Area Forecast Discussion
Issued by NWS Northern Indiana

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668
FXUS63 KIWX 090552
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1252 AM EST Sat Dec 9 2017

.SYNOPSIS...
Issued at 1250 AM EST Sat Dec 9 2017

A clipper system will bring light snow to the entire area through
early this afternoon. Most locations will likely receive between
1 and 3 inches, though lower amounts are possible southeast of US
24. Heavy lake effect snow is then expected to impact portions of
northwest Indiana and far southwest Lower Michigan late Saturday
morning through Saturday evening. Snow totals are expected to
exceed 6 inches in favored lake effect snow belts. This
accumulation, gusty winds, and intense snowfall rates will lead to
difficult travel conditions in these areas. Cold and remaining
active otherwise through next week as several more clipper systems
bring snow chances.

&&

.SHORT TERM...(This Evening through Saturday Night)
Issued at 240 PM EST Fri Dec 8 2017

Remaining cold with the first widespread accumulating snow of the
season Saturday...

A potent and compact shortwave over eastern Manitoba will dig
southeast through the Great Lakes bringing a period of light
synoptic snow later tonight into Saturday morning, followed by a
dominate LES band to nnw LE belts later Saturday morning through
Saturday evening. Strong dynamic forcing will be enough to overcome
dry CP airmass in place, with system snow beginning later tonight
into nw IN/sw Lower MI, then through the rest of the forecast area
Saturday morning. Still thinking a quick 1-2" for most locations as
brief nature to forcing and dearth of moisture limits accums.
Scattered snow showers and flurries will then be possible into the
afternoon everywhere as the trough axis and associated steeper lapse
rates pivot through.

The main focus Saturday morning into early Saturday afternoon
will turn to lake enhanced snow...then pure LES in the afternoon
and evening. The low level flow veers more nnw and then eventually
more nw, which will result in strong frictional/thermal
convergence along the long axis of eastern Lake MI. LES parameters
continue to favor good dendritic growth and the potential for
intense 1-2"/hr snowfall rates (near whiteout conditions and gusty
winds) within the dominate band. Berrien/St Joseph IN/LaPorte
still look to be within the pivot point of any banding, with lower
confidence in surrounding counties given the potential for
mesovorticies to force a more transitory/broken plume. It is worth
noting that a more organized band could reach well inland with
advisory level impacts given 35-40 knots of flow modeled at 925
mb. Steepening boundary layer depth may tap into some of this and
create strong winds and blowing snow/low visby`s, especially in
areas under a warning or advisory.

Drying/subsidence/backing winds will take its tool on inversion
heights and bring an end to any impactful LES later Saturday night.

&&

.LONG TERM...(Sunday through Friday)
Issued at 240 PM EST Fri Dec 8 2017

Highly anomalous upper troughing will remain steadfast across the
Eastern US Sunday into next week resulting in more of the same
(below normal temps and several clippers providing chances for
light synoptic snow and LES).

Weak pv filament and associated sfc trough does swing through on
Sunday. This feature may bring a few flurries to far northern zones
given some lake enhancement. Cold otherwise with another day of
highs near 30 degrees.

A more pronounced shortwave in nw flow (this one more of your
typical Alberta Clipper compared to Saturday`s Manitoba mauler) will
have good left exit upper jet support and enough of a low level
thermal gradient to force a developing sfc reflection east through
the Lower/Eastern Great Lakes Monday into Tuesday. Models continue
to oscillate a bit on where leading WAA/isentropic lift snow (1-3")
sets up Monday into Monday evening, though the trend has been more
north across WI and MI. Will continue to carry low-mid chance PoPs
during this time, highest across far ne IN/MI/far nw OH. Deep
northwest flow in CAA wing then brings LES back into play later
Monday night and Tuesday...again in favored NW flow lake belts where
significant snow accums/impacts will be possible. Rinse and repeat
then for the end of the week as another system translate through
in nw flow.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1250 AM EST Sat Dec 9 2017

Expect conditions to deteriorate through this morning and afternoon
as the clipper system currently over WI and Western Upper Michigan
drops southeastward into Northern Indiana. The worst conditions are
expected at KSBN, where Lake Michigan will provide additional
moisture/instability and enhance precipitation in the wake of the
low. At this point, have conditions dropping to MVFR by 9z at KSBN,
and to IFR/LIFR by 16z as the low is overhead. Per upstream
observations, it looks like once we overcome drier air we could see
visibilities drop to around 2 miles, then possibly dropping to less
than 1 mile in any bands that develop later this morning/afternoon.
There is some uncertainty as we seem to be struggling with dry air
in place over the area. This may prevent things from dropping as far
as I have in the TAF at the moment. Additionally, there is still
model disagreement about where the lake effect band is placed
tonight, with some shifting it westward of KSBN and others keeping
it directly overhead. Will add further detail to this scenario with
later issuances, but for now hedged on the side of caution and went
with LIFR conditions. At KFWA, expect we`ll see a drop down to MVFR
visibilities and ceilings today as the system crosses through. A
brief drop to IFR is possible, but wasn`t confident enough to
include in the TAF at this point given our dry air situation.
Otherwise, winds will shift to the northwest through the period, and
begin to gust into the 20-25 knot range by this afternoon.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Storm Warning until midnight EST /11 PM CST/ tonight for
     INZ003-004.

     Winter Weather Advisory from 4 AM EST /3 AM CST/ early this
     morning to midnight EST /11 PM CST/ tonight for INZ012-014.

     Winter Weather Advisory from 5 AM early this morning to midnight
     EST tonight for INZ005-015-016.

MI...Winter Storm Warning until midnight EST tonight for MIZ077.

     Winter Weather Advisory from 5 AM early this morning to midnight
     EST tonight for MIZ078.

OH...NONE.
LM...Small Craft Advisory until 10 AM EST this morning for LMZ043-046.

     Gale Warning from 10 AM this morning to 10 PM EST this evening
     for LMZ043-046.

&&

$$

SYNOPSIS...MCD
SHORT TERM...Steinwedel
LONG TERM...Steinwedel
AVIATION...MCD


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