277
FXUS63 KLOT 220343
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
943 PM CST Thu Nov 21 2024

.KEY MESSAGES...

- Spotty non-freezing drizzle possible tonight with lake effect
  precipitation continuing across parts of northwest Indiana.

- Temperatures remaining safely above freezing through tonight
  will prevent any re-freeze issues.

- Moderating temperatures for Sunday, then turning colder again
  Tuesday through the Thanksgiving Holiday.

&&

.UPDATE...
Issued at 943 PM CST Thu Nov 21 2024

Intermittent lake effect rain showers will continue tonight, but
these will increasingly focus into our northwest Indiana locales,
and Lake and Porter counties in particular. Can`t rule out some
snow mixing in with this activity at times, but profiles are
expected to slowly warm through the overnight. Elsewhere
regional radar mosaics reveal steadily-diminishing returns as
deeper saturation and the main synoptic scale lift is
diminishing. Forecast soundings, however, reveal a fairly deep
layer of low-level moisture will remain in place tonight which
will slowly slosh eastward into tomorrow morning. With several
mid-level upstream perturbations set to meander overhead, seems
like we may see the development of some spotty drizzle
overnight. Have added a mention into the grids with this update,
although not expecting any notable impacts with temperatures
expected to remain steady or even slowly warm, and with cloud
bases generally above 2 kft, no significant visibility
reductions are anticipated.

Tomorrow: noting a developing signal for additional rounds of
drizzle/light shower activity developing, especially into the
afternoon as a subtle shortwave (near 850-700 mb) slices
southward out of Michigan. No changes to the weather grids at
this time, but will mention the potential to the incoming
midnight shift.

Carlaw

&&

.DISCUSSION...
Issued at 224 PM CST Thu Nov 21 2024

Through Tonight:

The threat for impactful winter weather has pretty much come to an
end, as temperatures have warmed safely above freezing and the
snow has mixed with or changed to light rain/drizzle. The minor
exception to this is reduced visibility in snow and patchy slush
on roads south of I-80 as of this writing. With conditions also
expected to be steadily improving in these areas, we`ll allow the
winter weather advisory to expire as planned for Kankakee, Iroquois,
and our northwest Indiana counties. Opted to cancel the wind advisory
that was in effect given continued under-performance and near
term forecast soundings suggesting gusts generally up to 40 mph
through the early evening. Sporadic gusts up to 45 mph are
probable across interior northern Illinois and perhaps briefly
near the lake this evening when flow turns more northerly. Winds
will then steadily diminish through the night.

Steady light rain will likely hang on into the early evening for
locales near and west of I-39, and also near/south of US-24. For
the rest of the area, saturation depths may increase enough to
wring patchy light rain or drizzle out of the expansive stratus
deck. Overnight temperatures will be in the mid 30s to around 40F,
so we`re still not expecting any re-freeze issues.

Castro

Friday through Thanksgiving Day:

Aside from some lingering lake effect rain showers across parts
of Porter county IN, dry but cloudy weather is expected for
Friday. Temperatures during the day should be seasonable, with
highs generally in the mid 40s. However, with continued breezy
northwesterly winds (gusting at times to 25 mph) it will certainly
feel like a chilly day. High temperatures will remain similar on
Saturday as cloud cover hangs on across the area. The notable
difference on Saturday will be the lighter wind speeds expected as
a weak surface ridge shifts into the area.

Conditions will turn warmer for Sunday as the winds shift out of
the south following the eastward passage of the weak surface
ridge, and in advance of the next surface low quickly taking shape
across the central Plains. Increasing low-level warm air
advection on these southerly winds will thus foster a decent jump
in temperatures, with highs likely topping out around (or just
above) the 50 degree mark. These mild conditions are expected to
persist Sunday night into at least Monday morning as the area
remains in the warm sector of an approaching surface low and cold
front.

Timing differences continue to be noted with the passage of the
quickly approaching surface low (and it`s associated cold front)
on Monday. In spite of this, the primary message of the weather
turning colder late Monday into Tuesday remains of high
confidence. What remains of lower confidence for Monday is our
local chances for rain with the front. Low-level moisture is
expected to gradually ramp-up along the cold front later Monday
afternoon and evening. However, with the potential for a faster
passage of this cold front during the day on Monday, the best
chances for rain could end up largely remaining to our east.
Nevertheless, with a decent amount of spread noted with the timing
of this front, we have opted to continue the low chances (15-40%)
for rain offer up from the NBM.

A cold airmass will work in over the area through the remainder of
the week. This will result in a return to highs in the 30s and
overnight lows in the 20s. Later next week into the Holiday weekend
there are also some strong signs for a period of colder conditions
as a large upper trough digs over the Great Lakes. This could
result in highs potentially remaining below freezing for a period
during the Holiday weekend. Also with increased Holiday travel
later next week, and expectation for a somewhat active weather
pattern across the central CONUS, we will have to keep an eye on
the potential for more rain and/or snow chances near the area.

KJB

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 553 PM CST Thu Nov 21 2024

Key Messages:

- Lingering light rain/drizzle this evening.

- MVFR ceilings expected through most of the TAF period.

- Gusty northwesterly winds this evening and again tomorrow.


Most of today`s precipitation has ended at the terminals, though
a couple of bands of light rain/drizzle remain in the area on
the backside of the attendant low pressure system. Some MVFR
visibility reductions will remain possible over the next few
hours with the steadiest precipitation before the last remnant
band of precipitation shifts east of GYY as the aforementioned
low pressure system weakens and progresses eastward.

While ceilings may scatter out to VFR at the Chicago metro
terminals for a few hours this evening, residual moisture behind
the low pressure system will permit MVFR stratus to fill back
in over the area later tonight and then persist through most or
all of the day tomorrow.

Lastly, northwesterly/north-northwesterly winds are still
gusting into the 20-30 kt range early this evening. Gusts should
gradually subside in both magnitude and frequency over the next
few hours, but regular gusts to around 25 kts should resume once
again tomorrow morning.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 AM CST Saturday for Winthrop
     Harbor IL to Gary IN.

     Small Craft Advisory until 10 AM CST Saturday for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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