Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280510
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1210 AM CDT Thu Mar 28 2024

.KEY MESSAGES...

- An active weather pattern is expected from late this week
  through early next week with periodic chances for showers and
  storms

&&

.DISCUSSION...
Issued at 332 PM CDT Wed Mar 27 2024

Through Thursday Night:

A weak mid-level disturbance moving across the Missouri River
along the MO/IA line is evident in a batch of mid-level clouds
within an overall dry airmass across region. Cloud bases in the
4-7kft/700-800 hPa layer align well with weak isentropic ascent
that will gradually weaken with E or ESE extent through tonight.
While some radar returns have been evident in southwest IA and
northwest MO this afternoon, all but maybe a couple sprinkles
have reached the surface given the antecedent low-level dry
airmass. Continued dry air advection into the area through
tonight should limit precip from reaching the ground, so have
maintained a dry forecast across the area.

Moderating conditions on Thursday will result in a dry and
generally seasonable day for late March. A LLJ directed just
west of the forecast area Thursday night will support increasing
WAA with a stronger baroclinic zone across the forecast area.
Moisture return into the area appears to remain meager for any
appreciable precip chances, but will maintain slight chance PoPs
for isolated showers or sprinkles into mainly the south half of
the CWA during the evening and early overnight hours.

Kluber


Friday through Wednesday:

Late this week into early next week, a pattern change will bring
periods of rainy and stormy weather to the region. Mean ridging will
remain established over the southeastern CONUS throughout this time
with an energetic, anticyclonically-arcing jet stream wrapped around
the ridge`s northern periphery. Beneath the jet, a sharpening
baroclinic zone will set up shop in the region and serve as a focus
for convective development as multiple upper-level disturbances
navigate around the ridge.

An initial shortwave disturbance is slated to reach the area on
Friday, initially serving to bring in and thicken up a mid/upper-
level cloud deck. Despite the increasing cloud cover, modest warm
air advection off of southerly winds will push the 60 degree surface
isotherm up into our CWA, likely up to the I-80 or I-88 corridor,
where it will encounter a cooler, marine-influenced air mass that
will be pressing inland off of Lake Michigan. The net result of this
is that there will be a fairly notable temperature gradient across
our forecast area on Friday, with temperatures well into the 60s
in our southern counties and temperatures struggling to reach 50
degrees along the Illinois lakeshore.

It appears that we`ll remain dry on Friday until the nose of a low-
level jet and an associated theta-e plume impinge upon our forecast
area from the southwest, which likely won`t be until around or
after sunset. Once this better low-level forcing and higher quality
moisture arrives, a rapid uptick in shower coverage is expected,
particularly in the vicinity of the quasi-stationary frontal
boundary that was sharpened earlier in the day and will be
reinforced by a developing surface low to our west. Mid-level lapse
rates should be just steep enough to support at least isolated
thunderstorms Friday night into Saturday morning, but on the whole,
instability should be lacking for a more notable thunderstorm
threat to materialize. With storm motion expected to be somewhat
parallel to the aforementioned surface boundary, would not be
surprised to see training convection produce an axis of locally
heavier rainfall totals somewhere, but again, the overall dearth
of instability should be a limiting factor for more notable
hydrologic concerns arising.

Some chance for showers and storms may continue beyond daybreak on
Saturday, particularly in the eastern and southeastern sections of
our CWA, though this will largely depend on how quickly the surface
low is able to scoot eastward through the area. A slower progression
to the low could allow for storms to redevelop in our southern
counties Saturday afternoon in the system`s warm sector, and these
would stand a better chance of becoming surface based and having a
little more oomph to them than the overnight storms if this were to
be the case. On the other hand, a faster progression to the low
would result in our forecast area remaining largely or entirely
devoid of any precipitation during the daytime on Saturday.
Saturday`s temperatures are also likely to be influenced to some
extent by how quickly the low progresses through the area, with
a slower progression favoring 70+ degree temperatures being
achieved in our southern counties south of the aforementioned
quasi-stationary front before the system`s cold front sweeps
through.

Beyond Saturday, medium range guidance starts to diverge with
respect to the timing and track of subsequent disturbances
embedded within the active upper-level flow pattern, but there
is a signal for another disturbance to bring showers and possibly
storms to somewhere the region on Sunday. Whether these showers
and storms occur in our area will also, in part, depend on how
far south the low-level baroclinic zone is shunted on Saturday
and how far north it is able to return on Sunday. The forecast
for Monday follows a similar story, though it will feature the
arrival of a much more formidable southern stream trough
ejecting out of the southwestern CONUS that could potentially
phase to some extent with a northern stream trough coming out of
Canada. It`s still too early to say for sure what that will
entail for our area, but Monday could be a day to watch for a
potential severe weather and/or heavy rainfall threat somewhere
in the Midwest.

Ogorek

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1210 AM CDT Thu Mar 28 2024

There are no significant aviation weather concerns. Some
increase in VFR cigs is expected through this morning. Westerly
winds will gust at times towards 20 knots into the afternoon
before easing and turning northwesterly. Towards the end of the
ORD/MDW extended TAFs, winds will likely turn out of the
northeast, but this shift will be addressed with the 12z TAF
issuance.

Carlaw

&&

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

&&

$$

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