496
FXUS63 KILX 231754
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1254 PM CDT Mon Sep 23 2024

.KEY MESSAGES...

- Widespread showers and a few thunderstorms will lift northeast
  over central and southeast IL this afternoon and tonight, with a
  good chance of showers lingering into Tuesday. Storm total
  rainfall will be greatest along and south of the I-72 corridor
  where 1 to 1.5 inches of additional rain is expected, with less
  than a half inch of rain west of the IL river.

&&

.UPDATE...
Issued at 1055 AM CDT Mon Sep 23 2024

A shortwave ejecting northeastward into central IL is spreading
widespread rain northeastward into central IL this morning, with
embedded heavy bands setting up near the I-70 corridor. Near the
I-70 corridor, radar estimates of up to 2 inches have been noted
over the past few hours, on track to extend into southeast
portions of the forecast area near Effingham. Will need to watch
for localized urban flooding issues if over an inch per hour
occurs, but for the most part the rainfall still should be welcome
with drought conditions in the area. Have increased precipitation
amount projections and increased to categorical PoPs late this
morning and early afternoon for portions of the area south of
I-72, however PoPs continue to taper off to slight chance for much
of the area north of I-74, mainly west of Bloomington.
Instability still looks to be weak today for most of the area,
until this evening when the warm sector nudges northward into
areas up to around the I-70 corridor, which could bring several
hundred J/kg and more prevalent thunderstorms to near I-72, as
well as perhaps some strong to severe thunderstorms close to the
I-70 corridor. Otherwise, mild highs around 70 for much of the
area, and into the mid 70s south of I-70 look on track for today,
with light easterly winds.

37

&&

.DISCUSSION...
Issued at 400 AM CDT Mon Sep 23 2024

Predawn surface map shows 1012 mb low pressure over nw AR with a
frontal boundary extending through southeast MO, far southern IL
and nw KY and extending to 1009 mb low pressure over sw Ontario
province peninsula. North to NE winds over CWA have brought in
cooler temps in the low to mid 60s, except upper 60s from I-70
southeast. Dewpoints still fairly moist in the low to mid 60s,
except upper 50s to near 60F nw of the IL river. An area of very
light rain showers had tracked eastward over central portions of
CWA past few hours. Radar mosaic shows bands of convection over
central and southern MO and extending sw of there, tracking ne. IR
satellite imagery shows mostly cloudy to overcast skies over CWA
with low stratus decks below 1k ft common se of Peoria.

Latest CAMs take low pressure from nw AR northeast to sw IL and
near MO border by sunset as it deepens a bit. This will likely
spread showers ne over central/se IL during late morning or
afternoon with isolated thunderstorms possible over southern CWA.
Seasonably cool highs today in the lower 70s over much of CWA,
with upper 60s possible from Springfield sw and mid 70s over the
Wabash river valley.

Low pressure deepens to around 1006 mb as it tracks ne over se CWA
tonight and to near the eastern IN/lower MI border by sunset Tue.
This will likely continue showers and isolated thunderstorms over
central and se CWA tonight into Tue morning, and diminishing from
the west during Tue afternoon. SPC day1 outlook has marginal risk
of severe storms for hail and wind south of Clay, Richland and
Lawrenceville counties late this afternoon and evening where
instability is higher (MLCAPES above 1200 j/kg) and some wind
shear of 30-35 kts. If the warm front gets further north into
southeast IL this evening, that area se of I-70 may get a few
stronger cells too. SPC day2 outlook keeps marginal risk east of the
Wabash river on Tuesday. Lows tonight in the upper 50s to near 60F
over northern CWA and mid 60s in southeast IL. Highs Tue around 70F
to lower 70s in central IL and mid 70s se of I-70.

Very isolated light showers could linger Tue evening especially in
eastern IL with pops less than 20%. Otherwise drier wx expected
Tue night thru Wed night as surface low pressure pulls away from
area while upper level trof and cutoff low digs into MO/IL by dawn
Wed. Cooler lows Tue night in the low to mid 50s in central IL
and upper 50s in southeast IL. Highs Wed in the mid 70s with
partly to mostly sunny skies over the IL river valley in nw CWA
and still mostly cloudy skies lingering in southeast IL.

The cutoff low around 570 dm drops down into the Ozarks of
northern AR by dawn Thu while a strong tropical system lifts
northward over the eastern Gulf of Mexico and toward the FL big
bend region later Thu. ECMWF, GEM continue to show qpf into
central and especially southern IL by Thu afternoon/evening while
GFS has it mainly over southern IL Thu afternoon and Thu night. We
have 20-30% pops from I-72 south Thu morning and then slight pops
northern CWA Thu afternoon with 30-40% pops from I-72 south Thu
afternoon. A bit milder highs Thu/Fri in the mid to upper 70s.
The cutoff low meanders over the lower MS river valley late this
week and pulls the remnants of tropical system nw into TN river
valley Fri and being absorbed as it tracks over the lower Ohio
river valley Fri night. This will likely spread more showers into
central/se IL later Fri and Fri night and continued good chances
of showers this weekend as cutoff low weakens over the mid MS and
lower Ohio river valleys. Still quite a bit of differences with
deterministic models with the 00Z run and previous run so stayed
close to a blended forecast. WPC is giving 1-2 inches of rain over
central and southern CWA from Thu afternoon through early next
week with higher amounts (several inches of rain) in sw IL into
MO.

07

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1254 PM CDT Mon Sep 23 2024

IFR cigs are predominant along the I-72 corridor as an area of
rain and embedded heavy showers spreads over the area. To the
north, MVFR cigs and scattered light showers are in place, but it
appears northward shift of the precipitation shield should take
place this afternoon and evening, spreading the IFR cigs
northward. As the center of this system ejects northeastward close
to the I-72 corridor late this evening, scattered thunderstorms
should approach the I-72 terminals, so have included a period of
VCTS. IFR cigs look to continue through 18Z before significant
improvement, except at KPIA which should see some improvement by
around 16Z. Winds E 5-10 kts this afternoon, becoming light and
variable near the low center, then winds shifting to NW Tuesday
morning around 15Z as the low moves off to the northeast.

37

&&

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

$$