320
FXUS63 KLOT 072301
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
601 PM CDT Tue May 7 2024

.KEY MESSAGES...

- Threat for any additional severe thunderstorms ending by 5-6
 PM CDT today

- Another round of thunderstorms may develop late Wednesday into
  Wednesday night, some of which could be strong to severe,
  mainly south of I-80 into central Illinois and Indiana

- Cooler with periodic showers Thursday and then Friday night
  into the weekend

&&

.DISCUSSION...
Issued at 338 PM CDT Tue May 7 2024

Tonight through Wednesday Evening:

A post cold frontal short-wave may touch off a few showers and
thunderstorms across portions of far northern Illinois through
the early to mid evening, with slight chance (~15-20%) PoPs for
this activity. Generally quiet weather is then expected tonight
into Wednesday morning, as the mid-level short wave lifts
northeast of the area and short wave mid-level ridging develops
overhead. Winds will become light to calm tonight as weak
surface high pressure slides across the area. Forecast lows
tonight are in the mid to upper 50s, locally lower 50s.

The most recent guidance has trended drier through much of
Wednesday afternoon, enabling another warm day (mid 70s to lower
80s F) despite increasing cloud cover. The exception to the
warmth once to the early afternoon will be lakeshore areas due
to winds turning onshore synoptically and aided by lake influence.

From late Wednesday afternoon through Wednesday night, another
round of showers and thunderstorms is expected to develop. Some
scattered showers may develop across far northern Illinois and
across the state line into Wisconsin in the late afternoon. More
notably, the approach of the next short-wave will result in a
gradual uptick in showers and thunderstorms to the south of I-80
prior to sunset, and then spreading northward in the evening and
overnight.

A surface low pressure wave is expected to develop along the
cold/stationary front which will trail across the southern
Plains in association with this wave, which will then propagate
northeast into the mid-Mississippi Valley by Wednesday evening.
Overall, the guidance has come into better agreement in barely
returning the front northward into our far southern CWA (south
of US-24) as a warm front by Wednesday evening. This is where
some potential may exist for surface based severe weather
threats, primarily damaging winds and hail.

Otherwise, as most of our area will be on the cool side of
the front, the main concern will be elevated hail producing
thunderstorms , some of which may become marginally severe
(hail up to 1" diameter) as mid-level lapse rates steepen
amidst supportive effective bulk shear. In addition, seasonably
high PWATs may present a localized ponding or even flooding
threat, primarily near and south of I-80.

Castro/Ratzer

Late Wednesday Night through Tuesday:

A mid-level trough extending southwest across Quebec and
southern Ontario will phase with a mid-level low over the
Missouri Valley late Wednesday night. As the phasing wave
crosses the area on Thursday, a residual low to mid-level TROWAL
combined with PWATs around 1" and a deep layer favoring warm
rain processes supports the potential for a low-end localized
band of heavy rain (1-2" totals by mid day Thursday) across
portions of northern Illinois into southern Wisconsin. Outside
of this band, scattered diurnally enhanced showers and perhaps a
few storms are expected. Much cooler conditions are in store,
with highs only in the upper 50s to lower 60s inland and lower
to mid 50s near Lake Michigan. Adding to the cool feel, northerly
winds will gust up to 25-35 mph, strongest near the lake.

After a quick-moving ridge yields dry and seasonable temps on
Friday, another upper-level low is progged to cross the western
Great Lakes on Saturday. Anomalously cold mid-level temps
shifting across the area through the day will yield scattered
showers and storms, with some stronger cores likely producing
locally strong wind gusts. Diverging solutions by early next
week with regards to handling of the departure of Saturday`s
upper low and a building ridge to the west greatly diminishes
the forecast by early next week. It appears temperatures will
trend back to above normal by the end of the period.

Kluber/Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 601 PM CDT Tue May 7 2024

Key Messages:
- Breezy SW winds easing this evening
- A few showers/iso TS dissipating N and W of ORD/MDW this
  evening, possibly impacting RFD
- Wind shift to SE/E Wednesday early afternoon
- Increasing -SHRA changes late Wednesday, better chance in the evening.
  Low thunderstorm chances (<30%)

VFR conditions have returned behind the storms this evening, and
expect initially breezy SW winds to ease overnight. Some of the
showers and storms across the Mississippi River will make some
eastward progress toward KRFD, but should dissipate with medium-
high confidence before making it to ORD/MDW.

Winds will shift southeasterly and then easterly through the late
morning into the afternoon Wednesday. Another batch of precipitation
will shift toward NE Illinois later in the day. Confidence in
thunder toward the tail end of the 30 hr TAF is still below 30
percent, but there is a decent chance for showers, with highest
confidence for occurrence after 0000 UTC, and more so after
0200 UTC.

KMD

&&

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

&&

$$

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