Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 220432
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1230 AM EDT FRI JUL 22 2016

.UPDATE...
The AVIATION Section has 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 /Overnight/...
Issued at 929 PM EDT Thu Jul 21 2016

Convection from earlier this evening has diminished with remnant
cloud debris also waning. Sultry airmass remains over the forecast
area this evening with dewpoints in the mid to upper 70s for most
locations. 0130Z temps generally ranged from the mid 70s over the
rain cooled northeast counties to the mid 80s over the Wabash
Valley.

Primary forecast issue for overnight focuses on severe MCS diving
south-southeast through southern Wisconsin and northern Illinois
this evening. Model guidance has largely been useless all
afternoon and evening with respect to the evolution of this storm
complex as well as the earlier storms over the area. Mesoanalysis
will be a critical component in storm evolution and have leaned
heavily on current mesoscale setup/conditions for setting up the
forecast into the overnight.

Airmass remains unstable over central Indiana but the passage of
the storms earlier has knocked back MLCAPE values over the eastern
half of the forecast area with higher levels of instability over
western Indiana into Illinois. The theta-e ridge is aligned S/SE
from the eastern edge of the bowing line of convection...pointed
towards eastern Illinois and western Indiana. Suspect convection
will turn a bit more southerly from its current orientation in
response to the deeper moisture and instability present...
focusing towards the KBMI-KCMI-KLAF area by 04-06Z. Signs are
already developing at the western half of the line gradually
becoming the dominant part of the convective cluster overnight
along the instability gradient across central Illinois. Some hints
in the Hi-Res guidance at eastern flank of the convection
weakening from its current state as it moves into the region after
midnight...but confidence in this scenario remains low considering
how poor model guidance in general has been as of late.

Needless to say...lots of uncertainty in play here and feel it
would be wise to broadbrush pops with the focus for highest precip
chances over western forecast area after midnight. Besides the
prolific lightning...blinding rains and potential flash flooding
that this storm cluster would bring...damaging winds will be the
primary threat should the MCS remain severe into the region.

Zone and grids will be updated shortly.

&&

.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 220600Z TAFS/...

Issued at 1230 AM EDT Fri Jul 22 2016

Large convective complex with a well established cool pool, currently
dropping south southeast through northern Illinois and northwest Indiana.
The presence of the cool pool and 25 kts of flow in the 925-850mb layer
suggests convective threat will be rather high at the terminals later
tonight. This threat will probably linger well past sunrise Friday with
potential elevated development over the cool pool. Brief IFR visibility
restrictions and gusty shifting winds in and near heavier convective
cells. CB bases 030-040.

Outside of convective areas, threat for visibility restrictions in fog
overnight exists given the high dewpoints, but don`t think fog will become
too thick or widespread due to convection keeping the air mass mixed up.
Light surface winds overnight expected to become 220-250 degrees at 8-12 kts
by early afternoon Friday.

&&

.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...RYAN
SHORT TERM...TUCEK
LONG TERM...NIELD
AVIATION...JAS/CP


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