il discuss
Office: DVN
FXUS63 KDVN 091049
AFDDVN
Area Forecast Discussion
National Weather Service Quad Cities IA IL
549 AM CDT Wed Jul 9 2025
...12z Aviation Update...
.KEY MESSAGES...
- There is a daily risk of isolated to scattered showers and
thunderstorms(20-40%) that will be most favorable in the
afternoon and early evening. Thunderstorms later Thursday and
Thursday night will have the potential to be stronger as a
lead shortwave moves into the area. Strong storms with heavy
rain again possible on Friday and Friday night.
- Seasonal temperatures and humidity levels will continue through
the weekend and into early next week.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 315 AM CDT Wed Jul 9 2025
Today...Will continue to watch fog trends through dawn and issue a
headline if needed, otherwise will let the fog SPS ride or expand
that if warranted. Then the rest of the day looks to be a typical
mid July day with temps in the mid to upper 80s, some ambient CU,
and isolated pop-up showers and thunderstorms, buoyancy bubbles in
the afternoon heating. As yesterday, slow storm movement in a low
shear/light low to mid level vertical wind profile may allow for
very localized heavy rainfall and flooding.
Tonight...Any lingering isolated showers or storms will wane early,
then much of the night to be a lull period before the watch will be
on for for elevated return flow(convergent southwesterly 20 KT H85
MB winds) induced spotty showers and storms late toward dawn. Low
coverage and confidence in this sctrd linear line of precip
developing however...20 POPs. Some patchy fog possible again in
spots and low temps generally in the upper 60s.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 315 AM CDT Wed Jul 9 2025
Thursday...Ongoing high CAPE airmass of 2000-3000+ J/kg will look to
be acted upon by an approaching shortwave in broad west-
northwesterlies acrs the mid CONUS. Thus expect an uptick in sctrd
storm development as the day progresses, and storm layer effective
shear of 20-30 KTs will help the cause for strong to severe storms
if convective temps in the upper 80s can be reached. Damaging wind
gusts the primary threat, and PWAT's of 1.5 to 1.8 inches again will
fuel locally heavy rainfall and localized ponding water or flooding.
The storm threat will continue into Thu night, with ensembles
showing a nice plume of 25+ KT southwesterly H85 MB LLJ flow acrs
the region with ample THTA-E advection.
Friday...Assessing the latest suite of medium range model solutions
and ensembles, there is more uncertainty now regarding storm
strength and coverage this day. The models have generally slow with
the incoming seasonably impressive short wave, possibly keeping the
potential for more organized storm systems off to the west of the
local area. Closer to home we may have to just deal with sporadic
storm development on the remnants of boundaries and discrepancy
gradients lingering out of Thu night, if the slower wave progression
verifies. Will have to keep solid chance POPs going however, but the
target time may be switching to late Friday night and especially
Saturday. There may be the scenario of an MCS developing upstream
off to the west and then propagating eastward into the area later
Friday night into early Sat morning. Then that effects the Sat
potential.
Saturday through Tuesday...Depending on the progressive nature of
the Friday wave as mentioned above, Saturday may be an organized
storm day if the models are on track with the slowed progression of
the main upper trof. Strong to severe storms look possible if we get
the CAPE build-up(no debris or MCS out of Friday night) to go along
with stronger shear profiles of 35-45+ KTs. Timing will be
everything and will continue to monitor the Friday into Saturday
period. Besides the severe threat, ensemble indicated PWAT feed of 2
to 2.3 inches either for Friday and/or Saturday make for flash
flooding concerns with the potential rainfall rates that the wind
shear and juiced air mass will produce(1-2" an hour). Current timing
thinking suggests Sunday into Monday to be a quieter and seasonable
period after whatever Fri-Sat system can make it through the
region.
&&
.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 545 AM CDT Wed Jul 9 2025
Some fog of at least MVFR VSBY's may still creep into the VCNTY
of some of the TAF sites through 8 AM CDT, otherwise a VFR TAF
cycle through the period with light sfc winds under a passing
ridge of weak high pressure. Will also keep with the idea that
while most the area will stay dry today, it will be another day
with the chance for an isolated shower or thunderstorm to pop up
in the heating of the day. Late tonight toward dawn, will have
to watch for more patchy fog especially on the IL side, and the
chance for a band of sctrd to isolated elevated showers or even
a thunderstorm to develop on the convergent nose of a
southwesterly LLJ.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...Dense Fog Advisory until 8 AM CDT this morning for ILZ001-002-
007-009-016>018.
