Area Forecast Discussion
Issued by NWS Indianapolis, IN

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657
FXUS63 KIND 142011
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
311 PM EST Sun Jan 14 2018

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated
below.

&&

.SYNOPSIS...
Issued at 311 PM EST Sun Jan 14 2018

A clipper system will spread a swath of accumulating snow across
central Indiana late tonight and Monday. A reinforcing blast of
bitterly cold air will follow through midweek along with additional
chances for flurries and light snow showers on Tuesday. A warming
trend will commence for the second half of the week into the
weekend...with the next storm system producing rain across the
region this weekend.

&&

.NEAR TERM /Tonight through Monday/...
Issued at 311 PM EST Sun Jan 14 2018

Another cold January afternoon in what has been many of them so far
this month. Sunny day at least although mid and high level clouds
are beginning to overspread the region in advance of the storm
system poised to bring the next round of accumulating snowfall to
the region tonight into Monday. 20Z temperatures ranged from the
teens into the lower 20s.

The primary focus for the near term will be on the robust clipper
system set to swing through the area over the next 24 hours with a
nice shot of snow. Overall model guidance well aligned into Monday...
with high confidence in snowfall and impacts across central Indiana.

High pressure already moving away from the region this afternoon
with return flow developing on the back side. The storm system will
be anchored by two upper level waves...the first currently
depositing light snow over the Missouri Valley with the second being
the primary piece of energy associated with the clipper. This
feature is currently over the northern Plains and will arrive over
the region closer to daybreak Monday. Expect continued thickening
and lowering of clouds through sunset with light snow crossing the
Wabash River around or shortly after 00Z as the boundary layer
saturates ahead of the initial wave aloft tracking out of Missouri.
Snow will gradually expand across the forecast area through the late
evening and into the overnight as the wave tracks into the region.
Snow overall should be light into the first part of the overnight
but steady.

The transition to a heavier snowfall will take place during the
predawn hours and into Monday morning as the secondary and stronger
wave aloft associated with the clipper overtakes and absorbs the
initial wave as it tracks into the region. Mid and upper level
diffluence develops ahead of the wave which should only enhance
snowfall rates over central indiana late tonight. Banding of heavier
snowfall is also likely to become a factor towards daybreak as a mid
level deformation axis sets up ahead of the associated cold front
and could enhance snowfall rates further south through the forecast
area during the morning hours. Additionally...the dendritic growth
zone is stout through parts of the event and combined with expected
higher ratios in the ballpark of 20:1...snow amounts will be
enhanced. Current snowfall thoughts is a general 3-4 inches over the
northwest half of the forecast area with locally higher amounts and
2-3 inches over the southeast counties.

Snow will begin to taper from northwest to southeast during the
afternoon as the low occludes over lower Michigan and the front
swings east. May see flurries linger through dark but overall trend
towards snowfall ending as drier air wraps into the region behind
the front.

This snow will provide enhanced impacts for central Indiana for
several reasons and warrants a Winter Weather Advisory for the
entire forecast area. Snow will impact the region from this evening
into Monday...but the potential impact of the heaviest snow looks to
coincide fairly closely with the morning commute...even with lighter
traffic due to the holiday. Another factor will be winds which will
become increasingly gusty from late tonight through Monday as the
low passes by to the north. Due to the fluffy nature of the snow...
blowing snow will be an issue throughout the area and will likely
contribute to additional challenges for travel late tonight and
through the day Monday. Not going to get fancy with headline
segments and just plan to start the advisory at 03Z tonight and run
it through 21Z Monday.

Temps...trended towards cooler MET guidance for lows during the
evening tonight with temperatures rising after midnight. Quick shot
of warm advection immediately ahead of the front on Monday should
enable most areas to warm into the mid and upper 20s and leaned
towards the higher end of guidance as a result. Temps will fall
during the afternoon as colder air sweeps in behind the front.

&&

.SHORT TERM /Monday Night through Wednesday/...
Issued at 311 PM EST Sun Jan 14 2018

Forecast challenges focus on the potential for lingering flurries
and/or snow showers into Tuesday with an upper wave rotating into
the region...and with temperatures through the period as another
blast of bitterly cold air arrives.

Narrow surface ridging will align over the region late MOnday night
into Tuesday morning before the remnant upper wave and a surface
trough pinwheel back into the region from the north through the day
Tuesday. Model guidance showing plenty of lingering forcing aloft
with an elongated lobe of vorticity associated within the upper
wave. As the wave rotates into the area Tuesday afternoon and
evening...expect a resumption of flurries and scattered light snow
showers across the area and have raised pops accordingly. With snow
ratios being inflated even further in the bitterly cold airmass...
certainly not out of the question for some locations to see a light
accumulation of a few tenths or so Tuesday afternoon and evening.

The upper wave will shift east Wednesday with a strong area of high
pressure taking over as it tracks across the Tennessee and lower
Ohio Valleys. Model soundings indicating plenty of deep subsidence
through the column with skies returning to mostly clear for
Wednesday.

Temps...another blast of bitterly cold air will follow in wake of
the snow for tonight and Monday...with temperatures accentuated by
the fresh snow cover. Potential for another subzero night on the
docket Monday night as clouds scatter late and with winds
lingering...a Wind Chill Advisory may be needed over northern
portions of the forecast area Monday night and Tuesday. Trended
towards cold end of guidance Tuesday with teens and largely
undercut it entirely Tuesday night as lows again make a run
towards zero. Another cold day in store for Wednesday but should
see highs warmer near 20.

&&

.LONG TERM /Wednesday Night through Sunday/...
Issued at 207 PM EST Sun Jan 14 2018

Models are in decent agreement...although the new European is
slower in spreading precipitation into central Indiana this
weekend as it keeps Indiana dry until late Saturday night...
while the GFS and Canadian models are almost a day earlier.

The weather will become much warmer late this week as the
upper trough moves off the east coast and an upper ridge
moves east across our area Friday and early Saturday.  This
will be followed by an upper trough which will move into
the Central U.S. by Sunday.

In most cases stayed close to Superblend POPS and Temperatures.
However I tweaked highs down slightly Sunday.  All of the models
appear quite wet and mild by Sunday as low pressure moves into
the western Great lakes

&&

.AVIATION /Discussion for the 14/18Z TAF Issuance/...
Issued at 1200 PM EST Sun Jan 14 2018

VFR through early evening...then IFR or low MVFR with snow late
evening on.

High pressure over Ohio will move on to the east and low pressure
and associated cold front over the upper midwest will move towards
Indiana.   Expect increasing mid clouds by late afternoon and with
lowering ceilings and snow spreading east by late evening.
Indications are that we will have MVFR ceilings and IFR visibilities
at times late tonight and Monday morning with some improvement
towards midday.

South winds 5 to 7 knots this afternoon and early tonight will become
southwest 8 to 10 knots by Monday.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to 4 PM EST
Monday for INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JH
AVIATION...JH



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