Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 130542
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1242 AM EST Sat Jan 13 2018

.SYNOPSIS...
Issued at 635 PM EST Fri Jan 12 2018

Dry air continues to stream in from the north tonight and clouds
begin to break up away from the lake. Lake effect snow showers
will develop in northwest Indiana and southwest Lower Michigan
today. Minor accumulations are expected. Lows this morning will
be in the single digits and teens. Highs today will be around 20.
A clipper system will bring additional chances for accumulating
snow Sunday night into Monday. Lake effect will return again
Tuesday into Wednesday afternoon for north-northwest wind favored
snowbelts. Drier and slightly warmer conditions are expected at
the end of next week.

&&

.SHORT TERM...(This Evening through Saturday)
Issued at 339 PM EST Fri Jan 12 2018

...Cold with Lake Effect Snow...

I don`t know how AFD readers feel, but I am definitely happy to NOT
be writing much about today`s wintry Mix. I believe this storm
was a great lesson for everyone about hyping "big winter storms"
too far in advance, with most areas ending up below 2" of snow
accumulation (a few isolated 2.5 in reports as of 20z) and minor
ice accumulation. Will let the advisory expire this evening once
snow clears the area. The evening shift may be able to drop the
remaining western counties (including Allen, IN) early. A few
rivers have gone into minor flood stage this afternoon due to the
snowmelt and rainfall we received, so monitor our AHPS page for
any river flood warnings or statements.

We`re back to the snow and cold for the foreseeable future, and in
the case of the short term-Lake effect snow showers. As mentioned
in my earlier update, the beginnings of our post-system lake
effect are underway. We see the first signs of lake effect snow
bands on satellite/radar imagery, and a band over LOT`s CWA.
Expect this band to migrate slowly eastward this evening,
especially once winds become more north-northwesterly around 9z
and beyond. Delta theta-e`s are decent and there is enough
ambient synoptic support thanks to our upper level low, but drier
air may serve to undermine any significant accumulations. We
probably have more moisture than models indicate given the
northerly fetch, but things are already off to a slower start than
we had in the forecast previously.

Things look to improve Saturday for snow accumulation as winds
become northwesterly, and a shortwave pinwheels around the upper
level trough, traversing our CWA through the day. Delta theta-e`s
are sufficient instability wise, and we have a little increase in
the moisture content. Inversion heights at KSBN reach up to 6Kft
by the afternoon, so thinking we`ll see snow showers during this
time associated with the eastward migrating band. As far as QPF
goes, it looks to still be on the lower side but snow ratios might
be pretty good for dendrite production. BUFKIT soundings at KSBN
suggest that lift from the shortwave will be maximized in the DGZ
around the 15-18z time frame especially, so have adjusted pops
accordingly. Think we`ll get some snow with the short wave further
inland in the afternoon, but I am less confident in the extent.
For now have some lower chances in the northwest. Lake effect snow
accumulations look to be about 1-2 inches in favored regions,
with less than half an inch further inland.

High temperatures look to be around 19-20F, and lows tonight will
drop into the single digits north and from 10-15F elsewhere.

&&

.LONG TERM...(Saturday Night through Friday)
Issued at 339 PM EST Fri Jan 12 2018

...Clipper System & Lake Effect to Bring More Snow...

High Pressure and Ending Lake Effect: Saturday Night-Sunday

High pressure builds in and flow veers around to the west southwest
by late Sunday morning, bringing our lake effect snow to a temporary
end. Expect dry conditions, with highs again around 20F, and
overnight lows Saturday/Sunday night in the single digits and teens.
The pressure gradient begins to tighten by Sunday evening as another
system approaches the area, leading to gustier southerly winds.

Alberta Clipper: Sunday Night-Monday

Late Sunday night into Monday we`ll see our next chances for system
snow as a clipper system develops ahead of another stronger, more
potent shortwave trough aloft. The surface low will drop
southeastward out of Alberta, and models generally agree on the path
extending from WI/IL at 12z Monday through Lower Michigan by 12Z
Tuesday. It will continue eastward into the lower Great Lakes by
Tuesday afternoon as yet another 1048hPa high pressure sinks into
the northern and central plains, ridging into our CWA.

With good synoptic support and decent moisture, expect a widespread
light to moderate snow over the CWA. Soundings suggest snow ratios
initially around 12-15:1, rising to 17-20:1 by the late
afternoon/evening hours. The prime DGZ initially looks to be located
below 10Kft and the strongest/majority of the omega is above the
DGZ. This would favor more of a 12-15:1 ratio versus the consensus
blend`s 20:1 (which has been overdone several times this season).
Lowered the snow ratios to more what I would expect, as outlined
above. This gives us around 1-3" of snow accumulation Monday. Expect
we`ll see some disruptions to travel for the Monday AM/PM
Commutes.

Lake Effect Returns: Tuesday into Wednesday Afternoon

As winds veer around the surface low, we`ll see north-
northwesterly winds develop and strengthen. I`ve increased winds
above the consensus blend for this time period (and Monday) as
they seemed too light given the tighter pressure gradient.
Moisture around the lingering low, in addition to a lake superior
connection, and stronger delta theta-e`s look to bring us our next
lake effect event, specifically a "Type VI" event as mentioned in
our previous AFD. Synoptic forcing will abound as a shortwave
swings southwestward around the base of the upper level low
pressure system, which at 18z Tuesday spans Lake
Huron/Ontario/Quebec. Of course, with any lake effect confidence
is not high in exact location of the band setting up. Have
increased pops from consensus blend similarly to the previous
shift, as models seem to agree on the general pattern (with some
differences). We`ll see the snow-it`s just a matter of how much.

High temperatures Tuesday will be downright cold, only reaching into
the mid-upper teens. Lows Tuesday night will be in the single
digits. We`ll bounce back into the upper teens and low 20s Wednesday
afternoon.

Drying out and "Warming" Up: Wed Afternoon-Fri Night

Yet another high pressure system builds into our area by Wednesday
afternoon, and flow swings to the southwest. Additionally, models
have a highly amplified ridge building in aloft. This will force our
lake effect snow northeastward out of our CWA as they diminish under
increasing subsidence, and bring in the dry air. It will also allow
for some warmer temperatures to make it up to the Great Lakes.
Temperatures will start out Thursday in the mid 20s, and then
gradually rise into the low-mid 30s by Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1237 AM EST Sat Jan 13 2018

Strong northerly winds the main story for the early overnight on
the backside of a low pressure system tracking into the Northeast
US. Winds slacken some today, though cold/backing flow will allow
lake effect plume and associated snow showers to work into KSBN
later this morning/afternoon with periodic IFR/MVFR visibility
restrictions and some light snow accumulations. Could even see a
few snow showers or flurries briefly at KFWA later this
afternoon/early this evening.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory until 7 PM EST this evening for LMZ043-046.

&&

$$

SYNOPSIS...MCD/Roller
SHORT TERM...MCD
LONG TERM...MCD
AVIATION...Steinwedel


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