876
FXUS63 KILX 260241
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
941 PM CDT Tue Jun 25 2024

.KEY MESSAGES...

- Slight Risk (15% within 25 miles) of severe storms today and
  tonight, tapering to a Marginal Risk (5%) Wednesday across
  southeast Illinois.

- Expect a break from the heat starting Wednesday with highs
  generally in the lower to mid 80s through Friday. There will be
  a brief break from the humidity briefly Thursday with dew
  points dipping into the 50s.

&&

.UPDATE...
Issued at 941 PM CDT Tue Jun 25 2024

Storms continue over parts of the area, but appear to be
weakening as they move to the south-southeast Will update pops/wx
to reflect current situation for the rest of the night.

Auten

&&

.DISCUSSION...
Issued at 202 PM CDT Tue Jun 25 2024

As of 2pm this afternoon, storms are ongoing from near Mt Sterling
to Springfield in west central Illinois, and from Effingham to
Dennison in east central/southeast Illinois. These storms have
kicked out an outflow boundary that has surged well ahead, except
for the storms in east central Illinois which are riding the
outflow boundary and consequently have been much stronger. Ahead
of the outflow boundary, SPC meso-analysis suggests that around
3000-3500 J/kg MLCAPE is present coinciding with marginal
effective shear of around 25-30kt. There parameters continue to
support a chance for severe weather, but so far most of the
storms quickly fall behind the boundary where the severe threat is
much lower. While the outflow boundary continues to surge south
and southwest, it is encountering moderate WSW flow gusting to
around 20kt which will help impede its progress. Until there is
notable slowing of the boundary, storms forming on the front will
continue to fall behind and become elevated with low end wind/hail
threat. 18Z WoFS run suggests that new severe convection is most
likely near the I-70 corridor through 22Z, then diminishes in
coverage through 00Z as storms exit the forecast area.

This evening, a modest low level jet will set up across portions
of Kansas and Missouri with strongest focus near the IA/MO state
line initially. This should cause a renewed uptick in
thunderstorm activity within a still strongly unstable atmosphere
(MLCAPE in excess of 3000 J/kg per latest RAP). These storms
followed the cloud bearing flow and instability axis east-
southeast into portions of west central Illinois mid to late this
evening and elsewhere across central Illinois overnight. Some of
this activity may end of being shunted further south due to
ongoing convection, so will have to monitor trends with these
storms as some could once again be severe. Several CAMs indicate
these storms will grow upscale with a QLCS impacting areas from
eastern KS into central IL, though the further eastern solutions
may not pan out due to ongoing convection this afternoon.

Main H5 trof and attendant cold front (possibly locally enhanced
by remnant MCV) is poised to move across central Illinois
Wednesday morning and afternoon. Some modest destabilization is
possible across portions of SE Illinois by early afternoon, but it
remains uncertain if storms will be able to tap into this before
exiting the area with the cold front. Better chances for severe
storms are in place just S/E of the forecast area but will need to
keep a close eye on the counties south of I-70 before frontal
passage midday Wednesday.

High pressure will build across the Upper Midwest Wednesday behind
the departing cold front and precip chances will diminish
accordingly from the northwest through the day. Temperatures and
humidity levels will turn briefly more comfortable particularly
Thursday under the influence of this air mass. Highs will be in
the lower to mid 80s both days with dew points eventually
bottoming out in the upper 50s to lower 60s Thursday.

As the ridge axis shifts to the east coast late in the week,
return flow will overspread the lower and mid Mississippi River
Valley with dew points building back up to around 70 degrees
Friday. The chance for showers and storms will accompany the
increase in humidity as mid level warm air advection overspread
the area Friday, followed by more showers and storms as a cold
front sweeps across the region Saturday. Both the GFS and ECMWF
indicate that portions of the region will have instability and
shear favorable for severe storms, but details will have to be
ironed out in the coming days.

Deubelbeiss

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 636 PM CDT Tue Jun 25 2024

Though storms have moved south of the TAF sites early this
evening, another line of storms has developed across northern IL
into eastern IA and am expecting them to drop south back toward
the TAF sites in a few hours. Some HiRes models forecast show
storms getting toward the TAF sites tonight, while others have the
storms weakening as they move south. Current airmass over central
IL has been worked over quite a bit, so concerned that storms will
not hold together long after getting into the area. Do think
showers and VCTS will reach PIA and BMI in 3-4hrs, but only VCSH
reaching SPI, DEC, CMI later this evening. Any pcpn will not last
very long...maybe only 2-3hrs and then be done. MVFR clouds are
expected to arrive after midnight tonight and continue into the
early morning hours. Think more precip will be possible later
afternoon, but some uncertainty in this so have left out at this
time. Winds will be southwest through the night but then become
northwest after the FROPA tomorrow morning.

Auten

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$