Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 090533
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1233 AM EST Fri Dec 9 2016

.SYNOPSIS...
Issued at 1227 AM EST Fri Dec 9 2016

Cold west to northwest winds will continue to cause lake effect snow
overnight and Friday, mainly across southwest Michigan and the
adjacent counties in northern Indiana. High pressure will build into
the area by evening causing the lake effect to diminish to flurries.
Low pressure will move northeast from the southern plains across the
Midwest over the weekend causing snow Saturday night and Sunday,
possibly lingering into Monday. The snow will mix with rain south of
U.S. Route 30 before ending. A cold front will move through the
Midwest early next week, followed by very cold temperatures for mid
to late week.

&&

.UPDATE...
Issued at 857 PM EST Thu Dec 8 2016

Only minor changes to the going forecast this evening. Snow totals
so far have been fairly light but more dominant lake effect bands
beginning to develop and shift southward as expected given slowly
veering flow and increasing convergence due to lake aggregate
troughing. Previously forecasted snow amounts still appear to be
in good shape and expect a sharp increase in snow intensity
overnight as more organized bands drift south. Still some concern
that lake effect bands may reach further east, particular Branch,
Steuben, and Williams counties given latest RAP guidance, earlier
hi-res WRF-ARW and NMM runs, and quick peak at 00Z NAM12.
However, HRRR maintaining more westward placement of strongest
bands and this solution is better supported by latest surface obs
and radar mosaic. Will therefore hold off on any expansion/upgrade
this evening and continue to monitor band evolution overnight for
any final headline massaging. Lake effect will gradually wind
down during the day Friday as winds back and dry air advection and
subsidence increase.

&&

.SHORT TERM...(This Evening through Friday)
Issued at 359 PM EST Thu Dec 8 2016

Lake effect snow event will continue to be the primary forecast
concern for the short term. Broad cyclonic flow along with steep low
level lapse rates and weak embedded waves in upper flow have
sustained widespread light snow showers and flurries across the
region through the afternoon. Lake effect snow has had a difficult
time to this point with still some saturation issues at depths
sufficient enough for ice introduction. Mid level trough will drop
southeast across the southern Great Lakes tonight which will
augment depth of lake induced instability by the mid to late
evening hours, with better saturation into at least the lower
portions of the DGZ. In addition, lake aggregate troughing will
becoming sharpened tonight along eastern shoreline of southern
Lake Michigan that should focus lake effect snow bands in the 03Z-
12Z timeframe. Given fetch considerations, still believe the axis
of greatest snow accumulation tonight into Friday should extend
from northern Berrien county extending southeast across Cass/St.
Joseph counties, and possibly into Branch county. Did consider
going with a warning for Branch county, but not quite enough
confidence in this scenario to stray from current advisory. Snow
ratios/accumulation efficiency should start to diminish toward
midday Friday as mid levels begin to dry out and inversion heights
lower. Other than the addition of Hillsdale county to the advisory
this morning, no other changes to current lake effect snow
headlines are anticipated with the afternoon package. Have
maintained maximum axis of 4 to 8 inch accumulation with some
potential of localized higher amounts. Greater impacts now appear
to be more focused for the Friday morning commute as opposed to
early this evening. Wind chills will be the other story through
Friday morning with wind chills persisting in the 5 to 15 degree
above zero range.

&&

.LONG TERM...(Friday Night through Thursday)
Issued at 359 PM EST Thu Dec 8 2016

Lake effect snow showers will likely continue into Friday evening
but should become progressively more focused across southern lower
Michigan as low level flow slightly backs Friday afternoon.

A brief lull in the active pattern is expected late Friday night
through the day Saturday, but focus will shift to the Saturday
night-early Monday period for a possible two pronged event for our
area. Low level return flow will become established quickly
Saturday evening as flow deamplifies and becomes more progressive.
Strengthening low level flow and a strong baroclinic zone will
focus swath of warm advection snow Saturday night into early
Sunday. Still some uncertainty as to the southern extent of this
accumulation, but have hedged on even southern locations receiving
accumulating snow in this first phase. Overall it appears as
though a quick 1 to 3 inch type of accumulation would be possible
Saturday night/early Sunday.

A brief break in snow coverage/intensity is expected later Sunday
morning/early Sunday afternoon, but next progressive eastern Pacific
wave will be amplifying upstream across the central Plains inducing
another round of warm advection-forced snow. Higher chances of snow
should persist into Sunday night/early Monday as actual mid/upper
level wave tracks across the area. Consensus of model guidance has
trended toward the idea of a stronger wave somewhat like old EC
guidance was advertising. This stronger solution and more pronounced
thermal advection may very well also lead to some precip type
concerns and possible transition to rain across the south late
Sunday night, and across central portions of forecast area Monday
before diminishing. Still plenty of uncertainty how this will
unfold this weekend but 36 hour snowfall totals could add up to at
least advisory levels across portions of the area, with early
indications suggest northern half may be most favorable for higher
accumulation. This certainly will be a system to watch over the
next few days.

Medium range models suggest larger scale trough/strong cold air
intrusion may unfold toward middle of next week, with all
indications of much below normal temp pattern setting up middle to
late next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
Issued at 1227 AM EST Fri Dec 9 2016

Low level flow veering nw this eve causing a little heavier lake
effect snow showers to spread into SBN. Expect ifr conditions will
cont to predominate until late morning when subsidence should
cause snow showers to diminish to flurries. VFR conditions
currently at FWA expected to predominate through the night with
just light snow... though brief mvfr conditions psbl in heavier
shsn.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 4 PM EST /3 PM CST/ this afternoon
     for INZ003>007.

MI...Winter Weather Advisory until 4 PM EST this afternoon for MIZ080-
     081.

     Winter Storm Warning until 4 PM EST this afternoon for
     MIZ077>079.

OH...NONE.
LM...Small Craft Advisory until 7 PM EST this evening for LMZ043-046.

&&

$$

UPDATE...AGD
SYNOPSIS...JT
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...JT


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