Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 301743
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1243 PM EST Wed Nov 30 2016

.SYNOPSIS...
Issued at 1229 PM EST Wed Nov 30 2016

Dry and sunny conditions today give way to increasing cloudiness
by later afternoon as cooler air moves in. With the cooler air
around, some lake effect rain and snow showers are possible tonight
through Friday mainly north of route 6. Precipitation will be
light and temperatures will be in the 30s so expect little to no
accumulation of snow. It will be dry on Saturday but another
chance for light rain and snow will arrive on Sunday. Highs today
in the 40s to low 50s will drop into the 30s overnight.
Temperatures will then rise to around 40 degrees for Thursday.

&&

.SHORT TERM...(Today and Tonight)
Issued at 405 AM EST Wed Nov 30 2016

Quiet weather expected through the day today as we reside in dry
sector of expansive/barotropic low inching across the Great Lakes.
Removed all of the PoPs in our eastern counties for today as
convection over the Tennessee Valley and predominate SW flow
prevents more efficient moisture transport into our CWA. Sheared
vort max and associated cold front not providing much uvm either and
anticipate just some added clouds in our eastern half today. Passing
front will lead to a large gradient in high temps. Western counties
may struggle to get out of the mid 40s given early arrival of CAA
while our E/SE could make a run at mid/upper 50s.

Primary vorticity lobe will arrive overnight, along with cold(ish)
air. Moderate lake-induced instability still expected despite 850mb
temps only around -5C. Plenty of background/synoptic moisture with
this wave and inversion heights climb to around 8-10 kft by late
tonight. 0-2km delta theta-e values drop to around -1 C/km with a
wide area of reduced stability across most of the Great Lakes.
Problem for our area is the fetch which is actually WSW (around 250
degrees) for most of the night. Passing shortwave may be able to
touch off a few additional showers without direct lake contribution
but appears limited based on relatively dry forecast soundings. Have
therefore tried to confine the higher PoPs to the far northern
fringes of our MI counties. Did leave in a slight chance down to the
US-6 corridor but measurable precip appears unlikely there. Expect
primarily rain to start but will likely transition to some light
snow by early Thursday morning as boundary layer continues to cool
in CAA/evaporative cooling regime. Rates not expected to be heavy
enough to overcome warm ground though and little to no accumulation
is expected. Just a tenth or two at best on grassy surface in our MI
zones.

&&

.LONG TERM...(Thursday through Tuesday)
Issued at 405 AM EST Wed Nov 30 2016

Flow veers to a bit more westerly direction on Thursday. Slightly
better fetch for our CWA but also corresponds to lowering inversion
height and reduction in background moisture depth/magnitude. Models
do show a much weaker shortwave moving through late Thursday and
this, in concert with moderate instability/convective depths, will
likely be enough to at least keep some lake effect precip going in
out northern counties. Flow continues to veer slightly through
Thursday so did keep some slight chances along toll road but will
again primarily be a MI problem. Expect very limited diurnal range
on Thu given shroud of overcast skies. Still, should be enough
recovery to lead to primarily liquid precip types during the day.
Rates will remain on the low side and this will prevent accumulation
even if some snow does mix in at times.

Lake effect machine continues into Thu night and Fri (albeit in a
gradually weakening state) as cool, cyclonic flow persists over the
Great Lakes in wake of slowly exiting system. Thermal profiles
continue to slowly drop in a 270-290 degree flow but inversion
heights remain around 6 kft with a gradual increase in entrainment
of drier/more stable upstream air. This is enough to keep low/mid
chance PoPs going in out far NW (with slightly colder temps allowing
a bit more snow to mix in) but chances for accumulation and/or
impacts still appear low given very light rates and marginal surface
temps/warm ground.

Lake effect will gradually wind down late Fri into Sat but next
trough set to arrive late Sun with next batch of WAA/precip. Still
some slight timing difference but overall models in much better
agreement on evolution of this next system. Precip types are a bit
of a mess for Sunday. Current thermal profiles would suggest a
period of snow at the onset, followed by transition to rain as WAA
ramps up. Forcing is relatively weak with a progressive/open wave
but could see some light snow accumulation, especially in our N/NW
counties.

This will be followed by a warmup on Monday and Tuesday as
pronounced ridge builds over the Great Lakes. Consensus blends
included a residual low chance PoP Tue morning with a weak surge of
low level warm/moist air advection. 00Z model suite is primarily dry
during this period but after coordination with neighbors, decided to
leave in a small chance and see if trend continues with 12Z data. If
so, these PoP`s will likely be removed/delayed.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
Issued at 1229 PM EST Wed Nov 30 2016

An early area of sunshine and driness gives way to cloudiness,
mostly MVFR, later this afternoon as an upper level low pressure
system comes in. In between shortwaves, there may be a brief
period of increasing CIGs before the second shortwave comes in
with more moisture decreasing CIGs again towards daybreak
Thursday. Expecting lake effect precipitation to form and with a
wind veering to more northerly overnight, some lake effect
precipitation is possible at SBN later in the overnight.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Small Craft Advisory from 5 PM this afternoon to 11 PM EST
     Thursday for LMZ043-046.

&&

$$

SYNOPSIS...AGD/Roller
SHORT TERM...AGD
LONG TERM...AGD
AVIATION...Roller


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