Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 221846

Area Forecast Discussion
National Weather Service Indianapolis IN
246 PM EDT Sun Oct 22 2017

The LONG TERM Section has been updated below.


Issued at 235 PM EDT Sun Oct 22 2017

A cold front will sweep across Central Indiana tonight...bringing
large changes to Indiana`s weather in the week ahead. Rain showers
are expected ahead of the front tonight as it passes.

Colder air will arrive on Monday through Tuesday...along with
several passing upper level weather disturbances. This will result
in daily chances for rain showers through Tuesday along with below
normal temperatures.

Cool High pressure is expected to arrive in the area by the
middle of the work week with might lead to a first frost across
much of Central Indiana. Below normal temperatures are expected
through next weekend.


.NEAR TERM /Today/...

Issued at 235 PM EDT Sun Oct 22 2017

Surface analysis early this afternoon shows a cold front over
Central Illinois. Radar mosaics show an area of showers along and
in the wake of the front. Warm southerly flow was in place across
Central Indiana. Water vapor imagery shows plentiful moisture
streaming into Indiana on Southerly winds ahead of a deep trough
over the Central Plains. Dew point temps across the area were in
the moist upper 50s to near 60.

Rain is a good bet for tonight. the strong front will be quickly
swept east tonight as the models suggest the deep trough to the
west passes east. Forecast soundings and time height sections show
deep saturation through the column arriving in the area tonight.
Given the expected forcing...near 100 pops will be required. best
chances look to be 02Z-09Z as the front passes.

Given the expected cloud and rain will trend toward expected


.SHORT TERM /Monday through Wednesday/...

Issued at 235 PM EDT Sun Oct 22 2017

A big change is in store this period. Models suggest that as the
deep trough progresses east tonight...a broad deep trough is
reinforced over the Great Lakes and Ohio Valley through
Wednesday. Several embedded short waves are poised to push through
the region withing the broad cyclonic flow aloft. Models suggest
wave of moisture passing within this flow each day.

There will be a few dry spots between waves as depicted by the
forecast soundings. First dry spot looks to be monday afternoon
and evening as the cold front and associated moisture departs.

Better chances for rain will arrive as the next wave moves in on
Tuesday. Furthermore at that time...forecast sounding show a
favorable convective sounding with very cold air aloft. Convective
temperatures are only in the lower 50s. This should lead to cold
rain showers. Will trend pops on Tuesday afternoon a bit higher
than the forecast builder blend.

The large trough aloft appears to begin shifting eastward by
Wednesday. However...another short wave appears to push through
the area as a quick moving low pushes out of the upper midwest.
Thus more pops chances...particularly across the northeast will be

Given the strong cold air advection in the wake of the front will
trend highs as steady or slowly falling on Monday. This will
result in highs lower than the MAVMOS. Otherwise with the cold air
pattern through wednesday will stick close to forecast builder on
lows...but trend highs at or below the forecast builder blend.


.LONG TERM /Wednesday night through Sunday/...
Issued at 246 PM EDT Sun Oct 22 2017

Coolest weather of the Fall looks inevitable at some point this
weekend along with more showers. That said, deterministic models
have large differences midway and later in the long term regarding
timing and strength of a vigorous western Canadian system, which has
large implications of timing and magnitude of the cooler
temperatures as well as shower timing. The 500 millibar height
ensembles are not clustered well but the GFS and ECMWF ensemble
means are not too far off. Thus, this will be a low confidence
forecast regarding temperatures and pops, and so will not lean too
far away from the ensemble mean swayed blend.

Confidence will be better with the first three periods of the
extended, next Wednesday night through Thursday night as another
upper ridge dives southeast over the area. This feature along with
southerly flow should bring dry conditions and a slight warmup to
the area from the well below normal temperatures Wednesday. Then,
vigorous upper trough will move to somewhere around the upper
Midwest and western Great lakes by late weekend. WPC has lead cold
front moving through the area late Friday and Friday night along
with another surface system late Saturday and Saturday night. The
latter may supply the coldest temperatures of the year. The blend
starts off with highs Thursday and Friday in the upper 50s and lower
60s. By Sunday blend highs are in the upper 40s and lower 50s. The
operational GFS MOS even has temperatures as early as Saturday.
Blend overnight lows are only in the mid and upper 30s Wednesday
night and Saturday night. A mix with snow can not entirely be ruled
out overnight Saturday night, especially if the quicker GFS turns to
be right, but at this time will stick with all rain. The best chance
of showers looks to be Friday as moisture increases ahead of the
cold front.


.AVIATION /Discussion for the 22/18Z TAF Issuance/...
Issued at 1250 PM EDT Sun Oct 22 2017

Good confidence in VFR conditions through 00z tonight, but then
increasing chances of MVFR and possibly IFR conditions 00-03z and
beyond as showers overspread the terminals. The showers will become
less prevalent at the western airports after 12z Monday. Overall,
confidence in trends is good, but exact timing is not.

South and southwest winds to over 10 knots but gusting to 25 to 28
knots will decrease to 10 knots or less 21z-22z shift to northwest
behind the cold front that should reach LAF and HUF near 02z but the
other sites not until after 12z Monday.




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