Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 211920
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
320 PM EDT THU JUL 21 2016

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.

&&

.SYNOPSIS...
Issued at 249 PM EDT Thu Jul 21 2016

Hot and humid conditions remain the focus and continue into
Sunday under the influence of a broad heat dome in the central US
that builds over our region into Sunday.

Current trough offshore in Pacific Northwest will ride over the
top of the upper ridge and into the Great Lakes Monday. This will
sweep a cold front into our region to end the heat wave with more
seasonal temperatures and humidity for Tuesday through Thursday.

Scattered diurnal convection will be fairly limited until Sunday
when front gets closer. Nocturnal storm clusters are possible but
not certain and if they do form the question will be whether they
last into daytime to impact heating potential.

 &&

.NEAR TERM /Tonight/...

Issued at 249 PM EDT Thu Jul 21 2016

Main concern is how far southeast the tail of convection currently
forming as scattered cells in northwest Indiana make it into our
forecast area. Likewise...whether or not new convection firing in
the upper Mississippi Valley rides southeast on the Great Lakes
squall line and moves into our forecast area after midnight.

Current thought is that both current convective areas will have
some impact in our northern counties at the least. Current Great
Lakes convection continues firing new cells on southern flank but
they are not intensifying much before weakening suggesting they
may be running into drier air aloft or capping temps. Still expect
at least isolated to scattered evening across our northern row or
two of counties from Lafayette to Muncie. Models are not quite
capturing Upper Mississippi convection but rather hint at some
type of development from Quad Cities area across northern
Illinois, carry it southeast with not much development and
dissipate this over our counties Friday morning. Given the
variation in this signal with the models and uncertainty as to how
far south capping warmth aloft will allow storms to travel, will
keep chance pops going but expand that chance southeast overnight.

As for temperatures forecast and model consensus guidance numbers
on track and have remained with those.

&&

.SHORT TERM /Friday through Sunday/...

Issued at 249 PM EDT Thu Jul 21 2016

Concerns remain with mid-summer heat and humidity and will
continue Heat Advisory through Saturday. There may be a need to
extend this into Sunday but aforementioned convection concern and
impact on daytime heat preclude adding Advisory into Sunday at
this time.

Each new model run continues to back down on max temps. This is
likely tied to the nocturnal convection they try to develop with
diminishing convection in morning daylight hours...adding more
cloud to daytime hours than what likely will occur. Thus will
continue with max temps each day between 90 and 95 and with
dewpoints at least in mid 70s or higher will pump heat indices
easily into Advisory criteria and flirt with warning criteria.

As to daily convection...again not a lot of confidence or
certainty as to how much nocturnal convection occurs and whether
it last into daytime hours. Odds favor this further north since
warmer capping temperatures develop here. As with the last few
days...weak shear but strong instability will likely pop isolated
afternoon and early evening storms nearly anywhere in the forecast
area.

Again all models have been fairly similar with max and min temps
and saw no reason to deviate from current forecasts.

&&

.LONG TERM /Sunday Night through Thursday/...
Issued at 227 PM EDT Thu Jul 21 2016

Ongoing heat wave associated with broad upper ridge across much of
the nation will continue into early next week, but temperatures will
moderate some as longer term guidance depicts a slight weakening and
westward retrogression of the broader ridge, which may allow upper
level disturbances cresting the ridge to bring storms to the area at
times both early in the week and again later in the week.

Blended initialization handled this reasonably well and only minor
changes were required.

&&

.AVIATION /Discussion for the 21/18Z TAFs/...
Issued at 144 PM EDT Thu Jul 21 2016

Periods of MVFR possible across the sites this afternoon as a
cumulus deck fluctuates between SCT-BKN around 2500-3000 feet.
Additional MVFR and/or periods of IFR possible overnight in fog.

Cumulus development has occurred across the area and occasionally
been MVFR this morning. Expect a slow increase in cloud base heights
as the afternoon wears on but cannot rule out some periods of MVFR
in the first few hours of the TAF and will include TEMPO groups
accordingly.

Expect tonight to be similar to last night with little change in
airmass. Will bring outlying sites down to 3SM with a BCFG mention,
and BMG down to 1SM on a TEMPO basis. Other sites may easily get
down into IFR for a time as well, but this resulted in a lengthy and
complicated TAF so left it simpler for now. Will keep IND P6SM with
a BCFG mention, similarly to this morning.

Some guidance hints at potential development of a thunderstorm
complex to our northwest tonight, and this seems reasonable with
today`s complex laying down an outflow boundary in that area. This
is however low confidence as no models are handling the situation
particularly well. Will include a PROB30 for thunderstorms at the
sites near daybreak into the morning hours tomorrow.

Winds will be 10KT or less throughout the period, and occasionally
variable. They will be predominantly out of the southwest, however.


&&

.IND Watches/Warnings/Advisories...
Heat Advisory from 10 AM Friday to 8 PM EDT Saturday for INZ021-
028>031-035>049-051>057-060>065-067>072.

&&

$$

SYNOPSIS...TUCEK
NEAR TERM...TUCEK
SHORT TERM...TUCEK
LONG TERM...NIELD
AVIATION...NIELD



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