339
FXUS63 KIWX 111122
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
622 AM EST Thu Dec 11 2025

.KEY MESSAGES...

- 1-2" of snow is likely south of US-30 tonight with lows around
  20 and light winds.

- Very cold air is expected this weekend with lows near zero and
  wind chill values below -10, particularly Sunday morning.

- Periods of light system snow and lake effect snow are also
  expected Friday night through Sunday night.

- Warmer weather returns next week.

&&

.DISCUSSION...
Issued at 312 AM EST Thu Dec 11 2025

Residual lake effect flurries slowly winding down this morning as
winds continue to back, dry air entrainment increases, and
subsidence inversion lowers. No additional accumulation is
anticipated though scattered flurries may continue through the
morning hours. Today will be a relatively quiet weather day as we
are in between clipper systems. Current temps holding in the
mid/upper 20s under thick stratus blanket that will likely persist
through the day (though wouldn`t be surprised if there were a few
breaks). This will keep highs similar to present values of upper
20s/around 30F.

Classic clipper system then slated to zip through the region tonight
in very fast northwest flow. Midlevel shortwave is much more subdued
than the last event with precip driven by a brief period of moderate
285-295K system-relative isentropic ascent and associated tightening
thermal gradient/fgen. The problem is that this forcing is focused
well S/SW of our area with only our SW half even getting clipped by
highly elevated portions of this forcing. Narrow window of ascent (8
hours at best) and overall very stable profiles further limit
snowfall amounts in our area. Still thinking a quick 1-2" possible
south of US-30 but tightened the gradient even further with
little/no accumulation (or even PoP`s) north of there. An even
further southward shift is also possible, as suggested by some of
the latest hi-res guidance (including the 06Z HRRR), and have
lowered PoP`s even in our far southern counties. Lows tonight drop
to around 20F with light winds expected.

After another relatively quiet day on Friday, an active weekend is
expected. Arctic upper low settles into the northern Great Lakes
this weekend, bringing cold temps, gusty winds, and several chances
for snow. The initial shortwave crosses Fri night and will support
some lake-enhanced snow showers in westerly flow. Best chances for
accumulating snow will be in MI where 1-3" is possible but some very
light snow showers could clip as far south as the US-6 corridor in
Indiana. Another shortwave then arrives late Sat with another inch
or two mainly south of US-30 (though there is still lower confidence
on the exact track of this feature). This wave will mark the arrival
of truly cold air (850mb temps below -20C). Temps near zero expected
Sat night and Sun night with wind chill values -10 to -20F (coldest
Sun AM with wind gusts around 20 mph). Cold weather advisories may
be necessary. A decent lake response is also possible Sat night into
Sun given NNW flow and very high 850mb thermal differentials.
However, early indications suggest relatively low inversion heights
and a DGZ largely below the cloud-bearing layer. Much will depend on
exact flow trajectories and potential for more northerly fetch
favoring more organized, dominant band, which is difficult to
predict this far out. As of now, appears to be more of an advisory-
level lake effect snow event but this will be monitored closely in
the coming days.

We finally see a pattern shift next week with highs climbing above
freezing and rain expected in the Wed-Thu period. Cold air and snow
may still threaten the area at times but overall much more typical
Dec weather appears likely heading toward Christmas.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 622 AM EST Thu Dec 11 2025

Moisture-laden inversion will maintain stratus deck with
ceilings hovering around 3 kft through the early afternoon. Some
improvement expected during the evening as low level flow
becomes more southwesterly. Light snow will then spread across
the area late tonight associated with a weak clipper system.
Maintained PROB30 at KSBN but snow could remain just south of
the terminal. Much better chances for light snow/low MVFR
ceilings at KFWA but improvement anticipated by 12Z Friday.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for LMZ043-
     046.

&&

$$

DISCUSSION...AGD
AVIATION...AGD