Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 151033

Area Forecast Discussion
National Weather Service Indianapolis IN
633 AM EDT Sun Oct 15 2017

The AVIATION Section has been updated below.


Issued at 155 AM EDT Sun Oct 15 2017

A cold front will cross Indiana by evening. A high pressure system
developing behind it should extend from Texas to the Ohio Valley by
Monday, then show little change for several days.


.NEAR TERM (Today)...

Issued at 155 AM EDT Sun Oct 15 2017

The main issues are rain timing and how temperatures will evolve.

The models agree a front will bring showers today, but they should
end by evening.  The models also agree there will be enough CAPE for
a chance of thunder but not widespread storms. With strong cold
advection developing, clouds should persist through the day.

For details on rain timing, the ShortBlend syncs relatively well
with the convection allowing HRRR and will be used for the hourly

The MOS guidance looks OK for 12 hour highs. However, the incoming
front is strong enough so temperatures will peak early just before
it passes, then decline most of the day. To capture this hourly
temperatures will be based on the ShortBlend, not the standard
diurnal formula.

Boundary layer winds should be enough to cause gusts of 30 mph,
helping to make today feel the coldest so far this season.


.SHORT TERM (Tonight through Tuesday night)...

Issued at 155 AM EDT Sun Oct 15 2017

There is very good model agreement the weather will be dry. Clouds
may persist well into tonight with cold advection over the lakes and
boundary layer humidities staying high. By 12Z Monday the cold
advection will be over and we should start a prolonged clear spell.

With the coldest air so far this season arriving, frost is an
important issue.

It`s unlikely tonight. Unless the consensus lows are seriously wrong
for some non-apparent reason, temperatures will just be too warm.
Also clouds and wind associated with cold advection will undercut
frost chances.

Frost is more of a concern Monday night. The models introduce a
little warming, but also have dry air and light winds ideal for
radiation. It is too early to change the consensus lows with
confidence, but they are in the 30s in some places. Patchy frost
will be mentioned there.

Consensus also looks reasonable for highs based on the thermal


.LONG TERM /Wednesday through Saturday/...

Issued at 217 AM EDT Sun Oct 15 2017

Upper ridging will build across Indiana during the long term
period, bringing dry weather and slowly increasing temperatures.
High confidence in this as there is little model/mos variability
until the weekend. High confidence in high temperatures above
normal (63 for Indianapolis) through the long term, topping out in
the low to mid 70s Saturday.


.AVIATION /Discussion for 151200z TAF issuance/...

Issued at 626 AM EDT Sun Oct 15 2017

A line of moderate to heavy showers is moving through central
Indiana and should weaken over the next couple of hours. Only
isolated thunder seen within the line so will keep thunder out of
the TAFs. Conditions are mainly MVFR with these showers moving
through the sites and expect them to remain that way through the
day, with perhaps a brief scattering up to VFR later this morning
but then MVFR filling back in within a few hours of cold frontal
passage. LLWS still occurring at the sites for the next few hours,
but gusts of 20 to 25 kts or so are already occurring. Direction
at the sites will change from southwesterly to westerly to
northwesterly throughout the day, with gusts expected to continue
much of the day and increasing in the afternoon out of the
northwest. VFR could return to the sites starting after around
23-0z at KLAF and overspreading the sites from there. May add
tempo group for heavier showers in the first hour or two of the
forecast but will decide this right before issuance.




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