FXUS63 KIND 180444

Area Forecast Discussion
National Weather Service Indianapolis IN
1144 PM EST Sun Feb 17 2019

The AVIATION Section has been updated below.


Issued at 226 PM EST Sun Feb 17 2019

A Large but weak area of low pressure over Illinois will pass
across Indiana tonight before reaching the east coast on Monday.
This will keep a cyclonic flow across Indiana resulting in plenty
of lower level clouds and perhaps some light precipitation tonight
and early Monday.

High pressure will build across Indiana on Monday afternoon from
the northern plains and bring dry but cool weather through

On Tuesday night and Wednesday...a stronger low pressure system
will develop over the southern plains and push a warm front toward
Central Indiana. This may result in some mixed precipitation on
late Tuesday night before changing over to all rain on Wednesday.

Dry weather is then expected for the end of the work week before
more rain chances return on Saturday.


.NEAR TERM /Tonight/...

Issued at 912 PM EST Sun Feb 17 2019

Despite freezing radar echoes diminishing and ob trends, due to
reports of worsening road conditions, decided to go with a short
term Winter Weather Advisory for freezing drizzle through 06z
Monday. Do not think the more widespread drizzle over central
Illinois will make it this far based on radar trends. Additional
freezing drizzle should be patchy.

Previous discussion follows...

Issued at 226 PM EST Sun Feb 17 2019

Surface analysis early this afternoon show broad low pressure in
place across the region with the center over Central KY. A
surface trough trailed in the wake of the low across Indiana and
Illinois toward Iowa. GOES 16 show a tropical stream of moisture
streaming across Kentucky and Tennessee...while low clouds
associated with the surface low were engulfing Indiana...Illinois
and the upper midwest. Cold Easterly surface flow was in place
across Indiana...and the best forcing for precipitation had moved
east to Ohio.

GFS and NAM suggests a weak upper trough axis pushing across the
Great lakes and Indiana overnight. However best forcing looks to
remain well east of the Indiana. Within in lower levels broad
cyclonic circulation remains in place across the region overnight
as the previously mentioned trough will linger across the state
overnight. Time heights show dry air within the mid and upper
levels...but plentiful lower level moisture. Forecast soundings
show a similar story...with soundings below freezing and
saturation within the lower levels. Thus with weak forcing and
plentiful lower level moisture...some minimal flurries or freezing
drizzle cannot be ruled out overnight...but significant
measurable precipitation has come to an end. Still the isolated
freezing drizzle could result in a few slick surfaces overnight.
Given the expected clouds but counteracting cold air advection
will stick close to the forecast builder blends for lows.


.SHORT TERM /Monday through Wednesday/...

Issued at 226 PM EST Sun Feb 17 2019

GFS and NAM show the lower level flow becoming more anti-
cyclonic on Monday afternoon ans a large high pressure system
centered over the Northern plains begins to spread across the
Great Lakes and Ohio Valley. Surface ridging arrives across
Indiana by 00Z Tuesday...as does ridging aloft. Forecast soundings
show a dry column by Monday afternoon that persists through early
Tuesday evening. Thus from monday afternoon through Tuesday
evening...a dry forecast will be used. Again given the influence
of the cold High pressure system arriving from the northern
plains...will trend temps at or below the forecast builder

On tuesday Night the High pressure system will have moved well
east of Indiana. Meanwhile aloft a strong upper trough over the
Rockies will begin to push into the plains states. This will allow
warm and moist southwesterly flow aloft to begin to stream into
the Ohio valley on tuesday Night into Wednesday. As this upper
system moves east a surface low is depicted by the models to
develop in the southern plains...pushing a warm front toward
Central Indiana. forecast soundings on tuesday night and wednesday
trend toward deep saturation within the column...initially
starting below freezing. However with the arrival of the warm
front on Late Tuesday Night...soundings begin to show the classic
surge of warm air aloft...which may result in some mixed
precipitation. Finally by 15Z on Wednesday...the models suggest
the entire column above freezing....finalizing the transition to
rain. Additional strong forcing for Tuesday Night and Wednesday is
seen within the 290K GFS Isentropic surface...showing an
excellent set-up of up glide along with a surge of moisture rich
air as specific humidities surge over 5 k/kg. Thus confidence is
high fore precipitation on late tuesday and Wednesday as this
set- up arrives. However Timing and precipitation type confidence
will is low and will probably remain low for the next 24-36 hours.
Nonetheless...will use high pops on Tuesday Night and
Wednesday...trending lows warmer than the blends and sticking
close to the suggested highs given the expected precipitation.


.LONG TERM /Wednesday Night through Sunday/...
Issued at 325 PM EST Sun Feb 17 2019

Tail end of midweek frontal system will still potentially be
impacting the area Wednesday evening before the boundary is well
clear of the area and dry weather returns. Removed slight chance
pops across the far south Thursday afternoon and evening, as the
frontal zone will be well south of the area, and the GFS was the
only model producing precip in that area at that time - even with
its own forecast soundings depicting dry low and midlevel air and
increasing subsidence as the surface high noses into the area.

The next precipitation chances will come over the weekend as
another low develops along the frontal zone and moves into the
region. Much of this precipitation will fall as rain, but cannot
rule out periods where temperatures may be low enough for
snowflakes to fly.


.AVIATION /Discussion for the 18/06Z TAF Issuance/...
Issued at 1144 PM EST Sun Feb 17 2019

Confidence is moderate that mostly MVFR conditions will continue
through around 00z before things improve. BMG would be mostly likely
to see some IFR for a few hours at the onset per trends.

Winds will become west 8 knots and switch to northwest after 15z.


Winter Weather Advisory until 1 AM EST Monday for INZ021-028>031-



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