Aurora, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

261
FXUS63 KLOT 121747
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1247 PM CDT Tue Aug 12 2025

.KEY MESSAGES...

- Scattered to numerous showers and storms expected late this
  morning and afternoon. Localized torrential rainfall and
  isolated instances of flash flooding will be possible. A few
  strong-locally damaging downburst gusts possible.

- Uncomfortable heat and humidity will return for this weekend
  with heat indices 90 to 100 degrees, especially on Saturday.

- Chances for showers and storms early next week.

&&

.UPDATE...
Issued at 1029 AM CDT Tue Aug 12 2025

There are some lingering showers and storms in northern McHenry
and Lake, IL counties moving northeast. Otherwise, the rest of
the forecast area remains within a proverbial "calm before the
storm". Recent surface mesoanalysis shows a weak theta-e
gradient along Peoria to Chicago line. With weak capping in
place, the expectation is for this boundary to be the focus for
renewed shower and storm development. Guidance is still
suggesting initiation in the mid afternoon, but satellite
imagery is showing a small Cu field developing to the south with
some accas clouds bubbling up near Peoria. With the cap as weak
as it is, it would not be surprising if storms started to fire
around noon. Coverage should expand south and eastward through
the afternoon and evening. This mornings 12Z sounding measured
over 1.60 inches of precipitable water and with dew points
expected to increase back into the 70s this afternoon, the
primary concern remains the threat for localized flash flooding
from torrential downpours. However, the strongest storms could
produce strong precip-loaded downbursts which may have isolated
gusts near 60 mph.

DK

&&

.DISCUSSION...
Issued at 305 AM CDT Tue Aug 12 2025

Through Wednesday:

In the immediate near term, we`re closely monitoring a
thunderstorm complex rolling northeastward across eastern
Iowa, roughly straddling the Mississippi River. This is likely
associated with an MCV from convection across Kansas and
Missouri yesterday. An earlier line-preceding supercell was
clearly indicative of a mid and upper-level flow enhancement
near and ahead of this feature. Somewhat concerningly, latest
rapidly-updating guidance (RAP/HRRR) show steadily increasing
700-500 mb winds immediately ahead of this complex across far
northwest Illinois through early this morning. While instability
isn`t particularly substantial (generally about 1500 J/kg of
MUCAPE) and at least some modest surface-based inhibition is
present, a persistent region of higher velocities have been
noted on Davenport`s radar associated with the system`s rear
inflow jet. As of this writing, there haven`t been signs that
the more significant winds aloft are making it down to the
surface, but given the modeled increase in shear, will be
keeping a close eye on this, particularly given the recent
development of a bookend vortex west of Iowa City. With
northeast-orienated deep layer shear vectors, the southeastern
flanks of this complex, which have taken on more of a N/S
alignment, would be susceptible for outflow to push ahead of new
thunderstorm updrafts, blunting the wind gusts potential to
some degree.

As it stands right now, have boosted PoPs in our northwest,
particularly NW of a La Salle to Waukegan line during the
roughly 4 AM to 8 AM timeframe. Can`t totally rule out the
threat for a severe gust as this complex rolls through, mainly
northwest of an Amboy to McHenry line, and will continue to keep
a close eye on satellite, radar, and observational trends early
this morning. Finally, additional scattered thunderstorms may
develop east of this complex, and have dragged chance PoPs a bit
further eastward into Chicago and the west/south burbs to
account for this.

Once this system clears the region through mid-morning, there
may be a brief lull in activity. An outflow boundary or
differential heating zone (cooler temps northwest, warmer
southeast) may then serve as foci for renewed storm development,
potentially as early as late morning. Suspect that recent
guidance which isn`t convecting again until mid afternoon
remains much too late given steadily diminishing MLCIN amidst
low 70s dewpoints. Still a bit difficult to tell exactly where
the highest coverage will set up, but based on the latest
available guidance, have painted likely PoPs across the
southeastern 2/3rds of the forecast area. Expectation is for
additional showers and storms to focus near the aforementioned
boundaries, and then gradually expand and slowly build south and
eastward through the afternoon and evening.

While we`re not seeing signs of a widespread flash flood
scenario today, am a bit concerned that individual thunderstorm
segments could have a propensity to backbuild/train today given
southwesterly mean cloud-bearing flow around 20-25 knots.
Individual cells will be moving along at a decent clip, but
given the nearly parallel orientation to initiating boundaries
and the main moist axis, some training and localized flash
flooding appear to be a threat today with PWATs near and just
north of 2 inches. At this point, the flash flood potential
appears too localized, along with uncertainties with mesoscale
boundary placement, to justify flood watches.

