Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 240806

Area Forecast Discussion
National Weather Service Indianapolis IN
406 AM EDT Sat Mar 24 2018

The LONG TERM Section has been updated below.


Issued at 407 PM EDT Fri Mar 23 2018

An area of low pressure will bring accumulating snow to central
Indiana Saturday with rain elsewhere. Another frontal system will
bring rain chances to the area for much of next week. Well below
normal temperatures Saturday will give way to near normal readings
early next week.


.NEAR TERM /Rest of Tonight and Saturday/...

Issued at 959 PM EDT Fri Mar 23 2018

Made minor adjustments to POPs to account for current radar trends
and lowered QPF and snow accumulations for the early portions of
tonight as low levels remain quite dry. Low levels will continue
to saturate through the night. Relevant portions of previous
discussion follow...

Precipitation has developed across the far southwest forecast
area and will overspread the remainder of the southwest half of
the forecast area tonight. Precipitation will then overspread the
remainder of the area during the day Saturday.

A good low level flow will bring in moisture, while an upper wave,
surface low, and upper jet bring forcing. Frontogenetical forcing
and deformation will bring the possibility of banded heavier
precipitation. Thus by Saturday will have categorical PoPs most
areas, with likely PoPs far north.

That`s the bigger picture, but the devil is of course in the
details. NAM, SREF, HREF mean all keep an axis of heavier snow
across the northern forecast area. However, GFS, ECMWF, and Canadian
continue their southern trend. This leads to higher uncertainty
forecast than would be liked at this stage.

Thermal profiles remain marginal with large isothermal areas around
32 degrees. This means that even a small change in temperatures
could bring big changes to precipitation type and snow amounts. Why
not add more uncertainty by adding an initially very dry lower
atmosphere and a persistent drier easterly flow at the surface as
well as the aforementioned banding potential which would also
influence precipitation type?

Given the relatively large uncertainties involved, decided to
continue with gradual trends rather than latching onto any one
solution. Thus allowed axis of heavier snow to sink a little farther
south and continued lowering the snow amounts a bit.  This puts the
axis of heavier snow to near/south of I-74 and higher amounts
generally in the 3 to 5 inch range.

Ground temperatures will remain relatively warm thanks to today`s
sun. Air temperatures will not be that cold with lows only in the
upper 20s northeast to around freezing near I-74. Highs on Saturday
will be in the mid 30s. Thus (main) roads may not be that bad for
the most part (unless under a heavy band), and snow will compact

Given all the above decided with a Winter Weather Advisory for the
heavier snow area. While the far northeast may still get snow, it
now appears that amounts will be low enough to have no advisory.

With the uncertainty and the low changes needed in the atmosphere to
make a big impact, changes to the forecast at any one location are
likely as trends become clearer.


.SHORT TERM.../Saturday night through Monday/
Issued at 407 PM EDT Fri Mar 23 2018

Models are close enough that the model blend initialization
was accepted for most items.

Precipitation will end Saturday night with little additional
accumulation as the system exits. Sunday and Sunday night will be
dry with high pressure in control.

Rain chances will return Monday afternoon as another upper trough
approaches the area. With the rain will come temperatures closer to
average, with highs mainly in the 50s.


.LONG TERM /Monday through Friday Night/...

Issued at 404 AM EDT Sat Mar 24 2018

Central Indiana will remain under the influence of high pressure
through Monday morning, resulting in dry conditions.  However,
rain will increase from west to east by Monday afternoon across
the forecast area as a low pressure system approaches from the
Central Plains.  Latest blended initialization continues to trend
toward significant Gulf moisture and warm air filtering into
central Indiana ahead of this system, resulting in heavy rainfall
and embedded thunderstorms in the warm sector on Monday night and

Rain will linger into Wednesday, then taper off by Wednesday afternoon
in the wake of an associated cold front. Nonetheless, rain will
linger across the southern counties on Thursday, then fill in
across the remainder of central Indiana again by Thursday night as
an upper low enters the area. A few snow showers could mix in as
well on Thursday night with light accumulations.

Temperatures through the period will be above normal due to strong
warm advection with highs in the upper 50s and low 60s at times.
Meanwhile, overnight lows will be in the 30s and 40s.


.AVIATION /Discussion for the 24/06Z TAF Issuance/...

Issued at 141 AM EDT Sat Mar 24 2018

Conditions are currently holding at VFR levels. However, they
will quickly deteriorate to IFR or worse at times as rain and snow
overspread the TAF sites early this morning. There could be brief
periods of improvement to MVFR at times during lighter
precipitation, but MVFR will not become a prevailing flight
category until this evening when precipitation tapers off.
Meanwhile, winds will gust out of the east up to 30 kts today.


Winter Storm Warning until 11 PM EDT this evening for INZ028-

Winter Weather Advisory until 11 PM EDT this evening for INZ029-



NEAR TERM...50/White
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