Area Forecast Discussion
Issued by NWS Indianapolis, IN

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KIND 181435
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
935 AM EST Sun Feb 18 2018

.UPDATE...
The NEAR TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 341 AM EST Sun Feb 18 2018

After a dry and pleasant day today...a much more active and stormy
pattern will develop for much of the week and into next weekend. A
nearly stationary frontal boundary will remain in the Ohio Valley
for much of the week with multiple rounds of heavy rain and the a
growing potential for flooding possible into next weekend. Much
warmer temperatures are expected Monday and Tuesday with cooler
but still mild weather for the second half of the week.

&&

.NEAR TERM /Rest of Today/...
Issued at 929 AM EST Sun Feb 18 2018

Satellite indicates back edge of low cloud deck is beginning to
retreat back to the north across southern Indiana. Should see
these low clouds continue to clear out from the south, although it
may be towards midday or early afternoon before the clearing
reaches the far northeast zones.

Given the lingering cloud cover over the northeast, high in those
areas may be too warm. Will leave the highs alone for now and
monitor the progress of clearing over the next few hours.

Will also bump up the wind forecast a little, as this morning`s
upper air indicates some occasional gusts around 15 kts possible
this afternoon.

Previous discussion follows.

Drier air slowly but steadily building into the region early this
morning with high pressure. Lower stratus continues to impact most
of the northeast half of the forecast area as of 08Z but is
gradually eroding on its western flank. Temperatures ranged from the
upper 20s to the lower 30s.

The high will move quickly across the Ohio Valley today eventually
tracking to the Mid Atlantic coast by late day. The presence of the
high and deep subsidence through the column supports a mostly sunny
day for the region once the stratus fully departs. CAMs guidance
indicating that low level moisture up through 925mb will continue to
shift east with bulk of the lower clouds out of the forecast area
around or shortly after daybreak. Return flow developing on the back
side of the departing high will prompt warm advection for the
afternoon along with southerly winds increasing. A pleasant day to
be enjoyed before the active weather pattern returns for the
upcoming week.

Temps...Low level thermals and the arrival of warm advection support
going warmer than the MAVMOS and much closer to the MET. Expect
highs to top out in the upper 40s and lower 50s across the forecast
area.

&&

.SHORT TERM /Tonight through Tuesday Night/...
Issued at 341 AM EST Sun Feb 18 2018

Forecast challenges focus primarily on a prolonged heavy rain threat
that will commence during the short term and extend out beyond into
the latter half of the week with flooding potnetial increasing
through the week.

Confidence remains high on an extended period of heavy rain
impacting the region beginning early Monday and continuing through
much of the upcoming week. River and lowland flooding is likely to
become increasingly problematic through the week. The upper level
flow regime across the country will return to an amplified pattern
tonight and Monday as a strengthening upper trough carves out over
the western U S through midweek. On the flip side...an anomalously
strong upper ridge for this time of year will move west and entrench
off the southeast coast by late Monday into Tuesday. In between
these two features...a broad southwest flow energized by a potent
subtropical jet will align from Baja California northeast across the
southern Plains...Arklatex region and up into the Ohio and Mid
Mississippi Valleys. The flow regime within the trough to the west
and the ridge to the east will serve as a pathway for a plume of
exceptionally rich moisture with a Pacific and Gulf origin to advect
into the region ahead of a cold front through much of the short term.

Recent model trends have focused the ridge axis stronger and a bit
further west off the southeast coast by Monday night and
Tuesday...resulting in the axis of heavier rainfall being shifted
further west as well. After the initial surge of rainfall late
tonight and Monday morning as the low level jet noses into the
region...the axis of heaviest rainfall will likely align more over
the northwest half of central Indiana for Monday night and Tuesday
before transitioning back east into the entire area Tuesday night in
tandem with the cold front. Isolated thunder remains warranted with
weak instability levels present aloft.

The presence of strong low level forcing courtesy of the jet bursts
at 850mb will linger through the period and maintain the deep fetch
of moisture with PWATs anywhere from 1.3 to 1.5 inches in the region
through Tuesday. These values are essentially at or just above the
climatological max for this time of year at 300 to 350% of normal.
Will focus likely to cat pops over the northwest half of the
forecast area with chance pops further southeast for Monday night
and Tuesday. Precip amounts through Tuesday now are likely to remain
at an inch or lower over the southeast half of the forecast area
with 1 to 2 inches over the northwest half of central Indiana.

As the front shifts east into central Indiana Tuesday night...the
axis of deepest moisture and forcing will overspread the entire
forecast area with widespread locally heavy rainfall into Wednesday
morning. As impressive as the precip water values are through
Tuesday...peak values are likely to surge even higher Tuesday night
to 1.6-1.7 inches which are virtually unheard of prior to spring. A
warm layer extending up to 11-12kft in combination with the
extremely deep moisture will produce the potential for 1 to locally
2 inches on Tuesday night alone. While localized flooding is
possible through Tuesday...these amounts are likely to produce a
more widespread flooding threat going forward into the second half
of the week and next weekend. The presence of elevated instability
supports a convective threat as well and will continue to mention
thunder.

For more on the heavy rain and flooding threat for later this
week...please see the Long Term and Hydrology sections below.

Temps...much warmer than normal temperatures are expected through
the period as highs surge into the mid and upper 60s Monday...and
even warmer Tuesday with low to mid 70s possible across much of
central Indiana. Indianapolis is likely to flirt with a record high
on Tuesday (72 from 2016). Also...the record warm min for Monday
night of 52 (1930) is likely to be shattered based on current
trends. Leaned towards high end of guidance and warmer MAV through
much of the period.

&&

.LONG TERM /Wednesday through Saturday/...
Issued at 250 AM EST Sun Feb 18 2018

A couple of frontal systems and several upper waves will move
through the forecast area during the long term, providing plenty of
forcing for rain chances throughout. With surface high pressure off
to the east, warm, moist Gulf flow will be in play for all this
forcing to interact with. This will produce periods of moderate to
heavy rain during the long term. Given the amount of precipitation
leading up to the long term, the likelihood of the ground being
saturated and streams already bankfull is high. Significant flooding
is shaping up for the latter half of the week.

Temperatures will be warmer than normal given the southerly
component flow. However, there will be chances for rain to change
over to snow or a rain/snow mix in the wake of a cold frontal
passage Wednesday night, and north of a warm front Friday morning.
At this point accumulation looks unlikely.

&&

.AVIATION (Discussion for the 181500Z KIND TAF Update)...
Issued at 919 AM EST Sun Feb 18 2018

Southwestern edge of an MVFR deck 010-015 has moved little over the
past hour, based on satellite. However, it was beginning to lift
north through southern Indiana. Will hold onto the MVFR ceilings for
a little longer on the update.

Will also bump up the wind forecast this afternoon, with this
morning`s upper air suggesting occasional surface gusts near 15 kts
possible.

Previous discussion follows.

MVFR cloud deck/visibilities have worked their way back west and
over all sites but KHUF. Think this will continue to be the case for
the next few hours until sunshine and subsidence can help scatter
this deck out. VFR should be in place by the afternoon, and winds
will become southerly around 5-10 kts tonight after being light and
southeasterly today.

Tonight lower clouds and rain will move into the sites on isentropic
lift. The low level jet associated with this lift will bring LLWS to
the sites after around 0-3z and that will hang around through the
overnight.

&&

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

$$

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.