Area Forecast Discussion
Issued by NWS Indianapolis, IN

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435
FXUS63 KIND 272305
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
605 PM EST Mon Feb 27 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 329 PM EST Mon Feb 27 2017

An active weather pattern in place over central Indiana will keep
chances for precipitation including both rain and snow in the
forecast off and on through the period, and will also keep
temperatures bouncing between near normal and much above normal.
The arrival and passage of a strong frontal system brings
potential for severe storms Tuesday evening through Wednesday
morning.

&&

.NEAR TERM /Tonight/...
Issued at 329 PM EST Mon Feb 27 2017

The evening will start out dry with weak ridging pushing off to
the east. A warm front will move north through the area, bringing
an increase in clouds and then chances for rain moving in after 1
am. Isentropic lift combined with some elevated instability could
also bring isolated thunderstorms to the area. With all the clouds
and precipitation moving in low temperatures should remain
relatively warm in the low to mid 40s.

&&

.SHORT TERM /Tuesday through Wednesday/...
Issued at 329 PM EST Mon Feb 27 2017

Forecast focus is on thunderstorms chances and potential for
severe storms Tuesday through Wednesday. Models are still showing
differences in timing of the frontal passage and even precip early
Tuesday so confidence moderate at best.

Tuesday morning rain and isolated thunderstorms will likely be in
place across the area due to isentropic lift. Models have some
disagreement how long this precip will last and how much cloud
cover will remain in its wake, but generally preferred a solution
that took precip out by late morning from west to east leaving
only a slight chance for showers and storms behind. The area looks
between areas of forcing for some of Tuesday afternoon and thus
included only a slight chance during that time. By late afternoon
into early evening, depending on how much sunshine the area sees,
could see destabilization start to occur and perhaps some
scattered development. Concerns abound though about whether or not
the area will be trapped under a cap, and thus only included
low chances during this time.

After 0z Wednesday though a low level jet increases and moves
toward the area, being overhead by 6z. This jet seems to be
overdone in the NAM but more reasonably handled by the GFS with
around 60 kts or so of flow at 850 at 6z. This combined with an
upper wave and an approaching cold front should produce a line of
thunderstorms moving across the area sometime in the 3-9z
timeframe, give or take a few hours depending on the model. With
the possibly overdone jet, think NAM is also overdoing moisture
return and thus instability. However even more reasonable GFS
shows sufficient instability and shear for severe weather chances.
Damaging winds and large hail will be the main threats.

Whether this threat continues into Wednesday over
eastern/southeastern parts of the area is still up in the air. NAM
slows the front and would continue the severe threat, GFS looks
less ominous with a faster fropa. For now split the difference and
included chances for thunder through the morning for parts of the
area Wednesday and then a slight chance in the east in the
afternoon.

For temperatures generally used a model blend, but increased from
that for Tuesday a bit with the potential for some sunshine
between precip rounds.

&&

.LONG TERM (Wednesday night through Monday)...
Issued at 155 PM EST Mon Feb 27 2017

The deterministic models are in good agreement, and confidence is
high in the blended forecast, into Sunday. Dry weather should
predominate, but there will be some chances for both rain showers
and snow showers. If snow occurs, expect little or no accumulation.
Potential temperature errors are mainly 2 degrees or less.

The forecast becomes much more uncertain beginning Sunday night as
the GFS and European models handle an approaching system very
differently. Temperature forecasts may be off by 5 degrees or more
and POPs off by 20 percent or more. Snow is not expected in any
case.

&&

.AVIATION /Discussion for the 28/00Z TAFs/...
Issued at 558 PM EST Mon Feb 27 2017

VFR initially at all but BMG will give way to MVFR later tonight
and perhaps some IFR.

As a warm front approaches overnight showers may develop and
perhaps a few rumbles of thunder, although at this time chances
are too low for explicit inclusion. Will monitor trends through
the evening and may need to add this in at 06z. Winds will be less
than 10KT into late morning Tuesday before increasing and
beginning to gust into the low 20KT range at times.

No significant obstructions to visibility outside of showers
expected at this time.

&&

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

&&

$$

SYNOPSIS...CP
NEAR TERM...CP
SHORT TERM...CP
LONG TERM...JK
AVIATION...NIELD



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