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657
FXUS63 KILX 191558
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
1058 AM CDT Wed Jun 19 2024

.KEY MESSAGES...

- Hot and humid conditions will continue across central and
  southeast IL into this weekend. The hottest conditions will
  arrive Friday and Saturday when air temperatures climb into the
  middle to upper 90s, and heat index values peak near or just
  above 100 degrees.

- Isolated thunderstorms will be possible mainly northwest of the
  IL river this week, with a better chance for thunderstorms
  arriving Saturday night into Sunday as a cold front moves
  through Illinois.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1058 AM CDT Wed Jun 19 2024

Only minimal changes to timing of cloud cover and precip chances
today, delaying diurnal cumulus formation a few hours, and
precipitation chances until after 1 pm. With a frontal boundary
draped from Lake Superior to the TX/OK Panhandle area a few
counties west of the Mississippi River and making slow progress
toward the Illinois River this evening. Thunderstorms should be
able to form in this frontal zone. Average SBCAPE is around 1000
J/kg in this area, along with up to 30 kt deep layer shear, and
strong to severe thunderstorms could result in this area. A
Marginal Risk for severe storms has been designated as far
southeast as portions of Knox County, for potential for 60 mph
wind gusts. Otherwise, any storm activity should be more isolated
with lower shear and less instability as well as an absence of any
significant forcing mechanism. Highs still look on target to
reach the lower 90s across the area, with dewpoints in the lower
70s achieving mid to upper 90s heat index values for hot and humid
conditions.

37
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&&

.DISCUSSION...
Issued at 400 AM CDT Wed Jun 19 2024

Early morning surface map shows large high pressure anchored off
the mid Atlantic and New England Coast and ridging back into the
lower Ohio and mid MS river valley. A frontal boundary extended
from central WI through central parts of Iowa and Kansas to 1001
mb low pressure in central NM. Convection was over central IA and
nw MO into central KS, nw OK an far northern Texas. An outflow
boundary was producing a narrow band of showers and isolated
thunderstorms in southeast Iowa into north central MO. Very light
showers were noted east of IL over mainly central/eastern Indiana
and southeast lower MI. Water vapor loop shows tropical plume of
moisture from the central/western Gulf of Mexico had shifted
mainly east of IL over IN and Ohio. Subsidence noted nw of I-55.
IR satellite shows broken to overcast mid level clouds along and
east of I-55 with clear to partly cloudy skies west of I-55. Mild
temperatures were in the low to mid 70s with muggy dewpoints in
the upper 60s and lower 70s. Peoria tied another record warm low
of 75F on June 18, which was originally set in 2018.

A strong 597 dm 500 mb ridge over the mid Atlantic region and sw
New England was ridging back into the mid and lower MS river
valley. Latest forecast models continue to build the upper level
ridge westward next few days, with 500 mb height rising to
593-595 dm over central/se IL this afternoon, and up to 595-597 dm
on Thu. Latest CAMs show isolated convection possible this
afternoon nw of the IL river and near the Indiana border. SPC has
shifted marginal risk of severe storms ne of IL from eastern
Indiana ne across the southern Great Lakes and into northern New
England. Isolated convection possible again Thu afternoon north of
Peoria. Most areas will remain dry through Saturday. Main weather
story will be the high heat and humidity that continues into this
weekend. Highs today in the lower 90s with afternoon heat indices
in the mid to upper 90s. SSW winds will not be as breezy as past
two days so providing less relief from the high heat and humidity.
Lows tonight in the lower 70s. Highs Thu in the low to mid 90s
with afternoon heat indices of 95-100F.

Airnow.gov shows an orange category (Unhealthy for sensitive
groups) appearing over the Wabash river valley over eastern/se IL
(similar to this past Monday) with an air quality alert over much
of Indiana from midnight tonight through midnight Thu night.

Friday and Saturday will likely see the hottest temperatures with
highs in the mid 90s and a few areas reaching upper 90s.
Afternoon heat indices around 100 will be common and Saturday
could surpass 100F similar to conditions we had this past Monday.
Will issue another special weather statement to address this heat
wave into this weekend.

A stronger upper level trof moves into the Midwest during this
weekend finally pushing the strong upper level ridge southward
and allowing a cold front to push se through nw IL overnight Sat
night and thru central/se IL around Sunday as it weakens on Sunday.
Will see increasing chances of convection from nw to se during
Sat night, with 20-30% pops se of the IL river on Sunday. Heavier
rains appear to be nw and north of CWA late Sat afternoon and Sat
night and may be dealing with strong to severe storms over IL
river valley Sat evening. Highs Sunday in the lower 90s with heat
indices in the low to mid 90s in central IL and upper 90s in
southeast IL. Monday looks like a drier day as dewpoints could
slip into the upper 50s/lower 60s with highs in the upper 80s to
around 90F. Upper level ridge building back over IL next Tue/Wed
with sw flow returns heat and humidity with highs back in the low
to mid 90s and heat indices in the mid 90s to around 100F possible
again.

The Climate Prediction Center (CPC) 8-14 Day outlook for June 26
through July 2 has 60-70% chance of above normal temperatures over
IL. Currently through June 18, temperatures are 1.5-3 degrees
above normal in central IL, and we will likely be even more above
normal by months end.

07

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 555 AM CDT Wed Jun 19 2024

VFR conditions to continue across the central IL airports through
12Z/7 am Wed. Broken to overcast mid level clouds with bases
around 10k ft from I-55 east to scatter out during late morning
and early afternoon while few to scattered cumulus clouds with
bases around 5k ft develop. Isolated convection possible this
afternoon nw of the IL river, but kept PIA dry as convection
appears to stay nw of this airport with nearest convection
currently near the Quad cities and lifting ne. South winds 7-12
kts today and around 5 kts or less after sunset and SSE to SE
direction.

07

&&

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

$$