Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 181836
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
236 PM EDT Wed Apr 18 2018

.UPDATE...
The LONG TERM section has been updated below.

&&

.SYNOPSIS...
Issued at 200 AM EDT Wed Apr 18 2018

A quick moving area of low pressure will sweep into Central
Indiana this afternoon and exit tonight. This will bring chances
for light precipitation amounts to Central Indiana late this
afternoon and evening.

A Large high pressure system is expected to arrive in the are on
Thursday and linger across the region through at least the first
half of the weekend. This will bring dry weather with moderating
temperatures each day through Saturday.

A quick moving low is then expected to push across the Tennessee
River valley on Sunday. This system may bring some rain chances to
the Ohio valley on Sunday into Monday...however overall
precipitation chances remain low.

&&

.NEAR TERM /Rest of Today/...
Issued at 958 AM EDT Wed Apr 18 2018

Forecast is in pretty good shape. Adjusted morning sky cover based
on latest satellite imagery, but trend of increasing clouds looks
good as low pressure approaches the area.

Upped winds some based on latest data, so gusts near 40 mph are
possible this afternoon, especially south.

Left PoPs capped at 50 percent for now as am still unsure about
coverage. Did change wording though to scattered to imply some rain
in the area though. Will adjust this afternoon if necessary.

Temperatures could be tricky with a surface low moving through the
area this afternoon, leading to a temperature gradient in the
vicinity. Until trends can be seen better, made no changes at this
time.

Previous discussion follows...

Surface analysis early this morning shows a ridge axis of High
pressure stretching from the upper midwest...across Nrn Indiana to
SE OH. A deep low pressure system was found across eastern Kansas.
Aloft water vapor was showing a ridging in place across
Illinois...building eat toward Indiana. Strong subsidence was
seen in the wake of the low over western and Central Kansas.

Models suggest the upper ridge to west will quickly push over
Indiana today. Meanwhile the low over Kansas is expected to also
arrive in Central Indiana by late afternoon. National Radar
mosaics show precipitation only on the north side of the
approaching low...over NB. Lower level moisture fails to arrive
today as lower level flow only becomes east to southeasterly. The
GFS fails to show moisture arriving until really late this morning
and given that its rather shallow ahead of the approaching low.
Furthermore GOES16 is showing very little cloud cover with the
approaching system. Given current radar trend and expected
forcing...best chances for precip should be on the north side of
the system. GFS mid level RH fields support this also. THus will
trend best pops this afternoon across the northern parts of the
forecast area. Central Indiana should spend much of the day within
the warm sector with excellent sunshine and mixing, Will trend
High temperature above the forecast builder blends.

&&

.SHORT TERM /Tonight through Friday Night/...

Issued at 200 AM EDT Wed Apr 18 2018

GFS and NAm both suggest the quick moving low will exit Central
Indiana this evening. Associated moisture on the north and
backside of the low should allow for some precip chances early in
the evening...particularly across the northern parts of the
forecast area. In the wake of the low and associated cold
front...Time Heights keep some lower level strato-cu
trapped...providing mostly cloudy skies overnight. Furthermore an
upper trough will be passing across state overnight...which could
provide some weak forcing to the lower level moisture...resulting
in drizzle or even a flurry. THus will trend toward mostly cloudy
with stick close to the forecast builder pops...however
measurable precip will be most likely in the evening as the
system and stronger forcing departs. Will stick close to the
forecast builder blends on temps.

Quiet weather is then poised to settled across the area for the
rest of this forecast period. The GFS and NAM show strong ridging
building over the Central Plains on Thursday through Friday Night.
This will result in lee side subsidence and produce a strong
surface high pressure system in place across the Mississippi and
Ohio valleys. Forecast Soundings at this point show a very dry
column along with unreachable convective temps. Thus mostly sunny
days and clear nights will be expected to end the work week.
temperatures through Friday night will be warmer...however will
still remain below seasonal normals. Northerly surface flow ahead
of the surface high will keep our source air approaching from the
Great Lakes and Ontario. Thus will trend temps at or below the
forecast builder blends.

&&


.LONG TERM /Saturday Night Through Wednesday/...
Issued at 236 PM EDT Wed Apr 18 2018

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

The remainder of the weekend will be dry with high pressure in
control. Early in the week, the southern forecast area might get
grazed by a few showers from an upper low to the south of the area.

There are some differences in timing and location of the rain with
this feature, so confidence is lower here.

By mid-week, another upper low will move in from the northwest,
bringing more rain chances to all of the area.

Temperatures will be near normal to a little below normal for the
period.

&&

.AVIATION (Discussion for the 181800Z TAF Issuance)...
Issued at 1250 PM EDT Wed Apr 18 2018

Conditions expected to deteriorate to MVFR this afternoon,
persisting into Thursday morning. Some IFR is likely at KLAF
tonight. Gusty winds will occur this afternoon into early evening.

Low pressure will move across central Indiana later this afternoon
into early evening. This will bring a warm front through most of the
sites, and then a cold front right behind it. Thus expect fairly
rapid changes in wind direction this afternoon at most sites.

Confidence is only medium in wind direction at KIND due to
uncertainty on where the warm front will end up. Gusts near 30kt are
possible at most sites this afternoon.

Scattered convection will develop this afternoon, mainly at the
southern sites. Cannot rule out an isolated thunderstorm, but odds
are too low to mention.

Clouds will develop as the low moves in, with ceilings going down to
MVFR. An upper trough and cold advection will lower ceilings through
the MVFR category tonight (with some IFR around), and bring some
patchy light rain or snow (north).

&&

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

&&

$$

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



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