429
FXUS63 KLOT 231715
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1115 AM CST Sun Feb 23 2025

.KEY MESSAGES...

- Warming trend continues into the middle of next week.

- Chances for rain/showers Monday night (30-40%) and Wednesday
  into Wednesday night (40-60%)

&&

.DISCUSSION...
Issued at 145 AM CST Sun Feb 23 2025

Through Monday:

An upper-level wave extending from the Minnesota Boundary
Waters to the central Great Plains will bring a period of mid to
upper-level cloud cover across the area through the morning
hours. Decent ascent under the entrance of a jet streak will
yield plenty of virga across northern Illinois through the
morning, but a rather dry sub-cloud layer under 12kft should
preclude any snowflakes from reaching the surface. Clouds will
clear from west to east behind the wave this afternoon. Though
modest WAA will yield warmer conditions areawide today, thicker
morning cloud cover and existing snow cover across northern
Illinois will subdue potential warming to some degree. Expect
temps to range from the upper 30s near the Wisconsin line to
around 50 south of the IL/Kankakee River valleys.

Mid to upper-level cloud cover will increase again tonight and
especially Monday as a pair of waves, one crossing the northern
Great Lakes early Monday morning and another entering the
central Plains Monday afternoon, bring abundant Pacific-based
moisture over the region. Even with the added cloud cover,
continued low-level WAA and decent mixing within gusty southwest
winds should yield high temps Monday ranging from the mid 40s
north to the mid 50s (perhaps nearing 60) south.

Kluber


Monday Night through Saturday:

On Monday night, a robust jet streak will push across the
Mississippi River and across northern Illinois. An attendant
low-amplitude (but nonetheless sharp/potent) shortwave will
shift overhead through the evening. While large scale forcing
looks impressive, with robust DCVA and 500 mb height falls on
the order of 60 to 100 m/12 hours, tropospheric moisture looks a
bit more scant, with PWATs around or under a half inch. As
such, it remains a bit unclear just how widespread precipitation
will be as this feature rolls through. That said, cold 500 mb
temperatures will support a plume of fairly steep mid-level
lapse rates, nearing 7-8 C/km. Should sufficient saturation
occur, envision that some "streaky" convective elements could
develop, enough to justify 30-40 percent PoPs for scattered
showery activity. Thermal profiles are safely warm enough to
keep p-types as (non-freezing) rain.

Activity looks to largely shift east of the region through
Tuesday morning. While the NAM, in typical fashion, holds onto
a widespread low stratus deck through the day, this signal is
not evident in the rest of the guidance suite. Expecting clouds
to generally scatter out, which will allow temperatures to warm
at least into the 50s south of I-80. Depending on how much
insolation returns, highs may need to be boosted further.
Additionally, with the surface pressure gradient relaxing and a
nearly 15-20 degree temperature delta between the land and lake,
a weak lake breeze may try to meander inland during the
afternoon.

The next disturbance will arrive very late Tuesday night into
Wednesday. There has been, and continues to be, a large amount
of variability both in individual run-to-run output and across
individual ensemble suites, which lowers overall forecast
confidence during this period. Guidance suggests deeper moisture
will be available (PWATs possibly pushing past three quarters
of an inch), and jet forcing additionally looks a bit more
formidable than Monday night`s system. PoPs have been increased
a bit with this forecast package. Finally, given recent trends,
the threat for wintry precipitation with this system continue to
diminish and have pulled all mention of frozen precip from the
grids. Can`t entirely rule out a brief flip to a little snow as
the main surface low departs and winds turn northerly, but
latest soundings suggest dry air will effectively shut precip
off before the columns cools sufficiently to support a
changeover.

The active pattern will continue upstairs through the rest of the
week and into the weekend. Guidance is in reasonably good
agreement depicting an intense shortwave pivoting into the
Upper Great Lakes region on Friday, dragging an associated
sub-1000 mb surface low with it along the International Border.
Currently, we look too far removed from this system for precip
chances, but gusty southwesterly winds within an expansive low-
level thermal axis may once again help boost high temperatures
into the 40s and 50s. A strong cold front is then slated to
deliver a (temporary) surge of colder air to the region over the
weekend.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1115 AM CST Sun Feb 23 2025

The main aviation concerns for the 18Z TAF period include:

* LLWS late tonight into Monday morning

SSW winds near or just over 10 kt will persist into this
evening. Winds should subside to closer to 5 kt for the better
part of this evening before building back toward 10 kt tonight.
LLWS will materialize after 06Z and remain through the earlier
half of Monday morning with 40 to 45 kt of SW flow expected at 2
kft AGL. Gusts on Monday will build to around 20 kt as
direction veers from SW to W during the morning.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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