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303
FXUS63 KLOT 181900
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
200 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

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- 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.
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&&

.DISCUSSION...
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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
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&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1229 PM CDT Wed Sep 18 2024

There are no aviation weather concerns through the 18Z TAF
period.

Near-5kt winds should favor a S to SE direction through mid-
afternoon, but could vary at times. A shift to easterly is
expected at the Chicago sites later this afternoon. Confidence
is low on the timing of this shift, but best guess at the moment
is around 20Z at both ORD and MDW. Light and variable winds can
be expected tonight. Confidence is rather low on wind direction
during the day tomorrow. It`s looking like we`ll establish a
near-southerly or SSW direction when winds start to build a bit
around mid-late morning. A shift to SE is then expected to reach
MDW as early as mid-afternoon and looks to hold off until the
evening to reach ORD. Speeds during the day should largely
remain below 10 kt. Expect VFR throughout the period.

Doom

&&

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

&&

$$

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