440
FXUS63 KLOT 081900
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
200 PM CDT Sun Sep 8 2024

.KEY MESSAGES...

- There is an expected warming and drying trend that will
  feature summer-like temperatures through the week.

&&

.DISCUSSION...
Issued at 200 PM CDT Sun Sep 8 2024

Mid level water vapor imagery shows a clear cinnamon roll low
spinning over southern Quebec east of a ridge over the Great
Plains, keeping northwesterly flow aloft over the Western Great
Lakes. With wildfires burning in Western Canada, this has
translated in upper-level smoke moving over northern Illinois.
The HRRR smoke model has the thickest plume moving overhead
later today and through Monday morning while staying safely
above the ground. As a result, the forecast was updated to
mention partly cloudy skies through at least Monday afternoon to
account for the smoke mixing in with the mid level stratus and
higher cirrus clouds aloft. Temperatures are expected to still
cool through the partly cloudy skies overnight, with lows
tomorrow morning in the upper 40s and low 50s.

As the upper level ridge grows and drifts east through the
week, surface high pressure will develop and park over the
region. Guidance projects a weak embedded wave with a slug of
upper-level moisture ejecting out of the Plains around Tuesday,
but with a lack of instability, it should only translate into
some increased cloud cover. As 850 mb temperatures gradually
move into the upper teens (Celsius) through the week, surface
temperatures will be on the rise for more summer-like conditions
with highs in the upper 80s and isolated areas near 90. The one
bit of uncertainty is how models are handling dew points.
Depending on the degree of mixing each afternoon, there is the
potential for afternoon relative humidity values to dip into the
sub-20 percent range especially during the Monday to Wednesday
timeframe. Dew points were adjusted down, but taking a look
upstream at current obs of dew points in the 30s in southern
Missouri, there is a concern that the dew points/RHs on Tuesday
and Wednesday are still too high. Relatively light winds
(speeds generally in the 10 to 15 mph range) should temper the
overall fire weather threat, although drying fine fuels may
become receptive to increased grass/brush fire starts through
the end of the week.

There is also an eye being kept on the Gulf of Mexico and the
potential development of a tropical system this week. Long range
models have whatever develops moving northward toward the Ohio
River toward the end of the week, though differ on how far
north it can actually reach. For that reason, felt no reason to
change the slight (15 to 24 percent) chance for some showers
advertised by the NBM.

DK

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1230 PM CDT Sun Sep 8 2024

There are no significant aviation weather concerns through the
current TAF period.

Maintained a SCT deck aloft as smoke from Canada is expected to
move southward over the region through Monday. Winds will
remain out of the west with some intermittent gusts in the 15-20
knot range this afternoon. But with a lack of persistence it
was left out of the TAF. Quieter conditions overnight as winds
pick up marginally again Monday afternoon. VFR conditions
through the period.

DK

&&

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

&&

$$

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