Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 121728

Area Forecast Discussion
National Weather Service Northern Indiana
1228 PM EST Fri Jan 12 2018

Issued at 1015 AM EST Fri Jan 12 2018

A wintry mix of snow, sleet, and freezing rain will transition
from west to east to all snow through late morning. Light to
moderate snow will continue through early evening for locations
east of interstate 69, but areas to the west of the interstate
will see snow end by early afternoon. Temperatures will continue
to fall into the 20s through the day. Lows tonight will be in the
single digits and teens. Otherwise, lake effect snow will develop
in the northwest this afternoon and continue overnight. Elsewhere,
expect snow to end. For this weekend and next week, we`ll see
continued cold and several chances for snow.


Issued at 1015 AM EST Fri Jan 12 2018

The forecast looks to be on track as of 1515Z, with snow reported
across the northwest and central CWA (roughly along/west of I
69). Areas further east of I 69 are still reporting a mixture of
snow, sleet, and freezing rain per latest AWOS observations and
weather spotters. Thank you to those who have been giving us such
frequent reports this morning-it really is invaluable and we
appreciate it.

As for temps, we`re seeing temps in the mid-upper 20s in the NW, and
the low 30s in our far eastern CWA, with only a few far eastern
observations reporting temps of 33-34 degrees. Expect temps to
continue to fall through the day.  Northerly winds have gusted at
times to 30-35 mph in our far northwest, and expect gusts around 30
mph through the afternoon as we are able to mix slightly better.

Lake effect signals are already popping up north of our CWA, with
convective rolls observed in light radar signatures. Expect a single
band to develop today, impacting mainly the Indiana counties along
the lakeshore. Dry air looks to limit any significant accumulations,
but we`ll go more into that for the next update. Otherwise, light to
moderate system snow will continue for mainly the central/eastern
areas, gradually tapering off from west to east through this

Until then, roads will be slick and snow covered, with minor ice
accumulations still expected in areas that have yet to change over
to snow. Light to moderate snow continues in many areas. If you must
travel, drive slow on ice and snow!


.SHORT TERM...(Today and Tonight)
Issued at 429 AM EST Fri Jan 12 2018

...Winter Weather Advisory Continues...

Several challenges to short term forecast this morning. Main cold
front was just exiting our eastern area at 09z. Drastic temperature
change across the area as Lima was still in the lower 50s while
Monticello was down to mid 20s at 09z. Shallow arctic air was
undercutting warmer air aloft but eastward movement has been slowing
overnight. Last several runs of Hires guidance has been showing this
with temperatures in the far east not expected to fall to freezing
until between 14z and 16z. By the time this occurs, deeper cold
wedge will be arriving and low level thermal profiles begin to
cool quickly as southern stream wave deepens and pulls colder air
in mid to late morning. This looks to result in far less freezing
pcpn over the eastern half of the area with a later transition
from rain to sleet then snow with only a brief period of freezing
rain possible as this occurs.

Farther west, have already seen several reports of snow and UP
(which is likely sleet) in observations. Of main concern in the
near term is large area of precipitation moving north through
eastern IL and western IN that earlier model runs did not pick up
on. Latest runs of HRRR and RAP as well as 06z NAM show impressive
QPF with this deformation axis/fgen band moving into southwest
CWA before 12z and spreading northeast. Have used a blend of hires
and WPC QPF to account for this which leads to a bit more
snow/sleet in the west this morning than previous forecast. This
area will need to be watched closely as 07z hires guidance showed
QPF over a half inch but likely contaminated by bright banding in
reflectivity output. GOES-16 showed an impressive short wave
across the deep south with moisture plume streaming north into our
area and responsible for the uptick in pcpn returns and QPF.

Temperatures expected to continue falling through the day. Have used
a blend of consshort and HRRR for hourly temperatures and highs
for the day have already been reached. Have used the RAP for our
MaxTwaloft grids with some manual adjustments based on report
locations of snow, sleet and rain. This coupled with the hires sfc
temps have led to the changes in pcpn types and timing across the
local area.


.LONG TERM...(Saturday through Thursday)
Issued at 429 AM EST Fri Jan 12 2018

With focus in the short term with ongoing weather, few changes to
latest blended guidance. Lake effect snow showers expected tonight
into Saturday over NW Indiana but expecting accums of just a couple
inches given transitory nature of band which should waver west then
back east. Flow quickly backs Sunday ahead of potent northern stream
clipper which will dive into the Great Lakes. Model trends have
shifted surface low track north slightly but still spreads light
snow into most of our area Sunday night into Monday. For now looks
like a general 1 to 3 inch event but will have to watch for further
deepening as NAM12 shows 1.5 PVU surface dropping down to around
500mb. Would expect this clipper to be moisture starved in wake of
current system but some enhancement off of lake possible. A rather
decent lake effect event is possible Monday night into Tuesday
with possibility of another Type VI setup as an east-west surface
trough drops south lending to potential mesoscale low development
over the central part of the lake Monday night. Low level flow in
wake of this feature becomes northerly suggesting a trailing
single band possible. Models show various wind directions and
trajectories so confidence low right now in where this feature
will come onshore and best chances for accumulations will occur.
Bumped pops into high chance/low likely category for now across
most of the NW.

Very cold temperatures to continue for much of the week but next
moderating trend looks to be on the horizon by late week into next


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1228 PM EST Fri Jan 12 2018

Conditions will slowly improve through the afternoon as precip
shield shifts southeast and drier air continues to advect into the
area. Anticipate VFR by early evening at both TAF sites. Strong
northerly winds will continue through the evening but will
gradually subside. Lake effect snow and lower ceilings will impact
KSBN tomorrow but best chances appear to be just outside this TAF


IN...Winter Weather Advisory until 7 PM EST this evening for INZ007-

     Winter Weather Advisory until 1 PM EST /noon CST/ this afternoon
     for INZ003>006-008-012>017-020-022>024.

MI...Winter Weather Advisory until 7 PM EST this evening for MIZ080-

     Winter Weather Advisory until 1 PM EST this afternoon for

OH...Winter Weather Advisory until 7 PM EST this evening for OHZ001-

LM...Small Craft Advisory until 4 AM EST Saturday for LMZ043-046.



SHORT TERM...Lashley
LONG TERM...Lashley

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