Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 110204

Area Forecast Discussion
National Weather Service Northern Indiana
904 PM EST Wed Jan 10 2018

Issued at 409 PM EST Wed Jan 10 2018

A low pressure system will bring a wintry mix of rain, freezing
rain, sleet, and snow to the area this week. High temperatures will
go from well above normal today and Thursday to below normal by this
weekend. Light drizzle and rain showers will continue overnight,
with more substantial and widespread rain expected by Thursday
morning. Fog will lead to low visibilities, eventually dissipating
by Thursday afternoon. Otherwise, rain will mix with freezing rain,
sleet, and snow Thursday night, then finally change over to all snow
from northwest to southeast by late Friday morning. Snow will
continue into Saturday morning. Lake effect snow will develop in the
wake of the low pressure system, continuing from Saturday afternoon
into Sunday, as cold air filters into the region.


Issued at 900 PM EST Wed Jan 10 2018

An axis of very strong low level flow continues to overspread the
region this evening. Narrow thermal ridge/WAA accompanying this
strong advection appears to have helped improve vsbys across most
areas this evening, with a few holdout observations 1/2 mile or
less across southern Lower Michigan. Given current trends, will
likely be able to allow dense fog advisory to expire at 03Z for
southern Lower Michigan. If dense fog redevelops tonight, best
chance may be downwind of melted deeper snowpack across far
northwest portions of the area where will hit fog a little harder
overnight in comparison to the remainder of the area. Breezy
conditions to persist into the overnight hours with occasional
gusts to 25-30 mph continuing. Little in the way of temperature
fluctuation anticipated given strong flow/WAA/low level
moisture/cloud cover.


.SHORT TERM...(This Evening through Thursday)
Issued at 409 PM EST Wed Jan 10 2018

...Rain, Fog, and Unseasonably Warm Temperatures...

Today we dealt with a mix of drizzle and advection fog from the
incoming warm air, which is expected to continue overnight before
the main swath of rain moves into the CWA tonight.  A dense fog
advisory is in effect through this evening. Temperatures as of this
AFD were steadily rising, already into the Low-mid 40s along/north
of US 30 and the upper 40s to 50F south. Temperatures will slowly
rise into Thursday morning, with temps ranging from 47 to 53 around
8 AM EST. Obviously, snowmelt is underway and will continue through
Thursday afternoon. This will only contribute to the fog situation,
despite strengthening southerly flow tonight and Thursday.

Thursday will be even warmer than today, thanks to the incoming
warm/moist air straight out of the Gulf. 850mb Temps rise up to
around 8-10C ahead of the approaching cold front, with a stronger
LLJ ramping up to 45-55 kts. Southerly winds will gust up to 30-35
mph at times during the day, despite rain/cloud cover.

On a final short-term note, with the rain and snowmelt, expect minor
flooding near rivers/streams, fields, and in low-lying areas.


.LONG TERM...(Thursday Night through Wednesday)
Issued at 409 PM EST Wed Jan 10 2018

Bottom line up front: The models have trended further and further
southeastward with our "snow storm" originally forecast for Friday
night into Saturday. At this point, we`re not putting out any
watches/headlines, given the significantly lowered snowfall amounts
and the lower confidence in the storm impacting the area. Snow
totals will range from around 1-2" in the west and central, and up
to 2-5" in the very far southeastern CWA (as of the latest model
runs). Otherwise, a wintry mix of rain, freezing rain, sleet, and
snow is expected Thursday night into Friday morning, which will make
for potentially hazardous travel. Ice accumulations of up to 0.05"
are possible in the western and central CWA, and lesser amounts

Wintry Mix of Precipitation Thursday Night-Friday Morning

The cold front from the aforementioned system will be into our west-
central CWA by 18z Thursday-00z Friday, and will continue it`s
eastward progression through Friday morning. Behind the frontal
boundary, we`ll see the intrusion of colder air filtering in at
the surface. With warmer air still aloft Thursday evening, think
there will be a couple hour period of freezing rain, especially in
our west and central CWA, before things change to more
sleet/snow, so I do have light ice accumulations (Up to 0.05" max
at this time).

