Area Forecast Discussion
Issued by NWS Indianapolis, IN

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432
FXUS63 KIND 280221
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1020 PM EDT Sat May 27 2017

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

&&

.SYNOPSIS...
Issued at 134 PM EDT Sat May 27 2017

A pair of weather disturbances are expected to pass through the
region bringing showers and thunderstorms Central Indiana Tonight
and again on Sunday afternoon and evening. Some of the storms
could be severe...particularly across southern Central Indiana.

Weak high pressure is then expected to slowly build across Central
Indiana from Monday through the middle of the work week. This will
bring dry weather along with cooler temperatures for much of next
week.

&&

.NEAR TERM /Tonight/...
Issued at 925 PM EDT Sat May 27 2017

Tweaked pops a bit to match adjacent offices, otherwise, the bulk of
the convection should stay south of the forecast area overnight per
radar trends and High Resolution Rapid Refresh. That said, one upper
wave will move across the lower Great Lakes early overnight followed
by another across the Ohio Valley. In addition, a warm front will
lift north across central Indiana. With this synoptic forcing
combined with the deep moisture, will keep in at least chance pops
with the highest chances south, closest to the current
upstream convection and the second wave.

Previous discussion follows...
Issued at 134 PM EDT Sat May 27 2017

Surface analysis early this afternoon shows High pressure in
place across the Great Lakes. A weak trough of low
pressure/boundary was in place from Central Ohio...across Indiana
to southeast Missouri. Visible satellite imagery continues to
show linger low cloud across the area...however this is expected
to dissipate through the late afternoon. GOESR Shows a convective
cluster over Eastern Kansas...and it is this feature that we will
need to watch closely.

Dry weather will be expected through much of the evening hours as
forecast soundings and time heights keep a dry column in place
across the area. GFS and NAM have change a bit with the handling
of the approaching short wave...focusing best development to the
south...toward southern Indiana after 03Z. We will expect a sharp
cut-off across our forecast area on precip...with northern areas
perhaps seeing little to no rains overnight...much high pops
expected from I-70 southward as forecast soundings in these
locations show deep saturation as the upper wave passes. All of
this plus the surface boundary that appears in place seem
reasonable include high pops across the southern parts of the
forecast area...but tapering quickly lower to the north.
Again...given the convective nature of the expected MCS severe
storms...mainly due to straight line winds will not be ruled out.
As for temps will trend toward expected wet bulbs or use a blend.

&&

.SHORT TERM /Sunday through Tuesday/...

Issued at 134 PM EDT Sat May 27 2017

Mainly dry weather will be expected on Sunday morning as the
previous wave should be exiting or will have already exited
Central Indiana by 12Z Sunday as suggested by the GFS. Thus the
day should start out dry. However models suggest that our second
short wave and an associated cold front will sweep across Central
Indiana during the afternoon. Forecast soundings have begun
hinting at much more instability available on Sunday afternoon
than previous runs showing steep lapse rates. GFS IND soundings
suggests CAPE of 2500-3700 J/KG through the afternoon with easily
attainable convective temperatures in the upper 70s. MAVMOS
suggest good surface moisture available with dew points in the
lower 60s. Thus as daytime heating progresses on Sunday...and the
dynamics advance through the afternoon...storm chances will
increase. Will trend toward a categorical Pop by late afternoon
given the expected instability and dynamics lining up. Will stick
closer the the MAVMOS on Highs.

Convection across the area should continue into the early evening
hours as the previously mentioned forcing departs prior to 03Z.
Thus will need to continue to carry pops across the
area...especially across the southeast...where forcing will depart
last. After 06Z...forecast soundings suggest drying within the
column along with subsidence. Thus will trend to dry pops
overnight.

Model then suggest broad lower level cyclonic flow across the
area Monday...around low pressure well north of Indiana...near
northern Ontario. A weak trough looks to pass across Indiana on
Monday...however the forecast column appears very dry. Thus will
try to get to a dry forecast on Monday. A blend on temps will
work fine.

Monday night through Tuesday also appears dry as forecast
soundings suggest a dry column. At the surface...high pressure
over the central plains appears to slowly move east...building
across the Ohio valley. Support aloft remains minimal...as best
forcing within the broad cyclonic flow remains well north of
Indiana...over Ontario and the great Lakes. Thus will continue to
trend toward a dry forecast here along with a blend on temps.

&&

.LONG TERM /Tuesday night through Saturday/...
Issued at 204 PM EDT Sat May 27 2017

Ensembles in good agreement is slowly drifting an upper low
across the upper Great Lakes and into southeast Canada during the
period.

Appears an upper disturbance may rotate through the local area
around Tuesday night into Wednesday. Will keep some PoPs going for
parts of the area during that time.

Ensembles continue to be rather aggressive with the precipitation
threat late next week, although there are large differences as to
the timing of this system, ranging from as early as Thursday night
to as late as next Saturday. At this time, the best threat seems
to be Friday and Saturday, so will concentrate the PoPs in those
periods.

&&

.AVIATION /Discussion for the 280300Z IND TAF Update/...
Issued at 1020 PM EDT Sat May 27 2017

No need to change the TAF.

Previous discussion follows...
Issued at 650 PM EDT Sat May 27 2017

Conditions will start off VFR. Then, could see some MVFR in
thunderstorms this evening as upper energy approaches from the west.
Confidence in exact timing and coverage is not good, but convective
allowing models suggest a mention by 03z-06z except at LAF. The most
widespread convection will likely be south of the terminals until
Sunday afternoon as a cold front approaches. Will go mostly MVFR
all sites after 17z.

Winds will be light and variable tonight and then veer from south to
southwest less than 10 knots, ahead of the cold front and west and
northwest behind it toward 00z Monday.



Mid level vorticity center currently moving through western Iowa
and Missouri is expected to approach the western terminals around
280400Z, so threat for shower and thunderstorm activity should
increase at the terminals towards and after that time.

Surface winds generally 6 kts or less through this evening.

&&

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

$$

SYNOPSIS...Puma
NEAR TERM...Puma/MK
SHORT TERM...Puma
LONG TERM....JAS
AVIATION...MK



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