Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 280815
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
315 AM EST Tue Feb 28 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 /Overnight/...
Issued at 1245 AM EST Tue Feb 28 2017

Speed up small pops across the western counties based on radar
trends. Shower over the LAF area was up to 45 dbz but with no
lightning associated with it at this point.

Previous discussion follows...

Going forecast is in good shape with no significant changes
required. Continue to expect an increase in shower development as
isentropic lift increases across the area late tonight. Previous
discussion follows.

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 28/09Z IND TAF Update/...
Issued at 315 AM EST Tue Feb 28 2017

Per Awips distance speed tool, showers should make it in around 09z.
So moved them up an hour. Otherwise, no changes.

Previous discussion follows...
Issued at 1127 PM EST Mon Feb 27 2017

VFR initially will give way to deteriorating conditions near
daybreak with IFR developing later in the period.

As a warm front approaches overnight showers may develop and perhaps
a few rumbles of thunder, although at this time chances remain too
low for explicit inclusion. Winds will be less than 10KT into late
morning Tuesday before increasing and beginning to gust into the low
to mid 20KT range at times.

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

Thunderstorms will become more likely late in the period and will
handle this with a VCTS as uncertainty remains regarding timing and
impacts at the terminals.

&&

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

&&

$$

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


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