Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 271047
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
647 AM EDT Sat May 27 2017

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

&&

.SYNOPSIS...
Issued at 331 AM EDT Sat May 27 2017

Active weather will continue for most of the holiday weekend as
a frontal boundary oscillates over the region and interacts with
upper level waves moving through the Ohio Valley. Dry weather will
return Sunday night and Memorial Day with the passage of a cold
front. With the exception of a secondary front bringing low chances
for storms Monday night...expect primarily dry weather for much of
next week with seasonable temperatures.

&&

.NEAR TERM /Today/...
Issued at 331 AM EDT Sat May 27 2017

Isolated showers continue to move east across northeast portions of
the forecast area in the vicinity of a surface wave over north
central Indiana and the frontal boundary roughly extending west-east
from northern Vermillion County to Randolph County. These should
depart off to the east within the next few hours. Lower stratus
developing across most of central Indiana early this morning with
plenty of moisture in the lower levels. 07Z temperatures ranged from
the 60s to lower 70s.

Much of today will be quiet as weak high pressure briefly builds
into central Indiana as the frontal boundary sags south. The front
will eventually stall across far southern portions of the forecast
area or somewhere over southern Indiana this afternoon before
beginning to lift back north by early evening in response to a
stronger surface wave kicking out into the Missouri Valley. Could
see isolated convection by mid afternoon over far southern counties
as a moist and strongly unstable airmass develops in the vicinity
of and south of the boundary. However...do not anticipate storms to
grow in coverage in the absence of substantial forcing aloft. Over
the rest of the forecast area...model soundings show the airmass
becoming effectively capped for the duration of the day. Expect
partly cloudy skies and dry weather into the early evening.

The more significant convective threats will remain south and
west of the forecast area today. Two areas of ongoing convection
this morning of particular interest...the first currently over the
Ozarks is expected to track E/SE into the Tennessee Valley
through the morning and into the afternoon. The second area of
interest is the convective complex over northwest Kansas early
this morning associated with a wave aloft and low pressure at the
surface. This complex will play a large part in determining
convective strength... timing and track for tonight which will be
discussed in greater detail in the short term section. With that
being said ...hi-res guidance seems to have a decent handle on
tracking the convective complex east into the Missouri Valley by
late morning in a weakened state. Robust and rapid storm
development will take pace during the afternoon in the vicinity of
the surface low and wave aloft within a highly sheared and
unstable airmass over eastern Kansas and western Missouri. All
signs point to the newer area of convection becoming severe
rapidly...surging east and continuing to grow upscale through
Missouri into the early evening. More on expectations with this
activity in the short term section below.

Temps...generally split between the cooler MAV and warmer MET
guidance with highs ranging from the upper 70s to lower 80s for
most. Expect a distinctly humid feel to the airmass...especially
over southern counties.

&&

.SHORT TERM /Tonight through Monday Night/...
Issued at 331 AM EDT Sat May 27 2017

Forecast challenges primarily focus on convective threats tonight
and Sunday as the frontal boundary returns north and interacts
with waves aloft. Continue to stress that confidence is lower than
desired in this pattern with mesoscale factors heavily influencing
convective timing...location and intensity.

The aforementioned and likely intense convection ongoing over
Missouri this evening will be the primary focus for much of the
region. Axis of strongest instability and shear should focus from
central and southern Missouri into the Tennessee and lower Ohio
Valleys with the core of the convective complex tracking E/SE
through this area during the evening and early overnight. The
greatest threat for significant and widespread damaging winds will
be along this corridor and consequently...largely south of the
forecast area.

With that being said...the surface low will lift east from the
Missouri Valley and into the region overnight...pulling the frontal
boundary back north into the forecast area. The cap will weaken
sufficiently enough through the evening to enable convective
expansion on the northern end of the convective complex into central
Indiana during the evening and overnight. Lower confidence in how
expansive the coverage or intensity of storms will be over the
forecast area...but the threat will exist for strong to locally
severe storms with expansion of the low level jet into the area and
diffluence aloft interacting with the moist and marginally unstable
airmass present over the area.

Storms should diminish Sunday morning as the surface wave shifts
east. Scattered convection will increase again during the mid to
late afternoon ahead of a cold front and the parent upper trough.
Mid level cooling associated with the approach of the trough aloft
will weaken the cap and steepen low level lapse rates. With
instability increasing and plenty of BL shear present ahead of the
cold front...expect scattered strong to severe convection to
impact the forecast area for the second half of the afternoon into
the evening. The cold front will sweep east of the forecast area
Sunday night with rain and storms ending from the west.

High pressure will build in for Memorial Day with mainly dry and
breezy conditions as the Ohio Valley comes under the influence of
cold advection and cyclonic flow aloft. A weak secondary front will
slide into the area late day Monday into Monday night and may
generate a few showers and storms. Moisture is limited however and
hard to justify more than low chance pops at this time.

Temps...held close to a model blend for highs and lows through the
short term as they will be easily influenced by the timing and
location of convective complexes. Overall...expecting highs from the
mid 70s to lower 80s Sunday and mainly in the 70s on Monday. Lows
will fall back into the 50s behind the cold front Sunday and Monday
nights.

&&

.LONG TERM /Tuesday through Friday/...
Issued at 220 AM EDT Sat May 27 2017

The consensus forecast from Region will be used with moderate to
high confidence.

The main models agree in many respects,reducing the chance of big
errors. It is not always clear when there will at least some chance
of rain and when the weather will be completely dry. Potential POP
errors are about 10 percent. Potential temperatures errors, which
are related to chances for rain and clouds, are 1-3 degrees.

&&

.AVIATION (Discussion for 271200Z TAFs)...

Issued at 648 AM EDT Sat May 27 2017

Expect areas of IFR ceilings and local VLIFR visibilities in fog
early to give to exclusively VFR conditions by 16Z. Clouds will
rise to 10 thousand feet or higher by evening.

Thunderstorms are expected to develop tonight as a front approaches.
As storms increase, MVFR ceilings should become widespread. There
may locally be much lower conditions. Strong winds and hail are also
possible in storms tonight, especially over southern parts of the
area.

Winds outside storms should be mainly less 6 knots or less.


&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....JK
AVIATION...JK


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