Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 182028
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
326 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 182100Z KIND TAF Update/...
Issued at 326 PM EST Sun Feb 18 2018

No significant changes made to the forecast at this time. Previous
discussion follows.

Satellite indicates area of MVFR ceilings 010-015 lifting fairly
rapidly off to the north, and should clear the terminals by or
shortly after issuance time.

Threat for low level wind shear in the 010-020 layer will
increase towards/after 190600Z as short term model guidance
suggests a 55-60 kt low level jet will nose into the local area
during the pre dawn hours of Monday.

Surface winds 150-170 degrees at 10-15 kts this afternoon will
become 170-190 degrees at 8-12 kts after dark. A few surface gusts
around 18 kts possible towards 190600Z as the low level jet
increases.

&&

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

Potential for significant flooding continues across the area this
week.

Precipitable water values will be near the climatological maximum
into mid-week as the strong low level jet continues to pump in
moisture from the Gulf of Mexico. This will be briefly pushed south,
but then the values will return late week.

This means that several inches of rain are possible across the
forecast area this week. Exactly where the main band sets up is
still in question, with the potential for the heavier rain to be in
the northwest early this week and then across the south later this
week.

The northwest forecast area, where the first round of rain will be
heaviest, has been relatively dry lately. Thus they can handle more
water initially. With that, combined with the uncertainty on how far
northwest the first surge of rain will be, have decided to hold off
on the Flood Watch for now. Will continue to mention flooding
potential in the ESF, HWO, and social media products.

If trends continue will likely have to issue on for mid week as the
front moves into the area, especially if it slows down across the
area.

&&

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

$$

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


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