916
FXUS63 KLOT 031716
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1216 PM 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 /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1216 PM CDT Thu Apr 3 2025

Aviation forecast concerns for the 18Z TAFs:

- Breezy west winds diminishing this afternoon, eventually
  turning NE this evening and E Friday morning.

- High-end MVFR ceilings this afternoon mainly at KRFD.

- Rain showers develop northward into terminals late Friday
  afternoon/evening.

Westerly winds continue to gust near 25 kts at midday, though
these will diminish steadily this afternoon as the gradient
weakens ahead of an approaching high pressure ridge. Winds will
then turn light northeast later this evening as the ridge moves
through, and eventually east Friday morning. An area of MVFR
ceilings in the 2500-3000 ft range lingers across southern WI,
far north/northwest IL and eastern IA/MN, mainly affecting KRFD
this afternoon before scattering to VFR there. Otherwise, VFR
conditions are expected through the period.

Showers are expected to develop northward into the region Friday
afternoon, in association with an area of low pressure moving
into MO/downstate IL by Friday evening. Some spread remains in
various model guidance with how quickly and how far north these
showers make it by the end of the TAF period, though confidence
is high enough for a PROB30 mention for KORD/KMDW toward the
end of their current 30-hour forecast later Friday afternoon.
Thunder potential appears low at this time.

Ratzer

&&

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

&&

$$

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