Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 160944

Area Forecast Discussion
National Weather Service Northern Indiana
444 AM EST Tue Jan 16 2018

Issued at 406 AM EST Tue Jan 16 2018

Mainly light lake effect snow will continue this morning over
northwest Indiana and southwest lower Michigan with an inch or two
of accumulation possible. An intense single band of lake effect
snow is expected to develop offshore later today but there is a
high amount of uncertainty with where this band may come onshore
and produce heavy snow. Due to this uncertainty, a winter storm
watch continues for later today and tonight. Accumulations of 4 to
8 inches with snowfall rates of 1 to 2 inches per hour will be
possible with the band when it does move onshore. Otherwise it
will be cold with areas south of US 30 having wind chills as low
as 10 to 15 below zero this morning. A warming trend is expected
later this week with temperatures into the 40s this weekend with
rain likely.


.SHORT TERM...(Today and Tonight)
Issued at 406 AM EST Tue Jan 16 2018

Focus squarely on complex lake effect setup for today and
tonight. This is one of the more complex and unique Lashley-
Hitchcock Type VI setups I can remember with regards to where
event begins and how it will evolve.

What we do know right now is that cyclonically long fetch will
help develop an intense band of snow this morning that will have
about everything going for it for a window from mid morning
through mid evening tonight. 925mb low and vort center will move
east early this morning allowing low level directional shear to
decrease and flow to become better aligned down entire mid lake
axis. 0-2km thetaE lapse rates show plenty of instability with
values between -1 and -2 K/km the entire way and classic sfc-
850mb delta Ts in the mid 20s as well. Inversion heights to climb
to near 10kft allowing for deeper convection to develop. Already
seeing band formation along western shore of lake and expect this
to quickly intensify this morning. The question remains where and
even when this band will come onshore later today.

Model guidance remains largely split between a western and
eastern camp for where the more intense single band will come
onshore. The lower resolution spectral models and the NAM12
largely favor the band coming onshore mid-day into Laporte county
as previously anticipated. However, the last several runs of the
higher resolution mesoscale models are persistent in bringing the
mesovortex onshore this morning but keeping the intense single
band west before it moves east late this afternoon or this evening.
A few of these hires models even keep the band well west and
weaken it considerably as it finally moves east tonight.

Regional radar mosaic and surface obs at 03z suggested the 00z
NAM12 925mb omega and wind fields had a rather good handle on
where pcpn was falling at that time but as of 09z the low level
flow has kept upstream pcpn along the lakeshore where the NAM12
omega suggested it should have moved east over the lake. Thus
trends are leaning us to favor the western solutions a little more
now but still not discounting the eastern solutions as the 06z
NAM12 remains persistent bringing band east. The combination of a
complex mesoscale setup over the southern end of the lake with a
significant lack of observational data is leading to the high
uncertainty. Radar trends over last few hours suggest several
mesolows along trough across the lake. These features are now
beginning to sink south and expect light snow this morning in the
northwest with 1 to 2 inches generally but could see a few locally
higher amounts within one of the mesovortices. A break in snow or
at least more light snow likely in subsidence region behind
mesolow until main band finally moves onshore. Latest 08z runs of
RAP and HRRR are concerning in keeping majority of plume west of
our CWA or just into western Laporte county.

Given the unusual amount of uncertainty and model spread
along with the slower arrival, have collaborated with KLOT and
decided to take the rare stance of keeping the watch going until
we can actually see the single band become more defined and get a
better handle on the movement through the early to mid morning
hours. This seemed more prudent than dropping headlines all
together or issuing an unnecessary warning or advisory. This will
be more like a short term convective situation as it unfolds today
so stay weather aware and listen for updates on this unique


.LONG TERM...(Wednesday through Monday)
Issued at 406 AM EST Tue Jan 16 2018

Long term remains rather quiet with a warming trend into the
weekend. Rain becomes likely, especially later in the weekend as
deep trough develops in the southwest CONUS and lifts northeast.
Models continue to keep our area in the warm sector and
climatologically this setup during La Nina winters has yielded
some very heavy rainfall events in our local area. While system
appears progressive the potentially large surge of high PWAT air
with Central Pacific and GOMEX origins could yield high rainfall
rates which could produce an inch or more of rainfall. Would not
be surprised to see some convection and thunder chances as well if
stronger model solutions are correct. Just a possibility at this
time and low confidence this far out but worth noting and watching
for possible flooding concerns early next week.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1213 AM EST Mon Jan 15 2018

Moist/cyclonic low level southwest flow just south of an elongated
west to east sfc trough will continue to support a predominately
MVFR cloud deck at the terminals through the TAF cycle. Some
guidance does hint at a trend into IFR cigs today, though opted
to hold onto a more optimistic fcst at this point. Snow
showers/flurries will also be possible mainly at KSBN as trough
axis nears. Will need to monitor this evening at KSBN as a
dominate LE single band could edge in from the west with significant
impacts/restrictions (Tuesday evening/night).


IN...Winter Storm Watch from 9 AM CST this morning through late
     tonight for INZ003-012.

     Winter Storm Watch from 4 PM EST this afternoon through
     Wednesday morning for INZ004-014.

MI...Winter Storm Watch from 10 AM EST this morning through Wednesday
     morning for MIZ077.



SHORT TERM...Lashley
LONG TERM...Lashley

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