Light to moderate snowfall will continue through the day on Friday.
Snow accumulations look to be around 1-3" for most areas, with the
highest amounts further southeast. With light ice potential
overnight, and accumulating snow, the morning commute on Friday
morning could be a little dicey. Prepare for travel impacts
accordingly. Areas in the far southeast could also have a worrisome
evening commute, depending on where the low pressure system tracks
Friday Evening into Sat AM.

Speaking of our potential snow storm...the latest model runs,
including the 12z NAM/GFS/GEM and the 12z ECMWF, have come in
favoring something resembling something closer to what the GFS
originally had in mind: A further eastward track with the low
pressure center. Sampling of the pacific jet involved with our
system has just begun as it arrived onshore of the western CONUS, so
this may have course-corrected the models. It will be interesting to
see what the 00z runs come up with.

So what does this mean for the forecast at this point? The low
pressure system will develop on a negatively tilted upper level
trough, and basically sideswipe our far southeastern CWA (Jay County
and southeastern Adams counties in IN; and Van Wert, Allen, and
Putnam Counties in Ohio). Thus, a pop-chop and QPF cut were in order
for this period. From Thursday Night-Saturday morning, we have snow
totals of 3-5" in these counties, with the greatest totals along our
CWA borders. I would not be surprised if these totals were further
decreased in subsequent forecasts, but at this point confidence is
low given the variation in model solutions over the past week. Have
held off on any headlines at this point, given the lower confidence
in reaching more than advisory criteria in our far SE.

Arctic Air Returns: Cold Temperatures & Lake Effect

Cold, arctic air will intrude upon the CWA in the wake of the low
pressure system passing to our east. How quickly the intrusion takes
place will all depend on the strength and location of the
aforementioned low pressure system, and thus which model you side
with. The 00z ECMWF brings 850mb temps to -18 to -20C by 12Z
Saturday, while the GFS has them still lingering around -12 to -14C.
Both models have -17 to -20C for the 18z time frame, so it looks to
be downright chilly. This puts high temperatures Saturday-Sunday in
the teens and low 20s. Lows will be in the single digits.

Aloft, we`ll still be dealing with the trough that kicked off the
low pressure system to our east, so we`ll have plenty of weak-
moderate synoptic support to work with in terms of lake effect snow.
A strong pressure gradient will be in place thanks to the strong
high pressure system advancing southeastward from the plains this
weekend, and the exiting surface low over the New England States.
This will keep flow north-northeasterly, allowing for a single N-S
oriented snow band to develop over Lake Michigan, which will
gradually drift east-northeastward before dissipating Sunday
afternoon. Thus most of the snowfall will be to our west, or in the
far northwestern portions of our CWA. The biggest limitation to any
significant accumulations will be the incoming dry air.

Another low pressure system will develop in the north/central plains
and drift eastward Monday into Tuesday, leading to backing flow to
the southwest across the area and chances for snow. Additional lake
effect is possible in the wake of this second system, which will be
Tuesday afternoon-overnight. High pressure returns for Wednesday and
Thursday, so kept things primarily dry these days. High temperatures
Monday into Thursday will be in the teens and 20s. Lows will be in
the single digits and low teens.


.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 707 PM EST Wed Jan 10 2018

Opportunity for substantial improvement in terms of aviation
weather will be limited this forecast period as warm/moist air
mass combined with abundant low level moisture to melted/melting
snow keeps conditions IFR to LIFR. Will maintain the more
pessimistic conditions at KSBN in closer proximity to the initial
deeper snowpack with continued moisture source. Conditions even
have improved to lower end MVFR early this evening at KFWA. Have
noted upswing in vsbys across northern Indiana past few hours as
stronger low level jet/thermal ridge has advected across
northwest/north central Indiana. Still some concern that areas
across far north central Indiana into southwest Lower Michigan
could be susceptible to renewed vsby restrictions under a mile
later tonight, and at this point will not make major changes to
previous TAFs keep cigs at LIFR/IFR levels through the period.
Gusty south winds to continue, and even with the sfc winds gusting
to 20 to 25 knots, did maintain LLWS through most of this period
with 50-60 knot low level jet in place. Areas of drizzle should
transition to rain on Thursday as larger scale frontal forcing
increases in association with approaching arctic boundary for
Thursday night/Friday.


MI...Dense Fog Advisory until 10 PM EST this evening for MIZ077>081.

LM...Dense Fog Advisory until 10 AM EST Thursday for LMZ043-046.




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