792
FXUS63 KILX 061042
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
542 AM CDT Sun Apr 6 2025

.KEY MESSAGES...

- Seasonably cool temperatures are expected through Tuesday. Lows
  will be near freezing tonight, but the coldest temperatures are
  expected Monday night when lows fall into the mid 20s. The cold
  could harm any sensitive early season vegetation.

- Light rain remains possible south of I-72 today (20-40% chance),
  then north of I-74 on Monday (20% chance). After a few mostly
  dry days, rain chances return mid-week with a 50-70% chance
  during the Wed-Thurs timeframe.

&&

.DISCUSSION...
Issued at 225 AM CDT Sun Apr 6 2025

At the start of the period, an upper low was positioned near the
TX Panhandle, with a deeper upper low off to the north near the
Hudson Bay. As of 07z/2am Sun, light rain continued to overspread
areas south of I-72, and as the southern low lifts today it could
continue to aid precip development across these areas. Fcst PWAT
values are lower than previous days, around 0.75" south of I-70
and quickly decreasing to less than 0.5" along the I-72 corridor.
Any additional rainfall should be light enough that it will not
meaningfully worsen the exist flooding across SE IL. The 06.00z
HREF has just a 20-30% chance of exceeding a tenth of an inch of
rain south of I-70 during the day today, with even less expected
further to the north.

*** FREEZE POTENTIAL ***

The focus of the forecast then shifts to the freeze potential over
the next few nights. Mon night still looks like a slam dunk for a
freeze after cold FROPA occurs during the day Mon and sfc high
pressure moves in Mon night. There is a greater than 95% chance
for lows below freezing, and a hard freeze (below 28 degF) still
appears likely (60% south of I-70 to over 90% north of I-74).
Based on coordination with neighboring offices and planting
partners, a Freeze Watch has been issued from Schuyler to
Vermilion Counties and southward for Mon night. Barring a
significant change in the forecast, an upgrade to a Freeze Warning
is likely as we get closer to the event.

While confidence is high regarding Mon night, it is less so for
tonight (Sun night into Mon). Models indicate a sfc ridge axis
shifting SE across areas south of I-72 overnight. While winds
aren`t expected to be calm, they do stand a better chance of being
light in these areas compared to further north where a sfc low
over the upper Midwest will start to influence the wind fields.
Skies are also favored to become mostly clear for at least a few
hours across the southern half of the CWA overnight which will aid
cooling. CAMs have low temps right around 32-33 degF, and the NBM
has a 40-50% chance for lows below freezing south of I-72 (with
lower probs to the north, which aligns well with the prevailing
conditions outlined above). Even if sub-freezing temps do not
occur, areas of frost could develop and negatively impact
sensitive vegetation. Opted to issue a Special Weather Statement
to highlight this potential since it otherwise may go overlooked
given the even colder temps expected Mon night.

*** OTHER HIGHLIGHTS ***

With that aforementioned cold front progged to be pushing into
northern parts of the ILX CWA early Mon morning, we will likely
see a broad range in high temps across the CWA, ranging from
mid-40s north of I-74 to upper 50s south of I-70. For areas
near/south of I- 70, when the front does move through Mon
afternoon expect non- diurnal temp trends (falling temps during
the afternoon). The post- frontal airmass will feature breezy NW
winds, with gusts up to 30 mph. Precip chances appear low with
this front owing to a paltry airmass (PWAT values around 0.25").
That being said, fcst soundings do show a shallow layer of
instability just above the cloud bases which could support a few
sprinkles, especially near/east of I-57 where there could be a
slight moisture enhancement owing to advection off Lake Michigan.
Tues remains seasonably cool (highs near 50F) as the sfc high
slowly shifts SE through the region.

Into mid-week, southerly flow returns resulting a modest warmup
back to at least seasonable temps. A disturbance over the
northern Plains will deepen/amplify, providing rain chances to IL
during the Wed- Thurs period (50-70%). This system does not appear
to be a heavy rain producer. Even when accounting for timing
differences, the latest Grand Ens has less than a 10% chance of
exceeding 1" of rain in our area. It`s a little early to assess
the svr storm potential, but an early look at the environment
isn`t overly concerning, with just a 20-40% of exceeding both 250
J/kg of MUCAPE and 30 knots of deep layer shear, which is a low
bar to clear. Probabilistic guidance sources (including the NCAR
AI, CSU ML, and NSSL ML) keep severe probs below 5% across the ILX
CWA Wed-Thurs.

An amplified upper ridge will shift over the central Plains late
in the work week, which should result in a continued warming
trend as well as dry time as the associated sfc high shifts over
IL. Can`t completely rule out precip, but the thinking is that a
good portion of Fri-Sun will be dry. From next Sun into the
following week, the NBM suggests highs at least in the upper 60s
(>75% chance), with median values solidly in the 70s and a chance
(30-50%) that highs climb into the 80s.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 541 AM CDT Sun Apr 6 2025

VFR conditions are expected through the period. Mid-level clouds
around 10kft will gradually shift off to the southeast today, with
skies eventually become mostly clear overnight. Winds start off
out of the north-northeast around 10 knots, but become variable
this evening before eventually reestablishing out of the southwest
towards the end of the period.

Erwin

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late Monday night through Tuesday morning for
ILZ040>057-061>063-066>068-071>073.

&&

$$