Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 211857
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
256 PM EDT Sat Oct 21 2017

.UPDATE...The SYNOPSIS...NEAR TERM AND SHORT TERM sections have been
updated below.

&&

.SYNOPSIS...
Issued at 252 PM EDT Sat Oct 21 2017

A slow moving frontal system, quicker trailing system and an upper
trough  will bring showers to all or parts of central Indiana
overnight through Wednesday.

Much cooler air will move in Tuesday.

&&

.NEAR TERM /Tonight and Sunday/...
Issued at 256 PM EDT Sat Oct 21 2017

Main challenge to the near term will be timing showers into the
area. Models in general agreement that a Rockies upper trough will
move to the western Great Lakes and southern Plains by late Sunday.
Meanwhile, a cold front will move to near a Lafayette to Memphis
line by 00z Monday. Models continue to trend slower with the start
of qpf to the area. Prefer to continue with only small pops over the
western third of the area tonight and transition to likely or
categorical pops west by Sunday afternoon and taper off to dry over
our far eastern counties. Confidence in QPF trends is good, however
confidence is moderate at best in exact timing, placement of
heaviest QPF.

Instability progs continue to hint at some very weak elevated
instability. So, would not completely rule out thunder, but not
enough to include it.

Low level thermal progs and increased cloud cover and precip support
the blend temperatures with lows tonight in the middle 50s to lower
60s and highs Sunday in the middle 70s.

&&

.SHORT TERM /Sunday night through Tuesday/...
Issued at 256 PM EDT Sat Oct 21 2017

Main focus for the short term will be on shower coverage. Models all
now in good agreement on a quicker solution regarding a lower
Mississippi Valley upper low that will pivot northeast over the Ohio
Valley late Monday before opening up and being ejected northeast by
an upstream deepening upper low.

Models agree that an upper low will form in the southern Missouri
and northern Arkansas vicinity Sunday night. This will spin up a
wave along the cold front and cause it to slow down and or briefly
stall Monday. However, a deepening upper low will barrel down from
the northern Plains and sweep a reinforcing front through the area
Monday night. The result will be widespread showers that will
gradually spread from west to east starting Sunday night. By
Tuesday, the showers should be confinded by mainly to the northern
counties as the kicker moves nearby. Good confidence that much
cooler temperatures will arrive, in the wake of the second front,
per the blend.

Confidence in QPF amounts and placement is low, and with only a
modest low level jet, do not expect widespread excessive rain.

&&


.LONG TERM /Tuesday Night Through Saturday/...
Issued at 215 PM EDT Sat Oct 21 2017

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

Below normal temperatures will be the rule through much of the long
term period as a couple of upper level systems move across the area.
The first system will bring rain chances Tuesday night and across
parts of the area on Wednesday. Wednesday will be quite cool with
some areas not getting out of the 40s.

Briefly warmer conditions (closer to normal) will return Thursday
into Friday near and ahead of the next upper system. Rain moves back
in by Friday with the system. Colder air returns on Saturday.

00Z ECMWF remains farther west with the upper low which would lead
to a slower/warmer solution than the blend, but it is an outlier.
Lowered the blend a bit to help negate the influence of the Euro.

Frost will become a concern mid week with the colder air moving in.

&&

.AVIATION (Discussion for the 211800Z TAF Issuance)...
Issued at 1252 PM EDT Sat Oct 21 2017

Confidence is high that VFR conditions will be the rule. Expect low
level wind shear during the night.

Mid and high clouds will be the rule through the night, with
ceilings lowering from west to east on Sunday (but still VFR) as a
cold front approaches from the west. A few showers are possible
during the morning Sunday at the western sites, but expected
coverage is too low to put in TAF that far out.

Winds off the surface will increase during the evening, creating low
level wind shear conditions for the night. Mixing will occur Sunday
morning, generating surface gusts to near 25kt.

&&

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

&&

$$

SYNOPSIS...MK
NEAR TERM...MK
SHORT TERM...MK
LONG TERM....50
AVIATION...50


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