105
FXUS63 KILX 201730
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1230 PM CDT Thu Jun 20 2024

.KEY MESSAGES...

- Hot and humid conditions will continue across central and
  southeast IL into the middle of next week, with brief relief
  from the high humidity on Sunday night and Monday. The hottest
  conditions of the upcoming 7 days look to be Friday, Saturday
  and Tuesday when air temperatures climb into the mid 90s, and
  heat index values peak near or just above 100 degrees.

- Isolated thunderstorms will be possible this afternoon and early
  evening north of I-72. A better chance for thunderstorms
  arrives Saturday night into Sunday morning as a cold front moves
  through Illinois.

&&

.UPDATE...
Issued at 1037 AM CDT Thu Jun 20 2024

A warm front appears to be located near the northern edge of the
ILX forecast area, expected to slowly drift northward today. Just
northward from this boundary has been the focus for showers and
thunderstorms this morning, although trends have been diminishing.
High resolution models have backed off from thunderstorm activity
developing in the ILX forecast area through the morning hours and
into the early afternoon, so have lowered PoPs then, however, have
maintained slight chance/20 percent to as far south as 20-30
miles north of I-72 for the afternoon as models continue to depict
widely scattered activity spreading southward of the slowly
moving front. Moderate humidity with near 70 dewpoints and highs
in the lower to mid 90s still looks on track, as 10 AM
temperatures have already reached the mid 80s. Diurnal/daytime
cumulus cloud cover has started to develop across most of the
area, and should peak in the early afternoon before subsidence
associated with high pressure building into the Ohio Valley acts
to suppress cumulus from south to north by late afternoon.

37

&&

.DISCUSSION...
Issued at 400 AM CDT Thu Jun 20 2024

Early morning surface map shows large high pressure (1028-1030
mb) 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 nw IL near or just nw of the IL
river and extending into northern MO and southeast Kansas. A band
of convection was nw of the front over nw MO, southeast Iowa and
central WI and lifting northeast. IR satellite shows mostly clear
skies over central and southeast IL with patches of clouds, while
main cloud band was nw of central IL toward the Iowa border and
far nw IL. Mild temperatures were in the upper 60s to mid 70s
with muggy dewpoints in the upper 60s to around 70F. Patchy fog
noted over parts of Indiana and far southeast IL and may need to
add this to forecast over Wabash river valley early this morning.

A strong 597 dm 500 mb ridge over the mid Atlantic States
(Maryland and southeast PA) was ridging westward into the mid MS
river valley. The 00Z June 20th forecast model suite continue to
build/retrograde the upper level ridge westward today, with 500 mb
height rising to 595-597 dm today over CWA and near 598 dm high
over the lower Ohio river valley near Evansville this afternoon.
This will help push the front quickly north of CWA early this
morning and into northern IL, north of I-80 this afternoon. Have
isolated convection chances far nw CWA early today and then 20%
chance northern CWA this afternoon from Quincy to Bloomington
north.

The frontal boundary meandering over northern/ne IL tonight to
lift north of IL by supper time Friday and its convection chances
to generally shift north of CWA tonight through Friday night. Much
of area should actually stay dry through the daytime hours on
Saturday.

Main weather story will be the high heat and humidity that
continues into this weekend. Highs today in the low to mid 90s
with afternoon heat indices of 95 to 100 degrees. SW winds will
generally be fairly light again today at 5-10 mph so not
providing much relief from the high heat and humidity. Lows
tonight in the lower 70s.

Airnow.gov for Air Quality shows an orange category (Unhealthy
for sensitive groups) appearing over the Wabash river valley over
eastern/se IL today (similar to this past Monday). An air quality
alert is in effect over much of Indiana from through midnight
tonight.

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.
Still shy of heat advisory criteria of peak heat index of 105F or
higher on a day or 100-105F peak heat indices on four consecutive
days. Issued 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 IL late Sat night into Sunday morning and
southeast IL Sunday afternoon as it weakens on Sunday. Will see
increasing chances of convection from nw to se over central IL (nw
of I-70) during Sat night, with 20-30% pops se of the IL river on
Sunday. SPC day3 outlook has marginal risk of severe storms Sat
night nw of the IL river for damaging winds and hail. Locally
heavy rains also possible especially nw CWA Sat night. Highs
Sunday in the lower 90s with heat indices in the low to mid 90s in
northern CWA and upper 90s to near 100F from I-72 south. Less
humid air filters in on Sunday night Monday as dewpoints could
slip into the upper 50s/lower 60s with highs in the upper 80s to
lower 90s. Upper level ridge building back over the nations
heartland on Tue with sw surface flow returns heat and humidity
with highs back in the low to mid 90s and heat indices in the
upper 90s to lower 100s Tuesday afternoon and mid to upper 90s on
Wednesday. IL gets in a nw upper level flow during middle of next
week and may see more active wx return. Have 20-30% chance of
showers and thunderstorms in central IL Tue afternoon (highest
pops nw of IL river), then chance of convection over area Tue
night into Wed. Mainly isolated chances of convection Wed night
and Thu with highs next Thu in the upper 80s to around 90F and not
quite as humid.

The Climate Prediction Center (CPC) 8-14 Day Outlook for June 27
through July 3 has a 60-65% chance of above normal temperatures
over IL. Currently through June 19, temperatures are 2-4 degrees
above normal in central IL, and we will likely be in the top 10
warmest Junes on record. Peoria average temperature from June 1-19
is 75.1F and only 1 degree from being the 10th warmest June and 2
degrees from being the 5th warmest June.

07

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1230 PM CDT Thu Jun 20 2024

SCT-BKN cloud cover around 4000 ft AGL will continue until around
00Z. A few spotty showers/thunderstorms could develop north of
KSPI-KDEC-KCMI, however isolated coverage precludes mention in
the TAFs at this time. The best chance for any precip at or near
a station will be from PIA to BMI. VFR conditions will prevail
through the period. Winds SW 5-10 kts until 00Z, then light and
variable. SW winds 7-11 kts developing again after 16Z.

37

&&

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

$$