Area Forecast Discussion
Issued by NWS Indianapolis, IN

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818
FXUS63 KIND 182301
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
601 PM EST Sun Feb 18 2018

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 318 PM EST Sun Feb 18 2018

A warm and wet pattern will continue through the week, with
increasing chances for flooding across the area. A frontal system
will remain to the northwest into mid-week, allowing much above
normal warm and moist air to flow into the area. Although the front
will move through the area after mid-week, waves moving along the
front will keep rain chances across the area. Temperatures will
remain above normal even behind the front.

&&

.NEAR TERM.../Rest of This Afternoon and Tonight/
Issued at 318 PM EST Sun Feb 18 2018

Temperatures will continue to warm this afternoon with warm
advection ongoing and sunshine filtering through passing high clouds.

The warm advection continues tonight, and a low level jet will move
into the area. This will bring increasing moisture along with some
forcing, and an upper jet streak moving in will provide additional
forcing late tonight.

Thus expect rain to break out tonight. Doesn`t look like enough
forcing or moisture arrive until after midnight, so will keep the
evening dry. By the end of the night most of the forecast area will
have likely or higher category PoPs.

There could be some elevated instability west overnight, so added a
slight chance of thunderstorms.

Temperatures will reach their lows during the evening, and then
slowly rise overnight. Model blend looks reasonable for this.

&&

.SHORT TERM.../Monday through Wednesday/
Issued at 318 PM EST Sun Feb 18 2018

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

Forcing will be ongoing Monday morning as the initial surge of warm
and moist air continues, along with a weak surface trough moving
through the area. Thus will continue the high PoPs from the Tonight
period into Monday morning. As the surface trough and forcing move
off to the north during the day, PoPs will lower across most of the
area into early afternoon.

A large upper high off the coast of the southeastern USA will build
northwest into Tuesday night. This will keep a front at bay to the
northwest of the area. A low level jet will remain, keeping a flow
of warm and moist air into the area.

The low level jet and some impulses ride around the upper ridge will
keep rain across northwest sections of central Indiana at times
through Tuesday. Will go with likely or higher PoPs there, with
lower PoPs southeast.

The front will move into the area Tuesday night into Wednesday,
bringing more forcing. Plentiful moisture continues across the area,
so high PoPs look good everywhere during those periods.

Some instability will work in so continued with a thunder mention at
times during the short term.

Heavy rain will be a threat at times during the short term and
beyond. For more details, please see the Hydrology section below.
Regarding a Flood Watch, feel the initial surge of moisture tonight
into Monday will not cause any significant issues. With better
forcing off to the northwest Monday night into Tuesday, am not
confident enough to issue a watch for the northwest at this time. As
details get better refined, will likely have to issue a watch later
this week.

Temperatures will be well above normal Monday and Tuesday thanks to
the strong warm advection. Tuesday`s readings may be near record
values.

&&

.LONG TERM /Wednesday Night Through Sunday/...
Issued at 318 PM EST Sun Feb 18 2018

Ensembles are in good agreement in a fairly stable long wave pattern
across the country during this period, with troughing centered over
the Rockies and ridging over the East Coast.

Tail end of the system that is expected to affect the area late in
the short term will be in the process of moving through Wednesday
night and Thursday morning. Will keep PoPs in the forecast in these
periods to cover this feature. Might be enough cold air filtering in
for light mixed precipitation near the end of the event, but
accumulations not expected at this time.

Additional disturbances expected to periodically eject out of the
western trough late in the week and on into next weekend. Will go
with PoPs for rain starting on Friday, and continue them into next
Sunday. Progged precipitable waters are near climatological maximums
late this week, so heavy rainfall a threat.

&&

.AVIATION /Discussion for the 19/00Z TAFs/...
Issued at 601 PM EST Sun Feb 18 2018

VFR initially will give way to MVFR later tonight and likely some
IFR or worse conditions Monday.

Rain will move into the area later tonight, ahead of an
approaching frontal system. This rain will continue much of the
period.

Winds will generally be southeasterly early, becoming more
southerly and south/southwesterly with time. Sustained winds of
12-15KT will occur at times with gusts into the mid 20KT range
possible at times.

Low level wind shear will also be a threat, with winds at 2kft as
high as 50-60KT. Will carry this at all sites.

Visibilities will be reduced at times by fog and rain later in the
period.

&&

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

&&

$$

SYNOPSIS...50
NEAR TERM...50
SHORT TERM...50
LONG TERM...JAS
AVIATION...Nield



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