602
FXUS63 KLOT 030755
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
255 AM CDT Thu Apr 3 2025

.KEY MESSAGES...

- Periods of rain, possibly heavy, are expected Friday afternoon
  into Saturday, with localized flooding possible.

&&

.DISCUSSION...
Issued at 255 AM CDT Thu Apr 3 2025

Through Wednesday:

A cold front has shifted south and east of the area early this
morning with temperatures and dewpoints dropping steadily with
each passing hour in its wake. This boundary is forecast to
stall generally near the Mid-Mississippi and Ohio River Valleys
setting the stage for multiple days of heavy rain leading to
potentially significant flooding in those areas.

We`ll start the day here locally in the 40s this morning.
Increasing cloud coverage through the day combined with
continued west northwesterly cold air advection into the region
should keep temperatures closer to seasonable in to the mid 50s
north of I-80 and upper 50s to near 60 south. High pressure
begins to build over the Great Lakes into tonight allowing winds
to flop northeasterly. Prevailing onshore/northerly flow will
lead to generally cooler than normal temperatures for the next
several days in the upper 40s to lower 50s. A few light showers
may attempt to lift into southern portions of the area late this
afternoon through the early overnight hours (20-30% chance),
though the aforementioned surface high should help confine this
to areas mainly south of I-80.

A weak surface low is forecast to develop and move northeast
across central Illinois into northern Indiana late Friday into
Saturday. During this time the stalled surface boundary is
expected to lift back toward the area, with low level ascent
atop the boundary leading to increasing shower coverage (and
possibly a few embedded elevated storms) across the area Friday
afternoon through Friday night into Saturday. Given anomalously
high PWATS >1-1.5" (to potentially near 2" per the 0Z ECMWF),
torrential rain will be possible. At this range the highest
rainfall amounts currently favors areas south of I-80 where both
the GEFS and EPS show a ~30-50% chance of 2" of rain occurring.
This matches well with WPC`s latest Day2 Outlook for a level 2
of 4 threat of flash flooding. There has been enough variability
over the past several model runs to suggest a northward shift
of this axis into more of the Chicago metro area is possible,
however. This will remain a period to monitor closely for
flooding considering many areas received plentiful rain over the
past 24 hours. For now, plan to issue an ESF for areas
generally south of I-80 to highlight the increasing flooding
threat.

A potent short-wave is forecast to dive across the Great Lakes
early next week which will bring our next chance for
precipitation (likely in the form of snow) on Monday. Ensembles
continue to support temperatures dropping into the 20s Monday
night. Beyond Monday, an upper level pattern shift supports
temperatures gradually moderating through midweek with
temperatures in the 50s and lower 60s with occasional low rain
chances.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1230 AM CDT Thu Apr 3 2025

Forecast concerns include...

Gusty westerly winds through this afternoon.
Wind shift to northeast this evening.

A cold front has shifted east of GYY early this morning and
there may be a few sprinkles and brief mvfr cigs as it continues
moving east. Otherwise, westerly winds gusting into the lower/
mid 20kt range will continue through mid afternoon and diminish
with sunset. Winds will turn light northwest this evening and
then shift to light northeast by mid evening.

Some mvfr level cloud cover may spread back across northwest IL
and RFD by daybreak and persist through midday. Confidence is
low and its also possible this cloud cover may lift to low vfr,
3-4kft by the time it arrives.

There is a chance for showers tonight that may spread as far
north as GYY but the bulk of this activity is expected to stay
south of the terminals and no mention with this forecast. cms

&&

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

&&

$$

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