Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 080000

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

Issued at 655 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 late in the day Thursday, and especially
by Thursday night. Significant lake effect snow accumulations are
expected by early Friday. Thereafter, high pressure returns for
Saturday with more settled conditions, but snow is expected to
follow on 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 week.


.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 CONUS.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 700 PM EST Wed Dec 7 2016

Primary focus on deteriorating conditions at KSBN in seasons first
significant lake effect event and have included a 22 UTC IFR
dominant forecast to capture upswing in intensity expected, that
will persist and occasionally lower even visibilities both
horizontally and into vertical obscuration at times beyond/through
Thursday night. For most part, KFWA expected to remain on
southern fringe of lake effect snow event and maintained cigs aoa
2kft and only modest visibility reduction.


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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