, winds
could even push near or exceed advisory criteria (45+ mph gusts),
especially near/north of I-80.

Rapid spread of brush fires is possible with any remaining
dry/dead vegetation from prior seasons. Additionally, fine fuels
have started drying out given the recent lack of rain and
persistent days of lower RH values. A Fire Weather Watch may be
needed with this afternoon`s update. We opted to hold off on a
watch on this shift in coordination with neighboring WFOs. How
much rain falls and where may modulate the highest fire weather
threat zones on Friday at least somewhat.

In addition to the windy and dry conditions Friday, maintained
patchy blowing dust for much of interior northern Illinois away
from the Chicago/Rockford metros as soils in fields could result
in locally reduced visibility (particularly for NW to SE oriented
roads).

Late Day Friday-Friday Evening`s Thunderstorm Threat:

Even with the expected dry weather and brush fire concerns,
impressive lapse rates of 8-8.5C/km through much of the
troposphere will still promote high-based (10kft) cumulus during
the afternoon. A subtle mid-level impulse quickly tracking from
the western Rockies to the mid-Mississippi River Valley could
induce deeper growth of the high-based cumulus and ultimately
result in isolated to widely thunderstorms late in the afternoon
and early evening. Associated DCAPE values approaching 1500 J/kg
amid a deep sub-cloud inverted-V profile would support locally
damaging wind gusts with any thunderstorms. Can`t rule out some
large hail either. The southeast half to 2/3 of the area looks
most favored for this, especially near/east of I-57 towards and
after sunset until about midnight, fitting with SPC`s level 1 of 5
threat on the day 2 outlook.

After the thunderstorm threat ends in the wake of a cold front
passage, expect breezy and cooler conditions for the rest of the
night into early Saturday.

Kluber/Castro

Saturday through Wednesday:

A strong Hudson Bay high will gradually replace the strong
surface low through the weekend, allowing for cooler conditions
to filter over the area. High temps in the 70s area-wide on
Saturday will settle into the 50s along the shore to 70s well
inland on Sunday as a backdoor cold front crosses the area from
the northeast Saturday night. Next week, overall guidance is
painting another period of active weather as deep troughing over
the western CONUS slows or potentially cuts off over the region
by midweek.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1238 AM CDT Thu May 15 2025

Key Messages:

- 30-40% chance for thunderstorms to affect the terminals late
  this afternoon. IF storms develop, they will likely become
  strong to severe.

- Gusty southerly winds this afternoon, followed by a
  southwesterly wind shift behind a cold front during the late
  afternoon/early evening.

- 2-4 hour period of strong WSW wind gusts >30 kt may develop in
  the wake of thunderstorms early this evening (greatest
  potential at RFD).

Earlier concerns of the marine fog layer drifting as far inland
as ORD/MDW have decreased over the past few hours, with the
expectation that it remains north and east of the terminals.
Will continue to monitor satellite trends closely overnight,
however.

While an isolated shower or storm can`t entirely be ruled out
early this morning (~15% chance), confidence remains too low to
include in the TAFs with this update. There are attempts at
development across central Illinois though conditions become
less favorable with northward extent through the overnight
hours.

Late this afternoon, a cold front will approach the area from
the west, and as it gets close to the terminals, explosive
thunderstorm development is possible during the 22-01Z
timeframe. Confidence in whether a storm will develop over or
near the TAF sites is still only low-medium (about a 30-40%
chance at any particular site). However, wherever storms do
develop conditions are favorable for severe thunderstorms
capable of potentially destructive hail (2"+ diameter) and
damaging winds (>50 kt), in addition to lightning and visibility
reductions in heavy downpours. The threat for storms at the
terminals should end by about 01Z as the cold front pushes
through the area.

Lastly, south-southeasterly winds will become gusty during the
late morning, and pick up in intensity during the afternoon --
possibly gusting to around 30 kts at times. The prevailing wind
direction will likely turn due south or just west of south at
some point during the afternoon before turning southwesterly
after the passage of the cold front during the late
afternoon/early evening. We are also monitoring the potential
for a 2-4 hour period of strong WSW wind gusts >30 kt early in
the evening that may develop in the wake of any storms that
develop, which some of the hi-res guidance is attempting to
resolve. Confidence in this occurring remains very low;
however, there is perhaps a locally higher potential at RFD.

Ogorek/Petr

&&

.MARINE...
Issued at 345 AM CDT Thu May 15 2025

Key Messages:

- Dense fog continues through mid morning
- Small Craft Advisory in effect this afternoon/evening
- Severe thunderstorms possible late afternoon into early
  evening
- Gale Watch in effect Friday afternoon/evening for IL nearshore
  to Gary, IN

Dense fog continues to plague the southern half of Lake
Michigan in response to humid air pooling over the cool lake
waters. A Dense Fog Advisory remains in effect for much of
southern Lake Michigan through this morning. Expect very gradual
improvement from south to north through the morning hours.

Thunderstorms appear poised to develop just west of if not
directly over Lake Michigan late this afternoon into the evening.
Any storm may produce gale to storm force winds and damaging
hail. A brief period of southwesterly gale force winds cannot be
ruled out behind the storms, as well. A small craft advisory is
in effect this afternoon into the evening.

Finally, a period of southwesterly gale force winds are possible
Friday afternoon, particularly northwest of Gary, Indiana. A
Gale Watch has been issued to account for this.

Petr/Borchardt

&&

.CLIMATE...
Updated at 355 AM CDT Thu May 15 2025

Record high temperatures are possible today, Thursday May 15.

Here are the current record highs for May 15:

Chicago: 91 in 1962

Rockford: 90 in 1944

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Dense Fog Advisory until 10 AM CDT this morning for ILZ006.

     Dense Fog Advisory until 7 AM CDT this morning for ILZ103.

IN...None.
LM...Dense Fog Advisory until noon CDT today for Winthrop Harbor IL
     to Gary IN.

     Small Craft Advisory from noon today to 10 PM CDT this evening
     for the IL and IN nearshore waters.

     Gale Watch from Friday afternoon through Friday evening for
     Winthrop Harbor IL to Gary IN.

&&

$$

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