Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 210225
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1025 PM EDT Sun May 20 2018

.UPDATE...
The NEAR TERM and AVIATION Sections have been updated below.

&&

.SYNOPSIS...
Issued at 354 PM EDT Sun May 20 2018

An active pattern with a frontal boundary that refuses to leave
central Indiana will continue through Tuesday, when upper ridging
will build in and return dry weather and high pressure to the
area. The pattern becomes more variable again at the end of the
week, with thunderstorm chances for the holiday weekend.

&&

.NEAR TERM /Overnight/...
Issued at 1025 PM EDT Sun May 20 2018

Ridging aloft has reestablished across much of the Ohio Valley
this evening after the convective development late this afternoon
over eastern portions of the forecast area. With predominantly
high level clouds drifting across the region...02Z temperatures
ranged from the upper 60s north to the mid 70s south.

Expect the next several hours will remain quiet across central
Indiana with the ridging aloft and little to no instability for
any convection to fire off of. Focus however already shifting to a
well developed convective cluster trucking across Missouri this
evening. Unlike this time last evening...this complex appears to
be maintaining intensity and is tracking E/NE...influenced by a
stronger wave aloft and a surface low. Both features will track
towards the region early Monday which should keep the complex
moving in this direction.

What is more uncertain is what shape the storms will be in on by
the time they approach the Wabash River as extrapolation does not
bring activity into western Indiana until after 09Z. Hi-res
guidance keeps instability elevated and largely limited overnight
but the presence of a strengthening nocturnal low level jet nosing
into the Wabash Valley supports the complex persisting in some
manner through the night. Storms will likely be weaker and well
below severe levels...but the above thoughts warrant maintaining
and spreading precip chances into region from the west after
08-09Z. Will focus highest pops in the northern Wabash Valley with
lower chances south and east. Morning convection and cloud debris
increases the uncertainty in convective redevelopment and
intensity later Monday afternoon and evening.

Zone and grid updates out.

&&

.SHORT TERM /Monday through Wednesday/...

Issued at 354 PM EDT Sun May 20 2018

Forecast focus in the short term is on PoPs Monday into Tuesday.
Models are showing some agreement on overall pattern but some big
differences especially early on in the details of timing and
coverage. Given this, have concerns over pinning any one time as
highly confident of rain/storms or dry time either given the
variability. That said, after collaboration and considering
potential for development of an MCS overnight in Iowa/Illinois
area, went with likely pops moving across the forecast area from
the northwest in the morning. With a surface wave progged to move
across the area along the front during the afternoon, kept likely
pops going through the afternoon for all but the westernmost
counties. This is still a cut from model consensus due to lack of
confidence given the way the model solutions have been handling
convection (that is, poorly) but could not justify cutting down to
chance category given general model/MOS agreement and inter
office collaboration. Much of the area also wound up in a slight
risk for severe storms for Monday was well based on the amount of
instability expected and the front still in the area, but this
will be dependent on what happens in the morning with convective
remnants so low confidence in this as well.

By Monday night should see most activity moving east, with the highest
pops over the eastern counties. Since the front still doesn`t
quite kick out of the area until later Tuesday, maintain some
lower pops across the southern/eastern counties through the day.

Models indicate upper ridging will build in over the area starting
Tuesday afternoon/night, meaning dry conditions can be expected
by Tuesday night and through the day on Wednesday as surface high
pressure builds south into Indiana.

Above normal temperatures should be seen throughout the short
term.

&&

.LONG TERM /Wednesday night through Sunday/...

Issued at 354 PM EDT Sun May 20 2018

The long term starts out dry with an upper ridge of high pressure
building across central Indiana. High confidence this will bring
increasing temperatures Thursday and Friday, and fairly confident on
the dry weather lasting through Thursday night. On Friday models
start to indicate potential for an upper wave to depress the ridge a
bit and bring some chances for showers and thunderstorms in to the
area for the weekend. Many ensemble members are also showing this
trend, so have moderate confidence in this occurring over the course
of the weekend, but low confidence on any more specific timing that
"sometime during the weekend". There are indications in the
operational ECM and GFS that a surface frontal system could move in
to the area Saturday night/Sunday bringing thunderstorm chances with
it, but ensembles are still showing wide variability for that time
this far out, so confidence is low.

&&

.AVIATION /Discussion for 210300Z TAF Update/...
Issued at 1025 PM EDT Sun May 20 2018

Appears that the convective complex over Missouri may maintain to
some degree through the night and could approach western portions
of central Indiana after 09Z. Have bumped up VCTS mention by 2
hours at the terminals as a result.

00Z discussion follows.

VFR conditions expected throughout much of the forecast period.
Low confidence exists in convective coverage and timing.

Scattered convection developed late this afternoon to the east of
the terminals and has already moved out of the area early this
evening. The remnant frontal boundary appears to have shifted back
south closer to the Ohio River. With little in the way of forcing
aloft back across the region...think much of the overnight is
likely to be dry across central Indiana.

Beyond that however...model guidance continues to hint at a
convective cluster developing to the northwest of the region and
potentially moving into central Indiana on Monday morning.
Additional scattered convection may develop into the afternoon as
the frontal boundary returns north into the unstable environment
and an upper wave tracks into the region. High uncertainty in this
solution at this point in time...so will carry primarily VCTS
wording at the terminals from mid morning through the end of the
forecast period. Once again...expecting chaotic and variable wind
flow through the period at predominantly less than 10kts.

&&

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

&&

$$

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



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