799
FXUS63 KLOT 280856
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
356 AM CDT Sun Apr 28 2024

.KEY MESSAGES...

- Waves of showers and thunderstorms through Monday. Localized
  flooding remains possible early this morning, and there is a
  low (~15%) chance for an isolated severe thunderstorm or two
  to occur later this afternoon or evening.

- After a break on Tuesday, a stormy pattern returns midweek
  along with continued unseasonably warm temperatures.

&&

.DISCUSSION...
Issued at 356 AM CDT Sun Apr 28 2024

Through Monday:

It`s been a rainy and stormy early morning for much of the area as a
low-level jet has been funneling a persistent stream of moisture our
way. MRMS and radar estimates indicate that, through 345 AM, between
about 1 and 2.5 inches of rain has fallen across a corridor from
the southwest Chicago suburbs towards Peoria, with lower totals
elsewhere. With the low-level jet still going strong, rainfall is
expected to continue over the next few hours and may ultimately
culminate in some minor flooding of fields, ditches, and areas
of poor drainage, mainly in the aforementioned corridor. Fortunately
though, radar trends suggest that the instability reservoir in the
region has gradually become depleted as a result of the widespread
convection, and rainfall rates should continue to taper off as we
approach daybreak.

The shower/storm activity is expected to diminish over the course of
this morning as the low-level jet weakens, paving the way for much
of our forecast area to see plenty of dry time during the daytime
hours today. However, with isentropic upglide continuing along the
eastern periphery of a low pressure system situated beneath the
upper-level trough over the Great Plains, additional rain showers
will be funneled northward along the Mississippi River Valley
throughout the day. Some of these showers will likely trickle into
western portions of our forecast area this afternoon, though
overall coverage is expected to be no more than scattered. The
northward transport of warmth and moisture will also likely
support MLCAPE recovering to around 500-1000 J/kg this afternoon
in the zone of shower activity, so it`s very much possible that a
few storms develop within this corridor as well. Shear profiles
actually look fairly decent given the overhead placement of both
the low- and upper-level jets, so if some deeper convection can
get going, it could take on supercellular characteristics and
become capable of producing damaging winds and/or hail. Confidence
in this outcome playing out is relatively low, and even if it
came to fruition, the severe weather threat would remain isolated,
so the Storm Prediction Center`s Day 1 Marginal Risk covers this
possibility well.

This afternoon, several storms are also expected to develop along a
frontal zone to our west/southwest in Iowa and Missouri and will
probably consolidate into a more linear multicell cluster that will
propagate towards our forecast area this evening. Similar to
yesterday evening, these storms are likely to lose steam as they
encounter increasing quantities of convective inhibition with
time and eastward extent. Consequently, the likelihood of severe
weather occurring tonight as these decaying storms roll through is
quite low, but if they managed to maintain their intensity, then
some strong to marginally severe wind gusts couldn`t be ruled out.

Tonight`s band of showers/storms will likely depart our forecast
area early Monday morning as a mid-level dry slot barges into the
region. With low-level cold air advection yielding steepened
low-level lapse rates and the continued presence of the nearby
upper-level trough providing forcing support, isolated to
scattered low-topped convective showers may develop during the
daytime on Monday. However, the quality and depth of moisture
trapped beneath a low-level temperature inversion doesn`t look
great overall and could potentially prevent these showers from
developing altogether or, at the very least, limit their overall
coverage. Have slashed PoPs a good bit for Monday as a result,
keeping the highest probabilities focused in our southeastern
CWA, where the influence of the dry slot won`t be as great as
farther northwest and higher inversion heights will provide a
better chance for clouds to grow deep enough for showers to
redevelop. A cold front is then expected to pass through the
area during the latter half of the afternoon into the evening,
effectively shutting off shower chances behind it.

Ogorek


Monday Night through Saturday:

Heading into Monday night most of the area will be dry, though
a slower eastward push of the surface cold front would result in
showers and storms potentially lingering into early Monday
evening across portions of northwest Indiana. Modest upper-
level height rises are expected in the wake of the
aforementioned front which will promote a period of dry weather
through the daytime hours on Tuesday.

The reprieve looks to be short lived, however, as a series of
shortwave troughs are forecast to traverse across the north-
central CONUS. This will result in periods of showers and
thunderstorms beginning Tuesday night and persisting through at
least the end of the week. The details on timing and coverage of
showers and storms will continue to be refined with later
updates. Temperatures will remain unseasonably warm with
afternoon highs in the mid to upper 70s through Thursday then
turning a bit cooler and less humid heading into next weekend.

Yack/Petr

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1235 AM CDT Sun Apr 28 2024

Key Aviation Messages:
- Increasing shower/storm coverage tonight through mid morning
- SSW winds tonight (variable in and near TS), may turn SE
  toward daybreak then return to gusty SSW in the afternoon
- Another round of TSRA late Sunday evening and overnight

Clusters of showers and thunderstorms currently along/south of
I-80 will continue to lift northeast across the Chicago area
terminals over the next hour or two (later at RFD). The trend
in model guidance has slowed the exit of showers into the
morning hours and have accordingly extended the VCTS mention
through 14Z.

Winds prevail SSW overnight through may be variable at times in
and near any TS. Will keep an eye on a southward moving outflow
boundary from earlier storms in SE Wisconsin that may try to
briefly turn winds NW at ORD but the current expectation is for
it to stall just to the north. There remains a signal that winds
turn east to southeast due to remnant outflow in the wake of
the AM showers/storms before then returning to a gusty SSW by
the afternoon as the boundary retreats back to the north. There
may be a 2-3 hour window that gusts occasionally exceed 30kt in
the afternoon before easing again toward sunset.

Spotty showers and storms may try to redevelop by the afternoon,
especially toward RFD though confidence is not high enough to
include with this update. There is a better signal for
widespread showers and storms moving through during the late
evening and overnight hours from west to east with associated
vsby/cig reductions.

Petr

&&

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

&&

$$

Visit us at weather.gov/chicago