807
FXUS63 KILX 160531
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1231 AM CDT Mon Jun 16 2025

.KEY MESSAGES...

- Severe weather risks return this week...with the most favored
  time period from Tuesday night through Wednesday night.

- Typical mid-June temperatures will prevail...with a trend
  toward above normal readings in the 90s by next weekend.

&&

.DISCUSSION...
Issued at 211 PM CDT Sun Jun 15 2025

...Weak System Passing South of Illinois on Monday...

An upper low evident on 1830z/130pm water vapor imagery over
southwestern Missouri will gradually shift eastward into the Ohio
River Valley on Monday. Meanwhile a pair of short-wave troughs
currently over eastern South Dakota and northeastern Iowa will
track southeastward and weaken with time. As a result, the primary
synoptic forcing for precip development will remain focused across
the southern two-thirds of the KILX CWA late tonight through
Monday evening. Based on latest HRRR/RAP, have opted to keep the
forecast mostly dry for tonight...followed by just a 20% chance
for showers south of I-70 toward dawn. As the low tracks eastward,
scattered convection will develop...particularly during peak
heating. CAMs generally keep highest areal coverage along/south of
I-70 where 30-50 PoPs are warranted: however, cannot rule out a
stray shower or storm further north across the rest of central
Illinois during the afternoon. A few showers/storms will linger
along/east of I-57 into Monday evening, followed by dry weather
across the board Monday night.

...Potential MCS Tuesday night...

As has been seen by the past several model runs, the weather will
become more active by Tuesday night as MCS activity forms over the
Plains, then spills eastward toward central Illinois overnight
into Wednesday morning. 12z models generally have a good handle on
the situation...focusing convection across southern Nebraska/northern
Kansas late Tuesday afternoon. The nocturnal low-level jet is
progged to strengthen considerably...with the NAM depicting a
50-60kt 850mb jet from Texas to northwest Missouri by 06z Wed.
This will support an ongoing cluster of convection that will
subsequently track E/SE into west-central Illinois late Tuesday
night into Wednesday morning. Storms will likely be in a weakening
mode as they arrive, but may still pose a gusty wind/heavy
rainfall risk mainly along/west of I-55.

...Convective Re-Development Wednesday Afternoon/Evening...

As is typically the case this time of year, the exact track of the
overnight MCS will determine the evolution of convection later
Wednesday. With no high-resolution guidance at that time frame, it
is still too early to pin down specific details. Based on the
synoptic pattern and the likely position of the morning storms, it
seems reasonable to surmise the most likely location for storm
re-development Wednesday afternoon and evening will be along/east
of I-55. Given feed of rich Gulf moisture ahead of an approaching
front, surface dewpoints in the lower to perhaps middle 70s will
support SBCAPEs in excess of 2500J/kg where at least partial
sunshine returns after the morning rain/clouds. In addition, NAM
suggests 0-6km shear values increasing to 30-40kt in the warm
sector. These parameters will likely support a broken line of
strong to severe convection with an attendant strong
wind/hail/tornado risk.

...Hot Weather by the End of the Week...

Once the Wednesday system departs, a period of slightly cooler and
drier conditions will be on tap for Thursday before upper heights
rise and temperatures increase markedly. 12z NBM shows a high
probability (60-80% chance) of exceeding 90 degrees across much
of central Illinois next Saturday and Sunday. These temperatures
combined with seasonally high dewpoints in the upper 60s and lower
70s may produce heat index values of 100 degrees or above.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1231 AM CDT Mon Jun 16 2025

A weak ridge of high pressure will generally shift eastward and
weaken further over the upcoming 24 hours as a cold front
approaches from the west. Winds will be fairly weak under
influence of the high pressure, but cloud cover will be prevalent
much of the period as a disturbance moves into the Ohio Valley and
the front approaches from the west. Model guidance points toward
MVFR vsby in fog developing overnight at KSPI and KDEC given
higher dewpoints toward southern IL, continuing a couple hours
after sunrise. After sunrise, initial cumulus development should
result in a short period of MVFR cigs from around 15Z-19Z until
diurnal heating lifts cigs above 3000 ft AGL. Winds E-NE 3-6 kts
overnight, becoming S 5-10kts by 19Z.

37

&&

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

$$