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000
FXUS63 KLOT 150506
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1206 AM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Waves of showers and scattered storms develop early Tuesday
  through Wednesday. Some may be severe Tuesday evening into
  Wednesday.

- Windy late Tuesday through Wednesday with peak gusts 40+ mph,
  highest on Wednesday.

&&

.DISCUSSION...
Issued at 328 PM CDT Sun Apr 14 2024

Through Monday Night:

On what has been our warmest day of the year thus far (with both
Chicago and Rockford officially logging their first 80 degree
readings of this calendar year), a lake breeze/lake-enhanced cold
front is now marching inland from Lake Michigan. The more notable
temperature falloff is lagging behind this boundary a bit, but
through the remainder of this afternoon into this evening, expect
temperatures to drop into the 60s and eventually the 50s behind the
boundary as it steadily continues to press inland. Light winds at
the surface induced by nearby high pressure and skies remaining
clear to mostly clear will also contribute to the nocturnal cooling
efforts tonight, resulting in nighttime lows that should range from
the mid 40s to the low 50s across the area.

With high pressure still in the region come tomorrow, it should be
another uneventful day weather-wise here. High temperatures look to
be a few degrees cooler than today`s highs, but abundant sunshine
and relatively low dew points will once again favor temperatures
reaching the upper echelon of what forecast guidance is offering up,
which would be widespread mid 70s to near 80 degree readings away
from Lake Michigan. Closer to the lake, light onshore flow and
eventually likely a true lake breeze should keep temperatures below
70 degrees, and possibly even below 60 degrees, along the immediate
lakeshore.

Overnight, high-level cloud cover should start to spread over the
area in increasing quantity while warm air advection will start to
ramp up in advance of a deepening low pressure system over the
central Plains. It is possible that a leading band of showers and
storms reaches our southwestern CWA just before the night is over as
richer theta-e air begins to push into the area, but most locations
currently look like they will remain dry through daybreak. More
information on this incoming system and the showers and storms that
it will bring can be found below.

Ogorek


Tuesday through Sunday:

Confidence remains high in the potential for waves of showers
and scattered thunderstorms developing early Tuesday and
persisting into Wednesday across the area as an occluding
surface low moves across the region. Additionally, there remains
a signal for severe weather though with a trend toward later
timing, now favoring Thursday evening/night into early
Wednesday.


To start, early Tuesday the expectation is that elevated
showers and embedded non-severe thunderstorms will steadily
overspread the area during the day on Tuesday as warm advection
lifts into the area in response to the strengthening surface low
to our west. Surface winds will also steadily increase in
response to the approaching system and resultant tightening
pressure gradient, with gusts in the 30-40 mph range out of the
east and southeast expected on Tuesday. The resultant lake
cooled air will hold down temperatures across northeast Illinois
with afternoon highs only in the mid 50s to lower 60s. The
associated surface warm front will be slow to lift into the area
with temperatures warming into the 70s south of the boundary,
currently favoring locales south of I-80.

The slowed eastward progress of the surface low continues to
support a later trend for our strong to severe storm potential
with the best conditions for severe weather setting up across
northern Missouri and southern Iowa during the afternoon. With
even marginal to modest instability (MUCAPE of 500-1000 J/kg)
the clockwise curved low-level hodographs and strong dynamics
in place (0-6km Bulk shear 50-60kts), severe storms to our west
could very well continue east into the overnight hours across
northern Illinois and into northwest Indiana. The degree of
destabilization will likely factor into the coverage and upper
bounds of the severe threat. Nevertheless all hazards will be in
play (damaging winds, hail, and tornadoes).

As the upper low merges into the upper trough it takes on more
of a negative tilt early Wednesday morning with the region still
situated under the left exit of the southern stream upper jet.
While there are some questions as to how much instability there
will be to work with into early Wednesday morning and the timing
of the various waves as showers and storms wrap around the
surface low. With the slightly slower timing, forecast soundings
would support surface based convection persisting (or redeveloping)
Wednesday morning into early afternoon, especially east into
northwest Indiana. Will hopefully get a better idea of how late
the severe threat persists as high-res guidance becomes
available. Winds turn westerly on Wednesday with the strong
winds persisting and likely peaking during the afternoon on
Wednesday with gusts up to 40+ mph possible.

Beyond Wednesday can`t rule out some rain on the north side of
a weakening surface late Thursday into Friday then before
surface high pressure builds southeast into the Upper Midwest
bringing a cooler airmass for the latter half of the week with
high temperatures in the 50s to lower 60s and lows in the 30s
and lower 40s.

Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1206 AM CDT Mon Apr 15 2024

VFR with no noteworthy concerns for the next 24-30 hours. A
secondary cold front pushing across the terminals will bring
north-northeast winds overnight, shifting to east/northeast this
morning. East-northeast winds will then continue through tonight.
Prevailing speeds will average near/around 10 kt. Any isolated
SHRA/TSRA after toward 12z Tuesday are forecast to be well inland
of ORD and MDW.

Castro

&&

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

&&

$$

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