Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 130448

Area Forecast Discussion
National Weather Service Indianapolis IN
1148 PM EST Tue Dec 12 2017

The AVIATION Section has been updated below.


Issued at 332 PM EST Tue Dec 12 2017

Clipper systems will bring chances for precipitation Wednesday and
again Friday and reinforce below normal temperatures. After that
a warmup will arrive for the weekend, followed by more precip
chances to end the weekend and start next week.


.NEAR TERM /Overnight/...

Issued at 951 PM EST Tue Dec 12 2017

Surface analysis shows quick NW flow in place across Indiana with
a surface ridge over Illinois. Tight pressure gradient across the
area was resulting win steady winds. Of note were very dry dew
points in the single digits. This has resulted in temperatures
already falling into the teens at many locations. Satellite
Imagery shows limited cloud cover over northern Illinois and
Northeast Indiana...with much of Central Indiana clear. Thus have
trended lows a few degrees cooler than the previous forecast given
the quick cooling progress we have made this evening and the low
dew points. No other significant changes.


.SHORT TERM /Wednesday through Friday/...

Issued at 332 PM EST Tue Dec 12 2017

Forecast focus is on precipitation chances for Wednesday/Wednesday
night with a clipper system again moving through the Great Lakes.
Models are in fairly good agreement on the upper wave not
bringing any chances for precipitation into the forecast area
until at least late morning if not the afternoon. Warm advection
will take place during the morning across most of the area ahead
of the clipper, and this should allow the column to warm with
temperatures reaching into the 40s for the southwestern half or so
of the area, and mid to upper 30s over the remainder. Thus as
forcing from the clipper arrives, some of the area will likely
seeing rain or a mix of rain and snow. Also, the column looks
fairly dry to start the day, and it could take some time to reach
saturation for precip to make it to the surface. Expect to see
some cooling with precip onset for this reason as well. Thus even
spots that see rain initially could change over to a mix rather
quickly, especially in the northern half or so of the area. With
warmer temperatures to start though and some warming of the ground
amounts will be light. The highest snowfall totals will be in the
northeast where precip will likely remain snow the entire time.
Looking at around an inch to perhaps an inch an a half in isolated
parts of the northeastern counties. Northeast of Indy could see a
couple tenths to half an inch, with accumulation unlikely west
and south of I-74. Snow will continue over the far northeast
counties til midnight or so and this could have some lake

By Thursday morning dry weather will again be the rule until
Friday, when another system could bring some small chances for
snow back to the area. At this time accumulations look very
minimal. Temperatures will run below normal through the short


.LONG TERM /Friday night through Tuesday/...

Issued at 332 PM EST Tue Dec 12 2017

Friday night will begin the weekend a little cold with snow on its
way away from the area and only a slight chance for snow over the
eastern counties early. After that models are in agreement on the
upper pattern turning warmer and dry for most of the weekend with
upper ridging building over the area. Highs in the 40s and lows in
the upper 20s to low 30s can be expected. Starting Sunday
afternoon another upper trough begins to approach the area and
this will bring increasing chances for precipitation for parts of
the area. Models are showing more of a spread with the timing of
this next troughs approach and passage though, so low confidence
on timing of precipitation, and lower than normal confidence for
Monday through Tuesday temperatures. Prior to that, high
confidence in temperatures for the weekend and dry conditions
going into Sunday.


.AVIATION /Discussion for the 130600Z Tafs/...

Issued at 1150 PM EST Tue Dec 12 2017

VFR Conditions are expected to continue overnight and
through 18Z Wednesday.

Quick NW flow will remain in place overnight. Satellite shows some
mid and high cloud over NW Indiana poised to stream across IND and
LAF within the next 1-3 hours...however...surface ridging should
build east and allow unlimited CIGS for much of the overnight.

A short wave and associated cold front will push across Indiana
after 18Z Wednesday. This will result in some snow showers and VFR
CIGS eventually becoming MVFR CIGS in the wake of the cold front.
Time Heights and forecast soundings show saturated lower level in
the wake of the front for Wednesday evening.




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