Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 151131

Area Forecast Discussion
National Weather Service Northern Indiana
631 AM EST Fri Dec 15 2017

Issued at 109 AM EST Fri Dec 15 2017

A weak system will pass across the Great Lakes today bringing
scattered to numerous snow showers north of the Toll Road. Some
light snow accumulations of an inch or two are possible from today
through tonight, especially across southern Lower Michigan where
lake effect snow showers are expected to be more numerous. High
temperatures this afternoon will range from the mid 20s to lower
30s. Lows tonight will not be as cold, ranging from the mid to
upper 20s. The moderating trend will continue into the weekend
with highs in the 30s and 40s for Saturday and Sunday. The next
chance of rain and snow will arrive by Sunday afternoon.


.SHORT TERM...(Today and Tonight)
Issued at 239 AM EST Fri Dec 15 2017

A mid level shortwave will rotate southeast through central/upper
Michigan today, with the trailing trough axis swinging through the
local area from west to east this morning through early-mid
afternoon. Most of the impacts/accums will bypass north given far
northerly track of the system sfc reflection, though there will be
enough lake enhancement in strengthening westerly flow to generate
scattered to numerous snow showers mainly north of Route 6.
Steepening lapse rates/mixing into the lower portion of the DGZ
could support some stronger snow squalls and light accums in these
areas, which when combined with wind gusts of 20-30 mph and snow
already on the ground could promote patchy blowing snow and reduced
visibilities. Cool/breezy/cloudy with flurries possible elsewhere

Warm advection regime tonight will likely allow light snow to
develop near a trailing baroclinic zone leftover from the Upper
Midwest southeast into the Lower Great Lakes. Models are in pretty
good agreement in best snow chances (maybe up to an inch) northeast
of US 30 mid evening into the overnight.


.LONG TERM...(Saturday through Thursday)
Issued at 239 AM EST Fri Dec 15 2017

Positive PNA ridge along the West Coast will break down and allow
positive height anomalies to finally overspread the Eastern US this
weekend into early next week. The result will be a warming trend and
mainly dry conditions, though will have to watch a shearing southern
stream shortwave lifting northeast out of Texas for light rain
(possibly mixed with some snow) on Sunday. A rather benign, yet
still mild, pattern is then expected to persist into the middle of
next week as models agree on flatter/split flow downstream of an
amplifying Western US trough. This trough does eject east late in
the week with a decent mid latitude cyclone likely making a run for
the Great Lakes. The northerly track would favor more of a rainer
locally followed by colder/drier air in time for next weekend.


.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
Issued at 625 AM EST Fri Dec 15 2017

Water vapor imagery is clearly depicting the next fast moving
upper level short wave that will drop across northern Indiana over
the next several hours. The combination of forcing from this wave
and some lake enhancement with subtle veering of low level flow
should result in a period of scattered snow showers at KSBN from
mid morning to early afternoon. Onset of modest low level theta-e
positive advection this morning has resulted in an increase in
coverage of MVFR 2-3k foot deck and would suspect cigs in this
range to persist through much of the day as low level lapse rates
steepen in wake of approaching sfc trough. These steeper lapse
rates will allow for westerly gusts to around 25 knots later this
morning into this afternoon, before decoupling fairly quickly
early this evening. Still suspecting a 2nd wave of snow shower
activity this evening at KSBN with onset of low/mid level WAA,
but after 06Z focus for additional snow showers should lift north
of KSBN as thermal trough retreats northward. Will maintain MVFR
conditions at KSBN, with confidence too low to go IFR at this
time due to more favorable setup for greater snow shower coverage
just to the north of the terminal.


LM...Small Craft Advisory until 5 AM EST Saturday for LMZ043-046.



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

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