508
FXUS63 KILX 050137
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
837 PM CDT Tue Jun 4 2024

.KEY MESSAGES...

- Slight risk (15-39% chance) of excessive rainfall with any
  thunderstorms that develop along/west of I-57 this afternoon
  through tonight.

- Below normal temperatures will prevail through most of the
  forecast period. Highs remain mostly in the 70s and overnight
  lows dip into the 50s Thursday through next Tuesday.

&&

.UPDATE...
Issued at 835 PM CDT Tue Jun 4 2024

The presence of an upper low near the Quad Cities continues to aid
scattered t-storm development this evening, including some
approaching Peoria and others between Lincoln and Decatur as of
830pm/0130z. To this point, storms have remained well below severe
limits and that appears unlikely to change as we lose daytime
heating. High freezing levels (12.5kft on the ILX 00z sounding)
result in limited hail-growth zone CAPE. An occasional updraft may
pulse up at times and produce gusty winds/small hail, but a
persistent severe storm threat is unlikely. High-res models
generally show precip activity over the next 4-5 hours being
focused north of I-72, which tracks well with current radar
imagery. Accordingly, lowered PoPs a bit south of I-72, closer to
30% as opposed to 50% further north.

The cold front that will move through overnight is currently
located across central IA, and had just moved through Des Moines.
CAMs are not in good agreement regarding how widespread
showers/storms will be along the front as it moves through our
area overnight. Given this uncertainty, trended PoPs lower, or at
least focused the timing of the highest PoPs to just a few hours
at any one location, rather than having a persistent 60% chance
area-wide from midnight til 6 AM.

Erwin

&&

.SHORT TERM...(Tonight through Wednesday)
Issued at 211 PM CDT Tue Jun 4 2024

An upper low evident on 1830z/130pm water vapor imagery over
northeast Missouri will provide the lift for scattered
thunderstorm development this afternoon and evening. Severe
weather potential will remain quite low due to meager MLCAPEs
presently analyzed at just 1000J/kg and weak 0-6km bulk shear of
25-30kt. Primary risk with any convection that fires will be heavy
downpours and localized flash flooding. 12z KILX upper air
sounding showed precipitable water of 1.41 and the NAM indicates
this value will climb into the 1.75-2.00 range this afternoon,
which is close to the 99th percentile for this time of year. Due
to ample environmental moisture and the relatively slow storm
movement, think pockets of heavy rainfall will occur through this
evening. Latest satellite shows the most robust Cu along/southwest
of a Peoria to Decatur line, which will be the main area to watch
for storm development over the next several hours. Based on
satellite/radar trends and latest RAP/HRRR forecast, have ramped
PoPs up to likely along/west of I-55 late this afternoon and
evening.

Once the initial area of convection lifts into northern Illinois,
a lull in precip chances will be observed from mid-evening until
shortly after midnight when an approaching cold front pushes a
broken line of showers/storms into the area overnight into
Wednesday morning. Based on the forward speed of the front, have
dropped PoPs to slights along/west of the Illinois River by early
Wednesday morning...with all rain chances dropped along/west of
I-57 by early afternoon. May see a few showers linger near the
Indiana border through the afternoon, but the bulk of the rain
will be much further east by then.

Barnes

.LONG TERM...(Thursday through Next Tuesday)
Issued at 211 PM CDT Tue Jun 4 2024

A secondary cold front will drop southward into central Illinois
Wednesday night, potentially triggering scattered showers. Some of
the CAMs show the showers, while others are completely dry...so
forecast confidence is low at this point. Have included slight
chance PoPs for showers north of a Macomb to Minonk line during
the evening, but opted to go dry overnight as daytime instability
wanes. Once the front passes, a return to cooler/drier weather is
anticipated by the end of the week.

The extended forecast will be dominated by deep upper troughing
over the Great Lakes and prevailing ridging over the Desert
Southwest into the Southern Plains. Central Illinois will remain
sandwiched between these two features...leading to deep-layer
northwesterly flow and resulting below normal temperatures and
precipitation. Will need to keep an eye on nocturnal MCS activity
that will develop along the N/NE periphery of the upper ridge
Friday night through Sunday night: however, all synoptic models
suggest this activity will remain well S/SW of the KILX CWA. The
upper trough will likely be re-enforced by additional short-wave
energy diving southward out of Canada early next week. If this
scenario unfolds as currently thought, may need to add scattered
showers to the forecast next Monday afternoon as the trough
sharpens. For now will go with a cool/dry forecast with highs
mostly in the 70s and overnight lows in the 50s Thursday through
next Tuesday.

Barnes

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 626 PM CDT Tue Jun 4 2024

Additional scattered showers and isolated t-storm development is
possible this evening, primarily between 02-05z, at
KPIA/KSPI/KBMI. Late tonight, after 08z, a front will progress
from west to east across the area, resulting in another round of
showers and storms. Behind the front, winds turn to northwesterly
and low MVFR ceilings move in. Ceilings will improve from west to
east during the late morning, returning to VFR area-wide by midday
Wednesday. Confidence was too low to include a thunder mention in
the TAFs at this time.

Erwin

&&

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

$$