MO...None.
&&
$$
SHORT TERM...12
LONG TERM...12
AVIATION...12
Office: LOT
FXUS63 KLOT 091136
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
636 AM CDT Wed Jul 9 2025
.KEY MESSAGES...
- Dangerous swimming conditions will develop at Lake Michigan
beaches Wednesday afternoon into early Thursday, especially
east of Gary, Indiana.
- There is a low chance (20 to 30%) for isolated thunderstorms
today, primarily near the lakeshore.
- Chances for showers and thunderstorms return Friday and
Saturday with the best chance (50-70%) on Saturday. Strong/
severe storms and heavy rain/localized flooding are possible.
&&
.UPDATE...
Issued at 545 AM CDT Wed Jul 9 2025
Did end up having to hoist a Dense Fog Advisory for much of
northwestern Illinois this morning as visibilities uniformly tanked
to 1/4 to 1/2 of a mile. The expectation is for fog to
gradually erode in the next few hours as the sun angle
increases. The Dense Fog Advisory is in effect through 9 AM CDT.
The leading edge of the backdoor/lake enhanced front is quite
evident in satellite data, and is currently just north of
Sheboygan, Wisconsin. Based on the current speed, the front
should reach Waukegan by 11 AM and Chicago by 1 PM. There is
quite the expansive stratus bank behind the front, so clouds
appear poised to fill quickly across the area this afternoon and
evening.
One final note - would not be surprised to have to add central
Cook and Lake (IL) counties to the Beach Hazards Statement
pending how quickly winds and waves pickup behind the front.
Will let the incoming day shift take a close look at upstream
observations to inform any adjustments to the product during the
scheduled morning update time.
Borchardt
&&
.DISCUSSION...
Issued at 222 AM CDT Wed Jul 9 2025
Through Thursday:
A broad upper-level trough is evident across the Great Lakes
this morning in water vapor imagery atop a very weak/baggy
surface low pressure system centered over Lake Michigan. An
embedded shortwave within the broad trough is forcing an
expansive area of upper-level clouds from Lower Michgian though
Southern Illinois, with the back edge more or less oriented
along I-57 at press time. Meanwhile, a surface high pressure
system is building southward toward Lake Superior along the
backside/inflection point of the upper-level trough.
With nearly calm winds, clearing skies, and pockets of wet soil
from showers and storms yesterday, areas of fog are developing
early this morning. So far, the highest coverage of fog has been
near and west of I-39 (where clearing occurred earliest this
morning). Going forward, would expect fog to continue gradually
expanding and become locally dense with visibility less than 1/2
of a mile. For now, will plan to handle the locally dense fog
with a Special Weather Statement. However, will continue to
evaluate trends to determine if a targeted Dense Fog Advisory
will be needed instead.
After sunrise, any remaining fog should erode. Attention then
turns toward a lake-enhanced front due to race down and inland
from Lake Michigan from late morning through early afternoon.
Based on surface observations across the Upper Peninsula of
Michigan, the backdoor front appears to be approaching the
northern tip of Lake Michigan at press time. High res guidance
appears ubiquitous in showing the front zooming south throughout
the morning and reach northeastern IL in the 10 am to noon
window, and northwestern Indiana in the 11am to 1 pm window. The
front will then spread inland through the remainder of the
afternoon. Thanks to the seasonably warm lake water temperatures
in the upper 60s to lower 70s, the marine airmass won't be
particularly cool. With that said, highs will range from the mid
80s well inland to the mid 70s lakeside this afternoon.
Of greater interest will be in increase in wave heights behind
the front, with an attendant threat for rip currents
particularly this afternoon through Thursday morning.
Experimental WW3 model data run using winds exclusively from the
NAMNest (which typically performs well in these types of
regimes) shows waves hitting 3 to 4 feet by this evening along
beaches from Gary to Michigan City, Indiana. Considering
conditions will be rather pleasant this morning, would like to
get the message out for rapidly changing conditions this
afternoon. So, will go ahead and issue a Beach Hazards Statement
for Lake and Porter county beaches in northwestern Indiana (and
hold at a "Moderate" swim risk for northeastern Illinois
beaches).
