Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 231346
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
946 AM EDT Sun Jul 23 2017

.UPDATE...
The NEAR TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 945 AM EDT Sun Jul 23 2017

One more day with very humid conditions is expected today before a
cold front sweeps through the area tonight. Showers and
thunderstorms this morning should exit the area by early afternoon
but then could redevelop late afternoon into this evening ahead
of the front. High pressure will build in Monday bringing
dry...cooler and less humid air to central Indiana through the
first half of the week. Rain and thunderstorms return Thursday as
another cold front passes through the area before dry weather
returns to the Ohio Valley for next weekend.

&&

.NEAR TERM /Rest of Today/...

Issued at 945 AM EDT Sun Jul 23 2017

Significant changes made to the forecast for today with the
morning update. Convection this morning is much more widespread
than earlier indications. Based update mainly on current radar and
satellite trends with a lesser reliance on hi res models, which
have been woefully inconsistent. Large area of showers and storms
across the southern counties necessitates categorical pops, but
coverage across the northern and central counties only merits
scattered mention. Also across the central and north lightning is
not nearly as widespread and thus went with scattered showers and
isolated thunderstorms there over the next few hours. Satellite
data indicates cloud tops are warming in the south and
maintaining in the north but not cooling which should lead to less
lightning production with time. Have seen an uptick in lightning
over last 15 minutes though in the north so may need to increase
thunderstorm coverage wording there as well.

With the increase in convective coverage have also seen an
increase in cloud cover, so now not expecting much clearing until
mid afternoon. Adjusted high temperatures down a bit with this,
but not a lot as could still see enough sunshine for them to jump
quickly mid to late afternoon and early evening.

For this afternoon/evening convection, very low confidence on
forecast. Hi res models are indicating there should be dry time
starting around noon to 2 pm, but then show scattered redevelopment
starting around 5 with differences in timing and locations each
run. Looking at current conditions and upper wave moving in later
from the north, have medium confidence in a dry period early this
afternoon but low confidence in exact timing, and ultimately low
confidence in redevelopment with uncertainty concerning recovery
of airmass. Will maintain slight chance south and west and low
chance north and east for the afternoon/evening as inherited for
now, but closely monitor trends for another update.

&&

.SHORT TERM /Tonight through Tuesday Night/...
Issued at 332 AM EDT Sun Jul 23 2017

Forecast challenges focus on precip chances tonight before high
pressure takes over with cooler and less humid air finally arriving.

Any scattered convection with the secondary front this evening will
likely be ongoing at 00Z. Storms should diminish in coverage and
intensity by late evening with loss of diurnal heating and as the
upper wave shifts east of the region. Will maintain low chance pops
through 06Z then go dry.

The frontal boundary will sag to near the Ohio River by early Monday
morning...continuing further south on Monday into the Tennessee
Valley. High pressure will expand south from the Great Lakes and
finally advect a more refreshing airmass into central Indiana. The
high will serve as the dominant influence on weather across the
region for the remainder of the short term as it tracks east across
the Great Lakes. Cu remain possible during the afternoons but
overall cloud coverage will be low as model soundings show capped
mid levels and plenty of dry air and subsidence present aloft.

Temps...more seasonable temperatures will return through the period
as highs fall back into the low and mid 80s with lows in the 60s.
Maybe most importantly...the very high dewpoint air will be forced
south with the front tonight and Monday and will not return through
Tuesday night as dry low level flow from the north and east
persists.

Overall forecast confidence is high after tonight.

&&

.LONG TERM /Wednesday through Saturday/...
Issued at 215 AM EDT Sun Jul 23 2017

This is a high confidence forecast. Temperature errors should mostly
be 2 degrees or less. POP errors should be mostly 10 percent or
less.

Wind in the upper atmosphere are going to remain unusually strong
for this time of year, producing well defined weather systems
that are relatively easy to forecast. The American and European
systems are in good agreement, suggesting they are on the right
track.

&&

.AVIATION (Discussion for 231200Z TAFs)...

Issued at 651 AM EDT Sun Jul 23 2017

Thunderstorms are possible today and early tonight, but should avoid
the northern sites until at least 16Z.

VLIFR and strong winds are possible in storms, but will be of short
duration at any given site. The TAFs in this package can capture
this only in very general terms and may be updated frequently.

Otherwise, expect VFR with ceilings around 5 thousand feet today and
10 thousand feet or better tonight. Winds will become northwest less
than 10 knots today, then light and variable tonight.


&&

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

$$

SYNOPSIS...Ryan/CP
NEAR TERM...CP
SHORT TERM...Ryan
LONG TERM....JK
AVIATION...JK



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