Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 200418
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1118 PM EST Sun Feb 19 2017

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

&&

.SYNOPSIS...
Issued at 221 PM EST Sun Feb 19 2017

A weakening cold front is expected to move through the area Monday
night into Tuesday morning. A stronger low pressure system may
affect the area towards the later parts of the week.

&&

.NEAR TERM /Overnight/...
Issued at 1008 PM EST Sun Feb 19 2017

High pressure centered just east of the region with an upper ridge
centered just to our west. Skies were mainly clear with fog
starting the develop over the lower Wabash Valley. 03Z temps
ranged from the lower 40s to lower 50s.

The primary focus for the rest of the night will be regarding the
development of fog and lower stratus once again. Locally dense fog
has formed over the last hour or two across the lower Wabash
Valley where the stratus took the longest to mix out earlier
today. Hi-res guidance and simulated satellite products highlight
favorable conditions for fog expansion across central Indiana
overnight with light flow and a shallow but strong inversion
developing with moisture trapped beneath it. Model soundings
suggest the height of the inversion is likely to set up near or
just below 1000ft...which is lower than Saturday night and more
supportive of fog versus low stratus.

Have beefed up wording in the grids to include patchy dense fog
overnight across the entire area. Based on the above thoughts...an
argument for a dense fog advisory is certainly warranted. Think
though we have some time to see how widespread and thick the fog
can get before considering the advisory...and will introduce an
SPS at this time and continue to monitor.

Zone and grid updates out.

&&

.SHORT TERM /Monday through Wednesday/...
Issued at 221 PM EST Sun Feb 19 2017

Lingering fog early Monday morning should burn off by the mid to
late morning hours Monday.

Model data suggest a short wave trough will push through the Great
Lakes region Monday night and Tuesday, dragging a weakening cold
front through the local area. Appears there may a decent amount of
lift, albeit rather narrow, for a precipitation threat late Monday
night into Tuesday morning over the northern zones. Will go with
PoPs starting Monday night and continuing through early Tuesday
evening to cover the passage of this system, with the highest PoPs
coinciding with the best lift.

Some weak elevated instability may be associated with this feature
as well, but convective parameters not very impressive at this
point.

Will go with a dry forecast by Wednesday as upper flow becomes zonal
in the wake of short wave trough, and weak surface high pressure
develops over the area.

Progged low level thicknesses suggest the GFS MOS highs for Monday
may be on the cool side. Will nudge the guidance highs up a bit in
that period. The remainder of the periods look OK for now.

&&

.LONG TERM.../Wednesday night Through Sunday/...
Issued at 225 PM EST Mon Feb 19 2017

The highlights of the long term will be warm weather for the
remainder of next week with a return to seasonable temperatures by
Saturday. In addition, unsettled weather is on tap late week with
strong storms possible Friday.

Models are having temporal and spacial issues with a potent system
that will be developing over the Rockies midweek and lifting
northeast across the Plains and then Great Lakes late week and into
the weekend. Thus, confidence in timing and coverage of looming
convection is not great and will accept the Superblend which has the
highest pops Friday afternoon and evening and is dry by Saturday.
Prior to that, a front will drop southeast over the area before
lifting back to the north Thursday and Thursday night. Superblend
output has small pops over all or parts of the area by Wednesday
night.

Model instability progs support thunder chances Thursday afternoon
through Friday. Adjacent offices agreed through coordination. With
such strong dynamics and some instability...day6 SPC outlook
supports severe possibility with mainly a damaging wind threat.

Low level thermal progs and expected cloud cover support well above
normal blend temperatures in the mid 60s to around 70 through Friday
and more seasonable highs mostly in the 40s by Saturday in the wake
of the cold front.

&&

.AVIATION /Discussion for 200600Z TAF Issuance/...
Issued at 1118 PM EST Sun Feb 19 2017

Sub-IFR restrictions overnight through mid morning Monday in fog and
low stratus with a return to VFR conditions for the afternoon and
evening.

Skies remain mostly clear over much of the region late this
evening...although lower stratus and fog beginning to expand from
the lower Wabash Valley. With the upper ridge axis just to the west
of the region and light flow over the area...solid setup in place
for fog to overspread the area gradually over the next several
hours. Presence of a developing sharp but shallow inversion near or
just below 1000ft will likely create greater impacts for aviation
interests from fog as opposed to the lower stratus. Visibilities
will tumble late tonight towards daybreak Monday with confidence
growing in visibilities lower than 1SM impacting all terminals.

INcreased mixing in the near surface layer will help to weaken and
eventually dissipate the inversion around midday with partly cloudy
skies returning. Clouds will increase Monday evening as a frontal
boundary approaches from the west. Rain showers should hold off at
all terminals until after 06Z Tuesday. Southeast winds will be
generally less than 10kts Monday afternoon...veering to southerly
Monday night.

&&

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

&&

$$

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


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