As mentioned in previous forecast discussions, will have to
watch for the isolated to perhaps scattered coverage of showers
and storms along the front from late morning through early
afternoon. Owing to mid-level subsidence in the wake of the
departing upper-level trough, capping is expected to develop
around 600mb by early afternoon. as a result, what should be a
chunky cumulus field along the front may struggle to sprout more
than an isolated storm or two. All things considered, will
maintain the inherited 20 to 30% chances for showers and storms
through the evening hours, with the highest values along the
front.
The southward build of the Great Lakes high pressure system
will set the stage for a quiet night. A few patches of fog may
develop toward daybreak Thursday, mainly south of I-80 (south of
the remnant lake breeze/front). Overnight lows are expected to
fall into the low to mid 60s.
On Thursday, the upper-level pattern will be undergoing a
transition as a series of upper-level shortwaves propagate from
the central US toward the Great Lakes, south of a deeper trough
approaching from the Pacific Northwest. There is a growing
signal for one such shortwave to approach northern IL in the
late afternoon, though will have to think that the instability
gradient positioned well to our west would guide any upstream
convection safely around the perimeter of our area.
Nevertheless, this will be a trend to monitor. Thursday
otherwise looks like a nice day with highs in the low to mid 80s
and partly cloudy skies.
Borchardt
Thursday Night through Tuesday:
Primary forecast remains thunderstorm chances Friday through
Saturday.
There has been little change to the overall pattern/trend for
late week with an upper trough moving across the northern Plains
and upper midwest with a wave ejecting out of the central
Plains with an eventual surface low developing somewhere nearby
or over the Lakes region. There seems to be a bit better
consensus that much of Friday and Friday evening could be dry
for the local area with better chances northwest of the area,
with perhaps some decaying activity late Friday night/Saturday
morning across northwest IL. Then on Saturday when the the main
front moves through and a possible surface low is shifting east
of the area, this would be the best chance of thunderstorms.
Blended pops for Friday evening and Friday night are now high
chance, low likely and these seem too high based on the latest
trends but made no changes. Pops have increased to high chance
and likely on Saturday. Quite a bit of ensemble support for the
Saturday precip timing, especially from the ECMWF.
With timing looking a bit better for Saturday and perhaps early
to mid afternoon with the heating of the day, some stronger
storms are possible along with heavy rain and possible localized
flooding as precipitable water values will be around 2 inches
ahead of the front. Any thunderstorms on Friday and Friday night
would also have the potential to be strong and produce heavy
rain.
High pressure appears to move far enough into the area Saturday
night and Sunday to end the precipitation chances with Monday
also possibly being dry. High temps look to warm back into the
upper 80s/lower 90s Monday and Tuesday. Then by midweek, current
trends would suggest another larger trough/cold front moving
across the region. cms
&&
.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 636 AM CDT Wed Jul 9 2025
Forecast concerns include...
Lifr/Vlifr vis/cigs with fog this morning.
Wind shift to northeast this afternoon.
Chance of showers this afternoon.
Possible fog early Thursday morning.
Fog and low cigs are widespread across much of northwest and
central IL and will steadily lift/dissipate over the next few
hours. Few/sct ifr level clouds are still possible for ORD/MDW
but confidence has decreased for ifr cigs. However, as a cold
front moves south across the area late this morning into early
this afternoon, there is a potential for ifr cigs, though the
best chance for these lower cigs may be closer to Lake Michigan.
Light southwesterly winds will turn northwesterly this morning,
possibly northerly ahead of the front and then will shift to the
northeast as the front moves through. There may be some gusts
into the 15-20kt for a short time with and just behind the
front. Northeasterly winds will slowly diminish into this
evening and may become light northerly overnight.
There is a chance of showers this afternoon, likely confined to
the front as it moves inland. There may also be an isolated
thunderstorm, but overall coverage looks low and prob shower
mention still looks on track.
There is another chance for fog early Thursday morning, mainly
west and south of the Chicago terminals and included tempo
mention at RFD for this possibility. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Dense Fog Advisory until 9 AM CDT this morning for ILZ003-
ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012-ILZ019-ILZ020-
ILZ021-ILZ032.
IN...Beach Hazards Statement from 1 PM CDT this afternoon through
Thursday morning for INZ001-INZ002.
LM...None.
&&
$$
Visit us at weather.gov/chicago
Office: ILX
FXUS63 KILX 091110
AFDILX
Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
610 AM CDT Wed Jul 9 2025
.KEY MESSAGES...
