Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 172309

Area Forecast Discussion
National Weather Service Indianapolis IN
609 PM EST Sun Dec 17 2017

The AVIATION Section has been updated below.


Issued at 327 PM EST Sun Dec 17 2017

Rain will continue to move northeast of the forecast area as the
flow becomes more zonal aloft, but lingering low level moisture
will result in fog and drizzle through the night. After that, a
benign pattern will prevail through the end of the short term
period. In the extended, however, rain chances will increase with
a frontal boundary on Thursday night and even more so with a
strong cold front on Friday. Meanwhile, temperatures through the
forecast period will be well above normal.


.NEAR TERM /Tonight/...

Issued at 327 PM EST Sun Dec 17 2017

Current radar mosaic shows all rain showers confined to the
northeast portions of central Indiana as the flow aloft becomes
more zonal. Nonetheless, lingering low level moisture will become
trapped under an inversion tonight. So, the main focus will be
fog formation and reduced visibilities along with light drizzle.
The good news though is that temperatures will be in the upper
30s, so freezing will not be a concern.


.SHORT TERM /Tomorrow through Wednesday/...

Issued at 327 PM EST Sun Dec 17 2017

Dry conditions will prevail through the extended period as central
Indiana falls between disturbances. To the north, a strong cold
front will extend from the Great Lakes Region into the Plains. And
to the south, a low pressure system will makes its way out of
Texas and through the Deep South. Meanwhile, temperatures early in
the period will be well above normal with highs topping off in
the mid 50s by Tuesday with overnight lows only falling into the
upper 30s/low 40s tomorrow night. Some colder air from the
aforementioned front will filter into the area by Tuesday night
though, resulting in lows in the upper 20s to mid 30s. Daytime
highs Wednesday will be a tad cooler, too, with highs in the 40s.


.LONG TERM /Wednesday Night through Sunday/...

Issued at 229 PM EST Sun Dec 17 2017

ECMWF suggests a warmer than normal pattern during this time
period. A weak ridge of high pressure is expected to develop on
Thursday as a Low pressure system exits the Tennessee River
Valley. This will keep dry and mild weather across Central Indiana
through Thursday. As warm and relatively moist air arrives in the
area ahead of a frontal boundary on Thursday night...superblend
begins to insert pops. This seems overdone as forcing aloft and in
the lower levels is limited. Confidence is low for precip here.

Better chances for precip will be on Friday Afternoon through
Saturday morning as a strong cold front works across the states.
Here...better dynamics are in place aloft along with the surface
front. Thus during the Friday and Friday night time
frame...confidence for showers and storms is much higher.

A SW flow aloft is suggested by the ECMWF to develop by Friday
ahead of a broad trough over the the western United States. This
SW flow will remain in place through next weekend...keeping polar
air at bay to the north and result in above normal temperatures.


.AVIATION /Discussion for 180000z TAF issuance/...

Issued at 557 PM EST Sun Dec 17 2017

Currently VFR flying conditions will deteriorate tonight into the
LIFR range. Fairly high confidence in the development of low
ceilings, with lesser confidence regarding low visibilities, in
the warm sector of a low pressure system. Light advection of warm
moist air into the area will allow for development of initially
MVFR ceilings over the next few hours and then building downward
to LIFR a few hours after that. Could see some patchy drizzle as
well. Uncertainty regarding mixing in the lowest level means
leaving visibilities going no lower than 3SM at the sites for now,
but will have to monitor this closely with some models showing
much worse but others showing little reduction at all. After
ceilings bottom out around 3-400ft, should see improvement to MVFR
by around 18-21z Monday. Winds look fairly light throughout the
period, around 4 to 10 kts out of 200 to 230.




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