il discuss
Office: DVN
FXUS63 KDVN 072331
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
631 PM CDT Mon Jul 7 2025
.KEY MESSAGES...
- A few periods of showers and storms remain in the forecast,
mainly for this afternoon through Tuesday, and again Thursday
night through Friday. Severe weather potential remains low at
this time.
- Seasonal temperatures and humidity levels will continue this
week.
&&
.SHORT TERM /THROUGH TUESDAY/...
Issued at 219 PM CDT Mon Jul 7 2025
Isolated to scattered showers and storms have developed early this
afternoon, mainly along and just east of the Highway 218 corridor.
So far, thunderstorms have remain isolated and haven't reached
severe levels, but lightning and a brief heavy downpour remain the
main hazards with these. A weak mid-level shortwave has helped to
spark off this activity. Otherwise, partly to mostly sunny skies
will be common elsewhere.
Late tonight through Tuesday looks to be more active as a more
robust mid-level trough and attendant cold front approaches the
area. We will have to watch the current activity over South Dakota
as that is expected to eventually approach our region late tonight,
albeit in a decaying fashion. Other than some locally heavy rainfall
and gusty winds, strong to severe storms are not anticipated.
Chances of showers/storms are around 20-40%.
Tuesday will have relatively higher chances (40-60%) of storms,
especially in the afternoon. Analysis of the convective parameter
space indicates ample instability, with MLCAPE values around 1000-
2000 J/kg, but with very weak deep-layer shear once again. Low-level
lapse rates appear to be somewhat steep - around 6.5 to 7.5 C/km -
coupled with higher PWAT values (1.7 to 2.0 inches). With this said,
although SPC has kept our region out of any convective outlooks (we
remain on the northern cusp of a Marginal Risk to the south), there
appears to be some support for some locally gusty winds in any
storms that develop. Temperatures will be a little cooler due to
more cloud cover, with most areas reaching the low to mid 80s.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Issued at 219 PM CDT Mon Jul 7 2025
Tuesday night through Thursday: we should enter a period of largely
dry conditions, thanks to an upper-level ridge building across the
central Plains region. This should help keep any mid-level impulses
at bay for a time. Seasonal conditions should continue these days,
with highs warming to the middle to upper 80s for both Wednesday and
Thursday, along with seasonal humidity.
Thursday night and Friday: the next mid-level shortwave sweeps
through the area during this time, leading to another round of
showers and storms potential across the area (40-60% chances).
Unlike the last few rounds of strong to severe storms, Friday looks
to have stronger deep-layer shear and stronger flow in place, along
with abundant instability. The various extended machine learning
output continues to highlight the potential for at least isolated
strong to severe storms, so something to keep an eye on as we get
closer to the end of the week.
An early look at the upcoming weekend indicates a slight cooldown
for Saturday in the wake of Friday's fropa, with highs in the lower
80s for most, and perhaps some lingering shower and storm chances
Saturday morning. Sunday appears likely to remain dry, with
continued seasonal temperatures.
&&
.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 624 PM CDT Mon Jul 7 2025
Outside of any shower or storm, light winds and VFR conditions
are expected at all TAF sites. More widespread storms are
possible tonight across the area with the best time being just
before daybreak. Later in the period, more afternoon storms are
possible as well.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.
&&
$$
SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Gibbs
Office: LOT
FXUS63 KLOT 080531
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1231 AM CDT Tue Jul 8 2025
.KEY MESSAGES...
- Dangerous swimming conditions continue at Lake Michigan
beaches, but improving late this evening.
- Chance (30-50%) for scattered showers and thunderstorms on
Tuesday across primarily northern and central IL.
- Low shower/storm chances continue on Wednesday. Better chances
return Friday/Friday night.
&&
.DISCUSSION...
Issued at 226 PM CDT Mon Jul 7 2025
Tonight:
Expect partly cloudy skies and quiet conditions with seasonable
overnight lows in the lower to mid 60s outside of Chicago and
upper 60s in the city. The Beach Hazards Statement is set to
expire at 7pm for Illinois beaches and 9pm for Indiana beaches,
which looks reasonable per web cams and observations as of this
writing. There could be some patchy fog tonight near/south of
the Kankakee River overnight.
