Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 112025
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
325 PM EST Thu Jan 11 2018

.SYNOPSIS...
Issued at 313 PM EST Thu Jan 11 2018

A winter storm will bring a mix of precipitation to the forecast
area tonight into Friday, with freezing rain, sleet both possible.
Mixed precipitation will change over to all snow from northwest to
southeast as a cold front moves through tonight, with snow
gradually tapering off by Friday afternoon and evening. Expect 1
to 3 inches of snow and minor ice accumulations. Both the Friday
morning and evening commutes will be impacted. See the latest
winter weather statement for details.

&&

.SHORT TERM...(This Evening through Friday)
Issued at 313 PM EST Thu Jan 11 2018

...Wintry Mix of freezing Rain, Sleet, and Snow Expected...

Headline Decision: Winter Weather Advisory for all counties in the
CWA. See the latest winter weather statement for details on timing,
etc.

Well we`ve finally reached decision time. Thankfully, models are
still in agreement with regards to keeping the axis of heaviest
precipitation to our east. That being said, we still have a
winter weather situation on our hands with the wintry mix expected
tonight, and the transition to snow by late Friday morning. Snow
will continue through early afternoon in the west, and by the
evening in the east. Lake effect snow will develop with north-
northeasterly winds in the wake of the system Friday afternoon
into the remainder of the period.

The real tricky aspect: We`ll only have a short window of freezing
rain/sleet, up to about 2-3 hours for most locations. How much of
this will be freezing rain before it turns to sleet/snow, and how
much ice? From latest model runs, thinking it will be brief enough
that we won`t have more than 0.10" of ice accumulation...and this is
probably a higher-end scenario because we will could see a greater
mix of sleet than what we have in the forecast.

Adding to concerns, the 12Z NAM develops a bullseye of QPF over
our east-central CWA in response to the enhanced forcing in the
right entrance region of a strengthening 300MB Jet between 9-15Z,
which stretches over northern Lower Michigan/Ontario/Quebec. The
enhanced upper level divergence works to tilt our trough
negatively and contract (strengthen) the frontal zone across our
area. Looking at a cross section through the frontal zone, we see
a brief period of decent instability/CSI. If it occurs, this will
favor the development of heavier bands of snow, which supports the
idea of the NAM`s increase in QPF (including the FWA area).
Overall, however the time the ingredients come together is pretty
short-lived, and don`t expect too much in the way of additional
ice accumulations beyond those forecasted at this point.
Furthermore, thinking it will largely be more snow/sleet than any
freezing rain at the times of greatest instability. In the end,
put 2-3" snow in the forecast for the eastern half of the advisory
given the potential.

Adding to concerns, observations of the impending cold front rapidly
progressing across IL shows a large temperature gradient and sharp
wind shift to the northwest. Temperatures across eastern IL are in
the upper 50s to around 60F, but behind the front they quickly drop
to around 15-20F...which brings the concern for a flash-freeze
scenario. With recent snowmelt/ongoing rain, this brings the slick
road concern to the forefront (regardless of how much freezing rain
falls).

Overall, expect only 1-3" of snow accumulation as forecast
soundings suggest riming and low snow ratios will probably cut
down snow totals. Icing will be less than 0.1" total.

If you must travel tonight or Friday...DRIVE SLOW ON ICE AND
SNOW.

&&

.LONG TERM...(Friday night through Wednesday)
Issued at 412 AM EST Thu Jan 11 2018

Friday Night through Wednesday

Lake effect snow band will be underway across portions of NW
Indiana, likely somewhere around the Porter/LaPorte county area at
the start of the period. This band will transition slowly east with
time Sat into Sat eve before trying to transition back westward.
Have increased pops to likely Sat-Sun AM and added about an inch
of accumulations each 12 hour period. Potential exists for more
than shown, but given transitory nature and challenges with final
evolution of east coast sfc low will keep rather general.

Lake effect band will finally shift east and out Sunday afternoon as
the flow becomes more west and southwest in response to a piece of
the arctic upper low dropping rapidly south into the upper Plains
and then edging east into Tuesday. Likely to categorical pops are in
place for Sunday night into Monday with at least some light
accumulations for everyone. Lake response kicks in behind the low as
reinforcing shot of cold air arrives and slowly moderates into mid
week.

In terms of temperatures, while not as bitter as the last cold snap,
highs will generally only be in the teens to lower 20s through the
period with overnight lows in the single digits above (and possibly
below) with the coldest period likely Tues to Weds time frame behind
the clipper.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1157 AM EST Thu Jan 11 2018

Winds 15kts gusting to 25 kts expected throughout the forecast
period with southerly flow at the start shifting to northwesterly
after midnight with the approaching winter system. Precip moves
into TAF sites by this evening starting as rain and then after
midnight transitioning to freezing rain and sleet starting from
west to east. Then to all snow by 08z - 10z. Flight conditions at
the start of the forecast period will be MVFR but then deteriorate
down to IFR when precip begins.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 3 AM to 7 PM EST Friday for INZ007-
     009-018-025>027-032>034.

     Winter Weather Advisory from 10 PM EST /9 PM CST/ this evening
     to 1 PM EST /noon CST/ Friday for INZ003>006-008-012>017-
     020-022>024.

MI...Winter Weather Advisory from 3 AM to 7 PM EST Friday for MIZ080-
     081.

     Winter Weather Advisory from 10 PM this evening to 1 PM EST
     Friday for MIZ077>079.

OH...Winter Weather Advisory from 3 AM to 7 PM EST Friday for OHZ001-
     002-004-005-015-016-024-025.

LM...Small Craft Advisory until 4 AM EST Saturday for LMZ043-046.

&&

$$

SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...Fisher
AVIATION...Heidelberger


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