Area Forecast Discussion
Issued by NWS Northern Indiana

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257
FXUS63 KIWX 141726
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1226 PM EST Thu Dec 14 2017

.SYNOPSIS...
Issued at 415 AM EST Thu Dec 14 2017

Other than some light lake effect snow showers today for NW
Indiana and far SW Lower Michigan, weather will be dry. Partly
mostly cloudy skies can be expected, with highs only reaching into
the upper teens and low 20s north of US 30, and the mid-upper 20s
south of US 30. Lows tonight will range from 12 to 22 degrees.
Light snow is possible again on Friday into Saturday morning,
though little to no accumulation is expected. Lake enhancement in
west-northwest wind favored snowbelts could lead to snow totals up
to two inches by Saturday morning. Highs Friday will be in the 20s
and low 30s.

&&

.SHORT TERM...(Today and Tonight)
Issued at 415 AM EST Thu Dec 14 2017

With the eastward exit of our clipper system, the only feature of
interest today is the eastward progression of a lake effect band
from Lake Michigan this morning. Winds will shift from the NNE to
the WSW by this afternoon-lightening significantly As it does, the
lake effect band will drift eastward into LaPorte/Berrien Counties,
though I expect it to fall apart and diminish no later than early
afternoon under incoming surface high pressure, backing flow, and
crashing inversion heights. It will be rather chilly today, with
highs only reaching the upper teens in the far NE, and the mid-upper
20s across the southwest.

Another wave aloft will approach the area overnight, causing flow to
veer back to the west-northwest off the lake. With synoptic support
and onshore flow, expect lake effect snow showers to develop in west
wind favored snowbelts. Expect less than 1" of snow accumulation in
these areas overnight. Lows tonight will bottom out between
12-22F.

&&

.LONG TERM...(Friday through Wednesday)
Issued at 415 AM EST Thu Dec 14 2017

The upper level wave will drift eastward through the day, leading to
the spread of light snow inland from Lake Michigan, and continued
lake effect snow in the westerly wind-favored regions. System snow
would primarily impact areas along/north of US 30, though little to
no snow accumulation is expected in these areas. For areas impacted
by lake effect snow, expect as much as 1-2 inches by Saturday
morning, mainly along/north of the toll road. Highs Friday will be
in the upper 20s and low 30s, but by Saturday afternoon expect the
arrival a warmer airmass as winds become southerly and a low
pressure trough moves into the central CONUS. High temperatures will
rise into the 30s and low 40s, warmest south of US 30. This will
bring an end to our lake effect, and tighten the baroclinic zone
just to our north, oriented from roughly WNW-ESE across Lower MI/WI,
forcing it northward.

Meanwhile, both the GFS/ECMWF have a surface low developing in the
central plains by Saturday night in response to the digging trough
aloft. The solutions diverge from there, but both models lift the
low northeastward towards the Ohio Valley Sunday into Monday, with
the low and return flow around a strong high over the Atlantic
pumping up moisture from the gulf of mexico. The GFS pulls the low
into southern Indiana beneath the phasing northern/southern stream
of a coupled upper level jet, and then shunts it largely south of
the IWX area, with a sharp cut off to precipitation on the north
side. This isn`t totally out of the question, given we`ve seen where
things develop well over IND`s area, and then that prevents the
better moisture from reaching our area. However, the ECMWF has the
phasing jets further northward, and a steeper secondary trough to
our northwest, which brings that low north into our CWA Sunday. High
temperatures will likely be in the upper 30s in the north half, and
low-mid 40s further south, so it could be largely rain mixing in
with some snow. Given the extreme discrepancies with the previous
runs of the models at this time period, and the typical problems
we see with phasing north/south streams of the jet, kept consensus
blend for now with respect to pops. We`ll have to monitor this
one, as it will certainly be interesting to see how it plays out.

Finally, other than a few lake effect rain/snow showers Tue/Wed in
WNW wind favored snowbelts, we`ll see relatively mild temps and
quiet weather through Thursday. Highs on Thursday could rise into
the low-mid 40s on Thursday afternoon south of US 30, but otherwise
expect highs in the 30s through the remainder of the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1226 PM EST Thu Dec 14 2017

Backing flow and increasing dry air entrainment has disrupted
lake effect snow as expected this morning. KSBN could experience a
few brief periods of MVFR early this afternoon but confidence in
duration is too low for even a TEMPO mention given recent obs and
radar/satellite trends. Primarily VFR expected to continue through
tonight. Next clipper system arrives late tomorrow morning with
another round of light lake effect snow and lower ceilings that
could cause a period of MVFR conditions.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 4 PM EST this afternoon for LMZ043-
     046.

&&

$$

SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...MCD
AVIATION...AGD


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