Castro
Tuesday through Monday:
Forecast evolution for Tuesday remains a bit unclear, with some
timing differences in the handling of low-amplitude disturbances
noted in today's guidance. At the surface, a moist axis which is
currently displaced west of the Mississippi River will slosh
eastward into the region as low-level southwesterly flow returns.
Aloft, several vorticity maxima will be in the vicinity as a more
notable shortwave translates well to our north across the
Minnesota Arrowhead Region. Have expanded some 20-30 percent
PoPs a bit farther east across the region Tuesday morning as
very modest ascent within a moistening airmass could yield
clusters of showers and a few storms.
Through the rest of the day, upper 60s/near 70 degree dewpoints
are forecast to return, and most guidance commensurately
suggests capping will erode through the late-morning and
afternoon, even with muted insolation and the potential for
pockets of morning showers/storms tied to a 700 mb wave in the
region. While surface convergence isn't strongly defined
tomorrow, the presence of a moist/destabilizing airmass and
presence of several disturbances aloft suggests mid-range chance
PoPs remain appropriate to cover the potential for afternoon
and early-evening shower and thunderstorms. Mid-upper flow looks
fairly weak, so storms should remain disorganized and posing
primarily a locally heavy rain and gusty wind threat.
Some potential that activity festers a bit through Tuesday
evening, but should see a gradual diminishing trend as drier
low-mid level air spreads in from the north. Through the day on
Wednesday, forecast soundings look like they become increasingly
capped across the northwest half of the region as a subsidence
inversion pushes eastward. Deeper boundary layer moisture is
evident with south and east extent through the area, however,
resulting in more limited capping. A lack of defined upper-level
features suggests that any diurnally-driven activity may remain
more sparse in coverage, and tied generally to surface
boundaries.
Speaking of boundaries (on Wednesday): today's guidance is
starting to hit the wind response on the lake a bit harder as a
backdoor front drops down the lake, which conceptually fits the
set up of a near 1020 mb high pushing east across the UP of
Michigan. Gusty northerly wind response is not ubiquitous in the
model guidance today, but did boost winds a bit on the lake,
and will need to keep an eye on this window for a period of
moderate or greater swim risk.
Thursday could end up being largely dry in the wake of the
aforementioned front. The surface high won't build across the
entire area, and lingering moisture could hold on in our far
southern locales, enough to justify hanging onto some very low
(15%) PoPs south of the Kankakee River vicinity, but even these
could end up being a bit too high.
On Friday-Saturday, forecast confidence begins to diminish as a
fairly sharp shortwave trough slicing across the Northern
Plains starts to interact with remnant MCVs/vorticity clusters.
Deterministic GFS continues to advertise some severe weather
threat across northwest Illinois but currently remains a bit of
a south and east outlier across the guidance suite.
Carlaw
&&
.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1231 AM CDT Tue Jul 8 2025
Forecast concerns include...
Chance of thunderstorms this afternoon.
Low chance for showers through mid morning.
Potential for fog early Wednesday morning.
Current isolated showers across northwest IL are expected to
dissipate over the next few hours before reaching the Chicago
terminals, though an isolated shower will remain possible. A few
showers across southeast MN/western WI may continue to fester
through the overnight hours, bringing a chance for showers to
RFD after daybreak. If these were to materialize, they may
persist north of the terminals through the mid/late morning
hours.
There remains a chance of thunderstorms for all of the terminals
this afternoon, though coverage remains uncertain and maintained
prob mention for now. A large complex of thunderstorms is moving
southeast across southwest IA into northern MO. How these storms
evolve over the next 12 hours, will impact storm trends locally
this afternoon. The most favored areas appear to be west central
IL with activity possibly dissipating further to the northeast.
Overall, low confidence for trends, which will need to be
monitored for possible later forecast changes. After this
potential precipitation, the rest of this evening into early
Wednesday morning is looking mainly dry.
