205
FXUS63 KILX 030401
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1001 PM CST Mon Mar 2 2026

.KEY MESSAGES...

- Multiple rounds of beneficial rainfall are expected this week.
  The best chance of exceeding 2" of rainfall through Friday
  night is near and south of I-72 (50-70% chance).

- There is a marginal risk (level 1 of 5) of severe storms near
  and south of I-72 on Wednesday, with large hail the primary
  concern. Additional strong to severe storms are possible Friday-
  Friday night.

- A warming trend is expected this week, with highs reaching the
  70s by Friday (60-90% chance).

&&

.DISCUSSION...
Issued at 215 PM CST Mon Mar 2 2026

*** THROUGH TONIGHT ***

The first full week of meteorological spring brings a meaningful
pattern shift that will offer beneficial rain chances as well as
occasional windows for strong/severe storms.

Early Monday afternoon, sfc high pressure was positioned over New
England while a weak disturbance drifted east near the Ohio River
Valley. Lingering WAA and fgen forcing has resulted in a continued
band of light precip near and just south of I-70 as of
1245pm/1845z, evidence by weak radar returns and sfc reports of
drizzle or light rain. Sfc temps are above freezing, but fcst
soundings in that area do show a solid warm nose and small window
of negative (refreeze) energy, so can`t rule out some sleet mixing
in. Precip chances will gradually lessen as the afternoon unfolds
and the disturbance shifts away. Looking at the rest of the CWA,
visible satellite trends suggest the highest temps today will wind
up being near/north of the I-74 corridor (low/mid 40s) where
clearing is starting to occur. Areas to the south of a
Jacksonville to Mattoon line are socked in with clouds, and may
struggle to reach the low 40s.

*** TUESDAY - TUESDAY NIGHT  ***

Looking upstream, an upper trough is located over SW Idaho, and
this system will push eastward towards IL by Thurs, influencing
several rounds of precip chances as it does so. The first round
pushes in from the southwest early Tues AM as WAA/LLJ forcing
overspreads the area. Latest CAM timing suggests widespread
showers area-wide between 6 AM and 10 AM, beginning sooner than 6
AM across the southwest CWA and lingering later than 10 AM across
eastern IL. Instability appears muted with this round of showers,
with only a few hundred J/kg of elevated instability, enough to
support some embedded thunder but making severe storms unlikely.
There are cool temps aloft (-10 degC at 500mb) and modest mid-
level lapse rates (7 degC/km), so can`t rule out some small, sub-
severe hail with these storms despite the weak instability.

Another factor resulting in several precip chances across our CWA
is the presence of a stalled frontal boundary. One of the main
challenges is pinning down the latitude of this east-west oriented
front. This will have implications on both the forecast temps and
the corridor of highest rainfall amounts. Latest CAMs favor a
more southerly placement of the boundary Tues, which results in
most of the area only reaching the mid 40s/low 50s for highs
tomorrow, though areas south of I-70 could still climb near 60F.

After a brief lull in shower activity following the Tues AM
precip, CAMs depict another corridor of scattered to widespread
showers moving along the frontal zone beginning mid-afternoon Tues
and continuing through much of the night. Mean cloud layer winds
are oriented west to east, which given the boundary orientation
favors training which could drive locally high precip amounts.
Based on the placement of the front, the best chance of exceeding
1" of rain through Tuesday night is from near and south of I-72
(50-70% chance). Localized amounts upwards of 2-3" are depicted
among some of the CAMs (through Tuesday night). Given the
antecedent dry conditions, lack of frost depth, and 6-hour flash
flood guidance of 2.5+ inches, the chances of flash flooding seem
quite low, even with the potential for training precip.

Will also need to keep an eye on fog potential Tues night, given
the stalled frontal boundary and ample moisture present in this
airmass. HRRR hints at pockets of dense fog near the frontal
boundary.

*** WEDNESDAY THROUGH FRIDAY ***

The frontal zone remains stalled somewhere across the ILX CWA into
Wed. The GFS solution trended towards other guidance, now showing
a rather weak sfc low moving along the frontal zone. Guidance has
also trended a bit slower with the timing of this feature. These
trends lessen the sfc-based severe storm chances compared to those
outlined in earlier GFS solutions. In response to the approaching
upper low, temps cooling aloft will lead to steepening lapse
rates, and elevated instability values could approach 1000 J/kg.
Fcst soundings show a robust warm nose, which is not a surprise
given continued low- level WAA in response to the approaching
wave, which will largely limit sfc-based instability. The main
threat on Wed/Wed night would be hail, but some isolated damaging
winds can`t be ruled out. There is a marginal risk (level 1 of 5)
of severe storms near/south of I- 72.

Precip with this wave could linger into Thurs, but as it departs
height rises aloft suggest Thurs could be a relative lull in
precip activity compare to the rest of the work week. I don`t
think this trend is being captured by the model blend just yet,
which still depicts 60-80% chance of precip through the day on
Thurs. These may be lowered if current forecast trends continue.

Another amplified trough emerges onto the Plains on Fri, with the
Gulf moisture advection once again feeding into this system.
Strong southwesterly flow aloft will result in plentiful wind
shear, especially into Fri night as a robust LLJ (850mb winds over
50 kts) is depicted to develop overhead. Current deterministic
guidance depicts a warm front lifting north across the CWA during
the morning, with associated precip chances and low (but non-zero)
instability. Can`t rule out some isolated strong/severe storms
given the wind shear, but the more concerning timeframe seems to
be Fri evening/night. The exact diurnal timing remains subject to
change, but continued strong warm, moist advection could overcome
the usual loss of diurnal energy and keep a severe threat present
into the night. Even the blended guidance keeps sfc temps in the
mid 60s well into Fri night/early Sat AM, which is above the
record warm low temps for that time of year. The greatest severe
threat seems to be focused west of our area (more favorable
diurnal timing), with the SPC Day 5 Outlook extending as far east
as the IL/MO/IA borders, but CSU Machine Learning probabilities do
extend the 15% or higher risk of severe storms roughly from St.
Louis to Champaign and westward.

Between Wed AM and Sat AM, the NBM probability of 1" of rain is 70-
80%, and the probability of 2" is generally 15-30% north of I-70
and 30-50% south of I-70. These probabilities do not include the
aforementioned rainfall that could occur Tues-Tues night. The
active pattern appears set to continue into the second week of
March.

Erwin

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1000 PM CST Mon Mar 2 2026

IFR conditions have developed at KSPI, and will spread north
across the remainder of the terminals tonight. By 10-13z the first
wave of -SHRA will move in from the southwest. LIFR ceilings and
MVFR visibility will be associated with the -SHRA. While breaks in
the rain will occur, -SHRA will be the predominant conditions
through 06z Tue. IFR to LIFR ceilings will be common through the
remainder of the forecast as well. Isolated -TSRA can`t be ruled
out Tue afternoon/evening, but probabilities are too low to
include PROB30 groups at this time.  Winds to be light easterly
through the period.

25

&&

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

$$