Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 200828
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
428 AM EDT Mon Mar 20 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 348 AM EDT Mon Mar 20 2017

A frontal zone will sag through the area today, bringing showers
and a few thunderstorms to the area. This front will move south of
the area late tonight into early Tuesday. A weak upper disturbance
may bring additional showers to the area Tuesday afternoon and
evening before a dome of high pressure sliding through the Great
Lakes brings a mid week dry period to the area. Another stronger
frontal system late in the week and into the weekend may bring
more showers and storms.

&&

.NEAR TERM /Today/...
Issued at 348 AM EDT Mon Mar 20 2017

Broken convective line has developed from west central Illinois to
the Chicagoland area and into far southern Michigan. Several hail
reports noted with the strongest portions of the line, including
at least one golfball hail report thus far. Forecast soundings and
mesoanalysis indicate some elevated instability present over
mainly our northwest forecast area, but midlevel instability
profiles are somewhat less favorable over central Indiana than
upstream, so with a little luck the large hail threat may wane a
bit as the convection approaches later this morning.

This first round will move through the area this morning, and
guidance indicates potential for another round to fire later today
to our north/northwest and drop southeast through especially the
northeastern half of the area. Severe threat appears limited owing
to modification of the thermodynamic environment by the morning
convection and widespread cloud cover acting to limit
destabilization.

Consensus temperatures, though quite a bit warmer for much of the
area than in recent runs, appeared reasonable based on upstream
numbers and were only slightly tweaked.

&&

.SHORT TERM /Tonight through Wednesday Night/...
Issued at 348 AM EDT Mon Mar 20 2017

Will hang onto an isolated thunder threat across the far south
this evening as the front continues to drop southward, per SREF
thunder probabilities, but this threat will be limited at best.
Front will be rapidly moving out of the area and a dry forecast
will suffice late tonight into early Tuesday. Some guidance
continues to depict some showers from a weak upper level
disturbance sliding through the overall northwest flow aloft
Tuesday afternoon and evening, and will carry some chance pops
during this time frame as a result. The remainder of the short
term will be dry as strong high pressure pushes across the Great
Lakes.

Consensus temperatures tracked quite well with low level
thicknesses and upstream numbers, and were only adjusted minorly.

&&

.LONG TERM /Thursday through Sunday/...
Issued at 250 AM EDT Mon Mar 20 2017

Ensembles indicate a slowly progressive nature to the long wave
features during this period. Upper ridging, initially over the
area at the beginning of the extended, will gradually push off to
the east as an upper trough settles into the Midwest by next
weekend.

Ensembles are less bullish on the warm advection precipitation
threat for Thursday and Friday then they have been, probably due
to the fact that the mean upper ridge is still close by. Will keep
some small chance PoPs over mainly the northern zones during this
time, but precipitation threat in these periods seems to be
diminishing.

Better threat still looks like from Friday night through next
weekend as the upper trough moves overhead. Will go with PoPs all
areas during these times. Long range operational models suggest
some instability may be present with this system, so added a
thunder threat as well.

&&

.AVIATION /Discussion for the 20/09Z TAF Update/...
Issued at 428 AM EDT Mon Mar 20 2017

Have added some VCTS at LAF and IND for upstream convection which
may make these sites in the next several hours. Previous discussion
follows.

Issued at 1142 PM EDT Sun Mar 19 2017

Good confidence that VFR conditions will continue through 11z and
later this morning. Then, widespread showers are expected to spread
southeast across, especially LAF and IND, after 11z and bring MVFR
or worse conditions in. Could also see some thunder per instability
progs. However, not confident enough on lightning strike coverage to
mention in the TAFs, yet anyway, and expected upstream convection
has yet to develop over eastern Iowa. More storms are possible
after 16z as the atmosphere destabilizes and a front sags
southeast over the area. Models hint at a surface wave moving
along the front during the afternoon, so MVFR showers look
especially justified at IND and LAF. The showers will be east of
the area by 06z Tuesday if not sooner.

A front is expected to sag southeast over the terminals Monday after
noon, and a surface wave may move along it. Not confident on exactly
where the front or outflow will be, and consequently when the wind
shift will occur at each terminal. However, the trend will be for
winds to veer from south to northwest to north behind this front.
Winds will be south less than 10 knots overnight before they veer
and may reach 10 knots during the afternoon.

&&

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

&&

$$

SYNOPSIS...NIELD
NEAR TERM...NIELD
SHORT TERM...NIELD
LONG TERM...JAS
AVIATION...MK/NIELD



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