Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 222235
AFDIND

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

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
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
wetbulbs.

&&

.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
required.

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 230000Z TAFS/...
Issued at 635 PM EDT Sun Oct 22 2017

Short term model guidance suggests cold front moving through
eastern Illinois will settle into the west central and northwest
parts of the state later this evening and overnight. Lift will
gradually increase with time tonight, but it appears the most
organized lift probably won`t arrive until around 231000Z, with
the upper trough. As a result, shower activity is expected to
gradually increase in coverage throughout the evening and tonight.

Low confidence in ceiling and wind forecasts tonight, especially
in the KHUF/KLAF areas, as there is some question as to how far
front will get before stalling out. IFR ceilings exist just
behind front. Will drop ceilings to around 015 at those terminals
this evening, and keep ceilings VFR at the other terminals until
well after 230600Z.

Surface winds generally 150-170 degrees at 6-9 kts this evening,
with winds veering around to a northwest direction at the
KHUF/KLAF terminals later this evening. Max surface pressure
rises in the wake of cold front seem to be shifting more towards
the Great Lakes with time, so don`t think the 20-25 kt gusts over
eastern Illinois will affect the KHUF/KLAF terminals, but will
keep an eye on this.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...Puma
NEAR TERM...Puma
SHORT TERM...Puma
LONG TERM....MK
AVIATION...JAS


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