142
FXUS63 KLOT 091019
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
519 AM CDT Mon Sep 9 2024

.KEY MESSAGES...

- Warming trend with summer-like daytime temperatures through
  the work week.

- Persistent stretch of dry conditions will yield an increased
  threat for grass and brush fire starts.

&&

.DISCUSSION...
Issued at 213 AM CDT Mon Sep 9 2024

Expansive ridging will continue to build across a large chunk of
the CONUS today. While embedded perturbations will ride the
northern terminus of this ridging, all activity of note will
remain north of the region, yielding a stretch of very dry
conditions through at least Thursday, if not even through
Friday.

Smoke from western North American wildfires looks to make a
reappearance which will result in hazy and somewhat increased sky
cover through at least the middle of the week. Through Tuesday,
HRRR smoke output suggests there`s little threat of smoke reaching
the surface, however. Finally, expecting an increased dry
ground/PBL mixing feedback, resulting in afternoon minimum
relative humidity values falling into the 20-25 percent range
(potentially locally into the teens). Light winds will curtail a
more significant fire weather threat, but with fine fuel moisture
values already dipping to around 8-10 percent on Sunday, an
increased potential for grass/brush fire starts is evident this
week.

Today, temperatures will get a roughly 10 degree boost over
yesterday`s highs as the thickness ridge axis pivots eastward
into Illinois. High temperatures will increase further
Tuesday, and then should peak on Wednesday and Thursday, at
which point a smattering of 90 or lower 90-degree readings will
be possible. The gradient flow Thursday and beyond will become
east to northeasterly resulting in persistent lake cooling, at
least across our northeast Illinois locales, into the upcoming
weekend.

Regarding any fire weather potential: continued to make downward
adjustments to the NBM-delivered dewpoints each afternoon
through Thursday. It`s still a bit unclear exactly how deeply we
mix this week, and based on recent upstream trends, the GFS and
even the HRRR have recently been too "mixy" with low dewpoint
biases noted to our south and west. We`ll get a chance to see
how things evolve a bit closer to home today, but regardless,
lowered dewpoints closer to statistical MOS and raw ECMWF
guidance which seem to be handling things a bit better. As
stated above, a significant fire weather threat is not expected
owing to generally light winds, but the very dry conditions will
nonetheless increase the potential for fire starts.

By Friday into the weekend, attention turns to what happens with
what`s currently classified as Potential Tropical Cyclone Six in
the Bay of Campeche. Guidance is in good agreement lifting a
remnant low northward into Missouri and southern Illinois on
Friday. It remains a bit unclear how the antecedent dry
conditions locally will impact northward moisture return, but it
seems likely that this will at least stunt the initial
precipitation shield`s progress on Friday, particularly as upper
dynamics generally weaken as well. For the time being, did not
make significant adjustments to the slight chance-chance PoPs
offered by tonight`s NBM Friday into the weekend, but think
there`s a play where much of Friday and Friday night could
remain dry.

Carlaw

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 519 AM CDT Mon Sep 9 2024

Another tranquil VFR period is in store. There is a western
North American wildfire smoke layer aloft roughly between 9kft
and 15kft AGL that should dissipate/exit southeast this evening.
Westerly winds around 10 kt will occasionally gust to 15-20 kt
through early this afternoon at northeast IL terminals and then
return to light south and southwest with sunset this evening.

Castro

&&

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

&&

$$

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