Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 201930
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
230 PM EST Fri Jan 20 2017

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

&&

.SYNOPSIS...
Issued at 230 PM EST Fri Jan 20 2017

Mild and unsettled weather will continue across the Ohio Valley this
weekend with opportunities for scattered showers and a few
thunderstorms. After a brief break from the wet weather...another
storm system will track through the region the middle of next week
with colder temperatures more typical of late January and possibly
chances for light snow arriving by late week.

&&

.NEAR TERM /Tonight/...
Issued at 230 PM EST Fri Jan 20 2017

Damp gray afternoon continues across central Indiana as the region
remains under a shroud of thick clouds and patches of drizzle. A few
breaks in the stratus noted especially closer to the Ohio River...
but trend has been for those to disappear over the last hour or two.
A mild January day in progress as 19Z temps were primarily in the
50s.

First in a series of waves of energy aloft kicking out from the deep
upper low off the Pacific Northwest coast will rotate into the
northern Plains behind the wave from last night.  While this feature
will not have a direct impact initially on central Indiana...it will
aid in bringing a combination of weak isentropic lift and warm
advection expanding northeast with a warm front into the region
tonight. This will bring another round of showers...albeit they will
be more scattered and much much lighter compared to Thursday night.
Focus for the best threats for light showers and/or drizzle will be
across the northwest half of the forecast area where the isentropic
lift will be a bit more pronounced. Precip amounts will be a couple
hundredths at best and will not have any impact regarding ongoing
flooding concerns.

In addition...areas of fog will continue overnight as well and
possibly worsen after dark with the well defined inversion
persisting over the region. Should begin to see improvements develop
from the south predawn Saturday as low level mixing increases south
of the warm front and with the aid of a strengthening low level jet.

Temps...another night with very little movement regarding
temperatures. Lows will be well above normal as the southerly flow
and warm advection keeps the region largely in the lower and middle
50s. Trended much closer to the warmer MET guidance.

&&

.SHORT TERM /Saturday through Monday/...
Issued at 230 PM EST Fri Jan 20 2017

Forecast challenges focus on precip chances and temperatures
throughout the short term as the active...unsettled and mild weather
regime continues.

A moist southwest aloft will continue over the region into Sunday as
a dominant subtropical jet undercuts the upper low off the Pacific
Northwest and kicks out upper level waves downstream across the
eastern half of the country. Much of Saturday now appears relatively
quiet for central Indiana as the warm front lifts away to the north
and subtle ridging aloft develops between the aforementioned upper
wave tracking into the upper Midwest and a developing upper low
strengthening over the Southern Plains. Shallow isentropic lift will
continue on Saturday but limited forcing aloft at best should
maintain dry conditions across the forecast area until late day at
the earliest. Model soundings show the inversion persisting between
1000-2000ft for much of the day Saturday an combined with the
isentropic lift present below 900mb...suspect the stratus will
remain through midday in abundance with perhaps some breaks during
the afternoon as low level flow increases and aids in enhanced
mixing of the boundary layer.

A deep upper low sitting off the Pacific Northwest coast with a
strong subtropical jet undercutting the wave will maintain an active
weather pattern across much of the country through the weekend as
pieces of energy aloft continue to eject out into the central Plains
east into the Ohio and Tennessee Valleys and the Deep South. Upper
level flow over the region will largely persist in a moist southwest
regime through Saturday night.

Deeper moisture will be drawn north beginning late Saturday and
especially Saturday night as the southern Plains upper low tracks
east and an intensifying surface wave organizes over the mid South.
Increasing low level convergence and the development of diffluent
flow aloft supports scattered convection increasing across the
entire area Saturday night. Elevated instability maximizes with
progged MLCAPE values up to 500 J/KG and will continue with a
thunder mention as a result. Precip water values will rise up to
0.80 to 1 inch Saturday night...250-300% of climatological normal.
While higher precip amounts should be much more localized than
recent events...additional flooding concerns could extend out
through the weekend after the heavy rains experienced Thursday
night.

Rain chances will continue Sunday and Sunday night as the upper low
tracks across the Southeast and into North Carolina by Monday
morning...amplifying as it does so. The surface low will continue to
intensify as well...residing northwest of the upper low over the
central Appalachians by early Monday. The close proximity of the
surface low will maintain periods of generally lighter rain across
the region within a cyclonic flow. Should begin to see chances for
rain shift east of the area through the day Monday as the surface
low tracks slowly northeast into the mid Atlantic region and deeper
moisture gradually moves out of the forecast area.

Temps...warm weather will continue Saturday and Sunday as low level
thermals are supportive of highs ranging from the upper 50s to the
mid 60s north to south. While this is unusually warm...record highs
for both days at Indy look safe by several degrees. Noticeably
cooler weather with highs in the 40s are expected Monday as colder
air is drawn into the region behind the east coast storm system.Lows
will be generally in the 40s through the period.

&&

.LONG TERM /Monday night through Friday/...
Issued at 205 PM EST Fri Jan 20 2017

The long term will begin with above normal temperatures and small
rain chances moving out of the area as an upper ridge builds in
and moves across central Indiana. Tuesday night a low pressure
system will approach from the plains and bring small chances for
rain with it. By Thursday though a broad upper trough across the
western and central U.S. will start to slowly move east, and this
will bring cold more seasonable air back to the area. Temperatures
will drop back to near normal for this time of year. Little upper
waves ejecting out of the upper trough could bring some
precipitation chances to the area for the remainder of the
extended, but right now there isn`t a major forcing mechanism to
focus on so just used the small off and on chance pops from the
initialization. Because of the arrival of the colder air, could
see some snow or a rain/snow mix for anything that falls Wednesday
night on.

&&

.AVIATION /Discussion for 201800Z TAF Issuance/...
Issued at 1138 AM EST Fri Jan 20 2017

Poor flying conditions will continue for the rest of the day into
tonight with some improvements for Saturday.

Areas of fog and pockets of drizzle continue to impact the
terminals late this morning as moisture remains trapped beneath a
strong inversion. As progressively drier air advects into the
region...should see the drizzle diminish early this afternoon but
the lower ceilings will continue under the inversion. Expect
ceilings generally persisting at a sub-IFR level into the
overnight with visibilities likely holding in the 3 to 5SM range.
Light SW flow this afternoon will back to southerly and increase
tonight as a warm front lifts north.

The passage of the frontal boundary will enable a relaxing of the
inversion to some degree on Saturday and increased low level
mixing will enable improvements in ceilings into the MVFR category
through the course of the day. S/SW winds will continue with the
potential for gusts in some areas during the afternoon. It now
appears that rain and scattered convection now is likely to hold
off on causing more significant impacts at the terminals until
after 00Z Saturday evening.

&&

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

&&

$$

SYNOPSIS...RYAN
NEAR TERM...RYAN
SHORT TERM...RYAN
LONG TERM....CP
AVIATION...RYAN


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