Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 180825

Area Forecast Discussion
National Weather Service Indianapolis IN
325 AM EST Mon Dec 18 2017

The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.


Issued at 256 AM EST Mon Dec 18 2017

There continues to be a split flow pattern mainly over the
southwest and north central parts of the U.S. Central and southern
Indiana is underneath the southern regime of this flow. On the
surface, weak area of high pressure is across the south central
and southeast states which is leaving a light southwest flow over
the area. This has kept temperatures mostly in the lower 40s and
some upper 30s overnight, and there is patchy fog and low clouds
from light moisture across the area on Sunday.


.NEAR TERM /Today/...

Issued at 256 AM EST Mon Dec 18 2017

West to southwest flow will remain over the area today as a weak
low over the eastern Great Lakes moves off further to the east.
The patchy fog and low clouds will remain until later his
afternoon when some comparatively drier air tries to make it way
into the region. Think visibilities from the fog will improve a
bit this morning, but the low clouds will remain for much of the
day, and there could be some drizzle from these clouds. Not much
mixing is going to occur to thin out the clouds, but there may be
just enough insolation as the Sun works on the low clouds later
today. Temperatures may warm a bit then into the mid/upper 40s
with some lower 50s in the southern counties.


.SHORT TERM /Tonight through Wednesday/...

Issued at 256 AM EST Mon Dec 18 2017

A cold front will be making its way slowly southward as it is
embedded underneath the westerly flow at low/mid levels between
these two flow regimes. By Tuesday morning, there will still be a
west-southwest flow in the boundary layer enough to mix things up
enough for some low clouds, but allow more heating to get the
temperatures into the low-mid 50s. The front will make its way
into areas to the north of central Indiana impeded a bit from a
storm system that will stay to our south from Texas through MS and
AL. High pressure over central Canada will become more persistent
by Tuesday evening pushing the cold front into central Indiana by
Tuesday evening. Front will move through dry as any moisture from
the south will be tied up with that southern storm system. North
winds will then fall in behind the front Tuesday evening taking
lows back down into the low 30s and keeping highs Wednesday only
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 180600z TAF issuance/...

Issued at 1113 PM EST Sun Dec 17 2017

IFR ceilings will become common at the sites over the next hour or
so where they haven`t already developed, and then ceilings will
drop even further to around 300 ft starting after 8-9z. High
confidence in the low ceilings given the saturated profiles in the
low levels and the trends in satellite and observations.
Visibilities will likely drop some as well given the high dew
points and low dew point depressions, but less confident of this
given the winds staying up above 5 kts through the night. Will
keep MVFR visibilities through much of the night and watch for
development of anything lower. Ceilings may not improve until
after 13 to 16z, and even then improvement will likely take
several hours before reaching VFR conditions. Winds will shift
from 190 to 230 during the period, and speeds will remain around 5
to 10 kts.




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