Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 012351

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
651 PM CDT Sat Oct 1 2022

Issued at 202 PM CDT Sat Oct 1 2022

Through Sunday night...

It`s another gorgeous early-fall day with inland temperatures
rising through the upper 60s and lower 70s with some fresh
northeasterly breezes. An amalgamation of mid level cloud cover
isn`t too far off to our north and west, however, with several
low-amplitude waves skirting the northern fringes of the 500 mb
ridge axis across Minnesota. Some of this mid deck may start to
leak into our northwestern most locales later this evening, but
we`ll continue to precipitation-free trend.

A secondary weak cold front is dropping southward, towards the UP
of Michigan and across Lake Huron. Low level moisture increases
quite a bit behind this boundary--as elucidated by an arcing area
of low stratus into southern Ontario. Guidance today has trended a
bit more aggressive with associated cloud cover pushing across
Lake Michigan tonight, likely aided by some degree of enhanced
convergence near the lake/land interface. Have beefed up sky cover
a bit through the late-morning hours to account for this although
still some uncertainty regarding how stubborn any cloud cover will
be into the afternoon. Some guidance (RAP, NAMNest) suggest we
may stay socked in through much of the day with very little mixing
under a stout subsidence inversion. Currently thinking this is a
bit too aggressive and do show afternoon clearing across northeast
Illinois. Finally, as we`ve seen the last several nights, patchy
fog is once again possible although even stronger flow around
950-975 mb may help encourage a bit more in the way of mechanical
mixing and a propensity for just low stratus. Highs tomorrow are a
bit uncertain and will depend on the expansiveness of morning
stratus. Lower 70s do look to be a good bet south of I-80, with
lower 60s near the lake.



Issued at 250 PM CDT Sat Oct 1 2022

Monday through Saturday...

Quiet, dry and seasonable conditions will continue through at
least Wednesday as the weak omega block across the CONUS,
highlighted by troughs over the northern High Plains and northeast
states and a ridge over the Great Lakes, slowly breaks down.

A strong trough originating from northern Canada will absorb the
low drifting across the northern Great Plains late Wednesday. An
associated strong cold front with a band of showers will move
across the area Thursday morning, ushering in the coldest air of
the season. 850 hPa temps as low as -5C will produce daytime temps
in the low 50s on Friday and lake effect rain showers Thursday
night and Friday into northwest Indiana. Widespread frost and
localized freeze conditions are becoming more likely for Friday
night as a strong high builds across the mid-Mississippi River



For the 00Z TAFs...

* Low confidence in potential low CIGS Sunday

Tricky forecast with respect to low cloud potential Sunday.
Earlier forecast guidance indicated stratus would be in process of
developing over Lake Huron and into eastern lower Michigan by this
time, but thus far, no development noted on satellite imagery.
GOES derived soundings don`t show much in the way of low level
moisture in this area, though given the course vertical sampling,
it is certainly plausible that it could be missing shallow layer
of greater moisture. Short range guidance continues to suggest
developing stratus, but has delayed the onset, likely playing
catch up a bit due to initialization.

Models that show the stratus often tend to show a high bias with
respect to low level moisture, lending to the low confidence in
this forecast. For now, opted to maintain the course and make no
changes to the forecast with MVFR CIGS developing early Sunday
morning and scattering out early in the afternoon. Pondered
slowing the timing of the MVFR CIGS with this TAF issuance, but
decided to watch upstream satellite trends this evening before
making any changes. Worth noting, that if low CIGS do indeed
develop, then the improvement to VFR early in the afternoon could
be too optimistic.

Planning to reassess Sunday`s low CIGS potential with the 03Z TAF

- Izzi


LM...Small Craft Advisory...nearshore waters until 3 PM Sunday.



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