417
FXUS63 KILX 061129
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
529 AM CST Fri Mar 6 2026

.KEY MESSAGES...

- Widespread dense fog is expected east of the Illinois River this
  morning. Visibility should improve by mid-morning (around 9 AM).

- Multiple rounds of scattered storms are expected through
  Saturday morning, with the greatest coverage expected overnight
  (west of I- 57) into Saturday morning (east of I-57). Some of
  the storms could be strong to severe, especially late Friday
  afternoon into Friday night. There is a Slight Risk (level 2 of
  5) of severe storms west of I-55, and a Marginal Risk (level 1
  of 5) east of I-55.

- Unseasonably warm today, with highs reaching the mid 70s. Breezy
  southwest wind gusts of 30-35 mph are expected during the
  afternoon.

&&

.DISCUSSION...
Issued at 212 AM CST Fri Mar 6 2026

*** SYNOPSIS ***

Deep troughing was evident over the Rockies at 1am/07z Fri, with
clusters of t-storms ongoing from OK northeastward into IA. A
developing sfc low was present in the lee of the Rockies, with sfc
troughing extending well northward into the Dakotas. Closer to
home, an east-west oriented warm front will lift north through the
morning.

*** FRIDAY AM ***

Dense fog advisory remains on track at this time, with nearly all
locations west of the IL River reporting vis below 1 mile as of
0630z/1230am Fri. There may be a need to expand the dense fog
advisory to include areas west of the IL River. 06.00z HREF
suggests a 40-50% chance for vis below 1/4 mile in these areas,
albeit for a shorter period of time than areas to the east.
Additionally, obs from KPIA show ceilings trending lower in time,
now down to 200 feet from 800 feet just a few hours ago. Across
the entire area, vis should improve rapidly between 14-15z (8-9
AM) as the front lifts north.

WAA and convergence along the leading edge of the nocturnal LLJ
are expected to lead to scattered showers/storms lifting
northeast across the CWA, primarily between 09-15z (3-9 AM). The
better forcing is located west of our area, and thus the PoPs are
highest west of the IL River (50-80%, compared to around 40% to
the east). Recent regional radar imagery shows storms within this
WAA/LLJ forcing weakening over the last half hour, so may need to
lower PoPs soon if there aren`t renewed signs of development. If
any storms form this morning, they will be elevated (not surface
based). As the low-level WAA strengthens the warm nose, elevated
instability values could approach 1000 J/kg in spite of only
modest mid-level lapse rates (less than 7 degC/km). These
conditions could support a hail threat with these storms.

*** FRIDAY PM ***

The deep trough over the Rockies will break into two waves, the
first lifting NE Fri PM and the other becoming a cut-off low near
Baja California. The associated sfc low is expected to make its
way across KS/IA into Fri night. Persistent southerly flow across
the warm sector will advect unseasonable warmth and moisture into
the ILX CWA. Despite partly to mostly cloudy skies, high temps are
forecast to reach the mid 70s, which is 20-25 degF above normal.
Dewpoints will also be unseasonable, with latest models suggesting
values into the low/mid 60s which is an upward trend compared to
the forecast from a few days ago. This has implications for the
storm potential and timing.

Before discussing the storm threat, will also note that it will be
breezy today as strong low-level wind fields develop in response
to this amplified pattern. Forecast soundings show winds over 30
kts through much of the PBL. Even with the cloud cover, there
should be sufficient mixing (or at least periods of mixing) that
transport 30- 35 mph gusts to the sfc.

In prior forecasts, the storm evolution for today seemed fairly
cut and dry: a chance for elevated t-storms with hail during the
early AM, then strong capping limiting development area-wide
through the PM until the cold front arrived overnight. However,
the uptick in forecast low-level moisture makes the storm
evolution less certain, owing to reduced capping. Some CAMs depict
storm development near or NW of the IL River during the afternoon
despite somewhat nebulous forcing. The potential culprits include
outflow boundaries from convective activity this morning, as well
as activity currently across OK/SW KS holding together as it
tracks NE. If storms do form (or hold together), the parameter
space should be supportive of severe storms, with seasonably
moderate to high CAPE (1500-2000 J/kg), deep layer shear of 30
kts, and 0-1 km helicity (spin) over 100 J/kg. All hazards would
be possible.

Additional broken lines of storms are expected to push in from the
west during the late evening/overnight. CAMs appear somewhat
disorganized with this activity, with HREF members depicting two
broken, seemingly decaying lines of storms. Still, with MUCAPE
values over 1000 J/kg and a strengthening LLJ, severe hail/wind
threats will exist. There is uncertainty as to whether or not sfc-
based instability is maintained into the night. Even if its not,
it won`t take much for showers/storms to mix strong LLJ gusts to
the sfc. If sfc-based instability is maintained, LLJ forcing
increasing over 50 kts could support embedded tornadoes. Aside
from the instability, one potential limiting factor for the
tornado threat is that 0-3 km shear vectors are expected to be
roughly parallel to the convective lines, limiting the line-normal
shear component. Still, a conditional strong tornado threat
exists (2-5% chance of any tornadoes, reasonable maximum intensity
of EF2).

In summary, multiple opportunities for severe storms exist over
the next 24 hours, some of which are highly conditional. The
latest SPC Outlook features a Slight Risk (level 2 of 5) west of
I-55, with a Marginal Risk (level 1 of 5) to the east.

*** SATURDAY AND BEYOND ***

The cold front and associated convection are likely to be located
near or east of the I-55 corridor around daybreak Sat, with a
60-80% chance of precip east of a Rantoul to Pana line. As diurnal
heating increases instability ahead of the front, severe chances
could also increase, but this may not occur until after this he
front pushes southeast of the ILX CWA. Additionally, the upper low
will be lifting further away, making the upper levels less
conducive. Due to the progressive and scattered nature of these
storm chances, QPF amounts appear unlikely to exceed 1" (this
includes any storms on Friday).

Once this front moves through, the rest of the weekend appears
dry. A weak sfc high pressure axis will be over the area Sat
night, with lows expected to fall to the mid 30s. The sfc high
shifts east to the TN Valley on Sun, reestablishing southwesterly
flow locally into next week and keeping highs above normal in the
60s and 70s.

The cut-off low over the SW is finally progged to emerge by Tues-
Wed, with a northern stream wave providing additional forcing,
although whether or not these waves are phased remains to be seen.
At any rate, rain chances return sometime during the Tues-Wed
period (70-90% per the NBM). Given an unseasonably warm airmass
and ample wind shear, will need to monitor the potential for
additional strong to severe storms with this system.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 528 AM CST Fri Mar 6 2026

Fog and low ceilings are in place across the region, with LIFR and
VLIFR conditions common. The general expectation is an improvement
in conditions from south to north during the first few hours of
the period, with all sites returning to VFR conditions by late
morning (16-17z). Breezy southwest winds develop by midday,
gusting 25-30 kts, and persist through the remainder of the
period. There are multiple chances for scattered showers/storms,
but precip chances generally decrease with eastward extent. A
broken line of storms moves in from the west late in the period.
Included PROB30 group for thunder to account for this, with the
exception of KCMI where storms may not reach the terminal until
after 12z Sat.

Erwin

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CST this morning for ILZ031-037-
038-041>057-061>063-066>068-071>073.

&&

$$