Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 041729
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1229 PM EST Sun Dec 4 2016

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 333 AM EST Sun Dec 4 2016

An upper trough will move across central Indiana today bringing rain
and some snow to the area. A stronger system will bring mainly rain
to the area Monday night into Tuesday. Much colder air will move in
mid week and could bring some snow with it. More snow is possible
next weekend.

&&

.NEAR TERM /Rest of Today/...

Issued at 936 AM EST Sun Dec 4 2016

UPDATE...
Current radar mosaic shows highest reflectivities to the west of
forecast area...and current observations are indicating light
snow. However, precipitation is struggling to reach the ground
across Central Indiana at this time, expect best chances to be
this afternoon when forcing intensifies. By that time, warm
advection from the south should result in mainly an all rain
forecast across the majority of the forecast area. The exception
will be the far northwestern counties, which could be cool enough
for some light snowfall accumulations later today. Current temps
across the area are generally in the mid to upper 30s. Updated
grids have been sent.

PREVIOUS DISCUSSION...
Isentropic lift will increase across central Indiana today as an
upper level wave moves into the area. Q-vector convergence progs
show decent forcing as well. Moisture looks good. Thus expect the
area to see precipitation today. Went categorical PoPs all areas.

Timing of the best forcing and moisture is this afternoon, so that
is when PoPs will be highest. For the early to mid morning, dry low
levels will eat away at precipitation that develops across the area.

Main problem is precipitation type across the northwest forecast
area today. Temperatures will be cold enough this morning for any
precipitation that reaches the ground to be a mix of snow and rain
across much of the area, with snow more favorable northwest where
temperatures will be coolest.

Across the far northwest (Warren, and northwest portions of
Tippecanoe and Carroll counties), temperatures will struggle to get
above the mid 30s. Forecast soundings show temperatures remaining
below freezing for all but the near surface layer.

Unfortunately even a small change in forecast temperatures could
have big impacts on precipitation type there. For now feel that
readings will be cold enough for perhaps around 1 inch of snow today
in the extreme northwest. Will have to watch closely.

Elsewhere mostly rain is expected so little or no snow accumulation
is expected.

&&

.SHORT TERM.../Tonight through Tuesday night/
Issued at 333 AM EST Sun Dec 4 2016

Models are close enough that the SuperBlend initialization
was accepted for most items.

Dry air will work in quickly tonight behind the departing upper
trough. Went low PoPs during the evening, with most of the area dry
by midnight. Temperatures may cool enough for some snowflakes to mix
in across the north before precipitation ends.

High pressure will then build in briefly for Monday. However, lift
will increase Monday night as an upper low approaches the area from
the southwest. This system will have good forcing as the upper
system moves across, including pretty good frontogenetical forcing.
Will go likely to categorical PoPs by Tuesday morning. PoPs will
quickly lower Tuesday afternoon as the system exits.

Temperatures might be cold enough for some snow to mix in with the
rain Monday night as the system moves in. However, readings should
warm enough for all rain by late Monday night.

&&

.LONG TERM /Wednesday Through Saturday/...
Issued at 333 AM EDT Sun Dec 4 2016

Ensembles suggest the main weather feature during this period will
be a short wave trough that is expected to push across the Great
Lakes around Wednesday into Thursday. Will go with chance PoPs for
Wednesday night into Thursday morning to cover this feature.
Ensembles suggest snow will be the predominate precipitation type
with this system, although some mixed precipitation possible
Wednesday evening over the southern and eastern zones. Light
accumulations are possible.

Next upper trough is expected to move into the middle of the country
by next Saturday, although timing and location differences are large
at this time. Ensembles suggest some snow is possible within the
warm advection pattern ahead of this trough by next Saturday. Will
go with chance PoPs at that time.

&&

.AVIATION /Discussion for the 041800z Tafs/...

Issued at 1228 PM EST Sun Dec 4 2016

VFR Conditions will quickly deteriorate to MVFR...IFR and LIFR
this afternoon. IFR conditions likely to persist overnight.

Quick moving short wave and isentropic lift to push across the
forecast area this afternoon. Forecast soundings and time height
sections show deep saturation this afternoon and low level
saturation lingering tonight. Rapid refresh shows precipitation
over Illinois spreading eastward across the TAF sites late this
afternoon. Thus categorical rain this afternoon. As previously
mention IFR/LIFR Cigs are expected to linger after the dynamics
pass as time heights show trapped lower level moisture beneath an
inversion aloft.

A return to VFR will be possible on Monday as high pressure
arrives and mixing scours out the lower levels.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...50
NEAR TERM...TDUD
SHORT TERM...50
LONG TERM....JAS
AVIATION...JP


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