429
FXUS63 KLOT 161921
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
221 PM CDT Mon Sep 16 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 /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1208 PM CDT Mon Sep 16 2024

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

SEs under 10 kt will back to more of an easterly this afternoon
at the Chicago sites as a lake breeze pushes inland. Speeds
may build closer to the 10 kt mark in the vicinity of the
boundary. Winds will go light and predominantly SE, likely
variable at times, for this evening and tonight. Expect
easterlies below 10 kt during the day on Tuesday, possibly
gusting into the teens kts in the late afternoon. VFR can be
expected throughout the period.

Doom

&&

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

&&

$$

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