Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 161734
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1234 PM EST Tue Jan 16 2018

.SYNOPSIS...
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.

&&

.UPDATE...
Issued at 854 AM EST Tue Jan 16 2018

Holding with winter storm watch this morning. Mesovort moving
onshore in Lake, Porter and La Porte counties at this time has
dropped visibilities with light to moderate snow. Issued SPS to
address the potential hazardous driving conditions. Main concern
is single band still upstream that is starting to develop and
become organized. Will reevaluate the watch as new data starts to
trickle in this morning.

&&

.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
situation.



&&

.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 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1221 PM EST Tue Jan 16 2018

Impacts from lake induced low pressure on KSBN will be short lived
as this feature drops southeast over the next hour. The low may
rotate towards KFWA will a brief window of IFR impacts, but will
not reflect in TAFs at this time.

Focus will be on single lake effect band currently across western
Lk Michigan into NE Illinois. This will transition east after 00Z
and may give impacts as the band settles over KSBN. Some concerns
as to exact time and time near/over the site resulting in
remaining conservative in impacts to the airport until trends can
be better assessed. Impacts to KFWA should be with MVFR cigs from
lake effect cloud cover that will spread southeast into the area.

&&

.MARINE...
Issued at 1221 PM EST Tue Jan 16 2018

The Nearshore Marine Forecast is suspended until April 1, 2018 or
until ice coverage diminishes sufficiently to allow wave action.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST
     Wednesday for INZ003-012.

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

MI...Winter Weather Advisory from 4 PM this afternoon to 7 AM EST
     Wednesday for MIZ077.

OH...NONE.
LM...NONE.
&&

$$

UPDATE...Heidelberger
SYNOPSIS...Lashley
SHORT TERM...Lashley
LONG TERM...Lashley
AVIATION...Fisher
MARINE...Fisher


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