798
FXUS63 KILX 121054
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
554 AM CDT Mon May 12 2025

.KEY MESSAGES...

- Scattered afternoon showers and an isolated thunderstorm today
  and Tuesday.

- Near-record warmth by Thursday with a conditional threat for
  severe thunderstorms.

&&

.DISCUSSION...
Issued at 359 AM CDT Mon May 12 2025

Early morning WV satellite imagery depicts a deepening trough
carving into the western US, with a cut-off low still positioned
over Louisiana.  Model guidance remains in excellent agreement that
the former will help dislodge the latter, with the closed low
expected to open/lift toward the Tennessee Valley by Tuesday.  As
this evolution takes place, an influx of Gulf moisture and synoptic
ascent will overspread Illinois.  The net effect will be diurnally-
driven showers both today and Tuesday, and perhaps an isolated
thunderstorm as instability builds in the vicinity of the cold-core
low.  In addition to the scattered showers, the synoptic pattern
will be quite favorable for cold air funnels, and the normalized NST
parameter continues to flash values > 1 both this afternoon and
Tuesday afternoon, per recent RAP & NAM guidance.

Precip chances become muted by Wednesday once the upper trough
departs toward the Mid-Atlantic region and subsidence works into
Illinois ahead of an amplified ridge. Temperatures will become
seasonably hot (mid 80s) on Wednesday beneath the ridge axis, and
hotter still by Thursday (about 90) as a warm front surges north
across the region in tandem with an upstream lifting/pivoting
shortwave trough. In fact, Thursday`s forecast at Peoria will
threaten a 130-year record (93 degF, 1894).

The severe weather signal for Thursday remains poorly resolved by
mid-range global guidance (GFS/ECMWF). While the synoptic pattern
alone supports deep convection across portions of the Midwest,
there are plenty of mitigating factors looming that continue to
apply a downward pressure on predictability. Residual capping
across the warm sector, dry air entrainment in both the low- and
mid-levels, and displacement from the main upper forcing suggests
updrafts could struggle to reach the LFC on Thursday, especially
with only modest frontal forcing positioned beneath an otherwise
less favorable right-exit region of the upper jet core. On the
other hand, a stout EML, very steep mid- level lapse rates, and an
increasing belt of westerlies atop the front will offer
CAPE/Shear profiles that impress professionals and noobs alike.
This all adds up to a conditional severe weather threat for
central Illinois on Thursday. Both the 00z GFS & ECMWF largely
muted convective initiation across SE Iowa and W Illinois, while
only about half of their respective ensemble members indicated
convective initiation. This is in stark contrast to recent MPAS
guidance which convincingly points toward organized, all- hazards
convection across central IL Thursday evening. At this point, it`s
a true boom-or- bust scenario and either narrative is about
equally likely. The best we can do for now is monitor trends as we
eagerly await the hi-res CAMs to begin resolving the pattern with
finer detail.

Depending on how Thursday evening unfolds, there is another
conditional risk of severe weather Friday evening near and south of
I-70. More or less, if convection erupts Thursday evening across
east central IL, the front and any convective outflows will
probably favor redevelopment just south of our CWA by Friday
evening. By contrast, if it`s crickets around here Thursday
evening, the front may stay a little further north near I-70,
putting our southern counties at greater risk of severe weather
Friday evening.

A ridge of high pressure begins to nose across the Plains by
Saturday, offering a drier and more stable forecast.  Unsettled
weather is then quick to creep back in by early next week, with both
the GEFS & EPS offering some dirty-ridge, nocturnal-MCS action.

MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 528 AM CDT Mon May 12 2025

Clouds will increase and gradually lower today as an upper-level
disturbance lifts into the region from the south. We have added a
PROB30 for thunderstorms for all terminals except KPIA, with the
best signal coming between roughly 18z-00z. Ceilings will continue
to lower tonight into Tuesday as the upper-level disturbance
creeps into SE Illinois. A gradual lowering to MVFR (07z-09z) and
then IFR (09z-11z) is anticipated overnight amid a persistent
east wind.

MJA

&&

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

$$