- There will be daily chances (20-50% coverage) for showers and
storms over central and southeast Illinois through the
remainder of the week and into the weekend. Thunderstorms will
generally be favored during the afternoon and evening hours,
except for Friday night as a warm front lifts northward across
the area.
- Seasonable heat and humidity will remain 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. Friday will be
the hottest day this week with highs around 90 and afternoon
heat indices peaking in the upper 90s to around 100 degrees.
&&
.DISCUSSION...
Issued at 355 AM CDT Wed Jul 9 2025
The predawn surface map shows a frontal boundary draped north of
IL from central lower MI into southeast WI and central Iowa. Radar
mosaic shows scattered showers over eastern parts of Vermilion
and Edgar counties eastward into west central Indiana, with very
isolated light showers in southeast IL. Areas of fog had developed
past few hours over the IL river valley, west of I-55 where low
and mid level clouds had decreased. Though even in the cloudier
areas east of I-55 we are getting some fog with stratus clouds
like at Taylorville with 1/2 mile vsby and 200 foot ceiling. Have
increase coverage of fog over nw half of CWA into early morning
and will see pockets of dense fog too. We will monitor possibility
of dense fog advisory over parts of IL river valley if fog get
more dense and widespread next few hours. Fog should lift by mid
morning while more clouds prevail in east central and southeast IL
today. Isolated to scattered convection to develop this afternoon
with unstable airmass with MLCapes of 1400-1800 J/kg over
southern/eastern CWA but very weak wind shear values around 10
kts. So a few pulsey type storms possible this afternoon with
gusty winds and locally heavy rains. SPC Day1 does not have a
marginal risk over our area today and WPC Day1 ERO has marginal
risk of excessive rainfall over far se IL. Highs today in the mid
to upper 80s with heat indices peaking in the lower 90s this
afternoon.
Isolated convection early this evening otherwise much of tonight
dry. Could see patchy fog develop overnight over ne and eastern
CWA with light winds and moist boundary layer. Lows overnight in
the mid to upper 60s.
Isolated to scattered convection to develop during Thu afternoon
as airmass gets more unstable again especially sw half of CWA as
MLCapes rise back to 1400-1800 J/kg and wind shear values a bit
higher than today at 15-20 kts. SPC Day2 does not have marginal
risk of severe over CWA on Thu afternoon/evening (marginal risk is
over Iowa) but could be a few stronger cells with gusty winds sw
and west central CWA Thu afternoon and early Thu evening. Highs
Thu in the mid to upper 80s and afternoon heat indices in the
lower 90s so similar to todays readings.
A stronger short wave trof moving over the Midwest on Friday to
have higher chances of convection nw of CWA Fri afternoon with our
pops of 30-40% Fri afternoon, and mainly slight chance in
southeast IL. Gets more unstable Fri afternoon with MLCAPES 2-3k
J/kg (highest sw CWA) wind wind shear increasing as well to 25-30
kts by late day. Could be a few stronger storms especially nw CWA
Fri afternoon/evening with low level jet placing a role Friday
night. Warm front lifting northward Fri afternoon and Fri night
to bring hot and humid conditions with highs around 90F and
afternoon heat indices in the upper 90s to around 100 degrees on
Friday. Good chance of convection Friday night and Saturday
especially during the afternoon hours. More unstable airmass is
over southeast IL Sat afternoon with MLCAPes around 2500 j/kg so
could be some strong to severe storms Sat afternoon in southeast
IL.
Models have trended wetter over CWA by Sunday afternoon as a
system approaches from the Central Plains. Heat and more tropical
humidity looks to return early next work week as upper level
ridge builds more into IL as 500 mb heights rise to near or above
591 dm.
07
&&
.AVIATION... (For the 12z TAFs through 12z Thursday Morning)
Issued at 610 AM CDT Wed Jul 9 2025
Band of very low clouds and dense fog has hovered from KPIA-KIJX
the last few hours, and has struggled to make it much east of
KSPI-KBMI despite a period of clearing. However, some recent
development of dense fog has been taking place over parts of east
central Illinois, including KCMI. Already seeing some signs of
thinning though, and VFR conditions should prevail in a couple of
hours. After that, little in the way of concern. Can't rule out a
stray shower or storm in the afternoon, but confidence and
coverage is too low for a mention in the TAF at this point.
Geelhart
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
