236
FXUS63 KLOT 170530
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1230 AM CDT Tue Sep 17 2024

.KEY MESSAGES...

- Hot and dry conditions continue this week.

- Long-range models advertise a pattern shift during the last
  week of the month with a return of chances for rain. Time
  will tell if such a pattern change occurs.

&&

.DISCUSSION...
Issued at 221 PM CDT Mon Sep 16 2024

A stretch of incredibly quiet and dry conditions continues, with
expanding drought conditions across the area.

Regional low-level water vapor imagery this afternoon shows the
extent of an incoming plume of exceptionally dry lower-
tropospheric air, with brightness temperatures nearing 0 C. Model
guidance indicates dewpoints at 700 mb nearing -40 C, and this
appears to be corroborated by recent AMDAR soundings. This wedge
of dry air is forecast to linger overhead through about Thursday
as it will become caught between the tropical circulation in the
vicinity of the Carolinas and a digging/amplifying upper low
across the Great Basin. Based on how surface dewpoints are
responding across northern Indiana within the core of the driest
part of this airmass, have undercut blended guidance dewpoints
through Thursday afternoon, although not quite to the values
advertised by the HRRR/GFS which continue to show general low PM
dewpoint biases. Thankfully, light winds will preclude more
appreciable fire weather concerns. High temperatures will be a
degree or three "cooler" tomorrow compared to today as thickness
values decrease a bit.

Global/coarse-resolution guidance remains in good agreement
towards the end of the week, suggesting that increasing west and
southwesterly low and mid-level flow will begin to "fold over" the
higher theta-e airmass that`s been collecting across Iowa into our
area during the Thursday-Friday time frame. A modest increase in
low-level warm advection is forecast to develop across eastern
Iowa and far northwest Illinois Thursday night into Friday, and
with this, some signal for light QPF across our I-39 locales is
evident in today`s 12z runs. That said, forecast soundings
across our area suggests any activity that does develop during
this time frame will probably tend to fizzle with eastward
extent, and have capped any PoPs to slight chances across our
northwest locales with this in mind.

Beyond this into the weekend and next week, prospects for
widespread, soaking rains continue to look pretty slim as the
deepest moisture and more active southwesterly flow looks to
remain just to our west.

Carlaw

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1230 AM CDT Tue Sep 17 2024

No significant forecast concerns through the period. Light east
winds will likely become calm for many locations early this
morning then increase into the 5-8kt range mid/late morning. A
lake breeze will move through the Chicago terminals this
afternoon with speeds likely around 10kts. Easterly winds will
diminish to 5kts or less this evening, possibly becoming light
and variable by early Wednesday morning.

Some shallow ground fog or patchy fog may develop early this
morning and again late Tuesday night into Wednesday morning.
Favored areas for early this morning appear to be across far
northeast IL into southeast WI. Not expecting anything
widespread nor at the terminals. cms

&&

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

&&

$$

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