Area Forecast Discussion
Issued by NWS Indianapolis, IN

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859
FXUS63 KIND 252031
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
430 PM EDT SUN SEP 25 2016

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

&&

.SYNOPSIS...
Issued at 304 AM EDT Sun Sep 25 2016

A cold front will move through the area tonight into early Monday
bringing showers and a few thunderstorms to the area. An upper low
could bring a few showers to northern areas mid week. Dry conditions
will then prevail. After one more warm day today, cooler and more
seasonable readings will continue into next weekend.

&&

.NEAR TERM.../This afternoon/
Issued at 1026 AM EDT Sun Sep 25 2016

Vorticity lobe currently located near the Mississippi river is expected
to drift east during the day. This feature may spark off some convection
over the west central and northwest zones by mid to late afternoon. Will
extend the PoPs for later this afternoon into some of the west central
zones as well to cover this feature.

Previous discussion follows.

A cold front will approach the area today. Until later in the day,
high pressure should remain in control with just an increase in
clouds.

Some models bring in rain before 00Z to the western forecast area
ahead of the front. The Hi Res Rapid Refresh has convection into the
area by 19Z. This seems overdone given what little forcing will be
available before the front arrives.

However, the GFS and Canadian bring in rain before 00Z. Although
less weight is given to the GFS since it typically overdoes QPF
coverage, the SREF also hints at this possibility. Given the above,
and after looking at neighboring office`s input, have decided to add
some slight chance PoPs to the far northwest 21Z and beyond.

With some decent sunshine for at least the first half of the day,
feel that MOS is too cold. Went closer to a raw model blend of
temperatures.

&&

.SHORT TERM.../Tonight through Tuesday night/
Issued at 304 AM EDT Sun Sep 25 2016

Focus is on chances for rain. Models are close enough that a blend
was used.

The cold front will move through the area tonight. An upper jet will
provide additional forcing while 850mb winds over 30kt bring in
additional moisture. Decent frontogenetical forcing will be around as
well. Thus went likely PoPs most areas at some point during the
night, with later timing in the east.

Current expected timing of the system keeps rain still likely over
the east 3/8 of the area or so during the early part of the morning.
However, dry air moves in rapidly, so that by 15Z most areas are dry
and by 18Z everywhere is. Instability on Monday looks quite low so
removed any thunder mention.

Dry conditions should then prevail through Tuesday high pressure
nosing in.

An upper low will begin to move south out of the Great Lakes late in
the period. Models differ on path and how far south the rain gets by
late Tuesday night. Forcing doesn`t look impressive, and given the
uncertainty, was only comfortable adding in slight chance PoPs in
the extreme northeast forecast area.

For temperatures, generally stayed close to the model blend. Given
the dry air that will be in place for much of the short term, there
should be some decent diurnal ranges. The blend captures this pretty
well.

&&

.LONG TERM /Wednesday Night through Saturday/...

Issued at 242 PM EDT Sun Sep 25 2016

ECMWF showing some differences from superblend this period as the
ECMWF suggests that an upper low will settle across the Ohio
Valley through this period...pivoting several waves through the
area. GFS keeps this feature farther east...mainly over the middle
atlantic states. Thus confidence is low for now and have included
superblends low pops where it has been allowed. Confidence remains
low. However northwest continental flow does seem prevalent through
the period which should result in near normal tempertures.

&&

.AVIATION /Discussion for the 252100z TAFs/...

Issued at 430 PM EDT Sun Sep 25 2016

Bumped up timing of VCTS and added tempo -TSRA to KLAF from 22 to 0Z
based on movement of echoes currently in western Illinois and this
increasing confidence of current HRRR solution. For KIND just
updated current conditions as confidence of this early evening
convection affecting there is low. At this time have not changed
KHUF, but will closely monitor there for an early thunder addition
if radar trends in that direction.

Models suggest strong cold front arriving overnight as forecast
soundings and time heights become saturated. Thus expect a line of
shra/tsra to push across the state with MVFR CIGS and visibilities
possible after around 7z.

Strong Subsidence and dry air expected to arrive in the wake of
the cold front...improving all taf sites to VFR after 18Z Mon.

&&

.IND Watches/Warnings/Advisories...
NONE.
&&

$$

SYNOPSIS...50
NEAR TERM...50/JAS
SHORT TERM...50
LONG TERM....PUMA
AVIATION...JP/CP



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