633
FXUS63 KILX 040213
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
913 PM CDT Wed Jul 3 2024

.KEY MESSAGE...

- A couple rounds of showers and storms are expected Thursday; one
  during the morning and a second during the late evening and
  overnight. There is increasing confidence in a relative lull in
  precip coverage during the late afternoon and evening.

&&

.UPDATE...
Issued at 913 PM CDT Wed Jul 3 2024

While a stationary frontal boundary remains draped across central
Illinois this evening, the effective boundary is much further
south from the Ozarks into the Ohio River Valley where a broken
line of convection has developed. Other than an isolated shower
or two south of I-70, the majority of the KILX CWA will remain dry
for the balance of the evening and through a good portion of the
overnight hours. Clusters of thunderstorms currently developing on
the tail end of the stationary front across Nebraska/western
Kansas in association with a short-wave trough ejecting out of
the Rockies will track/develop eastward overnight. Latest runs of
the HRRR/RAP continue to suggest convection reaching locations
along/southwest of a Rushville...to Shelbyville...to Robinson line
before dawn Thursday. As the wave approaches, showers and storms
will overspread much of central Illinois after sunrise...before
shifting eastward into Indiana by midday. Have updated hourly PoPs
to better reflect current obs and expected trends tonight. Have
also added patchy fog to the forecast tonight as calm winds and
dewpoint pooling in the vicinity of the front will be conducive
for fog. CAMs have been slow to catch on, but the most recent runs
of the HRRR and GFSLAMP are trending foggier.

Barnes

&&

.DISCUSSION...
Issued at 209 PM CDT Wed Jul 3 2024

This afternoon, synoptic cold front is located roughly near the
I-55 corridor, while effective front from earlier convection just
barely clips the southeastern forecast area near Lawrenceville.
Temps jump from the low 80s north of the effective boundary to
around 90F south. Anticipate this to be the main focus of
convection as we head into the mid to late afternoon hours. Latest
RAP suggests around 1500J/kg or higher MLCAPE is in place on the
warm side of the boundary, but deep layer shear is marginal/sub-
marginal around 20-30kt. Storms should begin to increase in
coverage in this vicinity by late afternoon or early evening, and
a few could be strong to marginally severe. Latest HRRR keeps this
activity a county or two south of the forecast area which lines
up well with current location of the front.

Overnight into Thursday morning, a pair of shortwave troughs will
move across central Illinois resulting in an increase in showers and
a few storms. Weakening surface front will likely stay stalled
across portions of southern Illinois with weak/negligible
instability in place north of the front across central Illinois
which will keep the threat for severe storms out of the local
area.

After the shortwave exits central Illinois early Thursday
afternoon, there is growing confidence in a relative lull in
precip later Thursday afternoon and at least early evening before
a stronger shortwave digs across the Upper Midwest later Thursday
evening into Friday. Despite passage of the weaker shortwave
midday Thursday, mid level height falls will persist across
central Illinois through the day in advance of the next deeper
wave, contributing to at least some spotty convection during the
afternoon/early evening, but coverage should be fairly isolated at
this point, and should allow many locales to kick off their
Independence Day celebrations. By mid to late evening, moderate
instability (MUCAPE 1000-1500 J/kg) begins to lift back north into
portions of central Illinois coinciding with the arrival of the
deeper wave / closed 500mb low into the Midwest. Storm coverage
will increase in response. Unfavorable diurnal timing should keep
the severe threat low Thursday night into Friday morning, but a
few stronger storms are possible, especially west of I-55, with
seasonably strong deep layer shear overspreading central Illinois.

As upper wave begins to depart the region Friday, strong cold air
advection will overspread central Illinois in its wake and scour out
some of the low level moisture. There will be a brief respite from
the precip chances once this occurs and will persist into Friday.
Temps will be lower, too, with afternoon highs generally in the
upper 70s to lower 80s Friday and Saturday. Surface ridge axis will
shift across the area Saturday afternoon with return flow
overspreading the area Sunday. Heat and humidity will begin to creep
back up in response and broad upper troughing over the Great
Plains will be in place with several shortwaves ejecting across
the region Sunday through the first half of next week bringing
additional chances for showers and storms.

Deubelbeiss

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 639 PM CDT Wed Jul 3 2024

Diurnal MVFR ceilings that developed across central Illinois this
afternoon have scattered as of 2330z: however, a thick blanket of
cloud cover AOA 15,000ft continues to stream across the sky from
the southwest. Convective development has thus far been confined
to locations much further south near the Ohio River and will
continue to be focused south of the TAF sites through tonight.
HRRR/RAP have been consistently showing showers/thunder spreading
N/NE late tonight into Thursday morning, so have added a period of
predominant showers between 12z and 18z at KSPI and between 13z
and 19z at KDEC/KCMI. Further northwest, have only mentioned VCSH.
While thunder will be possible at the I-72 terminals Thursday
morning, have opted not to include it at this time until trends
become better established. Once the morning showers depart, a
relative lull in precip chances will be on tap for Thursday
afternoon. Winds will remain light/variable through the entire 00z
TAF period.

Barnes

&&

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

$$