Winds are light and variable and will become light southerly by
daybreak then become southwest by mid morning with speeds
increasing into the 10-12kt range. The forecast soundings
suggest there may be a period in the late morning, when gusts
into the 15-20kt range will be possible. Wind directions this
evening are uncertain. If there are storms, winds may favor a
light southeast direction.
Forecast soundings also show hardly any wind aloft early
Wednesday morning as weak frontal boundary sags into northern
IL. This would easily support fog development. However, fog may
be dependent on how widespread any precipitation becomes and the
best location for fog appears to be northwest IL, which would
be after the current 24 hour RFD taf period. But some fog
mention may be needed with later forecasts. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
Visit us at weather.gov/chicago
Office: ILX
FXUS63 KILX 080508
AFDILX
Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1208 AM CDT Tue Jul 8 2025
.KEY MESSAGES...
- There will be daily chances (20-50% coverage) for scattered
showers and storms, particularly during the afternoon and
evening hours. There is a marginal risk (level 1 of 5) for
severe storms Tuesday across portions of central Illinois.
- Seasonable heat and humidity will be in place the remainder of
the week into this weekend with afternoon highs generally in the
mid to upper 80s and dew points in the 70s.
&&
.DISCUSSION...
Issued at 211 PM CDT Mon Jul 7 2025
A weak area of high pressure is centered over the Great Lakes this
afternoon with ridging extending into portions of central
Illinois. This will help suppress the convective chances for the
remainder of today as well as provide brief relief from the muggy
conditions across the region with dew points generally running in
the 60s north of I-70. Some patchy fog will be possible overnight
into Tuesday morning within the weak flow, mainly over east
central and southeast Illinois.
Surface ridge axis will shift to our east Tuesday allowing
humidity to return across central Illinois with dew points
building back to around 70 degrees for most of the area.
Meanwhile, a shortwave trough is progged to move across the state
Tuesday afternoon/evening coinciding with peak heating and
allowing scattered thunderstorms to develop. Moderately strong
afternoon instability is expected to develop with MLCAPE values
advertised by the GFS expected to be around 1500-2000 J/kg.
Despite passage of the shortwave trough, deep layer shear will
remain sub-optimal for a more organized severe weather threat.
Nevertheless, a pulse severe threat will remain a concern Tuesday
afternoon and evening with downburst winds the primary concern.
Slow storm motions of 15-20 kt from west to east couple with PWats
approaching 2 inches will contribute to a localized heavy rain
threat. HREF LPMM indicates a couple very isolated pockets of
heavy rain (3-5 inches) will be possible.
Wednesday and Thursday will be characterized by weak upper level
troughing over the Great Lakes region with weak surface ridging
over much of the Midwest. Typical summer-time pop-up storms will
be possible each day within the weakly forced and modestly
unstable environment. Weak deep layer shear and more modest MLCAPE
values peaking 750-1250 J/kg both days will keep the severe
threat in check, but a brief pulse wind threat cannot be
completely ruled out along with slow moving storms that will be
capable of locally heavy rain.
Friday and Saturday will see a more notable upper wave traverse
the northern Great Plains and Upper Midwest. In response to this
wave, a warm front will lift across central Illinois Friday. A low
level jet developing Friday evening off to our west will allow
storms to develop and grow upscale and eventually track east along
the warm front into portions of Illinois late in the evening and
overnight. A severe threat will likely materialize with this
system, and depending on specific timing, could translate east
into portions of central Illinois. A cold front sweeping across
the region Saturday will result in another round of showers and
storms, again with a possible attendant severe threat depending on
timing and location of the synoptic front or effective cold front
as determined by the remnants of the Friday night storms.
Deubelbeiss
&&
.AVIATION... (For the 06z TAFs through 06z Tuesday Night)
Issued at 1208 AM CDT Tue Jul 8 2025
In the short term, quiet conditions expected aside from some
patchy light fog in east central Illinois toward daybreak. Main
concern will be with potential for thunderstorms in the afternoon
hours. Much will depend on residual boundaries from convection
currently west of the Mississippi River, but will maintain the
PROB30 mentions at all sites with some timing refinements based on
the 00z model guidance. Outside of the storms which will drop
visibility briefly, VFR conditions will prevail.
Geelhart
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
