942
FXUS63 KILX 221726
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1226 PM CDT Wed May 22 2024

.KEY MESSAGES...

- There is a 70% chance for thunderstorms Friday, with a level 1
  of 5 (marginal) risk some of these storms become severe. The
  strongest storms could produce damaging wind gusts and large
  hail.

- Scattered thunderstorms are likely (60-70% chance) on Sunday.
  Severe weather potential is unclear at this time, but the risk
  appears highest near and south of I-72.

&&

.UPDATE...
Issued at 1028 AM CDT Wed May 22 2024

Clear skies dominate much of central IL this morning with a cold
front stalling out in southeast IL. An upper wave could bring a
few elevated showers or storms in the vicinity of I-70 and areas
south this afternoon and into the early evening hours. Severe
storms are possible, but not looking likely. The SPC currently has
this area in a Marginal Risk for severe storms. The latest hi-res
model suite has trended lower on MUCAPE so believe the risk for
afternoon/evening severe storms has trended lower over the last
few hours. Updated sky grids for today. The rest of the forecast
looks on track for now. May update rain chances early this
afternoon based on new model data and the latest trends.

Knutsvig

&&

.DISCUSSION...
Issued at 300 AM CDT Wed May 22 2024

At 3am, surface observations suggest a cold front is somewhere
near I-55; behind it, winds are veering gradually to a westerly
direction, while dewpoints are dropping to provide us with a
milder and more May-like airmass this midweek. The front is
forecast to stall somewhere between I-70 and I-64 this afternoon,
serving as a focus for additional thunderstorms that will have a
small (5%) chance of turning severe. Looking at the 00z suite of
CAMs though, it`s looking like guidance has once more shifted
south and severe weather will focus near and southeast of the
IL/KY/IND state lines. Tonight, a weak mid level disturbance
lifting northeast out of the Ozarks will provide support for
showers and perhaps a couple rumbles of thunder near the I-70
corridor, with less than a 10% chance of anything getting to I-72
(or further north).

Aside from a couple morning showers near/south of I-70, tomorrow
should be dry under the influence of surface high pressure, but we
can`t guarantee nothing will fire during the evening in the same
area as forecast soundings suggest increasing elevated instability
and shear ahead of our next weather maker slowly approaching from
the Plains. Temps should reach 80 degF or better most locations -
about 5-6 deg warmer than today - given efficient radiational
warming with the drier airmass and (near) full sunshine near and
north of I-72.

Thunderstorm chances return for Friday afternoon/evening as another
mid level shortwave ejects out of the Plains and into the Midwest.
This feature is subtle and well south of the main upper wave which
will be lifting across the Northern Plains and into MN late Friday,
but it will bear watching. The NAM and GFS suggest shear will be on
the increase late while instability will be waning, and LREF
suggests the joint probability for more than 30 kt of shear and 1000
J/kg SBCAPE is only around 35-45% - highest southwest of a Galesburg
to Terre Haute line. However, outflow boundaries from upstream
convection could offer mesoscale forcing/locally enhanced shear to
favor storm development during the afternoon when instability is
much higher (NAM suggests upwards of 3000 J/kg SBCAPE in Peoria at
1pm). Friday`s temps are thus tricky to pin down, as the location
of the (1) warm front, (2) outflow boundaries, and (3) storms are
uncertain at any given time. Right now, we`ve got low to mid 80s
for forecast highs, but those are definitely subject to change.

Behind that system, we should get another break in precipitation
chances on Saturday before the next low comes our way out of the
Central Plains. Just looking at the deterministic ECMWF, the set up
looks messy with scattered thunderstorms beginning late Saturday
night and continuing all day Sunday. Given we`ll once again be near
the instability gradient with a stationary boundary oriented
northwest-southeast near/over our area, thinking is any of these
storms could turn severe with large hail and locally damaging winds,
with a conditional risk for more prolific damaging winds if a line
can become organized and propagate forward along the boundary; the
greatest potential for such a scenario would be once again near and
southeast of I-70. We`ll continue to monitor.

The pattern does look to finally turn cooler and more stable early
next work week, with near or below normal temps and perhaps a break
in thunderstorm chances. CPC advertises a roughly 45/33/22 percent
chance for below/near/above normal temps during the day 6-10
(Monday, 5/27 to Friday, 5/31) period.

Bumgardner

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1226 PM CDT Wed May 22 2024

Isolated showers may move through central IL this afternoon,
without much fanfare. Expect SPI to have VCSH early in the period,
but after that, will amend TAFs if any showers approach a
terminal. Thunder is unlikely as mean MUCAPE in the HREF model is
<100 J/kg, but it as high as 300-500 J/kg in the latest NAMNest
run (so it`s not out of the question). The upper wave responsible
for these isolated & elevated showers will move through central IL
this afternoon. So expect shower activity to be to the south and
east of the TAF sites after 00Z. Gusts this afternoon drop of
sharply around 23Z...with light and variable winds by 01Z or
shortly thereafter.

Knutsvig

&&

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

$$