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254
FXUS63 KLOT 080602 CCA
AFDLOT

Area Forecast Discussion...CORRECTED
National Weather Service Chicago/Romeoville, IL
102 AM CDT Wed May 8 2024

.KEY MESSAGES...

-- Changed Discussion --
- A 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
-- End Changed Discussion --

&&

.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 /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1259 AM CDT Wed May 8 2024

Key Aviation Messages:
- Wind shift from SW to E early this afternoon
- Scattered SHRA tonight (20% chance of elevated TS), with MVFR
  ceilings developing toward sunrise Thursday

VFR conditions are expected through at least this evening, with
generally FEW/SCT mid-level clouds. SW winds under 10 knots
early this morning may become somewhat VRB under 5 knots as a
weak surface ridge crosses northern Illinois. Winds are then
expected to shift E around 10 knots with lake-enhanced boundary
ahead of a surface low nearing central Missouri. E to NE winds
10-15 knots are then favored through the remainder of the
period.

A band of SHRA and perhaps isolated elevated TS is expected to
drift northward over the terminals late this evening and
overnight. TS potential of around 20% chance remains low enough
to keep TS mention out of the TAF this far out, but future TAF
updates may require introduction of TS if expected SHRA coverage
also increases. Otherwise, MVFR ceilings should advect into the
area late tonight, with some IFR ceilings possible Thursday
morning beyond the current forecast period (12Z Thursday).

Kluber

&&

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

&&

$$

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