Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 160235

Area Forecast Discussion
National Weather Service Indianapolis IN
935 PM EST Mon Jan 15 2018

The AVIATION Section has been updated below.


Issued at 307 PM EST Mon Jan 15 2018

Another blast of bitterly cold air will impact central Indiana
through midweek. Other than a few snow showers and flurries through
Tuesday evening...dry weather is expected the rest of the work week.
Temperatures will warm to above normal levels by late week...with
the next storm system tracking through the area this weekend
bringing rain as opposed to wintry precipitation.


.NEAR TERM /Rest of This Afternoon and Tonight/...
Issued at 307 PM EST Mon Jan 15 2018

Most of the steadier snow associated with the clipper is moving away
from the forecast area as of 20Z. However...the arctic cold front is
tracking into western Indiana and will carry a scattered snow
shower/squall potential with it for the next few hours. 20Z
temperatures were mainly in the 20s with temps falling into the
teens right behind the front.

Initial focus is on the cold front sweeping across the region late
this afternoon. CAMs have remained relatively consistent in tracking
a narrow line of squalls across the forecast area over the next few
hours in tandem with the front. Not really expecting much in the way
of additional accumulation out of these squalls...but the impact
they will produce across the region into the early evening warrants
an extension of the Winter Weather Advisory through 00Z. Within
these squalls...expect bursts of wind-driven snow with drastically
reduced visibilities for short time periods over short distances.
Any gains that have been made on improving travel conditions as snow
has slackened this afternoon may very well be lost as the arrival of
wind gusts to around 25mph will easily blow the light and fluffy
snow around. Furthermore...timing again is not ideal with the
squalls set to swing through during portions of the afternoon/early
evening commute.

The line of squalls should be east of the entire area by early
evening and outside of periodic flurries mainly this
evening...expect dry conditions for much of the rest of the night as
weak surface ridging builds in between the departing front to the
south and east and the cold pool associated with the upper low over
the western Great Lakes. May even see some scattering of clouds
after midnight.

Wind gusts will gradually diminish overnight...but presence of winds
near 10mph all night combined with temps dropping to near or just
below zero will produce wind chills that will fall below -15 degrees
for much of the area. Will be introducing a Wind Chill Advisory as a
result for the entire forecast area....beginning at 06Z and
continuing through Tuesday morning.

Temps...undercut available temperature guidance overnight as most
areas will be within a few degrees either side of zero. As mentioned
above...expect wind chills to bottom out in most areas in the -20
to -15 range during the predawn hours.


.SHORT TERM /Tuesday through Thursday/...
Issued at 307 PM EST Mon Jan 15 2018

Forecast challenges focus on flurries and light snow showers
Tuesday...and on temperatures through out the short term.

The aforementioned upper low will rotate southeast through the Ohio
Valley on Tuesday afternoon and evening...bringing scattered
flurries and perhaps a few lighter snow showers as well over
northern counties. The overall thermodynamic structure through the
boundary layer is less than ideal for more sustained snow showers
with poor lapse rates above 1-2kft and the presence of a subtle
inversion for much of central Indiana. Have confined much of the
light snow shower mention to northern portions of the forecast area
which may benefit from a brief period of lake enhancement during the
afternoon and evening as low level winds briefly align. Not out of
the question for a dusting over far northern counties by Tuesday
evening. The presence of an elongated vort lobe accompanying the
upper low will however support the potential for flurries for all of
central Indiana through Tuesday night.

The upper low and associated trough will shift east of the region on
Wednesday with high pressure over the southern Plains poised to take
over as the primary influence for central Indiana for the rest of
the short term. The high will track east into the Tennessee Valley
through Thursday with surface flow gradually transitioning from
westerly to southwesterly over the forecast area. Lingering clouds
are possible Wednesday over northeast portions of the forecast area
a weak upper wave passes through the Great Lakes...but the overall
trend will be towards mostly clear skies Wednesday into Thursday. A
tightening surface pressure gradient supports gusty winds developing
on Thursday over the region as well.

Temps...the climb out of the bitterly cold air will be slow but
noticeable...especially by the end of the short term. Trended
towards cool end of guidance for Tuesday and Tuesday night...then
largely took a model blend thereafter. Highs will remain in the
teens Tuesday...recover into the lower 20s Wednesday and be back
near freezing on Thursday.


.LONG TERM /Thursday Night through Monday/...
Issued at 215 PM EST Mon Jan 15 2018

A progressive upper air pattern will occur late this week and early
next week.  An upper trough near the New England coast Thursday
night will move to the east and an upper ridge will move east across
Indiana Friday and early Saturday.  As result temperatures will
become much warmer Friday and over the weekend.

Models move a surface low into the central plains over the weekend
and to the western great lakes by Monday with a trailing cold front
moving through Indiana early Monday.  This system will bring a
chance of showers over the weekend and a likelihood of rain Sunday

Models indicate near steady or slowly falling temperatures Monday
with arrival of colder air and some areas could see mixed
precipitation Monday.

Stayed close to Superblend POPS most periods and Superblend
temperatures Thursday night through Sunday.  Since temperatures will
be non-diurnal Monday...used hourly model surface temperatures to
recompute high and low temperatures for that period.


.AVIATION /Discussion for the 16/03Z TAF Update/...

Issued at 927 PM EST Mon Jan 15 2018

No changes.

Previous Discussion...
Conditions will continue to fluctuate between VFR and MVFR
for the duration of the TAF period as low pressure lingers over
the Great Lakes Region. The exception will be some brief
deterioration to IFR at KLAF this evening as some light snow
showers filter in on the back side of the aforementioned system.
Meanwhile, winds will be west/southwesterly at 10 to 14 kts into
tonight, then tapering off to 5 to 10 kts overnight.


Wind Chill Advisory until noon EST Tuesday for INZ021-028>031-



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