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611
FXUS63 KILX 251543 CCA
AFDILX

Area Forecast Discussion...CORRECTED
National Weather Service Lincoln IL
1043 AM CDT Tue Jun 25 2024

.KEY MESSAGES...

- A Heat Advisory remains in effect south of I-70 today as
  afternoon heat index readings peak at 100-105 degrees.

- Severe thunderstorms are possible across all of central and
  southeast Illinois today. The primary time frame will be
  afternoon and evening north of I-70...and evening into the
  overnight hours to the south.

&&

.MESOSCALE...
-- Changed Discussion --
Issued at 944 AM CDT Tue Jun 25 2024

Late this morning, a line of thunderstorms stretches from near
Galesburg to just north of Bloomington. Storms appear elevated
with outflow pushing about 20 miles ahead of the storms in
spots, but some new updrafts continue to develop atop/behind the
boundary and pulse to near severe limits at times. Ahead of the
outflow, temps are already in the low to mid 80s with dew points
in the low to mid 70s. These conditions, along with 8.6 C/km mid
level lapse rates that were sampled on the 12Z ILX sounding, are
contributing to around 2000-2500 J/kg MLCAPE which is expected to
increase above 3000 J/kg over the next couple hours. While surface
based parcels currently appear capped with RAP suggesting around
100 J/Kg MLCIN in place, cap is expected to erode significantly
by 11 AM / 12 PM CDT. This will set the stage for storms to re-
develop or re-intensify as they become surface based with an
attendant increase in the severe weather threat around that time.

Deubelbeiss
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&&

.SHORT TERM...(Today through Wednesday)
Issued at 355 AM CDT Tue Jun 25 2024

08z/3am regional radar mosaic shows a severe MCS tracking E/SE
across central Wisconsin into western Michigan. Based on radar
trends and consistent solutions from the HRRR/WRF-ARW, this system
will remain well N/NE of the KILX CWA early this morning. Further
south, a couple clusters of thunderstorms formed along and old
outflow boundary across northeast Illinois late last evening. One
cell has dropped S/SE into Iroquois County and will likely push
into northern Vermilion County over the next hour. Gusty winds
and large hail will be possible with this storm before it tracks
into Indiana and dissipates before sunrise.

Most CAMs suggest scattered convection will develop along the
trailing outflow boundary left behind by the Wisconsin MCS later
this morning. This should generally occur along/north of
I-80...with the storms gradually sinking southward into the
northern KILX CWA by mid-morning. As the atmosphere destabilizes,
some of these cells may pose a severe risk toward midday into the
early afternoon north of the I-72 corridor: however, am not
expecting widespread severe.

A more significant risk for strong to severe storms will
materialize late this afternoon into this evening as a cold front
dropping southward from the Northern Plains interacts with a
moderately unstable, but weakly sheared environment. 00z HREF
ensemble mean SBCAPEs are not quite as impressive as in previous
runs, with values of 1500-2500J/kg across central Illinois.
Meanwhile deep-layer wind shear remains paltry as evidenced by NAM
0-6km bulk shear of only around 20kt. Stronger instability/shear
appear to be focused further W/NW across central/southern Iowa
into far northern Missouri, where a greater potential for vigorous
updrafts and storm organization warrants a risk for large hail and
even a few tornadoes. Further east into central Illinois, the
weaker shear will likely mean loosely organized thunderstorm cells
primarily capable of scattered damaging wind gusts and localized
downpours. May see some large hail as well, but with lower SBCAPE
values and the freezing level near 15,000ft, think the potential
for hail larger than golf balls is slim. Based on model consensus,
have kept PoPs in the chance category through the day, then have
ramped up to likely to categorical (70-80%) this evening as areal
coverage increases in advance of the cold front. The storms will
drop southward overnight into Wednesday morning...with rain
chances coming to an end from north to south during the day
Wednesday. Storm total rainfall will be highly variable across the
area, but will generally range from 0.50 to 1.00. Some spots will
exceed 1 inch, particularly along/west of I-55 where storms may be
most concentrated tonight.

Barnes

.LONG TERM...(Thursday through Monday)
Issued at 355 AM CDT Tue Jun 25 2024

Once the front passes, high pressure will build into the Great
Lakes and bring central Illinois a period of comfortable weather.
Low temperatures Wednesday night will drop into the lower to
middle 60s while highs on Thursday remain in the lower to middle
80s.

Another cold front will approach from the northwest late in the
week, bringing rain chances back into the picture...particularly
Friday afternoon through Saturday morning. Temperatures will
briefly climb back into the upper 80s/lower 90s ahead of the front
on Saturday, but will once again drop back into the lower to
middle 80s after FROPA Sunday/Monday.

Barnes

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 546 AM CDT Tue Jun 25 2024

Main aviation forecasting challenge will be the timing of
potential convection today and tonight. 1030z/530am radar mosaic
shows a line of thunderstorms from southern Wisconsin to far
eastern Iowa near KMLI. The line will continue to push E/SE, with
the trailing end gradually settling southward toward the I-74
corridor by mid-morning. Have added a BKN mid-level cloud deck
after the 13-14z time frame at the I-74 terminals accordingly, but
will wait for clear radar trends before adding thunder. Most
models suggest thunderstorms will re-develop and become more
numerous late this afternoon into this evening. Based on latest
HRRR, have added predominant thunder between 23z and
04z...thinking that the bulk of the convection would then sink
south of the TAF sites toward midnight. Winds will become SW over
the next few hours with gusts increasing to 20-24kt. Winds will
then gradually veer to W/SW ahead of an approaching cold front
late this afternoon/evening.

Barnes

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for ILZ066>068-071>073.

&&

$$