094
FXUS63 KILX 211918
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
118 PM CST Fri Feb 21 2025

.KEY MESSAGES...

- Temperatures steadily warm into early next week, with highs
  reaching the 50s Monday-Wednesday, which is about 10 degrees
  above normal.

- There is a low chance (20%) for light rain Monday night north of
  I- 72, with a better chance (40-50%) for rain area-wide on
  Wednesday as a cold front moves through.

&&

.DISCUSSION...
Issued at 117 PM CST Fri Feb 21 2025

An expansive 1040-mb sfc high pressure was situated over the
Midwest Fri afternoon, centered roughly over the bootheel of
Missouri, and gradually shifting SE. As the high shifts southeast
of the area this weekend, persistent southwesterly flow will
develop and continue a welcome warming trend into early next week.
And while there is high confidence in that overall trend, it is
an interesting setup to try and pin down the exact temperature
forecast. The challenge stems from the current snow cover across
the Midwest, where there is a corridor of mostly bare ground
across portions of central Illinois north of Quincy to Paris and
expansive snow cover areas to the south including most of MO. Snow
depth is highest across southern MO (>5") compared to lesser
amounts north of I-70, per this morning`s OWP snow depth map.

Today, when advection was weak, temps have followed the expected
trends: cooler in the snow-covered areas and warmer in the snow-
free areas. Earlier this winter, we saw the NBM exhibit a cool
bias in a strong SW flow/WAA regime, and when factoring in the
bare ground locally this pattern would favor warming temps above
the NBM forecast. However, the southwest winds will be advecting
air across snow-covered MO. Looking at modeled snow depth
forecasts, most of the snow is progged to be gone by Mon, save for
maybe some lingering shallow snow cover across S MO, so any
impacts on the temp forecast should be confined to this weekend.
All of this is to say I don`t feel confident deviating much from
the blended guidance for this weekend, but that I wouldn`t be
surprised to see guidance "bust" one way or another on temps
despite the NBM 25th-75th percentile spread being just 5 degrees
(indicating minimal model spread despite the aforementioned
complicating factors). The southwest winds will be breezy at times
Sat-Mon, but certainly nothing out of the ordinary for central
IL. Ensemble guidance indicates the peak gusts will generally be
between 25-35 mph.

The warmup peaks Mon-Wed, with highs generally in the 50s but a
low chance (10-20%) temps could climb into the low 60s across the
southwest half of the forecast area (south of a Galesburg to
Paris line). The pattern becomes more progressive, with
disturbances trekking through the northern branch of the jet
stream positioned over the northern US. As an initial wave swings
by to the north Mon night/early Tues, there is a low chance of
light rain (~20%) north of I-72. If any rain does occur, it is
expected to be light, with less than a 10% chance of exceeding
0.10" of rain. A more appreciable chance for rain (40-50%) arrives
on Wed as a more robust wave sweeps a cold front across the CWA.
As we grow closer to spring, a pattern that features several days
of southwesterly flow in advance of a cold front at least warrants
an investigation of the severe convective potential, and frankly,
I am eager to write about something other than winter wx
features. However, severe storms are not expected locally with
this mid-week system. This is due in large part to a slow-moving
wave traversing the Gulf coast on Sun-Mon, effectively shutting
off Gulf moisture advection into our area. Additionally, the wave
passing by to our north early in the week swings sfc winds to NW
on Tues, breaking the SW flow regime. Forecast soundings also show
uninspiring mid-level lapse rates. The Grand Ensemble
corroborates this analysis, with the joint probability of
exceeding 250 J/kg of MUCAPE and 30 knots of shear on Wed less
than 10% area-wide. Given the lack of robust moisture, rainfall
amounts don`t appear particularly impactful, with just a 20- 25%
chance of exceeding 0.25".

Behind the mid-week system, temps trend cooler once more.
Amplified upper level troughing remains the dominant feature over
the eastern US/upper Midwest, favoring near to below normal temps
locally for the start of March. Normal temps for early March
feature highs in the mid-40s and lows in the mid-20s.

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1110 AM CST Fri Feb 21 2025

VFR conditions will prevail through the period. South-
southwesterly winds will continue through the period as well,
generally 5-10 knots but increasing towards the very end of the
period. A mid-level cloud deck will shift through the area late
during the overnight/early morning hours, resulting in scattered
clouds above 10kft at the I-72 terminals.

Erwin

&&

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

$$