593
FXUS63 KLOT 101046
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
546 AM CDT Tue Sep 10 2024

.KEY MESSAGES...

- Mid summer-like daytime temperatures through at least Thursday.

- Persistent stretch of dry conditions will yield an increased
  threat for grass and brush fire starts, especially south and
  western locales.

- Most of the appreciable rain with Tropical System Francine`s
  remnants should remain south of the area, with chances of
  widespread beneficial rain appearing low through the weekend.

&&

.DISCUSSION...
Issued at 319 AM CDT Tue Sep 10 2024

Through Thursday Night:

Expect well above normal daytime temperatures away from Lake
Michigan, though dry air aloft and dry ground feedback should
continue to lend to dew points mixing out and keeping afternoon
RHs low. The most aggressive mixing out of dew points (lower-mid
40s in spots) should occur today and then generally upper
40s-mid 50s Wednesday and Thursday afternoon. Forecast highs are
in the 80-85F range today and then mid-upper 80s on Wednesday
and Thursday. Modest lake cooling should hug the Illinois shore
today and then a bit more appreciable lake breeze cooling
(highs limited to upper 70s-lower 80s) will likely be confined
to the Illinois shore on Wednesday and then the entire shoreline
on Thursday.

The recent dryness, continued evaporation, and warm temps will
result in a threat for grass and brush fire starts despite
generally light winds. Aforementioned dryness will continue to
be favorable for large diurnal temperature spreads outside of
the Chicago urban heat island, though overnight lows will also
gradually trend upward the next few nights.

Smoke aloft (up at about 10-15kft AGL) from western North
America wildfires will vary in thickness, with the HRRR Smoke
forecast suggesting that skies may become more milky/opaque
tonight and Wednesday.

Castro

Friday through Monday:

Francine is expected to move ashore in Louisiana on Wednesday
and then slowly lift north. Strong mid-level ridging over the
Great Lakes should act as a roadblock from northward progress of
the remnants. Meanwhile, expansive surface high pressure from
the northeast back across the Great Lakes will result in drier
easterly low-level trajectories.

The initial push of showers on the outer edge of the weakening
circulation may make it into far southern areas (south of US-24)
for a time on Friday, and then most if any additional showers
will likely become suppressed south for most locales through
Saturday night. Once again, the Canadian global model and its
ensemble (CMCE) remain a notable northerly outlier with a more
phased and much more aggressively farther north solution. With
the remainder of the guidance strongly favoring the suppressed
south solution, trended PoPs lower and will message a primarily
dry forecast through Saturday.

Some of the moisture could eventually work north on Sunday to
support widely scattered showers in spots and perhaps a couple
thunderstorms. However, with upper support lacking, weak mid-
level lapse rates, and limited destabilization, the prospects
for widespread beneficial rain appear low at this vantage point.
Low precip chances should then generally trend downward again
into next work week. Some guidance suggests daytime temperatures
could be warmer than offered in the official forecast, which is
already solidly above normal through the period away from the
lake.

Castro

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 546 AM CDT Tue Sep 10 2024

There are no significant aviation weather concerns.
Light/variable winds will become southwesterly through this
morning and afternoon around 10 knots before diminishing
quickly this evening evening. A smoke layer between 150 and
FL250 will continue, with some indications it will thicken a bit
later this afternoon and tonight.

Carlaw

&&

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

&&

$$

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