Area Forecast Discussion
Issued by NWS Indianapolis, IN

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214
FXUS63 KIND 222026
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
426 PM EDT Mon May 22 2017

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

&&

.SYNOPSIS...
Issued at 338 PM EDT Mon May 22 2017

The brief period of dry weather will come to an end on Tuesday as
high pressure moves away to the east. An upper low will dive into
the Ohio Valley and spin up a strong low pressure system. This will
result in widespread rain and embedded thunderstorms from Tuesday
night into Thursday. High pressure will return again briefly for
late week before chances for rain and storms come back for the
holiday weekend with a frontal boundary in the region.

&&

.NEAR TERM /Tonight/...
Issued at 338 PM EDT Mon May 22 2017

Central Indiana enjoying a pleasant afternoon with high pressure
draped across the Ohio Valley. Under partly cloudy skies...19Z
temperatures were very comfortable with low humidities...ranging
from the mid 60s to lower 70s.

Overall...tonight will be quiet as the region remains under the
influence of the high pressure as it shifts into the northeast by
daybreak Tuesday. Area of thicker mid level clouds extending from
central Kansas northeast into the western Great Lakes ahead of an
elongated low pressure. This area of low pressure will shift east
tonight and become slightly better organized as the upper low
positioned over the upper Mississippi Valley splits with a piece of
it diving south into Minnesota and Iowa by early Tuesday.

Have seen light rain showers and sprinkles underneath the cloud veil
over northern Missouri and southeast Iowa so far this afternoon.
Expect the light precip to shift east tonight and align from central
Missouri to the Great Lakes by Tuesday morning. Not out of the
question that a few of these light showers may sneak into the
northern Wabash Valley towards daybreak...but confidence too low in
this occurring considering presence of drier air below 10kft. Do
anticipate an increase in mid level clouds late tonight which is
supported by RH progs and model soundings. Southwest winds will back
to southerly then southeast overnight.

Temps...an overall model blend was supported by low level thermals
as lows should fall into the lower and middle 50s...with coolest
temps over the east where skies will remain mostly clear the longest
before the clouds arrive.

&&

.SHORT TERM /Tuesday through Thursday/...
Issued at 338 PM EDT Mon May 22 2017

Forecast challenges focus on precip and storm chances as the arrival
of the aforementioned upper low and a strong surface low bring yet
another return to the active and unsettled weather pattern
experienced over the region in recent weeks.

The piece of energy broken off from the upper low will amplify as it
dives south then east across the region. The approach and
intensification of the upper wave will prompt low pressure to
develop at the surface Tuesday evening over the lower Ohio
Valley...pinwheeling north into the area and deepening on Wednesday
as the upper low arrives.

Model consensus agrees on this scenario...but offer subtle
differences with respect to the track of the surface low which will
ultimately determine where the heaviest rain falls. At this
point...prefer a blended ECMWF/GFS solution as the NAM appears to
hold back too much energy in the upper wave...leading to a deeper
surface low tracking further west than most all other model
guidance. The ECMWF/GFS blend would support the surface low lifting
north out of Kentucky and into central/eastern Indiana by late
Wednesday before gradually shifting the surface wave northeast
into the eastern Great Lakes with the upper low by late Thursday.

The main takeaway is that another bout of rain and embedded
thunderstorms is on the horizon for central Indiana for midweek
despite the ultimate track the surface low takes over the region.
Other than a few showers and thunderstorms focused over northwest
counties on Tuesday...expect Tuesday to be dry for most with a
continued increase in clouds. The arrival of stronger low level
forcing at the nose of an 850mb jet and development of the surface
wave will bring a quick expansion in rain Tuesday night from
southwest to northeast.

Rain will become widespread and could be locally heavy Wednesday
with the surface wave over the region. Low level forcing will remain
strong...with mid level deformation and subtle hints of a developing
TROWAL from the east likely enhancing rainfall. One interesting
component to Wednesday which should not be ignored...the presence of
such a strong surface wave at 995mb or lower is likely to contribute
to plenty of spin in the atmosphere with good amounts of BL shear
and storm relative helicity being present. While the rain and clouds
will keep heating substantially diminished...weak MLCAPEs peaking at
around 500 j/kg and LCLs generally below 2kft could enable brief
spinners with any stronger convective cell. Something to monitor
going forward.

Showers will continue Wednesday night and early Thursday before
gradually diminishing from west to east Thursday afternoon. With
precip water values peaking near 1.2 to 1.3 inches on Wednesday...
potential certainly there for another 1 to 2 inches by the time rain
ends on Thursday over the forecast area. Certainly could see locally
higher amounts wherever heavier convection impacts.

Temps...Trended generally closer to the cooler MAVMOS through the
period...especially for highs Wednesday and Thursday as rain and
clouds will keep highs down in the 60s both days. Lows will
primarily be in the 50s through the short term.

&&

.LONG TERM /Thursday Night through Sunday Night/...
Issued at 208 PM EDT Mon May 22 2017

Thursday night into Friday morning will be dry as a low pressure
system pushes farther away from central Indiana. However, the dry
weather will be short-lived as a surface low approaches from the
southwest and an upper low tracks across Ontario on Friday. This
active pattern will result in showers and thunderstorms at times
throughout the weekend. Latest initialization seems to be
following the pattern well though, so will not make any
modifications at this time. Meanwhile, temperatures through the
period will start climbing above normal once again with highs in
the upper 70s/low 80s and lows in the 60s. The only exception will
be the overnight lows in the low to mid 50s on Thursday night.

&&

.AVIATION /Discussion for the 222100Z KIND TAF Update/...
Issued at 423 PM EDT Mon May 22 2017

Some limited diurnal cloud based near 045 has developed over the
past hour or so. Will add this to the forecast through sunset.
Will also increase the wind speed forecast through sunset based on
current observations.

Previous discussion follows.

VFR conditions expected through the forecast period.

High pressure will drift across the Ohio Valley through this
evening...maintaining dry weather and scattered cirrus. More
extensive mid level clouds will arrive tonight at KLAF and early
Tuesday at the other terminals ahead of an upper low diving out of
the upper Midwest. Any rain associated with this feature however
will not impact the terminals until Tuesday evening at the
earliest. Southwest winds this afternoon will back to southerly
tonight then southeasterly early Tuesday.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan
SHORT TERM...Ryan
LONG TERM....TDUD
AVIATION...Ryan/JAS



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