East Hazel Crest, Illinois Weather Forecast Discussion

599
FXUS63 KLOT 201607
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1107 AM CDT Sat Sep 20 2025
.KEY MESSAGES...
- Scattered showers and embedded storms through early this
  morning, some with brief heavy rain and gusty winds.
  Additional threat for scattered gusty storms later this
  afternoon.
- Increasing signal for more widespread showers and embedded
  storms tonight/early Sunday morning, mainly north of I-80.
- Periodic chances for showers and some thunderstorms through
  early next week, though there will continue to be plenty of
  dry hours too.
- Afternoon temperatures will remain above normal through the
  Autumn Equinox (Monday at 1:19 PM CDT), though not quite as
  warm as they`ve been the past few to several days.
&&
.UPDATE...
Issued at 1107 AM CDT Sat Sep 20 2025
No big changes to forecast for today, but did nudge pops upward
some this afternoon, especially eastern half of the CWA where
it is looking there could be pretty good coverage of showers and
thunderstorms.
Morning soundings from DVN and ILX are moist with fairly modest
lapse rates. Some clearing across our area this morning is
allowing the boundary layer to heat. Modifying the morning
soundings, it`d only take sfc temps in the upper 70s with
dewpoints in the lower 60s to get MLCAPE around 1000 J/kg with
little CINH. Given the expected destabilization and lack of a
cap, the question becomes what will force storms.
Water vapor imagery this morning depicts a negatively tilted
trough across the mid and upper Mississippi Valley. Well defined
vort max is rounding the base of this trough, moving into
western Wisconsin late this morning. Diffluence is quite
evident over northern IL on water vapor imagery in the base of
the trough and on the southern flanks of the vort max.
Given the destabilizing boundary layer and sustained ascent
associated with the diffluent and divergent flow aloft, we
should see an increase in coverage of showers and thunderstorms
this afternoon. Greatest coverage of thunderstorms, including a
threat of a couple of stronger storms, should be over the
eastern half or so of our CWA. Weak shear profiles will likely
limit the severe threat, but certainly can`t rule out a couple
of stronger to possibly marginally severe storms this afternoon.
Updated grids and text products reflecting the higher precip
chances this afternoon have been sent.
- Izzi
&&
.DISCUSSION...
Issued at 328 AM CDT Sat Sep 20 2025
Through Sunday:
Messy/tricky forecast continues today with a main upper low to our
northwest and several embedded lower-amplitude vorticity maxima set
to pivot through the general vicinity today. Model guidance
generally has exhibited poor run-to-run consistency as well, and
appears to be having a difficult time handling the degree of mid-
level saturation and precise placement and magnitude of embedded
vort maxes. All of this casts some extra layers of uncertainty on
the forecast for today and tonight, although some trends are
beginning to emerge.
Through the rest of this morning, a north-south axis of
increased 800-600 mb moisture coincident with broad, modest warm
isentropic upglide is resulting in the development of elevated
showers and embedded storms. Through daybreak, have focused
the highest precipitation chances east of about a Pontiac to
Woodstock line, and particularly focused across Chicago and the
south/western burbs, although isolated convection will be
possible farther west. Some showers and storms may linger
through mid-morning across far northeast Illinois and over the
lake prior upglide weakening and deeper moisture pushing off to
the east. Thereafter, expecting a brief lull in activity during
the late-morning.
Towards midday, the main 500 mb shortwave axis should be
pressing across the southwestern third of the forecast area as
the primary upper low shifts into Wisconsin. An additional
subtle 700 mb trough axis currently moving across central
Missouri will commensurately lift northward across central
Illinois. As all of this occurs, a zone of modestly-increased
mid/upper flow--presently scooting across southern Iowa--will
start to impinge on the region. The Des Moines, Iowa VWP has
recently indicated flow near 40-45 knots at 500 mb associated with
this westerly jet streak, which is a bit stronger than current
model guidance would suggest. While it`s possible these readings
are a bit high and contaminated a bit by ongoing precipitation,
this could play a role in the evolution of this afternoon`s
weather.
