Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 131035
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
535 AM EST Wed Dec 13 2017

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

&&

.SYNOPSIS...
Issued at 328 AM EST Wed Dec 13 2017

Low pressure systems tracking through the Great Lakes later today
and again Friday will bring chances for precipitation primarily to
the northeast half of central Indiana. A storm system will track out
of the southern Plains over the weekend...bringing wet weather for
Sunday and Monday before high pressure returns.

&&

.NEAR TERM /Today/...
Issued at 328 AM EST Wed Dec 13 2017

Mid level clouds were spreading into the forecast area from the
north early this morning as low level flow was backing to a more
south-southwest direction with warm advection set to commence. MOst
locations had already reached their lows for the night...
temperatures were steady or slowly rising in response to the warm
advection. 08Z temperatures ranged from around 15 degrees into the
low 20s.

A strong wave aloft with an associated surface low were located over
the northern Plains early this morning. The upper wave will pivot
into the lower Great Lakes later today with the surface low set to
track across northern Indiana by early evening. Overall trends have
been further north over the last few model runs with the track of
the system.

Axis of warm advection snow showers/flurries extending from northern
Wisconsin S/SE towards the lower Great Lakes. CAMs have backed off
on more substantial impacts over parts of central Indiana with
presence of dry air through the boundary layer. Still though as this
feature drops southeast later this morning...a few flurries may be
generated over northeast counties. Any measurable precipitation will
focus more during the second half of the afternoon as the surface
low and associated cold front arrive from the northwest. Forcing
aloft from the upper wave remains modest but moisture is somewhat
lacking and largely focused in a shallow layer near and just above
the boundary layer.

Have backed off on pops as a result as have a hard time justifying
much more than low chance pops across any portion of the forecast
area with the system tracking further north through the lower Great
Lakes. Confining pops essentially northeast of Interstate 74 for
late afternoon as the front sweeps in...with a possibility that far
northeast counties are the only areas that see any measurable
precip. Low level thermals support precipitation remaining in the
form of snow roughly northeast of a Lafayette-Tipton-New Castle line
with rain mixing in further southwest.

The biggest impact for the forecast area today will be progressively
windier conditions through the afternoon with strong flow through
the boundary layer. Peak mixing levels will likely not get any
higher than 3kft but winds at 40-50kts as low as 925mb should be
tapped into with surface gusts maxing out at 35 to 40mph immediately
ahead of the cold front by late afternoon.

Temps...the quick surge of warm advection ahead of the cold front
with a dry airmass should enable temperatures to surge later
today...especially over the southwest half of the forecast area.
Expect a nice gradient up to 15 degrees from northeast to southwest
in highs temps this afternoon. Locations in the lower Wabash Valley
may make a run at 50 degrees.

&&

.SHORT TERM /Tonight through Friday Night/...
Issued at 328 AM EST Wed Dec 13 2017

Forecast challenges focus on lingering precip chances this
evening...followed by another chance for light snow on Friday as the
region again gets grazed by low pressure tracking quickly through
the Great Lakes.

The surface low will track into northern Ohio during the evening
with the cold front following suit. A trailing surface trough
extending west behind the low pressure not expected to pivot through
the area until closer to midnight or shortly after. Combined with a
secondary axis of vort energy aloft tracking across the
area...expect scattered precipitation to linger over the northeast
half of the forecast area through the evening. Highest confidence
exists over northeast counties where potential exists for a brief
burst of snow showers with perhaps a dusting. Further southwest...a
rain/snow mix will transition to light snow showers or flurries
before ending with no impact expected. Precip will end by 06Z as the
trailing surface trough shifts away to the east.

Clouds will decrease as high pressure builds in after midnight.
Northerly low level trajectories off Lake Michigan align during a
narrow window from the predawn hours through Thursday morning.
Anticipate a lake effect band to extend south through northwest
Indiana...with the potential for flurries to sneak into the northern
Wabash Valley before wind flow is disrupted. The rest of the day
Thursday will be quiet with high pressure over the area and the
potential for diurnal cu to develop within the cold advection regime.

In the northwest flow aloft...yet another system poised to swing
across the Great Lakes on Friday and Friday night as another sharp
wave aloft dives into the parent trough. Recent model trends over
the last day have shifted the track of this system further north
and away from central Indiana. While the passage of the system to
the north will bring increased cloud cover...the moisture again look
shallow with most of the forcing aloft displaced north of the
region. A few light snow showers or flurries may pass through
northeast counties during the afternoon and evening...otherwise
expect dry conditions to continue.

Temps...continued the recent trend of largely undercutting guidance
in the cold advection and trended lower with temps tonight and
Thursday. Expect some recovery in temperatures Friday but clouds
will temper rises. An overall model blend looked reasonable for
Thursday night...Friday and Friday night.

&&

.LONG TERM /Saturday through Tuesday/...
Issued at 222 AM EST Wed Dec 13 2017

Ensembles are in good agreement in suggesting a transition to a
more zonal and progressive upper flow during this period.

Main item of interest during this period will be a potential short
wave trough that is expected to move through the Tennessee Valley
around Sunday. The northern fringes of this system may affect the
local area. Will go with PoPs from Saturday night through Sunday
night to cover this potential. At this point, it appears most of
the precipitation will be in the form of light rain, however the
air mass may be cold enough to support mixed precipitation or snow
at the beginning and end of the event. Ensembles suggest there may
some minor snow accumulations Sunday morning over the northern
zones.

&&

.AVIATION /Discussion for the 131200Z TAFS/...
Issued at 534 AM EST Wed Dec 13 2017

Scattered to broken cloud layers above 050 expected at the
terminals for today, along with unrestricted visibility. Cloud
cover based 040-050 may begin moving over the terminals from the
northwest by mid to late afternoon.

Surface winds 180-200 degrees at 6-10 kts early this morning will
increase and gradually veer around to 220-240 degrees by late this
afternoon. Frequent surface gusts near 30 kts expected towards
the midday hours and on through the afternoon.

&&

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

$$

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


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