Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 082108
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
408 PM EST Thu Dec 8 2016

.SYNOPSIS...
Issued at 359 PM EST Thu Dec 8 2016

Lake effect snow showers will increase in intensity and coverage
this evening as cold air continues to overspread the region. The
most intense lake effect snow showers are expected from late this
evening through early Friday morning. Winter storm warnings and
advisories are in effect through Friday for southern lower
Michigan and far northern Indiana due to the combination of lake
effect snow and gusty winds causing blowing and drifting snow. In
addition to lake effect snow showers, very cold conditions will
persist into Friday with wind chills as cold as 5 above to 15
above zero.

&&

.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 18Z TAFS through 18Z Friday Afternoon)
Issued at 1237 PM EST Thu Dec 8 2016

Low pressure centered over quebec this afternoon will drift
eastward. Cold air advection is in full swing behind the trailing
cold front on west-northwest winds. Steep mid-level lapse rates
and daytime heating are allowing stronger winds aloft to mix down
to the surface, with gusts to 25-30 knots expected through the
afternoon. Otherwise, the main focus is on where heavier lake
effect snow bands set up this afternoon/evening into Friday
morning. Was pessimistic with the forecast at KSBN, with medium
confidence in the moderate-heavy bands reaching the site and
stronger wind gusts. If stronger bands do reach the site, expect a
trend from IFR to LIFR-especially if accumulations and wind
combine to cause blowing snow. Lesser impacts are expected at
KFWA...and confidence in any significant snow bands reaching the
site is low. Expect the bands to remain north of the
site...keeping conditions primarily MVFR. If moderate/strong bands
do manage to migrate south into the site...IFR conditions are
possible. For now, kept things conservative given the uncertainty.

&&

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

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

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

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

&&

$$

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...MCD


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