439
FXUS63 KLOT 030017
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
717 PM CDT Wed Apr 2 2025

.KEY MESSAGES...

- The threat for severe weather has ended for the evening.

- Periods of rain, possibly heavy, late Friday afternoon into
  Saturday morning, with possible localized flooding south of
  I-80.

&&

.UPDATE...
Issued at 717 PM CDT Wed Apr 2 2025

The last two counties (Jasper and Benton IN) were recently
cleared from the tornado watch. Thunderstorms will continue a
bit longer into portions of northwest Indiana (primarily Benton
Co), though the threat for severe weather has ended given that
multiple rounds of convection have thoroughly worked over the
airmass. Showers on the cold front near and west of I-39 in
north central/northwest IL as of this writing are unlikely to
intensify with veering winds and sunset approaching, as they
track off to the east through mid evening. We also allowed the
Wind Advisory to expire as planned at 7pm.

Castro

&&

.DISCUSSION...
Issued at 319 PM CDT Wed Apr 2 2025

Through Friday Afternoon:

The threat of showers and thunderstorms will come to an end
from west to east following a cold frontal passage this evening.
For more on the ongoing threat for severe thunderstorms,
reference the meso discussions above.

Meanwhile, the threat of strong southerly wind gusts up to 45
mph will continue in the going wind advisory through early this
evening. Accordingly, no changes are planned to the wind
advisory headline. The ongoing convection has acted to slow the
northward progression of the warm front for the last few hours,
and hence has kept the stronger southerly winds largely south of
the area. This should change within the next couple of hours,
however, as the warm front begins to surge northward in response
to the parent surface low quickly shifting northward into the
Upper Midwest. As it does so, expect the strong gusty southerly
winds to develop across the advisory area. There could even end
up being a short hour or two period early this evening where
winds gust 40-45 mph in areas north of the going advisory
(including the Chicago metro area) before the cold front shifts
across the area. Also, expect temperatures to jump up into the
60s across much of northern IL for a period early this evening
following the warm frontal passage.

Winds will turn westerly this evening following the quick
eastward passage of the cold front. While wind speeds tonight in
the wake of the cold front will not be nearly as strong as the
southerly winds ahead of the front, gusty westerly winds up to
around 30 mph are expected at times overnight into Thursday
morning before gusts ease Thursday afternoon. Expect a
seasonably mild day under mostly cloudy skies Thursday, with
highs ranging from the upper 50s to the lower 60s.

The surface cold front that shifts across our area this evening
will stall out across the Ohio Valley on Thursday into early
Friday. This front will become the primary focus for several
additional rounds of heavy rain producing showers and
thunderstorms Thursday through Friday as deep Gulf moisture
continually feeds into this frontal zone. Fortunately, a
majority of this heavy rain is expected to fall south of our
area across southern parts of IL and IN through Friday morning.
Accordingly, most of our area is likely to remain dry Thursday
through at least early Friday afternoon. The only exception
being a low chance (20-30%) for a few light showers well south
of I-80 Thursday afternoon and evening.

KJB

Friday Afternoon through Wednesday:

The threat for rain (and even some storms) will return to our
area late Friday through Saturday. This as several low amplitude
impulses begin to eject northeastward out of a potent
mid/upper-level trough/low shifting across the Desert
Southwest. Each impulse is expected to drive a wave of surface
low pressure northeastward along the remnant frontal boundary to
our south through the weekend. The first such wave will track
into central parts of IN Friday night into early Saturday
morning. As it does, it will aid in the northward push of
moisture over the surface frontal boundary, thus supporting
increasing rain (and perhaps a few embedded thunderstorms)
chances across much of our area Friday afternoon into Saturday.
Rain chances will peak in the 80 to 100% range areawide Friday
night, though the heaviest rainfall (1"+) is currently favored
to fall south of I-80 into Saturday morning.

Our next wave of low pressure is expected to track farther to
our southeast late Saturday into early Sunday morning. It
appears this wave may remain far enough to our southeast to keep
the threat for the next wave of rain south and east of our area
late Saturday into early Sunday. Accordingly, aside from some
low chance PoPs into Sunday morning (mainly south of I-80),
drier weather is favored for the end of the weekend.

Temperatures through the weekend will cool down as northerly
flow dominates. Daytime highs will generally be in the lower
50s, though even cooler conditions in the lower to mid 40s can
be expected near the lake due to the onshore wind component. A
period of even colder (below average) weather is then likely to
shift into the area for Monday as a stout northern stream trough
digs in over the Great Lakes. High temperatures will likely
remain in the lower 40s for Monday, and the potential exists for
periods of snow showers during the day. Conditions should then
gradually moderate into the middle of next week following the
eastward passage of a surface high.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 630 PM CDT Wed Apr 2 2025

The storm threat has ended across the terminals, with the
continued severe thunderstorm threat now southeast of the area.
Only a few lingering isolated showers are possible across the
area for the next hour or so.

A short period of strong gusty south winds (briefly up to around
35 kt) is expected across the eastern terminals just in advance
of a quickly approaching cold front. Otherwise, winds will turn
west-southwesterly this evening as the cold front shifts
eastward across northern IL. Winds will likely remain gusty (up
to 30 kt at times) in the wake of the front tonight into
Thursday morning. However, expect the winds to ease Thursday
afternoon as the pressure gradient relaxes. Otherwise, no
significant weather concerns are expected through Thursday
evening.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until noon CDT Thursday for the IL and IN
     nearshore waters.

&&

$$

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