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Area forecast discussion 
National Weather Service northern Indiana
530 am EST Friday Feb 12 2016

issued at 334 am EST Friday Feb 12 2016

An Arctic front will bring gusty winds and increasing chances for
snow showers to the region this afternoon. Most locations could
see a quick dusting to half inch of snow...with higher amounts
possible in far northern Indiana and lower Michigan. Highs this
afternoon will reach the low to middle 20s. Arctic air will then
continue to filter in behind this front Friday night into Saturday
with lows into the single digits above zero tonight...with highs
on Saturday only reaching the low to middle teens. Wind chills
between 5 and 15 below zero can be expected later tonight into
Saturday morning. Accumulating lake effect snow and blowing snow
will likely create difficult travel Friday night into Saturday
near Lake Michigan.


Short term...(today through saturday)
issued at 334 am EST Friday Feb 12 2016

Vorticity lobe nearing Western Lake Superior will translate southeast
through the Great Lakes under a James Bay negative height anomaly
expected to dislodge south toward New England. This process will
force an Arctic cold front through lower Michigan by late morning/early
afternoon and our in/Ohio counties this afternoon. Large scale ascent/q-vector
convergence through a deep layer and expectations for lake plume
to become entrained into frontal zone support high probability of precipitation for snow
showers along/behind this feature into northern zones...with lower
chances along/south of US 30 divorced from deeper ascent and lake
contribution. Steepening lapse rates/saturation into the dgz just
behind the Arctic front suggest the potential for higher
intensity/brief snow along the frontal zone...with a dusting
south of US 30 to around an inch or so along/north of the Indiana
toll Road. This combined with gusty winds and snow cover may make
for hazardous travel conditions late morning/afternoon across far northern
in/SW lower Michigan. Otherwise in the very near term (early this
morning)...could see some light snow (a quick dusting?) Clip
areas south of US 30 in Indiana on the northern fringe of a
separate/weak clipper system tracking into the Ohio Valley.

Another northwest flow lake effect event remains the larger story into
tonight and Saturday as Arctic airmass overspreads Post-frontal.
Trajectories tonight favor a Lake Superior connection...which when
combined with lake-800 mb temperature differentials pushing well into the
20s (inversion heights to 8-10 kft, lake induced cape to 6-7k j/kg)
highlight the potential for moderate-heavy lake effect snow showers in
favored northwest flow belts. Organization/intense banding over one area
should be limited by stronger flow at least into the evening/early
overnight. A plethora of needle generation also seems like a good
bet with bulk of ascent/saturation occurring just above the dgz.
This all points to another solid advisory event late morning
through Saturday...although gusty winds/blsn and more organization
than currently expected would be problematic for more significant
snow rates/accums and impacts.

Drying/subsidence and backing winds in response to ridge building
into the Upper/Middle MS valley will gradually take its toll on
inversion heights Saturday. The result will be a trend toward lower
intensity lake effect snow into west-northwest flow belts...with diurnal
component/backing likely allowing scattered flurries or light snow showers
to fill into eastern portions of the forecast area during the afternoon.
Winds will also be much lighter which will reduce the blowing snow
potential across northwest in/SW lower Michigan. Could still see some decent
additional snow accums (1-3 inches) in the advisory area into at
least the first half of Saturday as diminished flow/supersaturation
with respect to ice more focused into dgz possibly surprises (better
ratios/organization/troughing). Cold otherwise with wind chills
later tonight/Saturday morning prognosticated into the 5 to 15 below zero
range (advisory criteria locally is 15 below zero or colder).


Long term...(saturday night through thursday)
issued at 334 am EST Friday Feb 12 2016

Expansive area of high pressure will move across the area Saturday
Night. Lake effect will be ending as ridge moves in and flow weakens
while becoming southerly overnight. Clearing skies and light winds
expected to provide a brief window of good radiational cooling
before middle and high level clouds ahead of next clipper approach.
Temperatures will be tricky in this regime but any short duration of
radiational cooling in areas with fresh and deep snowpack to yield
sharp drops in temperatures. Continued to undercut MOS temperatures with lows
around zero and below zero temperatures where ideal conditions come

Fast moving weak clipper to move through Sunday with models
indicating weak lift and limited moisture. Snow ratios remain near
20 to 1 so an inch or two looks plausible at this time across the
area. Focus then shifts to southern stream wave that induces
cyclogenesis Monday night and Tuesday over the southeast Continental U.S..
models have tightened the deformation area and now keep most precipitation
just southeast of our area. Maintained low chance probability of precipitation from
superblend init for now due to model uncertainty.

Another weak short wave and surface front to move through late Tuesday
bringing a last shot of colder air for Wednesday before what appears
to be a nice warm up to end the week. Could be some lake effect snow
showers Wednesday before another large area of high pressure moves
in. Return flow behind this ridge brings very warm air aloft into
the Great Lakes to end this period and just beyond with a more zonal
middle level flow.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 526 am EST Friday Feb 12 2016

VFR/light SW winds will persist at terminals early this morning.
Snow showers, increasing/veering winds, and ceilings lowering to
MVFR/low VFR can be expected along and behind an Arctic cold by
approximately 15-16z at ksbn and 17-18z at kfwa. Snow showers may
reduce visibilities to IFR at chances at ksbn where a
tempo group was retained. Winds will also pick up Post-frontal as
mixed layer deepens and pressure gradient tightens. Mainly
MVFR/VFR at kfwa and IFR/LIFR at ksbn otherwise into tonight as northwest
flow lake effect snow develops.


Iwx watches/warnings/advisories...
in...Winter Weather Advisory from 10 am EST /9 am CST/ this morning
to 4 PM EST /3 PM CST/ Saturday for inz003>005.

Michigan...Winter Weather Advisory from 10 am this morning to 4 PM EST
Saturday for miz077>079.

Lm...heavy freezing spray warning from 7 PM this evening to 7 am EST
Saturday for lmz043-046.

Gale Warning from noon today to 7 am EST Saturday for lmz043-046.



short term...steinwedel
long term...Lashley

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