264
FXUS63 KLOT 091040
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
540 AM CDT Thu Oct 9 2025

.KEY MESSAGES...

- A few showers possible late Friday afternoon into Friday
  evening, otherwise dry weather through the upcoming weekend.

- More seasonable temperatures expected through the weekend.

&&

.DISCUSSION...
Issued at 311 AM CDT Thu Oct 9 2025

High pressure over the Great Lakes and southeastern Canada
early this morning will move east to New England later today.
Easterly winds and seasonably cool air on the back side of the
high will result in some lake effect stratocumulus blowing into
NE IL early this morning. As the high shifts farther east, winds
will turn more southeasterly and the marine layer will
stabilize, so even areas near the lake will turn sunny by later
this morning.

Tonight should remain clear, but with a bit more of a gradient
than this morning, so frost threat tonight appears lower tonight.
Northwest Indiana still stands the best chance given their
closer proximity to the departing high, but seems to be a more
marginal set-up, so was planning to hold off on adding frost
into the grids/forecast for tonight and let the day shift take
another look.

Attention for Friday and Friday night turns to the compact upper
low seen on water vapor imagery early this morning over northern
Saskatchewan. The operational GFS and ECMWF have been, and
remain, in reasonably good agreement in dropping this small,
but potent, upper low quickly southeastward into the upper Great
Lakes by Friday evening. Sfc low is progged to be tucked
closely underneath the mid-upper low with a cold front trailing
southwest across the northern IL by early Friday evening. No
meaningful moisture return will take place in advance of this
front and with the brunt of the colder air aloft likely to
remain to our north, it seems the most likely scenario is that
the front should move across the area with little precipitation.

However, the NAM digs the upper low farther south and as is
typically the case with the NAM, it is more moist in the
boundary layer. Thus the NAM does suggest that there could be
some showers with the front Friday evening. The NBM came in with
just some low chance pops over our northeastern CWA and given
the small chance that the NAM were to verify, and the ECMWF and
GFS were to trend farther south, there could be some showers
into mainly our eastern CWA. So while the chances appear low,
some showers cannot be ruled out over mainly our eastern CWA.

Guidance continues to depict a fascinating and fairly complex
evolution of things over the weekend into early next week.
First, our potent upper low is progged to stall out over the
eastern Great Lakes this weekend before eventually phasing with
a developing extratropical cyclone that is progged to move up
the East Coast. With the upper low progged stall out and spend
the weekend in the eastern Great Lakes, that will slow the
eastward progression of the upper ridge and delay our progged
warm up.

NBM has been gradually trending cooler for high temps for over
the weekend, but is still notably warmer than the operational
ECMWF, GFS, and GEM would support. There is still a 40 degree
spread in the GEFS for Sunday`s temps, ranging from the warmest
member (lower 80s) to the coldest member (lower 40s). While the
spread among the extremes is still large, there vast majority
of the members are tucked closer the to mean and median, which
have been trending progressively cooler with time. It seems
likely that there will be easterly flow off the lake Sunday and
with marine layer temps likely in the lower 60s, felt comfortable
lowering NBM high temps over northeastern IL into the low-mid
60s for highs Sunday.

Lower than average confidence in the forecast heading into next
week as medium range models are notorious for struggling with
systems phasing and also with handling blocking patterns. Both
are progged to take place this weekend into early next week, so
there will likely be some changes in later runs in how the
pattern evolves. Given this lower than average confidence, saw
no justification to make any adjustments to the NBM guidance
beyond Sunday.

- Izzi

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 540 AM CDT Thu Oct 9 2025

VFR conditions are expected through the 24-30 hour TAF cycle.
Easterly winds less than 10kt are expected through this evening
with winds gradually becoming south late tonight. South-
southwest winds around 10kt are expected Friday morning.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Frost Advisory until 8 AM CDT /9 AM EDT/ this morning for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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