Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 281110
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
610 AM CDT Thu Mar 28 2024

.KEY MESSAGES...

- Warming temperatures through weeks` end

- Periods of showers and storms Friday night through the weekend

- Another storm system likely to impact the area early next week

&&

.DISCUSSION...
Issued at 358 AM CDT Thu Mar 28 2024

Through Friday:

Mid-level ridging will continue to build into the southern
Great Lakes today allowing temperatures to warm toward more
seasonable readings. However, lingering cold temperatures aloft
due to an upper low to our north will limit the amount of
warming today with highs expected to top out in the upper 40s to
mid-50s. In addition, the colder air aloft will also promote
some deeper diurnal mixing today which some guidance suggests
may pull down drier air and limit the low-level moist advection.
While our current forecast does have humidities this afternoon
remaining in the 35 to 40 percent range, if dew points are able
to mix down this afternoon RH readings could verify lower to
around 30% especially across northern IL. Thankfully, winds
today should be somewhat light with gusts generally under 20 mph
which should limit any fire weather concerns this afternoon.

Heading into tonight, a surface baroclinic zone will begin to
lift into the area which will likely generate a bit of a north-
south temperature gradient with overnight lows. Guidance also
continues to show a weak mid-level impulse pivoting atop this
baroclinic zone which looks to be sufficient to generate some
isolated to widely scattered showers across the southern 1/3 of
our forecast area (areas south of the Kankakee River Valley).
However, forecast soundings continue to show a decent amount of
dry air in the sub-cloud layer which may limit the overall
coverage. Therefore, despite a large guidance support for higher
POPs, I have decided to maintain the advertised 15 to 20
percent chances for showers this evening through about midnight.

Otherwise, expect dry conditions to once again prevail through
Friday afternoon with warmer temperatures in the mid-50s to
mid-60s. Though onshore winds along the IL lakeshore will keep
temperatures notably cooler in the 40s.

Friday night through Wednesday...

Several periods of active weather will begin to establish
across the central CONUS, including our area, Friday night as a
broad upper trough moves onshore over southern California and
progresses eastward through the early part of next week. The
first period of inclement weather for our area is expected
Friday night as a modest shortwave passes through the southern
Great Lakes and interacts with the aforementioned baroclinic
zone which is expected to be stalled across northern IL. As
these features interact a weak surface low will develop across
eastern Iowa and propagate eastward along the boundary
generating a broad area of showers and perhaps thunderstorms as
it does so.

Given the non-favorable diurnal time, instability over northern
IL and northwest IN looks to be somewhat modest at best but
still sufficient for at least scattered embedded thunderstorms
particularly in the warm sector south of the boundary. As a
result, widespread severe weather is not expected. However,
there will be a stout 500 mb jet pivoting into the area Friday
night which should develop 40 to 50 kts of deep layer shear and
possibly allow for some more robust cores to develop. Any storm
cores that area able to take advantage of the shear may be able
to produce localized instances of small hail and possibly some
gusty winds. Additionally, PWATs of 0.75 to 0.90 inches are
forecast to advect into the warm sector of this system which may
yield some heavier downpours especially with any robust storm
cores. Given that soil moistures are above average and the lack
of green vegetation yet, runoff from the rain could lead to
instances of river and stream rises and result in a concern for
localized flooding.

Guidance continues to depict that showers and storms should
wane Saturday morning as the surface low exits into northern
Indiana, but some guidance does redevelop convection in the warm
sector Saturday afternoon. Whether or not this warm sector is
in our area remains uncertain. A similar story can be told for
Sunday as the potential for showers and storms will depend on
how far south the baroclinic zone gets shoved in the wake of
Saturday morning convection and whether or not it can retreat
back into our area prior to storms developing Sunday afternoon.
Due to these uncertainties I have decided to maintain the 20 to
30 percent chances for showers in our southern CWA both
Saturday and Sunday.

Heading into Monday, the aforementioned trough is forecast to
be ejecting into the southern plains with a strengthening upper
jet aimed at the southern Great Lakes. This broader forcing is
expected to be enough to surge the baroclinic zone back north as
a new surface low develops somewhere across the Mississippi
Valley. However, where this surface low will track once it
develops remains very uncertain among guidance members which
will play a major role in what impacts we see. While it does
appear likely that we will see some additional rainfall from
this system, the intensity of said rainfall and whether or not
any strong to severe storms develop into our area will be
something to monitor over the coming days.

Yack

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 610 AM CDT Thu Mar 28 2024

There are no significant aviation weather concerns through the
TAF period.

A deck of VFR cigs (around 050) will prevail across the
terminals this morning. No precipitation is expected at the
terminals.

Light southwesterly winds will become a bit breezy/gusty later
this morning and afternoon with occasional gusts around 20 kts,
perhaps briefly a bit higher late this afternoon prior to
sunset. Winds will then become nearly light and variable before
trending northeasterly Friday morning. A weak lake breeze will
probably turn GYY`s winds northeasterly early this evening.

Carlaw

&&

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

&&

$$

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