Area Forecast Discussion
Issued by NWS Northern Indiana

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223
FXUS63 KIWX 080531
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1231 AM EST Thu Dec 8 2016

.SYNOPSIS...
Issued at 1223 AM EST Thu Dec 8 2016

A strong low pressure system moving slowly east across
southeast Canada will cause cold west to northwest winds across
the Great Lakes resulting in significant lake effect snow over
southwest Michigan and far northern Indiana over the next couple
of days, with scattered snow showers over northwest Ohio and most
of the rest of northern Indiana. A low pressure system is
expected to move east across the Midwest this weekend causing snow
in our area, mainly Saturday night and Sunday. An arctic airmass
is expected to plunge southeast into the Great lakes region by the
middle of next week resulting in bitterly cold temperatures and
probably additional lake effect snows.

&&

.SHORT TERM...(This Evening through Friday)
Issued at 350 PM EST Wed Dec 7 2016

Lake effect snow event Thursday/Friday and onset of much colder
temperatures will be the main stories for the short term.

A broad sheared upper level trough approaching central CONUS will
be associated with continued mid level cloud this evening, and
passage of this wave will allow for reinforcement of low level
cold advection tonight. Some subtle veering of low level wind
profiles in the wake of this wave should allow for eventual
development of lake effect snow showers across southwest lower
Michigan late tonight. While lake induced instability will be
increasing, saturation to depths sufficient enough for snow
production will be in question through about 12Z.

Inversion heights to rise more substantially on Thursday as lake
effect snow showers become more widespread. West-northwest low
level trajectories should favor southern lower Michigan and areas
closer to the MI/IN stateline for snow shower development. 800-700
mb dew point depressions should remain on the marginal side
through the day which should limit snow shower intensity through
much of the day. A couple of inches of accumulation is possible
Thursday afternoon across southern lower Michigan, possibly
extending into far northern Indiana. Deep mixing on Thursday
should allow for wind gusts into the 25 to 30 mph range in the
afternoon, so despite the relatively light lake effect
accumulations anticipated through mid-late afternoon, some issues
with blowing/drifting snow will be possible.

Of greater concern in terms of lake effect is the Thursday night-
Friday period as another upstream vort max dives across southern
Great Lakes providing a period of deeper moisture profiles. Lake
induced instability will also maximize during the nighttime hours,
and all indications still point to the Thursday night/early Friday
morning period as potential greatest impact period. Cross sections
still suggest strongest low level lift may reside just below DGZ
or clipping lower portions of DGZ. Of concern however, is expected
weakly confluent/convergent flow pattern associated with
approaching mid level wave that could further act to sharpen lake
response/banding. Lake aggregate troughing also should tend to
sharpen banding Thursday night/early Friday.

Given the above factors, have upgraded the winter storm watch to
a warning and maintained advisory counties as is. Have delayed
onset of the winter weather advisory until 15Z, and maintained 09Z
start time for the winter storm warning for the three southern
lower Michigan counties. It should be noted, this onset time may
need to be delayed a bit depending how things with evolve
overnight tonight. Confidence is on the high side that highest
impacts should hold off until late Thursday afternoon/night. The
other big story will be the trend to much colder temperatures with
afternoon highs only into the mid 20s Thursday, and wind chills
Thursday night/Friday morning dropping to 5 to 15 above. Lake
effect snow showers should tend to diminish in intensity Friday
afternoon/evening. On Friday, deeper moisture profiles will
gradually erode with some backing of low level winds eventually
confining most of additional lake effect to southern lower
Michigan.

&&

.LONG TERM...(Friday Night through Wednesday)
Issued at 350 PM EST Wed Dec 7 2016

A brief lull in the active weather is expected Friday
night/Saturday, although some lingering lighter lake effect snow
showers may be ongoing across southern lower Michigan.

A period of fairly strong warm advection should ensue for
Saturday afternoon/Saturday night as next upper PV anomaly emerges
in the lee of the Rockies. Warm advection snow should develop
particularly across northern half of the forecast area by Saturday
night with some light to moderate accumulations possible.
Consensus guidance still suggests prolonged event into Sunday as
next upstream short wave progresses across the area, although
medium range models still exhibiting quite a bit of spread and
volatility in the details regarding strength/progression of this
wave. Have kept precip all snow for Saturday night/Sunday,
although outlier 12Z ECMWF would suggest rain/snow issues. ECMWF
represents a stronger/slower outlier at this time with more
copious moisture transport ahead of this wave, and have opted to
put more weight into GEM/GFS blend. This system will need to be
watched for possible headlines over the next few days, as several
inches of snow accumulation appear to be a strong possibility for
at least portions of the forecast area. Some lake effect is
possible behind this system. Otherwise, very cold conditions look
to be in store middle of next week with strong low level thermal
troughing overspreading much of eastern CONUS.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1223 AM EST Thu Dec 8 2016

Deep low over james bay will move slowly east with a trailing trof
dropping sewd across the grtlks this taf period. Extensive strato cu
deck over the upr midwest/grtlks has been slowly advecting sewd into
nrn IN and this should continue overnight. Flurries upstream across
the upr midwest suggest decent low level moisture advecting toward
our area as well. This in combination with continued caa/increasing
inversion heights should lead to lake effect shsn developing early
this morning and then continuing and grdly intensifying through the
period with ifr conditions expected by this eve at sbn. Lower
inversion heights at fwa suggest just ocnl -shsn at this terminal
with mvfr predominating.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory from 10 AM this morning to 4 PM EST
     Friday for INZ004>007.

MI...Winter Weather Advisory from 10 AM this morning to 4 PM EST
     Friday for MIZ080.

     Winter Storm Warning from 4 AM early this morning to 4 PM EST
     Friday for MIZ077>079.

OH...NONE.
LM...Small Craft Advisory until 7 PM EST Friday for LMZ043-046.

&&

$$

SYNOPSIS...JT
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...JT


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