802
FXUS63 KILX 241045
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
545 AM CDT Sat May 24 2025

.KEY MESSAGES...

- Below normal temperatures persist, with several days of highs
  ranging from the mid 60s to low 70s. There are a few light rain
  chances Sunday into next week, with the best chance being on
  Tuesday (40-50%). Severe thunderstorms are not expected.

&&

.DISCUSSION...
Issued at 254 AM CDT Sat May 24 2025

A low-impact forecast period continues across central IL, with the
main forecast concern being occasional light rain chances. Early
Sat AM, satellite imagery showed ample mid/high cloud cover
overspreading the ILX CWA, helping to keep temps warmer than Fri
AM, in the 50s as of this writing. A pleasant late spring day is
in store across the region today as broad, weak sfc high pressure
(1022- mb) nudges in. High temps rise into the low 70s, while
winds will be light, and dewpoints only in the 40s result in
afternoon RH values between 30-40%. Another synoptically-enhanced
lake breeze arrives late this evening. Unlike previous
occurrences, this one isn`t expected to be too breezy, but will
result in the onset of northeasterly winds overnight.

For Sun into early next week, IL will find itself positioned
between a deepening sfc low over the southern Plains and sfc high
pressure over the Great Lakes. Periods of weak ascent from the
system to our southwest will have to work against persistent,
(relatively) dry, northeasterly flow due to the high pressure to
the north. This pattern leaves me thinking that the model blend
PoPs are generally overdone. However, one period where forcing
looks sufficient to include low chance (20%) precip mention is
late Sat night into Sun, when models show an east-west oriented
band of low-level FGEN forcing. This forcing is initially focused
north of I-74, but does slide south Sun afternoon. Fcst soundings
never fully saturate, but do appear to be near saturation
throughout the day. So, in a deviation from previous forecasts,
PoPs were expanded northward on Sun, now including a 15-30% chance
across the entire CWA. On the flip side, for Monday, the sfc high
sinks closer to the area and most guidance suggests precip stays
just southwest of the ILX CWA. The forecast blend kept 20-40% PoPs
south of a Galesburg-Paris line, but if current trends hold I`d
expect these PoPs to lower in the coming days.

By Tues, the shortwave responsible for the southern Plains system
lifts into the mid-MS Valley, shunting the sfc high pressure a bit
northeast and providing the best chance for rain during this
forecast period (40-50%). Forecast soundings and instability progs
only show weak instability, but perhaps enough for a few rumbles
of thunder (MUCAPE values of a few hundred J/kg). Total QPF
amounts through Tues night are light, with just a 30-50% chance to
exceed 0.25" north of I-72, and a 50-70% chance to the south.
Skies will be partly to mostly cloudy each day through Tues, with
seasonably cool temps as highs continue to range from the mid 60s
to low 70s each day.

For the latter half of the work week, the forecast will be
influenced by the evolution of a closed upper low over the
northern Plains/upper Midwest, which is expected to be slow to
evolve. Guidance eventually slides this upper low to the east, at
which point ensembles show an amplifying upper pattern with long
wave troughing developing over the eastern US while a separate
upper low cuts off off the coast of SoCal. The closed upper low
traversing the upper Midwest will result in some mention of
precip in the forecast during the latter half of the week. At no
point in this pattern is there a clear signal for strong
southwesterly flow across the Midwest, which means temps will be
slow to warm and the svr storm threat stays low through the week.
The probability of high temps above 80F is below 50% each day through
the end of May (though the probs are around 40-50% for the
western half of the CWA by Sat May 31). Normal high temps for late
May are in the upper 70s/near 80F.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 543 AM CDT Sat May 24 2025

VFR conditions prevail through the period, along with an easterly
wind component. Winds should stay below 10 knots. Broken mid-level
cloud cover will be prevalent throughout the period. There is a
low chance (15%) of light rain towards the end of the period
(06-12z), but did not feel this warranted a precip mention in the
TAF.

Erwin

&&

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

$$