407
FXUS63 KLOT 160528
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1228 AM CDT Tue Jul 16 2024

.KEY MESSAGES...

- Strong to severe thunderstorms expected late this afternoon
  into tonight. Locally heavy rainfall possible, which could
  lead to additional flooding.

- Additional thunderstorm chances continue Tuesday, mainly
  south of I-80/east of I-55.

- Pattern breaks by Wednesday, with dry weather and seasonable
  temperature and humidity through the weekend.

&&

.DISCUSSION...
Issued at 247 PM CDT Mon Jul 15 2024

Through Tuesday Night:

Showers and storms may linger into the morning hours, especially
across the southern portion of the CWA. There is a chance that
the cold front associated with the storms may set up in a west
to east fashion and stall out across the southern portion of the
area, which could lead to storms persisting into the evening
over this area. However, most of the 12Z CAMs show this scenario
playing out south of the area. Although the chances of this
seem to be on the lower side, did include chance PoPs across the
southern CWA through Tuesday afternoon to account for this
possibility.

With the cold front moving through the area, Tuesday will be
cooler than today with temperatures in the mid-to-upper 80s.
Dew points will still be around 70 degrees, so it may still feel
a bit on the humid side, but peak heat indices will only be in
the 90-95 degree range.

Carothers


Wednesday through Monday:

The main upper trough axis is expected to shift east across the
forecast area Wednesday. Despite steep low-level lapse rates
depicted in forecast soundings, warm mid-level temps (700-600
mb) look to provide a capping inversion with respect to surface
based convective development. Therefore, forecast for Wednesday
is dry at this point. Broad surface high pressure then builds
across the area through the end of the week, setting the stage
for a well-deserved period of dry and seasonably mild but less-
humid weather conditions, downstream of a high-amplitude upper
ridge which develops over western North America.

Ratzer

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1219 AM CDT Tue Jul 16 2024

Aviation Forecast Concerns:

- Isolated SHRA in the vicinity of Chicago terminals pre-dawn.

- Period of MVFR ceilings likely into mid-morning.

- Light SW-NW winds becoming more solidly NNW by afternoon.

Severe squall line has cleared the terminals as of midnight,
with a few scattered showers lingering across SE WI and LM which
may pass through the vicinity of the Chicago metro terminals
into the pre-dawn hours. Moist low-levels in the wake of the
storms and in advance of a weak cold front which will move
through the area by midday will likely support at least patchy
MVFR ceilings and visibility in stratus and light fog. Surface
cold front moves through by midday, with winds shifting
northwest and conditions improving to VFR. Can`t rule out some
spotty showers along the front midday/early afternoon, though
coverage/probability look too low for TAF mention at this time.
Scattered thunderstorm potential of better coverage looks to be
well south of the terminals Tuesday afternoon.

Winds remain northerly into tonight, and may briefly turn
slightly NNE at KORD/KMDW, though confidence is low in a
prolonged shift to NE.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flood Watch until 3 AM CDT early this morning for ILZ032-
     ILZ033-ILZ039.

IN...Flood Watch until 4 AM EDT early this morning for INZ019.

LM...None.

&&

$$

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