Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 072058

Area Forecast Discussion
National Weather Service Northern Indiana
358 PM EST Wed Dec 7 2016

Issued at 350 PM EST Wed Dec 7 2016

Colder air will filter southeast into the area through Thursday.
This will result in light lake effect snow showers developing late
tonight into early Thursday morning. The lake effect snow showers
will become more intense later in the day Thursday, and especially
by Thursday night. Significant lake effect snow accumulations are
expected by Thursday night and early Friday. Thereafter, high
pressure returns for Saturday with more settled conditions, but
snow is expected to follow for Sunday as a low pressure system
moves through the area. Cold air, once again, moves in following
this system with a chance for more lake effect snow early next


.SHORT TERM...(This Evening through Friday)
Issued at 350 PM EST Wed Dec 7 2016

Lake effect snow event Thursday/Friday and onset of much colder
temperatures will be the main stories for the short term.

A broad sheared upper level trough approaching central CONUS will
be associated with continued mid level cloud this evening, and
passage of this wave will allow for reinforcement of low level
cold advection tonight. Some subtle veering of low level wind
profiles in the wake of this wave should allow for eventual
development of lake effect snow showers across southwest lower
Michigan late tonight. While lake induced instability will be
increasing, saturation to depths sufficient enough for snow
production will be in question through about 12Z.

Inversion heights to rise more substantially on Thursday as lake
effect snow showers become more widespread. West-northwest low level
trajectories should favor southern lower Michigan and areas closer
to the MI/IN stateline for snow shower development. 800-700 mb dew
point depressions should remain on the marginal side through the day
which should limit snow shower intensity through much of the day. A
couple of inches of accumulation is possible Thursday afternoon
across southern lower Michigan, possibly extending into far northern
Indiana. Deep mixing on Thursday should allow for wind gusts into
the 25 to 30 mph range in the afternoon, so despite the relatively
light lake effect accumulations anticipated through mid-late
afternoon, some issues with blowing/drifting snow will be possible.

Of greater concern in terms of lake effect is the Thursday night-
Friday period as another upstream vort max dives across southern
Great Lakes providing a period of deeper moisture profiles. Lake
induced instability will also maximize during the nighttime hours,
and all indications still point to the Thursday night/early Friday
morning period as potential greatest impact period. Cross sections
still suggest strongest low level lift may reside just below DGZ
or clipping lower portions of DGZ. Of concern however, is
expected weakly confluent/convergent flow pattern associated with
approaching mid level wave that could further act to sharpen lake
response/banding. Lake aggregate troughing also should tend to
sharpen banding Thursday night/early Friday.

Given the above factors, have upgraded the winter storm watch to a
warning and maintained advisory counties as is. Have delayed onset
of the winter weather advisory until 15Z, and maintained 09Z start
time for the winter storm warning for the three southern lower
Michigan counties.  It should be noted, this onset time may need to
be delayed a bit depending how things with evolve overnight
tonight. Confidence is on the high side that highest impacts
should hold off until late Thursday afternoon/night. The other big
story will be the trend to much colder temperatures with afternoon
highs only into the mid 20s Thursday, and wind chills Thursday
night/Friday morning dropping to 5 to 15 above. Lake effect snow
showers should tend to diminish in intensity Friday
afternoon/evening. On Friday, deeper moisture profiles will
gradually erode with some backing of low level winds eventually
confining most of additional lake effect to southern lower


.LONG TERM...(Friday Night through Wednesday)
Issued at 350 PM EST Wed Dec 7 2016

A brief lull in the active weather is expected Friday
night/Saturday, although some lingering lighter lake effect snow
showers may be ongoing across southern lower Michigan.

A period of fairly strong warm advection should ensue for Saturday
afternoon/Saturday night as next upper PV anomaly emerges in the lee
of the Rockies. Warm advection snow should develop particularly
across northern half of the forecast area by Saturday night with
some light to moderate accumulations possible. Consensus guidance
still suggests prolonged event into Sunday as next upstream short
wave progresses across the area, although medium range models still
exhibiting quite a bit of spread and volatility in the details
regarding strength/progression of this wave. Have kept precip all
snow for Saturday night/Sunday, although outlier 12Z ECMWF would
suggest rain/snow issues. ECMWF represents a stronger/slower outlier
at this time with more copious moisture transport ahead of this
wave, and have opted to put more weight into GEM/GFS blend. This
system will need to be watched for possible headlines over the
next few days, as several inches of snow accumulation appear to be
a strong possibility for at least portions of the forecast area.
Some lake effect is possible behind this system. Otherwise, very
cold conditions look to be in store middle of next week with
strong low level thermal troughing overspreading much of eastern


.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 1226 PM EST Wed Dec 7 2016

High clouds are coming in from the south and cooler air coupled with
clouds are coming in from the north and west to start this period.
The cooler air will help to set off some light lake effect snow
showers that reach SBN overnight, but should stay north of FWA
due to a lack of a northerly component in the flow. Later
Thursday, a better chance for accumulating snow at SBN occurs.
CIGs north and west of SBN are already into MVFR, but some models
slow the trek of the clouds into SBN by around 00z.


IN...Winter Weather Advisory from 10 AM Thursday to 4 PM EST Friday
     for INZ004>007.

MI...Winter Weather Advisory from 10 AM Thursday to 4 PM EST Friday
     for MIZ080.

     Winter Storm Warning from 4 AM Thursday to 4 PM EST Friday for

LM...Small Craft Advisory until 7 PM EST Friday for LMZ043-046.



SHORT TERM...Marsili
LONG TERM...Marsili

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