932
FXUS63 KLOT 022346
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
646 PM CDT Sun Jun 2 2024

.KEY MESSAGES...

- Scattered thunderstorms possible Monday and Monday evening.
  Any thunderstorms Monday afternoon and evening could produce
  locally damaging winds and flash flooding.

- Potential for additional showers and storms Tuesday.

- Last chance of thunderstorms for the week looks to be on
  Wednesday, mainly in the morning southeast of I-55.

&&

.DISCUSSION...
Issued at 250 PM CDT Sun Jun 2 2024

Through Monday Night:

After a cloudy start to the morning, stratus has cleared for
all but the extreme southern CWA and given way to scattered
diurnal cumulus this afternoon. Weak ridging over the area along
with a surface high exiting to the east will yield dry
conditions through at least this evening and likely through
sunrise Monday morning.

Focus then turns to the early stages of developing convection
ahead of a mid-level wave across southeast Wyoming into
southeast Utah. Loosely organized upscale growth of convection
is expected to develop within increasing low-level flow and
moisture transport across Nebraska this evening, with a
potential remnant MCV lifting northeast across Iowa late tonight
into Monday morning. The antecedent airmass across the
northwest half of the CWA ahead of this MCV will be marginally
favorable for elevated convection to persist into areas west of
the Fox Valley and generally north of the Illinois River through
late morning. This scenario will be conditional upon sufficient
saturation in the LPL (900-850 hPa) fully realizing a higher
MUCAPE reservoir amid modest mid-level lapse rates. If storms do
materialize, small hail cannot be ruled out.

Veering low-level flow tonight through Monday will draw a
relatively moist airmass northward through the Mississippi
Valley, with surface dew points likely nearing 70F in portions
of the western CWA by late Monday afternoon. A generally
uncapped and moderately unstable airmass owing to the higher dew
points will support convective initiation with any notable
forcing mechanism Monday afternoon before the remnant wave
across the central Plains shears out across the western Great
Lakes late Monday evening into the overnight hours. Meanwhile
potential residual MCS activity across the southern Great Plains
will near from the southwest Monday night. Per recent CAM
guidance, potential initial foci of convection during the mid-
afternoon to early evening range from lingering vort arcs on the
tail of the morning MCV to stalled outflow boundaries. So while
development is far from certain, steep mid-level lapse rates in
a weakly sheared environment suggest that any initial cells
would produce pulse-like characteristics, with resultant
outflows cascading into a very messy radar representation. Any
prominent cells or congealing cold pools will be capable of
producing strong to locally severe wind gusts. Furthermore,
modest SW low-level flow within weak mid-level flow combined
with PWATs up to around 1.8" indicate weak/NE backward
propagation vectors supportive of localized flash flooding. If a
more expansive growth of convection occurs by early evening,
primary concerns will turn to flooding through the remainder of
the evening before convection dissipates or shifts east through
the overnight hours.

Kluber


Tuesday through Sunday:

Tuesday`s evolution remains unclear at this range, with
numerous disturbances and potentially convectively-augmented
vorticity maxima traversing the region (or very nearby). It
seems like most of the morning may end up mainly dry in the wake
over Monday`s convection. That said, there`s at least some
signal across the guidance suite that a coherent mid-level
impulse will lift north or northeastward across the region
towards midday or during the afternoon. This feature looks like
it may be associated with the impulse currently sweeping across
northern New Mexico, and will likely get several vorticity
boosts through mid-level latent heat release processes as
several rounds of strong to severe convection develop across the
ArkLaTex through Monday evening. It`s no surprise that there`s
a huge spread with this feature`s location come Tuesday morning,
although it looks like it`ll end up somewhere in our vicinity.

The background/synoptic kinematic field is not overly
supportive of organized convection Tuesday afternoon, with
mainly multicell/pulse-type convection favored with meager deep
layer shear. However, a well-developed/intense MCV would
certainly locally-augment the low and mid-level wind field and
could yield a threat for more organized strong to severe storms,
and something that`s hinted at by some extended hires guidance.
For now, saw little reason to make alterations to the NBM-
delivered likely PoPs during the afternoon given an only weakly-
capped airmass during the day and decent agreement that at least
scattered convection will develop. Whether a severe risk
accompanies this activity will be tied to the evolution of
upstream thunderstorm activity today and tomorrow.

Turning ahead to Tuesday evening and overnight, the lead
impulse will be exiting to the northeast, with a much stronger
short-wave impinging upon the northern Plains and upper Midwest.
Extensive convection out ahead of the system`s cold front west
of the MS River will translate southeastward into a less
supportive environment (diurnal decrease in instability and
marginal wind shear). Thus following the probable dissipation of
afternoon pulse convection, it`s a bit unclear how robust
upstream storms will be as they approach from our west in the
late evening and overnight. While we do have PoPs peaking in the
60-80% range given the overall global model and ensemble member
signal for convection during this time, there conceptually
appears to be a path toward lower convective coverage surviving
eastward overnight.

The cold front will sweep across the area Wednesday morning.
Unless overnight convection dissipates much quicker and sets up
for destabilization ahead of the front by the mid to late
morning across much of the area, it appears that areas southeast
of I-55 have the best chance for any renewed development ahead
of the front, or intensification of existing showers and
embedded thunderstorms pushing eastward. The rest of Wednesday
will likely be drier, breezy, and increasingly sunny, with
seasonable temperatures in the upper 70s to lower 80s.

Deep upper level low pressure from the aforementioned strong
mid-week short-wave will then become quasi-stationary from the
northern Great Lakes across northeastern North America Thursday
through the weekend. This will bring a period of near to
slightly below normal temperatures (highs in the 70s away from
any lake cooling, primarily dry weather, comfortably low
humidity (daytime dew points in the 40s and 50s), and breezy
daytime conditions.

Carlaw/Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 646 PM CDT Sun Jun 2 2024

Forecast concerns include...

Chance of thunderstorms Monday afternoon/early evening.
Gusty south/southwest winds Monday.

Light easterly winds will become southeasterly this evening and
south/southeast Monday morning. Speeds will increase into the
10-15kt range during the mid morning hours with some higher
gusts likely. Wind directions are expected to turn to the south/
southwest Monday afternoon with gusts into the mid 20kt range.
Wind directions are somewhat uncertain Monday evening, but
speeds are expected to diminish under 10kts.

There will likely be some decaying thunderstorms or showers
across far northwest IL after daybreak Monday morning. There
remains quite a bit of uncertainty regarding coverage. Current
prob mention for showers at RFD seems reasonable for now. While
scattered thunderstorms are possible Monday afternoon into
early Monday evening, there remains uncertainty for coverage,
location and duration. While tempo mention will likely be needed
with later forecasts, maintained prob mention for a longer time
period when thunder will be possible at the Chicago terminals.
Its possible that the decaying showers noted above will redevelop
into thunderstorms by early afternoon, likely west of ORD/MDW
and that activity moves across the terminals by late afternoon.
cms

&&

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

&&

$$

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