936
FXUS63 KLOT 301920
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
220 PM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Wind gusts 50 mph or higher possible around/just after
  midnight as a line of decaying showers/isolated thunderstorms
  moves across the area.

- Gusty westerly winds to 30 mph Wednesday.

- Additional periods of showers and thunderstorms Wednesday
  night through Friday.

&&

.DISCUSSION...
Issued at 220 PM CDT Tue Apr 30 2024

Through Wednesday Night:

The primary forecast focus and concern is regarding what the
HRRR and several other models are showing late this evening into
the early overnight hours, which is the potential for wind gusts
50 mph or higher. As showers and a few thunderstorms move into
the western area late this evening, they will be in a weakening
phase and as they dissipate across the local area, the models
are showing the potential for strong winds mixing to the
surface. Of note with the HRRR is that it has been doing this
consistently, run after run today. There is a narrow time window
of strong winds via a low level jet and whether the models are
mixing into this low level jet or trying to develop a wake low
is not clear. Confidence is low for how this will evolve and
trends with convection across IA will need to be monitored into
this evening. Have bumped up winds tonight, with gusts into the
30-35 mph range but if what the HRRR and some of the models are
showing does continue in later runs this evening, its possible
a short duration wind headline may be needed. The models show
these stronger winds diminishing in the predawn hours.

Winds turn westerly Wednesday morning and now appear to be a bit
stronger than previously expected, especially along and north of
I-80 where wind gusts to 30 mph are possible. Winds slowly turn
northwesterly Wednesday afternoon with speeds/gusts slowly
diminishing in the mid/late afternoon. This may allow a lake
breeze to develop into northwest IN by late afternoon but
confidence is low for a lake breeze into northeast IL late
Wednesday afternoon.

The next system will bring a chance of showers and possibly a
few thunderstorms to the area late Wednesday night into early
Thursday morning. Confidence is fairly low for coverage and its
possible that much of the area may remain dry, with the best
chances across the northwest cwa. cms

Thursday through Tuesday:

Discussion will be issued soon.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 105 PM CDT Tue Apr 30 2024

Main Concerns:

- Wind shift to southeast early this evening

- Decaying SHRA moving across the area late tonight

- A period of strong (>40 kt) south-southwest wind gusts
  possibly accompanying the decaying SHRA, with at least 25-30
  kt range gusts appearing probable

- Potential for a period of MVFR CIGs early Wednesday, primarily
  at RFD

West-southwest winds around 10 kt with occasional gusts will
shift to southeasterly early this evening. A true lake breeze
shift to easterly appears unlikely.

Tonight, expected severe TS west of the MS River will weaken
quickly as they move east-southeast across the region, with
TEMPO mention in the TAFs. The HRRR model has shown a fairly
consistent run to run signal for very strong south-southwest
winds gusting to 40-50+ knots associated with the rapid decay of
the SHRA. Change with this TAF issuance was to bump up prevailing
south-southwest winds to ~15-20 kt with ~25-30 kt gusts, which
appears probable, even if the HRRR scenario doesn`t pan out.

Forecast soundings suggest MVFR CIGs are briefly possible behind
an early morning cold front passage. Included TEMPO mention in
the RFD TAF where confidence was a bit higher. Winds will shift
to westerly with 20-30 kt gusts behind the front, strongest
Wednesday afternoon.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 11 PM this evening to 7 PM CDT
     Wednesday for the IL nearshore waters.

     Small Craft Advisory from 11 PM this evening to 1 PM CDT
     Wednesday for the IN nearshore waters.

&&

$$

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