343
FXUS63 KILX 201558
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
1058 AM CDT Fri Sep 20 2024

.KEY MESSAGES...

- There is a marginal risk (5-15% chance) for severe weather east
  of the I-55 corridor between 2pm and 8pm today. Primary threats
  will be damaging wind gusts and large hail.

- Greater rain chances materialize Saturday night through Monday.
  There is a 50-60% chance of 1-2 inches of rain across central
  Illinois during that time period.

&&

.UPDATE...
Issued at 1058 AM CDT Fri Sep 20 2024

15z/10am surface analysis shows a weak cold front along the
Illinois River...with the band of showers/storms that impacted
parts of the area early this morning now completely dissipated
across western Indiana. Sunny skies currently prevail across the
KILX CWA: however, models continue to indicate widely scattered
thunderstorm development along/ahead of the advancing front this
afternoon. HRRR has been consistently keeping things dry until
about 5-6pm when a few storms form along a Champaign to
Taylorville line. With dewpoints hovering in the upper 60s to
around 70 degrees, SBCAPEs are progged to exceed 2000J/kg by peak
heating. Despite favorable instability, mitigating factors for
widespread storms will be weak convergence along the boundary and
strongest deep-layer shear lagging well to the W/NW of the
instability axis. Nevertheless, a few strong storms with isolated
damaging wind gusts and hail will be possible this afternoon and
evening...focused east of I-55 between 2pm and 8pm. High
temperatures will range from the upper 80s in the Illinois River
Valley to around 90 degrees elsewhere.

Barnes

&&

.DISCUSSION...
Issued at 345 AM CDT Fri Sep 20 2024

Early morning surface map shows a cold front from western WI into
far eastern Iowa and nw MO. Isolated showers had recently develop
nw of Lincoln while more widespread showers and a few
thunderstorms were over southeast WI and northern IL, mainly north
of I-88 and supported by a 25-30 kt sw 850 mb jet. Variable sky
cover over CWA, with less clouds in eastcentral and southeast IL
and more clouds over western/sw CWA. Temps ranged from 58F in
Danville to 75 in Springfield, while more moist dewpoints were in
the low to mid 60s, except mid to upper 50s from Rantoul to Terre
Haute east. Aloft a strong 592 dm 500 mb high was over central
Texas and ridging ne into IL and the central and eastern Great
Lakes. A strong 553 dm 500 mb low was over east central Manitoba
with a 567 dm 500 mb low off the southern CA coast.

Latest CAMs push cold front se across the IL river valley late
this morning and thru rest of central IL during this afternoon
before stalling in southeast IL this evening. Isolated to
scattered showers and isolated thunderstorms possible into mid
morning over central IL, then a lull late morning and mid day,
before more isolated to scattered convection develops along and
ahead of se moving cold front in east central IL during mid/late
afternoon and moving into southeast IL during this evening. SPC
day1 outlook continues marginal risk of severe storms from
Kankakee to Decatur to Taylorville and East St Louis east from mid
afternoon (after 19Z/2 pm) into mid evening. There is 5% risk of
damaging winds and large hail. Wind shear is 30-35 kts in east
central IL and 25-30 kts in southeast IL, while MLCAPEs peak at
1-2k j/kg by late afternoon. Upper level ridging over IL keeps low
lapse rates and limiting factor for more widespread strong to
severe storms. Much of area should be dry overnight into Saturday
with slight chances of convection Saturday afternoon west of
Springfield and Peoria as warm front lifts back north/ne over
central IL on Saturday.

Very warm and rather humid conditions prevail today and Saturday
with highs in the upper 80s to around 90F, with afternoon heat
indicies in the low to mid 90s today and upper 80s and lower 90s
Sat (mid 90s southeast of I-70 Saturday afternoon). A stronger
cold front to move se into nw IL by dawn Sunday and more
widespread convection to spread over central IL during overnight
Sat night into Sunday morning. Fairly high chances of showers and
thunderstorms expected to continue Sunday through Monday night
with frontal boundary over central IL and moving into southeast IL
Monday night. Rainfall amounts from overnight Sat night through
Monday of 1-2 inches likely with locally high amounts nw of I-70
possible. Cooler highs Sunday in the mid to upper 70s in central
IL and lower 80s in southeast IL. A few degrees cooler Monday with
highs in the lower to mid 70s in central IL and around 80F in
southeast IL.

Larger model spread during middle and later part of next week and
stayed close to model blend with generally dry conditions Tue thru
Friday and highs in the 70s with lows in the low to mid 50s
Tue night thru Thu night.

07

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 639 AM CDT Fri Sep 20 2024

Showers and isolated TSRA will push east of the KCMI terminal
by 13z. There is a low chance (30%) for TSRA to develop ahead of
a cold front over eastern IL this afternoon, but current guidance
shows this will be southeast of the KCMI-KDEC terminals so left
mention out of TAFs. Southwest winds ahead of the front this
morning will veer northwest behind the front this afternoon, then
northeast or light/variable tonight. Patches of MVFR ceilings are
possible ahead of the front, but coverage looks low so kept
SCT025 cloud bases into this afternoon.

25

&&

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

$$