Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 081940

Area Forecast Discussion
National Weather Service Northern Indiana
240 PM EST Fri Dec 8 2017

Issued at 240 PM EST Fri Dec 8 2017

A clipper system will bring light snow to the entire area later
tonight into Saturday morning. 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 later 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 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1254 PM EST Fri Dec 8 2017

VFR conditions will prevail through 6Z Sat before the next system
begins to impact the area. Light snow will overspread both TAF
sites starting between 6 and 9Z at KSBN and 8 to 11Z at KFWA with
MVFR visibilities settling in at the respective sites. Given some
concerns as to how fast impacts will occur a downward trend is
noted, but nothing below 2 SM for this package. It is possible
that pockets of lower vsby and cigs could materialize with the
initial snow, but not worth addition of a tempo at this point.

Lake effect snow showers will organize and likely impact KSBN at
some point after 15Z. Some concerns as to exactly how fast the
band develops and how long it resides over/near the airport.
Potential exists for much lower cigs/vsby with sig impacts at
times at KSBN if the main band settles over the airport. While
some impacts are possible from the band at KFWA, many more
variables warrant low confidence.


IN...Winter Storm Warning from 1 AM EST /midnight CST/ Saturday to
     midnight EST /11 PM CST/ Saturday night for INZ003-004.

     Winter Weather Advisory from 4 AM EST /3 AM CST/ Saturday to
     midnight EST /11 PM CST/ Saturday night for INZ012-014.

     Winter Weather Advisory from 5 AM Saturday to midnight EST
     Saturday night for INZ005-015-016.

MI...Winter Storm Warning from 1 AM Saturday to midnight EST Saturday
     night for MIZ077.

     Winter Weather Advisory from 5 AM Saturday to midnight EST
     Saturday night for MIZ078.

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

     Gale Warning from 10 AM to 10 PM EST Saturday for LMZ043-046.



SHORT TERM...Steinwedel
LONG TERM...Steinwedel

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