Area Forecast Discussion
Issued by NWS Indianapolis, IN
FXUS63 KIND 250222
Area Forecast Discussion
National Weather Service Indianapolis IN
1022 PM EDT SUN JUL 24 2016
The AVIATION Section has been updated below.
Issued at 300 PM EDT Sun Jul 24 2016
One more relatively warm and humid day is expected
Monday before slightly cooler and less humid air filters
into our area Tuesday and Wednesday. The change in air mass will
be accompanied by scattered thunderstorms though not all
locations will receive this rain. The next weather system and
return of slightly warmer and humid air will bring a better
rain/storm coverage for the latter half of the week.
Temperatures for this period will start above normal then dip to
seasonal values for the balance of the week.
.NEAR TERM (Tonight)...
Issued at 820 PM EDT Sun Jul 24 2016
The convection allowing models concur the storms now over Illinois
will eventually make it into the northwest CWA but probably not
all the way to the southeast. This is captured fairly well in the
latest hourly POPs from the CONSHORT model, which will be used
with the forecast update.
Precipitable waters remain very high. So does the freezing level,
suggesting a lot of warm rain process, which we have seen many times
in this air. Heavy rain will be mentioned in storms.
Guidance minimum temperatures a tad on the warm side the last few
days and will go just below those, but with winds to remain up a
little, minimums should be several degree warmer than this morning.
.SHORT TERM /Monday through Wednesday/...
Issued at 300 PM EDT Sun Jul 24 2016
Models are in fairly good agreement on movement and position
of front over the next several days as high pressure takes over.
The front will move from just north of our area at daybreak
Monday to our southern counties by sundown. With the strongest
wind fields and best upper support well to the north and northeast
convection should be relatively scattered. Where storms do
develop expect heavy rainfall given our fairly high precipitable
Do not plan to add Heat Advisory for Monday with heat indices
at highest just over 100 in our southern counties. Monday will
still feel relatively warm and humid though. Will keep max temps
near guidance and previous forecast. Rain chances will likely
follow diurnal trend with better chances at peak heating and
along and ahead of southeast advancing cold front. Again given
best dynamics being well northeast would expect no more than
scattered convection and pops still in the chance category.
For Tuesday and Wednesday the frontal boundary will slip south
of the Ohio River. Current forecast of rain chances in
southern counties may be a bit pessimistic as high pressure may
more likely drive rain chances south of the Ohio River. Will keep
low chances for now but another model run may suggest their
Temperatures Tuesday and Wednesday still look fairly good with
mid and upper 80s appearing reasonable. Might be a tad high on
holding southern county dewpoints in the lower 70s. High pressure
scouring out the tropical air may reach south of our area by
Wednesday and may need future adjusting.
.LONG TERM /Wednesday night through Sunday/...
Issued at 218 PM EDT Sun Jul 24 2016
Main challenge for the long term will be timing various upper waves
moving through and ahead of a mean Mississippi Valley trough.
Judging by the differences in the operational GFS and ECMWF and
individual ensemble spaghetti plot members, the confidence in
strength and timing of these waves is not good. For instance, the
00z and 12z GFS runs have a strong wave moving through Thursday
night, while the 00z ECMWF version is much weaker. Thus, will
accept regional blend, which has chance pops Wednesday night through
Low level thermal progs support normal to slightly below normal
blend highs in the lower to mid 80s. Meanwhile, look for overnight
lows mostly be in the mid to upper 60s.
.AVIATION /Discussion for 250300Z TAF Update/...
Issued at 1022 PM EDT Sun Jul 24 2016
Main adjustment for the evening update is to place more detailed
timing for convection into KLAF terminal. Primary impacts from the
line of storms expected between 03-05Z with potential for LIFR and
lower conditions in heaviest storms. Confidence remains low on
whether the convection can make it all the way to KHUF and KIND
later tonight and will maintain VCTS mention at those two terminals
at this time.
00Z discussion follows.
Restrictions possible within convection overnight and Monday
otherwise predominantly VFR conditions expected.
Convection has been slow to develop but has finally started to
become better organized over northern Illinois since 22Z.
Convection developing in the vicinity of a prefrontal trough
and aligned with an axis of strong instability with MLCAPEs in
excess of 5000 J/KG. Central Indiana remains under the influence
of the ridge aloft and effectively capped with 700mb temps around
That presents the question of how far south the northern Illinois
convection comes over the next 6-8 hours as storms move against
the ridge flank. It has been another difficult day for model
guidance...most of which has been grossly overdoing the convective
development to the northwest. The parallel HRRR has the most
reasonable solution at this point and loosely utilized it for
timing and southward extent to convection into the overnight. The
only terminal with medium to high confidence in convective impacts
at this point is KLAF with the potential that KHUF and KIND are
also impacted after midnight. Introduce VCTS at KLAF at 02Z with
more specific impacts in the 05-10Z period. Will maintain a VCTS
mention only at both KHUF and KIND until a better determination
can be made regarding whether storms will directly impact either
site late tonight as airmass quickly becomes less favorable for
convection to persist further south.
Storms are likely to diminish in coverage and intensity overnight
as instability is lost...then refire by Monday afternoon south of
I-70 along and ahead of the cold front in the moist unstable
airmass. Will focus VCTS after 17-18Z at KBMG and KHUF and may
eventually need to include KIND as well. Drier air will advect in
from the north by Monday evening.