681
FXUS63 KILX 211737
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1237 PM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Very warm weather will continue today as afternoon high
  temperatures once again top out in the upper 80s and lower 90s.

- Beneficial rainfall is on tap for all of central and southeast
  Illinois from late tonight through Monday night. Storm total
  rainfall will range from 1 to 2 inches...with some locations
  along and south of I-70 potentially picking up 3 inches.

&&

.UPDATE...
Issued at 1105 AM CDT Sat Sep 21 2024

15z/10am surface analysis shows a stationary frontal boundary
extending from Evansville, Indiana northwestward to near
Kirksville, Missouri. Easterly flow to the N/NE of the front has
brought lower dewpoint air into much of central Illinois this
morning...with readings in the upper 50s/lower 60s along and north
of I-74. Further south closer to the boundary, lower 70s dewpoints
persist south of I-70. Scattered showers and thunderstorms
presently across southern Iowa into Missouri will continue to
shift slowly eastward today: however, they will be encountering a
drier environment as they cross the Mississippi River and will
thus decrease in intensity and areal coverage. Have maintained
low chance PoPs (20-30%) along/west of the I-55 corridor through
the afternoon as the showers gradually try to work eastward.
Otherwise it will be another very warm day. Highs will be held in
the middle to upper 80s west of the Illinois River due to
increased cloud cover and shower chances, but will reach the lower
90s further east where sunshine will be more prevalent.

Barnes

&&

.DISCUSSION...
Issued at 345 AM CDT Sat Sep 21 2024

Areas of fog had developed past few hours east of I-55 with
patchy dense fog from Champaign to Decatur to Taylorville east
where more moist air present with low to mid 60s dewpoints and
very light to calm winds. Some cirrus clouds arriving from the
west has been keeping the dense fog from getting too widespread
while less high clouds further east over Indiana to allow more
widespread dense fog formation and they have a dense fog advisory
until 8 am cdt. Have increased fog wording in eastern IL until 9
am, and will continue to monitor dense fog coverage and dense fog
advisory possibility early this morning. A special weather
statement will be issued for the patchy dense fog in eastern IL
early this morning with visibilities restricted to a quarter mile
at times.

A frontal boundary over southeast IL and into sw IL, will lift
back northeast across central IL during this afternoon. Dewpoints
to increase back up into the upper 60s and lower 70s while highs
reach the upper 80s and lower 90s, with afternoon heat indices
peaking back in the 90s. Limited forcing today, but MLCAPES rising
to 2k j/kg over western/sw CWA by mid/late afternoon with wind
shear values of 20-30 kts could support a few strong storms
western and sw CWA from mid afternoon into early evening for hail
and gusty winds. SPC day1 outlook officially keeps marginal risk
nw of CWA over much of Iowa, nw MO and central/western WI closer
to a cold front.

This cold front progged by CAMs to track se into nw IL late
tonight and moving into central IL during Sunday afternoon. This
system has stronger forcing and will produce more widespread
showers and a chance of thunderstorms arriving late tonight into
Sunday. SPC day2 outlook has marginal risk of severe storms sw of
St Louis over central/southern MO. Cooler highs Sunday in the mid
to upper 70s central IL and around 80F in southeast IL. Frontal
boundary will be near southeast IL Sunday night and Monday as
another system moves along it and likely brings another round of
showers and a few thunderstorms with the heavier rains focused in
southeast IL during that time frame. SPC day3 has marginal risk of
severe storms over far southern IL from Carbondale to Evansville
south on Mon/Mon night. Precipitatable water values of 1.5-2
inches are expected Sunday into Monday so heavier rain showers are
possible at times. Between 1-2 inches of rainfall expected over
CWA Sunday through Monday night with 2-3 inches possible in
southeast IL where rain likely linger into Tue morning. Even
cooler Monday with highs in the lower 70s over much of central IL
with mid to upper 70s in southeast IL.

Models diverge with handling upper level pattern during mid/late
week so stayed close to model blend with this forecast package.
Generally dry conditions forecast for Tue night through Thu with
below normal temperatures with highs in the low to mid 70s and
lows in the low to mid 50s from Tue night through rest of the
week. There is potential for tropical system to move northward
over the Gulf of Mexico and into the central Gulf coast or
southeast States late next week. Consensus of models keep its
moisture south and southeast of central and southeast IL. Highs
get closer to normal for late September in the upper 70s on
Friday and next Saturday.

07

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1237 PM CDT Sat Sep 21 2024

1730z/1230pm radar imagery shows a broken line of convection
extending from KGBG to just west of KIJX. This activity has been
steadily pushing eastward, but is encountering a drier/more stable
environment as it does so. Based on latest radar trends, have
opted to add thunder mention at both KPIA and KSPI between 18z and
20z...but have left the remaining sites dry as the line will
eventually dissipate as it crosses I-55. Winds are initially
southeasterly, but will veer to the south late this afternoon and
evening, then to the southwest overnight. The next wave of
precipitation is still on target for late tonight, with HRRR/RAP
timing similar to the previous TAF forecast. Have only made a few
minor adjustments, bringing predominant light rain into KPIA by
09z then further east to KCMI by 12z. Ceilings will initially be
VFR, but will lower to MVFR an hour or two after the rain begins.
MVFR ceilings will then persist through the remainder of the 18z
TAF period.

Barnes

&&

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

$$