Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 181435

Area Forecast Discussion
National Weather Service Indianapolis IN
1035 AM EDT Mon Sep 18 2017

The AVIATION Section has been updated below.


Issued at 229 AM EDT Mon Sep 18 2017

A weak frontal boundary will linger across Central Indiana over
the next few days. This in combination with a warm and humid air
mass over Central Indiana and a few passing upper level weather
disturbances will result in chances for showers and storms the
next few days.

Strong High pressure is expected to redevelop across the area by
mid-week...and continue to control Indiana`s weather into the
weekend. This will bring more dry weather with above normal
temperatures this weekend.


.NEAR TERM /Today/...
Issued at 952 AM EDT Mon Sep 18 2017

Mid level vorticity center over west central Indiana is progged by
short term model guidance to drift northeast into northern Indiana
by late this afternoon. Areas of showers and occasional embedded
in cloud lightning ahead of this feature. Current precipitation
should diminish or move out of the area by the early afternoon
hours as upper feature drifts off to the northeast. Widely
scattered convection possible later this afternoon as convective
temperatures are rather low today.

Will bump up PoPs over some of the eastern zones through about
181700Z given current activity, then taper off PoPs a bit later
this afternoon.

Will keep highs today intact at this point, as this morning`s
upper air generally supports them, but if cloud cover lingers
longer into the afternoon highs may not be reached.

Previous discussion follows.

Surface analysis early this morning shows weak high pressure in
place across the upper midwest and the deep south. a poorly
defined frontal boundary/cusp area was found between these two
systems...stretching from SE Michigan across Indiana to Oklahoma.
GOES16 shows a band of clouds along the boundary and radar shows a
few lingering showers in the forecast area...mainly north of I70.
Dew points remained in the mid and upper 60s across Indiana. Water
vapor shows a stream of tropical moisture stretching from Texas
toward the Great Lakes with several weak embedded short waves
within the flow.

Models suggest a weak short wave exiting the area today as another
approaches the area shortly after 00Z. Confidence in models
handling the upper waves is low. However several things remain in
place that will necessitate pops today. The very warm and humid
air mass remains across the region. The weak frontal boundary/cusp
remains across Indiana as it appears to be slowly getting
elongated and washed out...yet still providing a source of lower
level convergence. Finally...forecast soundings show steep lapse
rates again this afternoon with attainable convective temperatures
and CAPE over 1500 J/KG. Thus with these favorable ingredients but
marginal and uncertain upper level support...will keep pops in the
chc category...with best chances expected this afternoon when
instability is best. Given our very dry ground and some partial
sunshine through the day will trend highs at or above the
forecast builder blend.


.SHORT TERM /Tonight through Wednesday Night/...
Issued at 229 AM EDT Mon Sep 18 2017

GFS and NAM suggest yet another...stronger short wave passing
across Central Indiana late tonight amid the W-SW flow aloft.
Ample moisture remains in place across the area and Time heights
show lift toward 12Z and good saturation within the lower and
middle levels. Forecast soundings show rather moist column.
However with loss of will there be a loss of
instability. Confidence also remains marginal regarding the
models handling of these weak waves. Thus will stick close to the
blend for Pops tonight as these dynamics pass. As usual...with the
warm and humid air mass in place along with the possible
showers/storms will trend lows at or above the forecast builder

On Tuesday little in the overall pattern has changed. The models
suggest that the previously mentioned short waves will be exiting
the area...while SW-W flow remains aloft. Forecast soundings
continue to suggest a rather unstable column on Tuesday
afternoon...with attainable convective temperatures in the lower
80s and again near 1500 J/KG of CAPE. Thus even with the marginal
dynamics departing...will need to keep some chance pops again on
Tuesday...again...mainly in the afternoon for instability
showers/storms. Again will trend highs at or above the forecast
builder blend.

On Tuesday night through Wednesday...the upper pattern suggests
more ridging aloft with any dynamics supporting precip shifting to
the east. Forecast soundings begin reflecting subsidence and
drying within the column on Tuesday night through Wednesday Night.
meanwhile at the surface...the models suggest that strong high
pressure re-establishes itself...stretching from the eastern
Great lakes...across the Ohio Valley to the deep south. Thus will
trend toward a dry forecast Tuesday Night through
Wednesday...along with temperatures at or above the forecast
builder blend.


.LONG TERM /Thursday through Monday/...
Issued at 257 AM EDT Mon Sep 18 2017

Long term period of the forecast will be dominated by a large area
of surface and upper level high pressure centered over the Great
Lakes. This will likely provide dry weather throughout the period
and above normal temperatures, and at least on temperatures and
sky cover, blended initialization performed well.

Had to remove some splotchy slight chance pops which made little
coherent sense, likely as a result of models` tendency to overdo
precip in warm airmasses, especially at longer ranges.

Otherwise, few major changes required.


.AVIATION /Discussion for the 18/15Z IND TAF Update/...
Issued at 1035 AM EDT Mon Sep 18 2017

Had to bring temmpo IFR ceilings in through 17z based on current
conditions and trends.

Previous discussion follows...
Issued at 702 AM EDT Mon Sep 18 2017

Predominantly VFR through the period. some MVFR fog will mix out
quickly at HUF.

Convection will be possible today with showers and perhaps a few
thunderstorms. Timing and placement of thunder quite uncertain and
will carry only VCSH as a result.

Winds through the period will be light and variable.




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