Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 180239

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

The Synopsis, NEAR TERM, and Aviation Sections have been updated


Issued at 930 PM EST Sun Dec 17 2017

Lingering low level moisture will result in patchy fog and
drizzle during the overnight. 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 /Rest of tonight/...

Issued at 930 PM EST Sun Dec 17 2017

High confidence in cloudy skies tonight and lows in the mid 30s
to lower 40s, but low confidence on precipitation and fog
potential. Still wide model/guidance range in visibilities
overnight and through the morning, with some showing reductions
only down to 4 to 6 miles but others showing less than a mile and
even potential for dense fog. Model soundings show more of a low
clouds and drizzle profile. Overall think patchy fog and patchy
drizzle starting up in a couple of hours seems the most likely
scenario. Continued with mention of areas of fog for a few hours
late during the overnight/early Monday morning since not confident
enough to change it. Will continue to monitor for trends in either
direction for the fog.


.SHORT TERM /Monday 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 930 PM EST Sun Dec 17 2017

Updated to decrease conditions to MVFR an hour or two earlier than
initially forecast based on observations and satellite trends. No
other changes made. Previous discussion follows...

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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