Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 060017

Area Forecast Discussion
National Weather Service Northern Indiana
717 PM EST Tue Dec 5 2017

Issued at 300 PM EST Tue Dec 5 2017

Strong winds will gradually diminish overnight. Winds tomorrow will
not be as strong but still gusting to around 30 mph. A few flurries
are possible but mainly dry conditions will persist through
tomorrow. Lake effect snow will then be possible Wednesday night
into Thursday with 1 to 3 inches for areas north of the toll road.
Cold conditions will persist through the weekend with highs around
30...lows around 20...and wind chill values in the teens.


Issued at 715 PM EST Tue Dec 5 2017

Have allowed the wind advisory to expire across all but Berrien
county. Latest sfc observations at KBEH still indicating gusts to
around 45 mph at 00Z. Have blended previous grids with latest LAV
trends in maintaining these higher gusts through about 03Z, with
better chance of gusts dropping below advisory criteria after this
time. Low levels will remain well mixed overnight which should
keep gusts of around 20 knots going through the night. A few
flurries may affect far northern Indiana/southern Lower Michigan
over next few hours before shifting off to the east in association
with upper level short wave working across the Great Lakes. Skies
should clear later this evening, but mid clouds likely to
increase toward daybreak in advance of next approaching wave in
northwest flow. Previous grids have these trends well in hand.


.SHORT TERM...(This Evening through Wednesday)
Issued at 300 PM EST Tue Dec 5 2017

Wind gusts just upstream finally ramping up to advisory criteria at
press time as gradient and mixing heights increase. This is due to
strong vort max swinging through the southern Great Lakes and should
promote a period of stronger gusts for our CWA in the next few
hours. Some concern that this may result in advisory needing a few
hour extension this evening. However, with loss of insolation and
overall marginal nature of advisory to begin with, will hold off on
extending for now. Regardless of exact end time, winds will
gradually wane through the overnight as gradient weakens and
stability builds. Will still be on the breezy side tomorrow with
westerly gusts to around 30 mph under moderate mixing but nowhere
near advisory criteria.

Still an outside chance of a flurry tonight into tomorrow as
multiple shortwaves pass but forecast soundings/RH fields are
incredibly dry and trend in NWP QPF has been less and less. Lake
thermal differentials would suggest some lake response but airmass
is just too dry with fast WSW flow. Have therefore removed
measurable PoPs through early tomorrow afternoon and trimmed back
flurry mention. Also raised tonight`s min temps a bit based on
latest guidance and the expectation that we remain mixed through the
night. Expect lows in the mid/upper 20s with highs in the mid/upper
30s and wind chills hovering in the teens.


.LONG TERM...(Wednesday Night through Tuesday)
Issued at 300 PM EST Tue Dec 5 2017

Lake effect will begin to ramp up tomorrow night into Thursday. More
formidable shortwave trough axis will pass during that
time...allowing winds to veer and inversion heights to rise. Still
not a great lake effect setup though. Inversion heights max out
around 6 kft with moderate 300-320 degree flow limiting ability for
more organized/dominant band to develop. Also a relatively narrow
time window for best fetch...roughly 06-18Z Thursday. 0-2km theta-e
lapse rates also on the marginal side and for a similarly limited
time window. Do expect accumulating snow in our N/NW zones during
this time but amounts should remain around 1-3 inches. Backing flow
and sharply increasing dry air entrainment should bring an end to
lake effect by Thu evening. Lowered PoPs significantly for Thu night
and Fri based on dry/WSW flow seen in both NAM and GFS soundings.
850mb temps remain on the cold side but dry air will likely win out,
especially given SW flow by Fri.

Attention then turns to next potent shortwave vort max diving into
the Great Lakes Sat. Models continuing to struggle with exact track
and evolution so did not deviate too far from concensus chance PoPs.
Could be our first shot at accumulating snow for much of the CWA
(along with decent lake effect behind it) but still too much
variance to nail down any details. Anticipate any accumulation will
be on the light side though given limited moisture available.

Cold temps will continue to be the other main story. Expect highs to
remain below freezing through the weekend. A brief/marginal warmup
may be possible on Mon but confidence in details at that range are
low. Overall longwave patterns favors below normal temps for the
foreseeable future.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 715 PM EST Tue Dec 5 2017

Gusty west-southwest winds will gradually diminish this evening,
but well mixed boundary layer should keep winds gusting to around
20 knots during the overnight hours. VFR low clouds should depart
northeast Indiana over the next few hours, with lake effect clouds
likely to affect areas north of KSBN overnight. Some increasing
mid level cloud expected late tonight into early Wednesday as next
northwest flow wave interacts with fairly strong low/mid level
baroclincity. Low level wind field will remain fairly strong into
Wednesday with continued breezy conditions and late
morning/afternoon westerly gusts to around 25 knots. Potential of
some lake effect snow showers will increase beyond this forecast
valid period as low level flow veers more north-northwest in wake
of this approaching short wave.


MI...Wind Advisory until 10 PM EST this evening for MIZ077.

LM...Gale Warning until 7 AM EST Wednesday for LMZ043-046.




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