751
FXUS63 KILX 290014
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
714 PM CDT Sun Apr 28 2024

.KEY MESSAGES...

- Another round of showers and thunderstorms will push through
  central Illinois tonight: however, the severe potential has
  greatly decreased.

- Above normal temperatures will prevail for the remainder of the
  week with occasional rain chances.

&&

.UPDATE...
Issued at 714 PM CDT Sun Apr 28 2024

00z surface analysis placed 1004 mb low pressure in northwest IA,
with a well defined warm front stretched east into southern WI,
and a cold front extending south through the southern Plains. This
placed central IL firmly in the warm sector with SSW winds and
upper 50s to lower 60s dewpoints. A 40-50 kt SW 850 mb jet was
oriented from MO into the southern Great Lakes, providing good
moist advection this evening. This will allow an area of showers
and storms currently over SW to central MO to expand northeast,
affecting much of the area west of I-57 by midnight to 1 am, then
shifting east over the remainder of the area overnight. Looking at
convective trends, the severe weather risk appears quite low
given weak low level lapse rates, increasing CINH, and meager
instability (MLCAPEs 200-400 J/kg). 40-50 kt of deep layer shear
will be present well into the overnight owing to the LLJ, which
could favor a few sustained updrafts that would be capable of
producing small hail. Locally heavy rain will also be a risk, with
latest CAM output pointing to 1-2" totals east of I-55, where the
LLJ shows better convergence late tonight. 3-hr flash flood
guidance is around 2-3" in this region and with most of the rain
falling in a 3-6 hour period this shouldn`t pose much of a flash
flood risk, but will be something to monitor should localized
training develop.


25

&&

.SHORT TERM...(Tonight through Monday)
Issued at 322 PM CDT Sun Apr 28 2024

19z/2pm regional radar mosaic is mostly devoid of convection
across the Midwest...with the closest lightning strikes observed
across Arkansas. Aside from a stray shower along/west of I-55, the
balance of the afternoon will remain mostly dry across central
and southeast Illinois. As has been the case for the past couple
of nights, convection will once again be largely driven by the
nocturnal low-level jet. 18z NAM shows the 850mb jet oriented from
eastern Texas into Missouri/Illinois strengthening to 40-50kt
after dark. Given the increasing forcing ahead of a cold front
extending from western Iowa into Texas, think showers and
thunderstorms will blossom within the jet by mid-evening. Most
CAMs suggest convection will develop upstream across Missouri,
then develop/spread northeastward into locations along/west of
I-55 before midnight...with a line of showers/thunder then
progressing eastward to I-57 overnight. The atmosphere preceding
the convection this evening will be highly sheared, but only
weakly unstable. Current mesoanalysis shows 0-6km bulk shear of
45-55kt west of I-55, but MLCAPEs well under 500J/kg. There will
be a slight uptick in instability as the LLJ strengthens, but
MLCAPE values are only expected to climb into the 500-1000J/kg
range. This may be enough energy to produce a few stronger cells
with gusty winds/small hail, but the overall severe weather risk
appears to be minimal.

Showers will push into east-central Illinois late tonight and
diminish in intensity/areal coverage by dawn. Other than lingering
showers along/east of I-57 early in the morning, Monday looks
mostly dry across the KILX CWA. Will still need to watch for the
potential for scattered convective development along the slowly
departing cold front during the afternoon: however, none of the
CAMs are particularly bullish at this time. Deep-layer shear and
instability parameters are both meager, so am not anticipating
widespread severe weather with any storms that fire along/east of
I-57 late in the day.

Barnes

.LONG TERM...(Tuesday through Next Sunday)
Issued at 322 PM CDT Sun Apr 28 2024

Once the front exits into the Ohio River Valley and high pressure
builds into the region, a pleasant spring day with light winds is
anticipated for Tuesday as high temperatures top out in the middle
to upper 70s. A short-wave trough ejecting northeastward out of
the Rockies will track N/NW of Illinois Tuesday night into
Wednesday. This feature will push a weak cold front into the NW
CWA, potentially triggering scattered showers/thunder mainly
along/northwest of I-55 Tuesday night. Once the main forcing lifts
into Canada, Wednesday will be a dry day across central Illinois
despite the lingering nearly stationary frontal boundary.
Temperatures will climb above normal into the lower to middle 80s.

The next significant chance for rain will arrive Thursday
afternoon into Thursday night as a stronger wave approaches from
the west. With strong forcing along/ahead of an associated cold
front and GFS precipitable water values increasing to 1.50-1.75,
have opted to carry likely PoPs west of I-55 Thursday afternoon
and everywhere Thursday night. There is a possibility that rain
chances will need to be delayed by 6-12 hours, focusing mainly on
Thursday night/Friday morning, if the slower ECMWF/GEM verify.
Once this system passes to the east, cooler/drier weather will be
on tap for next weekend with highs dropping back into the upper
60s and lower 70s.

Barnes

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 613 PM CDT Sun Apr 28 2024

An area of SHRA and embedded TSRA will spread northeast across the
terminals later this evening, lasting several hours before
tapering off late tonight. This should predominantly produce high
MVFR to low VFR conditions, with brief but significant drops
possibly down to IFR in TSRA. Have TEMPOed in some lower MVFR
periods to account for this. After the rain pushes off, MVFR
ceilings are expected Monday morning, with bases rising to VFR
levels during the afternoon. South to southwest winds will persist
through the period, gusting over 20 kt for much of Monday.

25

&&

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

$$