While it remains a bit unclear how much insolation we`ll see
today following the morning activity, trends suggest at least
filtered sunshine will develop, allowing temperatures to push
into the upper 70s/near 80 degrees. With dewpoints possibly
rising through the mid 60s and 500 mb temperatures near -15 C,
MLCAPE values around 1500 J/kg may materialize through early
afternoon, along with diurnally-eroding CIN. The arrival of the
aforementioned shortwave will likely serve as the main large
scale driving mechanism today, and if we destabilize as
currently expected, scattered showers and thunderstorms may re-
develop. At this time, the main focus area appears to be about
along/east of I-55, where the strongest DCVA is expected to
encounter the greatest instability. Accounting for perhaps a
little more mid-level flow than guidance currently indicates
(based on upstream radar observations), deep-layer shear values
near around 30 kts may be sufficient for at least ephemeral
updraft organization. Suspect the HRRR is too aggressively mixing
dewpoints out again, and resulting in deeper inverted-V soundings
than we`ll see in reality, but regardless, stronger cores today
may be capable of strong/gusty precip-loaded downbursts.
This evening and tonight, a trailing shortwave currently over
Nebraska will slide into the region. At the same time upper
divergence is forecast to increase under the right entrance
region of an anticyclonically-arcing jet streak. Given this
recent trend, while model guidance does not universally show
increasing precipitation coverage, based on upstream
observations and ongoing model trends, elected to boost PoPs
late this evening and overnight, mainly near and north of I-80,
with the expectation of increasing shower and embedded
thunderstorm coverage. Low-level flow again does not look super
concerning from a backbuilding/training perspective, but
some very localized training could materialize.
Precipitation may persist into Sunday morning, although expect
a gradual diminishing trend through the morning once again.
Model guidance has been all over the place regarding the
handling of follow-up shortwaves/convectively-augmented MCVs in
the vicinity, so forecast confidence on Sunday remains notably
low. Increased cloud cover could also end up muting insolation
to some degree as well, all of which suggests capping PoPs in
the 30-50 percent range for now. Can`t rule out the potential
for a few stronger storms given indications of some stronger
700-500 mb flow riding in overhead, but there are too many other
uncertainties to pin this threat down at this point.
Carlaw
Sunday Night through Friday:
Intermittent shower and thunderstorm chances will persist Sunday
night through Tuesday as additional disturbances ripple through
the west to northwesterly flow aloft. A chaotic upper pattern
into the middle and end of next week will likely continue to
result in lower-than-typical forecast confidence. Some signal
remains in the extended guidance for at least a brief return to
drier conditions (especially near/north of I-80) in the wake of
a cold front towards midweek, but depending on the influence of
another upper low towards the end of the week, this could end
up being short-lived. The latest GFS in particular would
indicate little/no break in the action with a Fujiwhara dance
taking place between several robust disturbances across the
central CONUS.
Temperatures this upcoming week will start out solidly above
normal (along with fairly humid conditions as well), with highs
well into the 70s to near 80F through Tuesday, then trending
closer to normal and a bit less humid in the mid to late week.
Carlaw/Castro
&&
.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 630 AM CDT Sat Sep 20 2025
Key Aviation Messages for the current TAF period:
- Multiple rounds of showers and thunderstorms
The first round of showers and storms is slowly eroding and
pushing east out over Lake Michigan and northern Indiana.
However, another cluster of storms is moving over northern
Illinois. While the RFD TAF will start out dry as these storms
are already east, these storms are expected over Chicago area
between 14Z and 16Z. There is some uncertainty in how much they
will maintain their current strength as the move northeast, but
it warranted a TEMPO at DPA and ORD, with a VCTS at MDW. A break
in the rain is expected after they pass.
Winds are expected to start out light and out of the southeast
today before switching to the southwest around midday for the
remainder of the TAF. The next round of showers and storms are
expected to move into northern Illinois and northwest Indiana
this afternoon. These storms will have the potential to have
localized downpours that could reduce vis down to MVFR levels
and wind gusts around 25 knots. There is some uncertainty with
wind directions this afternoon. In the wake of the storms, there
is a chance that they could become locally southeast or east
for a short window. However, there was higher confidence in a
southwest wind remaining for a longer period.
There is uncertainty with how much showers linger over the area
past 00Z after the main wave of storms pushes through, so VCSH
was kept prevailing through the end of the TAF. A PROB30 was
added as well for the potential for yet another round of showers
and storms, though it is expected to remain near and north of a
KVYS to KMDW line.
DK
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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NWS LOT Office Area Forecast Discussion