Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 211502
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1100 AM EDT Mon May 21 2018

.UPDATE...
The Near Term and AVIATION sections have been updated below.

&&

.SYNOPSIS...
Issued at 202 AM EDT Mon May 21 2018

Several upper level weather disturbances are expected to pass
across Central Indiana today and tonight. A warm and humid air
mass was in place over the region. These two ingredients should
result in scattered showers or thunderstorms across Central
Indiana today and tonight.

High pressure is then expected to build across Indiana from the
upper midwest on Tuesday Afternoon. This will bring a return of
dry weather for the middle of the work week.

The High pressure system will drift east and warm and humid air
is expected to return to Central Indiana over the Holiday weekend.
This will result in chances for showers and thunderstorms
returning to the forecast.

&&

.NEAR TERM /Rest of Today/...

Issued at 1100 AM EDT Mon May 21 2018

Widely scattered showers showing up over southwestern parts of the
forecast area on radar at 1030 am, and visible satellite loop shows
mostly cloudy skies from convective blowoff with some breaks here
and there. The warm front, while somewhat diffuse, appears to be
somewhere in the vicinity of I-74. For the update, made some tweaks
to the hourly PoPs and increased cloud cover this morning. Still a
good amount of uncertainty regarding severe storm potential, with
the cloud cover tending to put a damper on instability growth.
However, the front across the area will still serve to increase
shear (especially low level shear) locally, and upper waves moving
through will increase the forcing, so still going with increasing
chances for thunderstorms this afternoon and evening and still on
board with slight risk over part of the area. Previous discussion
follows...

GFS and NAM continue to suggest several short wave moving across
the forecast area this morning and a second wave this evening.
Many favorable ingredients for shower/storm devlopment today.
This includes the surface boundary in place across the forecast
area...forecast soundings showing good instability today with CAPE
near 2000 J/KG with attainable convective temperatures and the
approaching upper support. Caveat here may be blow off clouds from
showers/storms upstream may result in a reduction in heating.
Time height sections show deep moisture and lift through the
day...particularly in the afternoon. HRRR is progressing the bulk
of the moisture with the upstream storms to the north of Central
Indiana...but does suggest some development on the southern edge
of the storms. Thus it doesnt appear an all day rain in
store...and a few items are dependent for how much development
does occur. However...high pops through the day...particularly in
the afternoon and early evening seem quite reasonable given the
previously mentioned set-up. Will stick close to forecast builder
pops...but trend highs pops in the afternoon. Also will stick
close to the forecast builder temps.

&&

.SHORT TERM /Tonight through Wednesday Night/...

Issued at 202 AM EDT Mon May 21 2018

The GFS and NAM show little overall change in the set-up this
evening as yet another short wave looks to pass across Indiana
during the evening hours before drifting southeast after midnight.
Lingering showers/storms will still be possible after
00Z...winding down from the daytime convection. Time heights show
best deep moisture exiting the area after 00Z. However confidence
that precip will have exited the area by 00Z is low and pops will
be needed early on. As the night progresses...the upper wave
departs and precip should come to and end. Forecast soundings show
dry air intruding into the column after by 12Z Tuesday. Thus will
trend pops lower as the night progresses...hoping to arrive at a
dry forecast by 12Z.

The GFS and NAM Suggest ridging and high pressure building aloft
over the plains states on Tuesday night through Wednesday Night.
This results in cooler NW flow in place aloft...along with lee
side subsidence over Indiana. Within the lower levels high
pressure begins to set-up over the Great Lakes and Ohio
Valley...as gulf air is cut-off and cool northeast flow persists.
Forecast soundings respond through Wednesday night indicating a
dry column. Thus will trend toward a dry forecast on Tuesday night
through Wednesday night...trending temps at or below the forecast
builder blends given the cooler NE flow expected.

&&


.LONG TERM /Thursday Through Sunday/...
Issued at 232 AM EDT Mon May 21 2018

Models are close enough that the model blend initialization
was accepted for most items.

Upper ridging and surface high pressure will keep most areas dry
Thursday and Friday. An upper trough and surface front will then
bring rain chances to the area for the weekend.

Confidence is medium to high in dry weather most areas through the
daylight hours of Friday. Confidence lowers then for timing and
extent of higher PoPs for the weekend with some uncertainty on how
the upper trough will interact with an upper low in the Gulf of
Mexico.

Temperatures will remain above normal through the period.

&&


.AVIATION (Discussion for the 211500Z TAF Issuance)...
Issued at 1100 AM EDT Mon May 21 2018

Updated current conditions, and increased winds through the daylight
hours by a few knots to better match obs and trends. Previous
discussion follows...

Outside of convection, VFR conditions are expected.

Convection across Illinois is having a hard time moving into
Indiana. Will include a vicinity mention this morning for the
possibility of some pop up showers or remnant showers from the
Illinois convection.

Better chances for convection will arrive this afternoon.
Uncertainty is too high most sites to go anything other than a
vicinity or PROB30 mention, but trends may become clearer later
today.

By mid to late evening convection should have moved off/diminished
enough to leave out all mention.

&&

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

$$

SYNOPSIS...Puma
NEAR TERM...Puma/CP
SHORT TERM...Puma
LONG TERM....50
AVIATION...50/CP


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