Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 101119

Area Forecast Discussion
National Weather Service Northern Indiana
619 AM EST Sat Dec 10 2016

Issued at 417 AM EST Sat Dec 10 2016

Low pressure will move northeast from the Southern Plains towards
the region tonight into Sunday night bringing an extended period
of precipitation, starting as snow. The snow is expected to
mix with or possibly change over to rain south of Route 30 before
ending. Significant snow accumulations are possible Saturday
night through Sunday night for parts of the area. Even colder air
will move into the Great Lakes region behind a cold front expected
to move through around the middle of next week.


.SHORT TERM...(Today into Sunday Night)
Issued at 417 AM EST Sat Dec 10 2016

Forecast not a whole lot clearer for the short term as models
continue to vary on how fast saturation occurs later today into
tonight and northward extent/speed of brief window of warmer
temperatures Sun afternoon/eve. Models at least generally agreeing
on the track of the sfc low to the nw of the area. Now to the
finer details.

Passing mention to start things out with light lake effect
snowshowers/flurries persisting across far southern Lower Mi.
Expecting little/no accumulation with these with rapid decrease in
coverage near/after 18z as increasing flow ahead of the next
system cuts off any activity. NAM remains the fastest and most
aggressive not only in arrival of snow late afternoon/early
evening but also the degree of warm air surging north. GFS/ECMWF
has a slightly slower onset of light snow (more after 00z).
Elevated mixed layer on KILX 00Z sounding should be starting
saturation as we speak with mid level increase in moisture
arriving. This should hopefully allow precip to reach the ground
rather quickly as condensation pressure deficits in the 285 to 290
K surface drop below 20 mb and then bottom out on Sunday as stout
burst of isentropic lift occurs with main low level jet
impingement. With the further NW track of the surface low a surge
of above freezing temperatures well north through the area would
normally be a slam dunk. However timing of this area and shallow
cold surface temps may complicate things further.

So....with regards to headlines and accumulations...precip will be
all snow tonight into at least the first part of Sunday with the
potential for several inches over roughly an 18 hour period. At
the point QPF potential is highest is when the warmer air begins
to arrive, potentially reducing amounts across the board as snow
ratios drop, especially south of US 30. Extensive collaboration
took place with surrounding offices and resulting in hoisting of a
Winter Weather Advisory generally either side and north of route
6. Advisory type snow amounts are still gridded up further south
to the US 24 corridor, but warmer surface temperatures will likely
keep travel hazards minimized. If the precip remains as snow north
of Us 6 for the bulk of the event, then 6 to 9 inches would be on
tap for these areas. Little in the way of wind is expected so no
concerns for blowing/drifting snow. If warmer air is faster/more
pronounced as depicted in the NAM, then snow amounts across the
board could be reduced by several inches, especially south of
US 30.

Any mixed precip will quickly end Sunday night as colder air moves
back in and deeper lift/moisture depart to the east.


.LONG TERM...(Monday through Friday)
Issued at 417 AM EST Sat Dec 10 2016

Few changes to long term with focus on pending winter event next
36 hours or so. Piece of arctic air still in store for mid to late
week with what appears to be limited lake effect potential as
fetch may end up more westerly and deeper moisture/dgz interaction
may be limited. Coldest temps will take place Thursday with lower
to maybe middle teens for highs and lows into the single digits
above zero. Wind chills Thursday night may drop into the zero to
10 below range.

Next system will arrive late in the period but have held with slgt
chc/chc pops for now with plenty of time to sort out.


.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 611 AM EST Sat Dec 10 2016

Backing winds aloft have shifted lake effect snow bands north into
MI. VFR conditions across most of nrn IN but still some patchy
strato cu mvfr cigs. Fcst VFR conditions to predominate today
but can`t rule out brief mvfr cigs at least through the morning.  -SN
should overspread the area tonight with greatest impacts at SBN
where ifr conditions should prevail. Lesser potential for deep
saturation at FWA so kept taf mvfr above fuel alternates


IN...Winter Weather Advisory from 9 PM EST /8 PM CST/ this evening to
     4 AM EST /3 AM CST/ Monday for INZ003>009-012-014-016.

MI...Winter Weather Advisory from 9 PM this evening to 4 AM EST
     Monday for MIZ077>081.

OH...Winter Weather Advisory from 9 PM this evening to 4 AM EST
     Monday for OHZ001-002-004-005.



LONG TERM...Fisher

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