Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 142337

Area Forecast Discussion
National Weather Service Northern Indiana
637 PM EST Sun Jan 14 2018

Issued at 412 PM EST Sun Jan 14 2018

A clipper system will bring 2 to 4 inches of snow to the area
tonight into Monday, with the highest accumulations in the
northwest. Lake effect snow will develop in the wake of this system
Monday night, and continue into Wednesday, bringing additional
accumulations to the snow belts. High pressure will bring quiet
weather through Thursday. There is a chance for rain and snow next
weekend. Highs this week will be in the teens and twenties, lows
will be in the single digits and teens. By the end of the week,
we`ll see a slight warming, with highs into the 30s and 40s by the


.SHORT TERM...(This Evening through Monday)
Issued at 412 PM EST Sun Jan 14 2018

...Clipper System Tonight & Monday...

The primary concern of the short term is our incoming clipper
system. 12Z guidance is fairly similar to the previous runs, and
most of the guidance remains consistent with the placement and
timing of major features, including the upper level trough and the
surface low. The 12z Raobs this morning also appear match up well
with model depictions of the upper level pattern. Confidence in
the overall event occurring as forecast is high.

That being said, an upper level low will develop over Minnesota by
12Z Monday, sinking southeastward and centering over Lower
Michigan by 12Z Tuesday. The surface low dives into IL by 12Z
Monday, then has it slowly weakening as it drifts through our CWA
into Lake Erie through Monday night, leaving us in cyclonic flow
(hence setting us up for lake effect in the long term).

Starting this evening, we`ll see weaker isentropic ascent on the
295k sfc (western CWA), which will strengthen and continue through
Monday. This will bring a widespread light snow to our area. The
best synoptic support from the left exit region of a decent 300mb
jet streak arrives Monday morning, between 9-12Z, and exits the
area in the 21-00z time frame, weakening as it moves east. This
will lead to some periods of moderate snowfall, mainly in the west
and central, with visibilities potentially reduced to around 1/2
mile at times. Those commuting monday morning should be prepared
for delays. Hopefully the MLK holiday will cut down on the amount
of people traveling to work around this time.

The biggest limitation for the event will be the lower moisture
content. As previous AFD mentioned, mixing ratios look to be
around 1-2 g/kg, and best moisture transport looks to be to remain
south of our area. With the limited moisture (lack of consistent
supersaturation wrt ice) and distribution of lift in the DGZ
expect snow ratios to be around 15:1, and accumulations to be on
the lighter side, especially in the east when main forcing starts
to decrease.

Looking at 24 hour amounts from 7 pm tonight through 7 pm Monday
evening, expect 2-3" for most areas, with amounts as high 4" in
the advisory area (particularly the western portions). Per
collaboration with surrounding offices, have put up an advisory
for all counties in IN and most counties in southern MI. Opted to
leave NW Ohio and Hillsdale, MI out given amounts are closer to
1-3" than 3-4"-especially in our easternmost CWA. ILN has slightly
lower criteria for advisories, thus they have issued an advisory
further east than us. CLE/DTX and I were in agreement that an
advisory was not needed for our bordering counties. Handled these
with an SPS for now.


.LONG TERM...(Monday Night through Sunday)
Issued at 412 PM EST Sun Jan 14 2018

Lake Effect Snow & Cold Monday Night-Wednesday:

Monday night into Wednesday

Expect lake effect snow to Kick in Monday night and continue into
Wednesday. Not much has changed since the previous forecast, with
cyclonic flow overhead, the trough at the surface, and decent
delta theta-e`s developing in the wake of our clipper system.
Combined with lingering moisture, we`ll see lake effect develop in
the north- northwest favored regions and continue into through
mainly Wednesday morning. There are still differences in how
models handle the dropping trough and resultant mesolow and single
band, so despite higher confidence in the lake effect occurring,
there is lower confidence in amounts and exact time/location-as
usual with these types of events. Right now, the NAM depicts the
mesolow dropping into Berrien/LaPorte counties near Lake Michigan
by early Tuesday morning, which then sinks inland through the day.
Thus the highest amounts, using 18-20:1 ratios, are in
Berrien/LaPorte counties. At the moment, I have 4-5" of additional
snow as compared to 1-3" further inland in the surrounding
counties, but this is all subject to change depending on where
things set up exactly. Otherwise, dominant single band develops
and shifts eastward through Wednesday, where winds back to the WNW
as a surface high edges into our southwestern CWA.

Temperatures will be on the colder side, especially Monday night
into Tuesday morning. Winds will stay up through Tuesday, with gusts
to 10-15mph inland, and as high as 20 mph near the lakeshore. With
lows forecast to range from 1 to 15 above (warmest near lakeshore),
and highs in the teens and low 20s, this puts wind chills in the 5
to 15 below zero range. Winds will lighten up Tuesday night, Wind
chills won`t be as much of a concern for that period and into
Wednesday. Lows Tue night and Wed night will be in the single digits
and teens. Highs Wednesday will be around 20F.

Discrepancies appear for the end of the week with regards to
conditions Thursday night into the weekend, but kept chance
consensus pops in for now. The GFS tries to develop a little upper
level low, while the ECMWF keeps a ridge overhead...long story
short, not going to pick one or the other at this point. That being
said, high temps will warm into the 30s and 40s by Saturday, and
Sunday may even reach into the upper 40s. Any precipitation will be
a rain/snow mix, which is what I put in the forecast for this
period. We`ll see how it shakes out.


.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
Issued at 635 PM EST Sun Jan 14 2018

High pressure continues to leave to the east and low pressure
comes in from the northwest. This will allow moist advection and
for snow to break out across the area starting by 4z at SBN and by
6z at FWA. With column saturation by a couple hours after
midnight, feel flight conditions will be able to drop into MVFR
overnight and IFR within the heavier snow during the morning and
midday time frame as stronger lift comes in. Then drier air will
come in by evening or early overnight and snow will end.


IN...Winter Weather Advisory from 10 PM EST /9 PM CST/ this evening
     to 7 PM EST /6 PM CST/ Monday for INZ003>009-012>018-020-

MI...Winter Weather Advisory from 10 PM this evening to 7 PM EST
     Monday for MIZ077>080.




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