478
FXUS63 KIWX 072008
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
308 PM EST Fri Nov 7 2025

.KEY MESSAGES...

- More widespread rain is expected Saturday night into early
  Sunday, especially north of US-24. Rain may mix with or change
  entirely to snow Sunday morning with some accumulations
  possible.

- Turning sharply colder Sunday night with lake effect snow
  developing Sunday night through Monday. While details remain
  uncertain on the timing, placement, and intensity of these
  lake effect bands, the potential exists for several inches of
  accumulation in favored corridors from Sunday night through
  Monday.

- Temperatures will trend back to seasonable temperatures by the
  end of the week and have a good chance to reach 40 degrees on
  Tuesday. As a result, snow should be able to melt.


&&

.DISCUSSION...
Issued at 257 PM EST Fri Nov 7 2025

Within this positive Pacific North American (PNA) pattern, wave
breaks in the eastern Pacific enhance a ridge across the Western
CONUS and this helps to send shortwaves down into the trough to
continue to dig (enhance) the trough across the Eastern CONUS.

One such shortwave departed the area this morning and its associated
cold front ushered in drier air behind the morning showers, but a
secondary cold front comes down the lake and the moisture advection
out in front along with an area of instability allows for a chance
for a brief period of lake enhanced rain showers tonight that end
early Saturday AM. That shortwave quickly leaves the vicinity of
Lake MI before the next wave arrives on the Pacific Jet along the
thermal gradient left behind. Behind the departing shortwave early
Saturday morning, surface winds turn more eastward and this is
expected to push the area that receives lake enhanced rain farther
westward away from the area by Saturday morning. Despite the fact
that by Saturday morning, two cold fronts have swung through, low
level temperatures stay fairly similar through the day Saturday as
our next low pressure system approaches along this gradient for
Saturday afternoon. This provides additional rain to the area into
Sunday morning before it begins to mix with and potentially
changeover to snow in a few spots (with wet bulbs dropping to
freezing) Sunday morning into the afternoon. All told, these systems
provide an additional 0.25 to 0.5 inch rainfall to the area between
this afternoon and Sunday morning.

An upper low in south-central Canada pinwheels another shortwave
down Lake MI and this is what finally sends the cold air southward,
behind the prior system as it departs. Just to show this cold, 850
mb temperatures 00z Saturday evening start at -1C over SBN and
decrease to -8.5C Sunday evening with a 1040 mb high pressure
system centered over the Dakotas. There is still quite a bit of
uncertainty with the modeling of this lake effect event. On
southerly winds, the lake effect snow band begins to move into
the LaPorte area between 4am and 9am (wide time range because of
the uncertainty). Trajectories become more northwesterly
through the day Sunday so expect the banding to pivot eastward.
The main very vigorous vort max and associated upper low arrives
Sunday night, but there`s still quite a bit of uncertainty in
the track that that vort max takes. The 00z ECMWF/GEM kept the
upper low west whereas the 6z GFS/NAM were farther east. It is
interesting to see the 12z NAM/GFS come in farther west with the
upper low energy in between these two camps. Lake induced
instability increases from 250 J/kg of CAPE to 850 J/kg of CAPE
with Delta Ts reaching 25 to 35 degrees and this increases the
chances for heavier rates downstream and a possible mesolow (at
least ECMWF/GEM) formation. Heavier snow rates making it inland
will depend on whether or not there`s breaks in the banding to
make it more cellular and allow drier air to entrain in. This
time of year, given the warmer roadways, it probably is going to
take heavier snow rates to overcome melting despite
temperatures falling below freezing Sunday night. It`ll be
interesting to see how cloud cover plays a role in warming of
high temperatures on Monday, if CAA can keep the area below
freezing or not, and whether or not melting can occur Monday
during the daytime. One interesting thing is that SBN has had
low temps within 5 degrees of freezing as far back as 10/30 so
perhaps that could play a role in if snow could stick or not.

Those freezing and above temperatures on Monday potentially causing
melting and standing water could allow for some refreezing as
temperatures drop back down into the 20s, but we`ll have to see how
much moisture/snow is left over on roadways. As the trough pivots
eastward, it is expected that wind gusts pick up and this should
help augment drying so it is possible that refreezing is a non-
hazard. Within the upper northwest flow, a shortwave does traverse
the southern part of Lake MI Tuesday morning and so models appear to
pump out some light precipitation on low level southwest winds.
Temperatures are expected to warm back up above freezing, with upper
30s to low 40s forecast for highs on Tuesday as WAA ensues.

Height rises take over as soon as Monday night, which could affect
the chances for Tuesday`s precip. but sfc high pressure to the south
noses in providing dry weather through the end of the week. Highs
trend back toward seasonable temps as well.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1257 PM EST Fri Nov 7 2025

The primary low level moisture axis with a lead short wave that
brought rain to the region today has shifted east of the area.
Some lingering MVFR cigs on 1500-2500ft will likely persist at
KFWA through 19Z or 20Z before dissipating. Another short wave
will allow a secondary stronger cold front to drop across the
southern Great Lakes overnight. This should allow some cold
advection stratocu to work back south across the terminals late
tonight into Saturday. Bases are expected to be primarily VFR,
but cannot rule out pockets of cigs 2-3k feet at KSBN for a time
Saturday morning. Gusty westerly winds behind initial front
this afternoon will subside toward the 22Z timeframe. Winds will
veer to the northeast for Saturday in response to weak sfc high
drifting across southeast Ontario and next sfc low development
across northeast Kansas. This Kansas low will bring next good
chance of rain late Saturday afternoon and especially by
Saturday evening.

&&

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

&&

$$

DISCUSSION...Roller
AVIATION...Marsili