379
FXUS63 KILX 131105
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
605 AM CDT Fri Jun 13 2025

.KEY MESSAGES...

- Daily chances of rain favor above-normal rainfall through the
  middle of next week. The normal weekly rainfall for the middle
  of June in central Illinois is about 1.1 inches.

- A warm and humid pattern favors slightly above-normal
  temperatures through the middle of next week. The normal daily
  temperatures for the middle of June in central Illinois are a
  high of 85 F and a low of 63 F.

- The risk for severe weather returns Tuesday evening and extends
  through at least Thursday.


&&

.DISCUSSION...
Issued at 334 AM CDT Fri Jun 13 2025

Early morning observational trends exhibit an upper-level trough
slowly lifting across the Ozarks, with light to moderate rainfall
spreading into Illinois. Hi-res guidance remains in excellent
agreement that periods of rain will persist through much of the
day as the upper trough meanders toward us. Showers may become
more convective in nature by this afternoon as a modest LLJ veers
into SE Illinois, helping boost MLCAPE values over 1000 J/kg.
Still, the overall severe threat for today will be limited by low
shear (< 30 kts) and poor lapse rates (< 6.5 C/km).

The more apparent risk for today is for localized urban flooding
across portions of southeast and east-central Illinois. While
forcing for ascent is somewhat weak, its persistent. And when
combined with seasonably high PWATS (> 95% of mid-June climo); a
moist vertical profile (low/mid RH > 90%); a deep, warm cloud
layer (> 12 kft); and relatively slow cloud-layer flow (20 kts),
any shower that does develop will have a tendency to be highly
efficient. This becomes even more true later this evening as the
upper trough moves over east-central Illinois and both cloud-layer
winds and Corfidi up/downshear vectors slow, increasing the
prospect for training or backbuilding.

The most recent 00z CAM guidance hints at localized rainfall
totals exceeding 2-3 inches through tonight, but in areas
generally near and south of I-72/Danville.

Scattered showers and isolated thunderstorms will likely linger
(> 60% chance) through Saturday afternoon in areas near and east
of I-55, before the upper trough departs to the east by Saturday
evening. The severe weather risk will remain low, but with a
medium risk for localized urban flooding  similar to the previous
days environment.

A lull in the precip activity is becoming more evident Saturday
evening through Monday as shortwave ridging builds across the
region, followed by a brief blocking pattern (split flow). With
the spigots turned off, and periods of sunshine returning Sunday
and Monday, afternoon temperatures will warm into the mid 80s.
Overnight lows will be buoyed by soupy dewpoints, generally
cooling into the upper 60s.

The synoptic pattern becomes more conducive for showers and
thunderstorms from Tuesday onward, particularly across the
Northern Plains and Upper Mississippi Valley where a moderately
buoyant airmass builds beneath a strengthening mid-level jet core.
This influx of CAPE & shear will increase the specter of severe
weather as early as Tuesday night across our north, perhaps
becoming more widespread Wednesday or Wednesday evening. Certainly
more details to come, especially as mid-range guidance begins to
break down the upper ridge with better consistency in coming days.

MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 558 AM CDT Fri Jun 13 2025

Mainly MVFR conditions at the onset as a band of light rain lifts
across the regional terminals.  Visibility has generally been
between 4-6 SM, and this should be the rule through the remainder of
the morning.  Ceilings on the other hand will continue to lower,
from about 5-10 kft to about 1.5 kft, throughout the morning as a
weak frontal system lifts and fills into central Illinois.

Short-term models show signs (particularly the HRRR) that rain
coverage will diminish beyond 15z, becoming more scattered and
convective in nature beyond 20z. Thinking thunder chances are
highest along the I-72 terminals (KSPI, KDEC, and KCMI) where the
instability axis is greatest into the afternoon. Have therefore
maintained prob30 groups for thunder at these sites, and have
omitted the mention further north at KPIA and KBMI.

Low ceilings and reduced visibility are anticipated to persist
through the remainder of the TAF period, with ceilings perhaps
lowering into the IFR range late tonight as the surface low settles
right overhead.

MJA

&&

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

$$