Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 131153
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
653 AM EST Wed Dec 13 2017

.SYNOPSIS...
Issued at 438 AM EST Wed Dec 13 2017

A clipper system will bring light to moderate snow to the area
today, with the best chances for accumulations north of US 30 and
east of US 131. Conditions may be hazardous for the evening commute
in these areas. Otherwise, expect light lake effect snow tonight
into Thursday. Highs today will be in the 20s and 30s, warmest in
the southwest. Lows tonight will drop into the single digits and
teens. It will be colder Thursday, with highs only reaching into the
upper teens and 20s. Additional light snow is expected this weekend
with another system that will move through, followed by more lake
effect.

&&

.SHORT TERM...(Today and Tonight)
Issued at 438 AM EST Wed Dec 13 2017

The primary concern for the short term is the clipper system moving
into the area today and tonight. Opted to air on the side of caution
and issue a winter weather advisory for the northeast-most portions
of our forecast area (Branch/Hillsdale, MI; Fulton, OH). If the
forecast plays out as expected, accumulations of 2 to 4 inches are
expected in the advisory area, and less than 2" elsewhere. A few
localized higher amounts up to 5" are possible north of US 12 in
Hillsdale/Branch counties, MI where the better forcing will be.
Confidence in this playing out as planned is medium, as there are
several concerns to contend with.

On the pro-higher accumulations side, we have the low pressure
system dropping down across our forecast area, with the low tracking
from southern Lake Michigan at 21z into northern Indiana by 00z, and
southeastward into Ohio by 06z tonight. Guidance shows a pretty
potent wave aloft with this system, which is confirmed by recent
water vapor imagery. With a stout 40 knot jet streak ahead of the
low, there will be at least some WAA/moisture transport into our
area starting this morning, with the best 850-500mb qvector
convergence during the 18-00z timeframe.

The thing we lack is moisture, and the worry is that dry air to our
southwest will significantly limit the amount of moisture that is
lifted into the system ahead of the low/warm front. I think we`ll
miss out largely on this initial swath of precipitation that some
models are suggesting we`ll see, as higher-res guidance has things
staying fairly dry until 18z or so, before picking up in our far
northeast for at least a few hours. However, in collaboration with
neighbors decided to start the advisory at 15z, just in the event we
see some light snow on that northern side earlier today.

So for the forecast, I cut qpf/snow amounts fairly decently, with
the maximum potentially in far northern Hillsdale/Branch counties
north of US 12. Up to 4" is expected in northern Fulton, OH. Some of
the guidance shifts the axis of heavier precipitation slightly
southward, so I wouldn`t be entirely surprised to see perhaps
Steuben, Williams, Henry, and St. Joseph get added to the advisory
later this afternoon, but confidence was not high enough to put
them in now. I think that the drier guidance has a better handle
on current conditions, thus migrated more towards those when doing
my snow forecast. Impact wise, expect periods of low visibility,
and slick snow covered roads-especially in the advisory area.
Winds won`t be gusting as much as in the previous event, but we
could see some patchy blowing snow during the peak of the event
this afternoon/evening.

Otherwise, expect lows to bottom out into the single digits tonight
as cold air filters in. This colder air will also bring decent
chances for lake effect snow in the west, with NNE winds gradually
becoming more northerly. This keeps the band largely west of our CWA
until later in the overnight, when winds shift northwestward and
bring the band inland in LaPorte/Berrien counties. Expect light
accumulations with this, mainly 0.5" or less.

&&

.LONG TERM...(Thursday through Tuesday)
Issued at 505 AM EST Wed Dec 13 2017

Lake effect is the focus of the long term, in addition to a couple
additional systems that move through our area. Once our system today
exits the area overnight, we`ll see a transition to light lake
effect snow for north-northeasterly favored areas initially (western
LaPorte county, possibly western Berrien) and then shifting inland
and eastward as the night goes on, diminishing by the afternoon
hours Thursday. Weak high pressure will establish itself under the
upper level trough, which both the ECMWF/GFS agree will kick off
yet another surface low that descends upon Upper and northern
Lower Michigan by Friday morning. Thus, other than some light lake
effect in westerly wind favored regions Thursday afternoon-
overnight, expect dry conditions. Lows Thu night will be in the
teens and 20s, slightly warmer than tonight.

Friday into Friday night we`ll see continued lake effect in westerly
wind favored regions, and thus kept the higher pops in these areas,
mainly in Michigan counties, through early Saturday afternoon. With
the surface low passing to the north of our forecast area into
Lake Huron, locations mainly north of US 30 will see some light
snow Friday into Friday evening-with amounts less than one inch.
The best accumulations, of around 1-2" possible, will be in the
west-wind favored snowbelts by early Saturday morning.

Lake effect snow showers finally come to an end with partly cloudy
skies, warming temps and southerly flow on Saturday afternoon. Highs
will climb into the 30s for most areas, and even a few 40s in the
far southwest. Locations in the northeast, mainly NE IN, NW OH, and
Southern Michigan will see highs only in the upper 20s.

While there are still discrepancies between models, another system
swings into the area from the southwest and phases with the wave to
our northeast Sunday afternoon into Monday morning. This brings a
swath of precipitation to the area, and with temperatures in the 30s
and 40s by Sunday, this will be a rain/snow mix, starting out as
mostly snow and transitioning to rain through the day-then back to
snow overnight as temps fall in the north. Light lake effect is
possible in west-wind favored regions again, mainly in the form of
snow but mixing with rain as temperatures warm through the day.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday Morning)
Issued at 642 AM EST Wed Dec 13 2017

Strong warm advection/isentropic lift will overspread the
southern Great Lakes/Ohio Valley region this morning. Moisture
will be a limiting factor in terms of realizing snowfall with this
initial forcing with best chance of a brief period of light snow
likely remaining north of the terminals. Cannot rule out a brief
period of light snow or flurries at KSBN in the 14-16Z timeframe
but will hold off at this time. Better chances of snow for
terminals should hold off until this afternoon/evening as a pair
of upper level systems drop southeast into the area. Did include a
period of IFR vsbys at KSBN in closer proximity to this forcing
and where better moisture is likely to reside. The late
afternoon/evening period should also be accompanied by MVFR cigs,
and possibly to below 2000 feet for a time this evening before
cigs improve late evening into the overnight. Winds will also
become gusty this afternoon in advance of deepening sfc low
pressure, with continued gusty post-frontal winds this evening to
20 to 25 knots before diminishing overnight.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...Winter Weather Advisory from 10 AM this morning to 11 PM EST
     this evening for MIZ080-081.

OH...Winter Weather Advisory from 10 AM this morning to 11 PM EST
     this evening for OHZ002.

LM...Small Craft Advisory until 10 AM EST Thursday for LMZ043-046.

&&

$$

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


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