Finally, the strongest storms this afternoon/evening could
produce strong precip-loaded downbursts, a few of which could
near 60 mph.

Activity could continue to fester a bit this evening and
overnight south of I-80 as the incoming cold front/surface
trough will be doing so quite slowly. By Wednesday morning,
expect all lingering activity to have pushed south of the
forecast area.

While the forecast for Wednesday afternoon remains precip-free
at this time, healthier cumulus build-ups appear likely,
particularly in the vicinity of an inland-moving lake breeze and
south of I-80. Forecast soundings show a decent amount of
subsidence capping with a prominent warm and dry layer around
700-600 mb. This will effectively put a lid on the cumulus
depth, but a small amount of surface-based instability within
the cloud layer could support a few showers/sprinkles. Chances
appear too low to introduce into the grids at this time though.
Otherwise, more comfortable conditions are expected, with
dewpoints falling into the 60s and air temperatures in the low
80s (a bit cooler near the lake).

Carlaw


Wednesday Night through Monday:

During the latter part of this week, upper high pressure will
build over the south-central and southeastern CONUS. Being
comfortably parked beneath the ridge, all synoptic precip
systems should steer away from the local area into this weekend.
Seasonably warm conditions are expected for Thursday with highs
in the lower and middle 80s, likely a few to several degrees
cooler around the lakeshore with onshore winds.

After moving onshore the PNW coast early tomorrow, a low
amplitude upper wave will develop along the northern periphery
of the upper high and drive a center of surface low pressure
across the northern Plains and upper Midwest Friday and
Saturday. Low level flow will turn southerly ahead of this wave
reeling a warm, moist, and highly unstable airmass into the
region. Highs on Friday are forecast to reach the middle 80s to
near 90 and afternoon heat indices look as high as upper 90s.
Despite as many as a few thousand Joules of MUCAPE possible in
our west Friday afternoon, guidance is in solid agreement on
keeping the CWA dry while the upper high keeps all forcing and
deep moisture just out of reach.

Higher instability will spread east behind the wave as it moves
across the upper Midwest and leaves behind a frontal boundary
that will be quasi-stationary across central/northern WI on
Saturday. The GFS and Euro plot between 3,500 and 5,000 J/kg of
nearly-uncapped surface-based instability around the CWA on
Saturday afternoon. Still under the shield of the upper high
though, upper flow will be awfully quiet, layer moisture very
poor, and there are no apparent features around to trigger
convection locally. Convection appears likely not far north of
here along that front, and some guidance wants a few
showers/storms to drift south into our northern CWA, possibly
along outflow boundaries pushing south out of WI, but this is a
fairly weak signal in ensemble output. And free convection
should be difficult to achieve on Saturday given the dry
boundary layer air. Saturday also looks uncomfortably warm with
highs forecast in the lower and middle 90s and afternoon heat
indices near or in excess of 100 degrees.

The front will propagate south on Sunday and should cross the
IL-WI stateline during the latter part of Sunday. Scattered
shower and storm chances will build in from the north as the
front approaches and will remain through Monday while the
effective front meanders about central/northern IL. While shear
will be very poor early next week, high theta-e air gathered
south of the front may hint at a potential for severe convection
at times. Whereas guidance was previously drying out for
Tuesday, a rather new signal among medium range camps is for
another wave to develop upstream along the baroclinic zone and
move across the region. This could bring some additional precip
to Tuesday before quieter conditions look to ensue for the back
half of next week.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1247 PM CDT Tue Aug 12 2025

A somewhat diffuse SW to NE oriented surface boundary just west
of the Chicago terminals will become a focus for TS developing
this afternoon. The environment is already uncapped as of TAF
issuance, with a couple attempts at TS already apparent along
the boundary. TS coverage should become numerous this afternoon
with a mix of individual cells and small linear segments, all of
which will be capable of producing localized strong winds and
torrential rainfall. There is likely to be multiple rounds of
TS, supporting a longer TEMPO period from 19-23Z at ORD and
20-00Z window at MDW.

With the main front still west of the terminals this evening,
TS will be slow to exit. Cannot rule out isolated TS continuing
for a few hours behind the main area of convection. MVFR
ceilings may develop and winds will likely become SE for a
couple hours behind the convection as is typically observed. TS
should end by mid-evening, with the main front shifting winds
NW after midnight. Then, expect a lake-enhanced NE wind shift
early Wednesday afternoon.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until midnight CDT tonight for ILZ013-ILZ103-
     ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Flood Watch until midnight CDT tonight for INZ001.

LM...None.

&&

$$

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