966
FXUS63 KIWX 172242
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
542 PM EST Fri Jan 17 2025

.KEY MESSAGES...

- A strong cold front arrives overnight into early Saturday,
  which will bring in precipitation that starts as rain and
  quickly changes over to snow. Brief, slushy snow accumulations
  up to 1" are possible.

- Dangerous cold begins filtering into the area Sunday and lasts into
  the middle of next week. Monday and Tuesday will be the
  coldest days of the season thus far with highs in the single
  digits! Wind chills as low as 20 to 25 below zero are expected
  especially Sunday night through Tuesday night.

- Depending on how frozen Lake Michigan will be, lake effect
  snow could occur from Sunday to Tuesday.

&&

.DISCUSSION...
Issued at 255 PM EST Fri Jan 17 2025

With in a broad trough across the area a low pressure area down in
the Southern Plains States and one in south central Canada interact
to provide forcing and moisture transport. Given strong warm
advection today, temperatures have able to warm above freezing with
some areas reaching the upper 30s for highs. Some diurnal trend in
temperatures exists this evening, but it appears the biggest cause
of temperature drop is dynamic/adiabatic cooling with wetbulbing.
Dew points at or above freezing in the southwest are still expected
to allow rain to be the dominant ptype. However, areas north of US-6
where precipitation arrives first will have the chance to wetbulb in
snow, although a brief period of rain is possible at the onset.
Where dew points are a below freezing farther east in the I-69
corridor to start the evening, a start time closer to 6z may allow
additional positive theta-e advection so wetbulbing may take some
time there to start snowing. Noting most roads have been able to
take some warmth and that melting has taken place so am more
confident in less icing occurring. Above freezing and marginal
temperatures as well as riming on snow are expected to lessen snow
accumulation, but wouldn`t be surprised to see places get around an
inch of snow accumulation. Better DGZ/omega cross hair is observed
early Saturday morning for a brief period and that may help to
contribute to locally higher amounts.

Behind the cold front on Saturday, expect slowly dropping
temperatures through the day with the high temp in the morning.
Saturday night, temperatures either side of 10 degrees isn`t too out
of the ordinary as we just experienced zero degrees a couple
mornings ago. The wind doesn`t really pick up until we get to Sunday
night and Monday where 20 to 30 mph gusts will become more
possible. The winds die off to some extent Tuesday and then pick
up Wednesday. 850 mb temperatures drop from -10C Saturday night
to -28C or so Tuesday and Wednesday. Those temperatures
combined with the gusty winds will allow for a period of cold
weather advisory type wind chills at or around -15F from Sunday
evening into Wednesday morning. However, an area of warm
advection is shown on models on the back side of a high pressure
system that may briefly warm things up above advisory threshold
Monday evening. The cold and wind parameters combined allow for
securely into advisory criteria wind chills, but may make
warning criteria difficult. The coldest 850 mb temperatures
come in here Tuesday and Wednesday, but the period of warm
advection may affect how cold temperatures can get even Tuesday
morning. This could make Monday and Wednesday have the coldest
wind chills. How quickly gusts pick up each of the days will
factor in as well. Given this uncertainty on which time periods
have the best days to see warning level wind chills (-25F), have
decided to stand pat on headlines for now.

Lake effect snow is expected to kick off Saturday night, but
inversion heights are shallow enough and delta Ts are low enough to
keep hazardous lake effect snow at bay. Better signals begin to
arrive Sunday morning as the upper PV energy begins to swing through
and inversion heights achieve 7000 ft and delta Ts reach 25 to 30
degrees. Differences between low and hi res guidance in terms of how
much low level moisture resides in the lowest levels which can also
impede inland progression of lake effect snow needs to be resolved
before greater confidence in higher end snow accumulations results.
Another shortwave passes through Tuesday and this may help to
invigorate lake effect snow some although GFS bufkit soundings don`t
show any noticeable uptick in LES ingredients as a result. High
pressure sitting to our southwest helps to adjust trajectories
to out of the south Wednesday and this should to shut off lake
effect snow.

For late week, an upper low becomes cutoff over southwestern CONUS
and vorticity becomes sheared out overhead. Energy to the north
approaches and that keeps a chance for precipitation possible there,
but it stays to our north keeping us out of precipitation
chances.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 542 PM EST Fri Jan 17 2025

VFR/skc will dramatically turn lower into widespread IFR
through late evening as leading moisture plume arrives and rapid
development of rain ahead of strong cold front advancing ewd
out of the plains. Relatively deep warm sector out ahead will
yield rain to start with a changeover expected toward daybreak
with the wrn flank of the precip shield. Some brief mod snowfall
likely with an inch of less accum. Otherwise LLWS present
through mid evening in the warm sector with gusty swrly sfc
winds veering nwrly by daybreak.

MVFR Sat with continued gusty nwrly winds and vigorous snow
showers invof KSBN.

&&

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

&&

$$

DISCUSSION...Roller
AVIATION...T