222
FXUS63 KLOT 190528
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1228 AM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Summer-like daytime warmth continues through Saturday (last
  day of astronomical summer!)

- Potential for isolated to widely scattered showers and
  thunderstorms late Thursday night into Friday with a cold
  front.

- Chances for more widespread rain return Sunday into early next
  week, though extent of drought relief is uncertain.

&&

.DISCUSSION...
Issued at 200 PM CDT Wed Sep 18 2024

Through Friday:

The broad area of high pressure over the eastern Great Lakes
will continue to promote dry and summer-like conditions through
Thursday. Therefore, expect high temperatures to once again top
out in the mid to upper 80s Thursday afternoon with overnight
lows in the mid-50s to lower 60s. Additionally, the combination
of dry conditions and warm temperatures will also allow dew
points to mix down into the lower 50s on Thursday resulting in
afternoon humidity values in the 25 to 35 percent range. Given
that winds are expected to be light (speeds generally under 10
mph) the threat for fire weather concerns appears to be low, but
caution should be exercised with any burning due to dry fuels
which could yield quick fire starts.

Heading into Thursday night, rain chances will gradually begin
to increase from west to east as a cold front, currently over
the central Plains, moves in. However, the antecedent dry
conditions and aforementioned dew points do look to limit the
coverage of showers, especially with eastward extent, as the
drier air will be working against the limited moisture along the
front. That said, there could be some locations that don`t pick
up much in the way of rainfall. Though, rainfall totals are
only expected to be in the 0.10 to 0.20 inch range for those
that do see rain; which will do little for our worsening
drought. Additionally, the limited moisture also looks to hamper
the destabilization Friday afternoon which means that thunder
coverage will likely be very isolated but did maintain a slight
chance (around 20%) mention for thunder in the off chance a more
robust core can materialize. Nevertheless, showers and any
storms are expected to conclude by Friday evening as the front
exits to the east.

Yack

Friday Night through Wednesday:

In the wake of Friday`s front, a slightly drier air mass is
expected to filter into the area Friday night into Saturday.
That, in combination with modest height rises in the wake of
Friday`s weak shortwave will keep rain chances low and mainly
sub-mentionable Friday night through Saturday evening. By
Saturday night and Sunday, a longwave trough will emerge east
of the Rockies across the Plains states. A weaker, more subtle
shortwave trough may precede this larger trough and could bring
with it a threat of some showers and possibly isolated storms
later Saturday night into Sunday, but there is spread in
guidance in the handling of this more subtle feature leading to
lower than average confidence. While there is some threat for
beneficial rainfall this weekend, it is also plausible that many
areas squeak out a mostly rain-free weekend.

The Plains trough is progged to phase with northern stream trough
as they both progress east into the Mississippi Valley Sunday
night into Monday. While by no means a slam dunk with timing and
magnitude of phasing still uncertain, this system could be the
area`s best chance of some much needed rainfall across most of the
area through Monday night (40%+ chance PoPs).

Friday night will be relatively cool with lows in the mid-upper
50s outside of Chicago (low-mid 60s in the city). Daytime high
temperatures will remain unseasonably warm this weekend with
highs in the 80s away from the lake on Saturday (with low
humidity due to dew points mixing out into the 50s), and mid
70s to lower 80s on Sunday (with higher humidity/dew points in
the 60s). In the wake of Sunday night/Monday trough, somewhat
cooler/more seasonable temperatures (highs in the 70s) are
expected during the early to middle part of next week for the
first work week of astronomical fall (autumn equinox is at 7:43
AM CDT Sunday).

Castro/Izzi

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1228 AM CDT Thu Sep 19 2024

Forecast concerns include...

Lake breeze/southeast wind shift mid/late afternoon.
Chance of showers early Friday morning with thunder possible.

Light/calm winds overnight will become south/southwest after
daybreak with speeds into the 6-10kt range. A lake breeze will
develop by early afternoon and there is uncertainty for how far
inland the lake breeze will move, likely reaching both ORD/MDW
though only medium confidence for timing, which could be late
afternoon at ORD. Even if the lake breeze doesn`t make it to ORD
or MDW, winds will shift back to southeast by early this evening
across the entire area. Winds are then expected to slowly turn
back to the south/southwest early Friday morning.

There will be a chance of showers early Friday morning, likely
just after 06z at RFD and in the predawn hours for ORD/MDW.
Opted to add prob mention for the 30 hour ORD/MDW tafs though
whatever precipitation does develop may be dissipating as it
moves across northeast IL. There is also a small chance for an
isolated thunderstorm, with the best chance, though still low,
across northwest IL and at RFD.

Fog potential early this morning looks rather low with perhaps
the best chance across far northeast IL and into southeast WI.
Not planning any fog mention for the terminals at this time. cms

&&

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

&&

$$

Visit us at weather.gov/chicago