289
FXUS63 KLOT 111124
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
624 AM CDT Tue Jun 11 2024

.KEY MESSAGES...

- Scattered thunderstorms possible Thursday, some of which may
  be severe in the afternoon and evening.

- Hot/humid conditions expected early next week.

&&

.DISCUSSION...
Issued at 236 AM CDT Tue Jun 11 2024

Through Wednesday:

It will be a notably cooler start to the day with temperatures
having already dropped into the upper 40s and lower 50s with few
more hours of cooling yet to go. As a shortwave mid-upper ridge
axis and associated surface high pressure shifts to the east,
wind directions return to a prevailing southwest to westerly
direction. This will allow temperatures to readily warm back
into the mid-upper 70s today. Increasing cloud cover this
afternoon from an approaching disturbance to our west will
likely limit the degree of warming, however, and have
accordingly nudged down temperatures a bit out toward Rockford
and near the WI/IL stateline. If clouds arrive later than
expected, some spots could reach the lower 80s.

As for rain chances today, vertical profiles suggest the lower-
levels will remain quite dry through most of the day. A lead
axis of showers may remain mostly in the form of virga late
afternoon/early evening, with perhaps a few sprinkles or stray
shower (20% chance). With time the column will attempt to
saturate, potentially enough for slightly greater coverage of
showers overnight as the mid-level wave moves overhead. Any
showers that do develop likely outrun any lingering weak
instability west of the Mississippi River and have opted to
remove any mention of thunder with this update.

Wednesday will be notably warmer after the cool start to the
workweek with highs back into the upper 80s to around 90. With
hi-res guidance beginning to capture the Wednesday afternoon
period, there are indications that a lake breeze may attempt to
push inland enough to limit warming to the upper 70s/lower 80s
near the immediate lakeshore. Dry conditions are forecast
through Wednesday afternoon.

Petr


Wednesday Night through Monday:

Two primary concerns for the extended, thunderstorm chances on
Thursday and heat/humidity next week.

A cold front will be moving southeast across the upper midwest
Wednesday night. Convection is expected to develop ahead of this
front across MN/WI/IA and move southeast. There still remains
uncertainty for how much, if any, of this activity will reach
the local area Thursday morning before dissipating. The general
consensus has been that at least showers with perhaps some
thunder will reach the northwest cwa by daybreak Thursday in a
weakening phase. Chance pops across the northwest cwa seem on
track. It may be difficult to get any more specific with this
time period until trends emerge Wednesday evening.

While convective trends on Thursday may be impacted by earlier
precipitation Thursday morning, which would push the effective
front into the southern cwa, there also seems to be a trend in
the models of the main cold front possibly reaching the I-80
corridor by early Thursday afternoon. This would allow the
focus for new thunderstorms to be mainly across the southern cwa
Thursday afternoon into Thursday evening, before exiting to the
south. Severe thunderstorms and heavy rain/flooding will still
exist wherever thunderstorms develop. Blended pops for Thursday
afternoon and evening are generally in the 40 percent range and
that seems reasonable for now, perhaps too high in the north if
the southern development materializes.

High temps on Thursday may be tricky if precip/cloud cover move
further into the area Thursday morning and/or thunderstorms
develop further north than currently expected. Highs in the
upper 80s to lower 90s are possible, but also may end up a few
degrees too warm. Highs will be back into the lower/mid 80s on
Friday and Saturday, cooler near the lake.

The upper ridge will begin to build across the region Sunday
into Monday next week with high temps likely to be in the lower
to mid 90s. With dewpoints possibly into the lower 70s, heat
index values may reach 100 by Monday afternoon.

Most of the models show a chance of thunderstorms skirting the
northern cwa Sunday afternoon/evening as the ridge is building
north, but overall, Monday and Tuesday are looking dry with the
ridge possibly breaking down Tuesday night or Wednesday. With
the ring of fire nearby, forecasts this far our can often turn
out different and maintaining slight chance pops Monday
afternoon/evening seem reasonable with chance pops Tuesday
afternoon/evening. cms

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 624 AM CDT Tue Jun 11 2024

Only forecast concern this period remains a chance of showers
this afternoon into this evening. The low levels will remain
fairly dry as a weak disturbance moves across the area. There
will likely be virga/sprinkles with this system and possibly a
few showers. Continued with a dry forecast for now but some
tempo/vicinity shower mention may eventually be needed.

Calm winds to start will become southwest later this morning
with speeds generally under 10kts. A lake breeze is expected
this afternoon, but will remain near the lake in IL but will
likely shift winds to the northeast at GYY. Winds will turn
light southerly this evening and then turn back to southwest
overnight and turn westerly Wednesday morning. cms

&&

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

&&

$$

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