Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 280709
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
309 AM EDT Wed Jul 28 2021

.Short Term...(Today through Thursday Night)
Issued at 308 AM EDT Wed Jul 28 2021

...HEAT AND HUMIDITY AND SEVERE POTENTIAL...

The heat and humidity along with severe potential will be the
highlight of the short term as an upper wave and low level jet will
likely team up to kick off an MCS this evening over Minnesota and
Wisconsin. However, prior to that, the massive heat dome of high
pressure over the central Plains and Rockies will continue to
dominate over central Indiana with another day of hot temperatures
with above normal afternoon highs in the upper 80s far east, further
away from the influence of the high, to the lower and middle 90s
southwest. To compound the hot temperatures, low level moisture will
start increasing as well as the surface high starts to drift
southeast. The rest will be an afternoon heat index 100 degrees or
slightly higher over the Wabash Valley. HRRR Vertically Integrated
Smoke graphic does suggest there will be a haze overhead which could
slightly reduce afternoon high temperatures and increase in low
level moisture could lead to some afternoon cu per cu development
progs. So, with borderline to slightly below afternoon heat induces
and the other factors, will not be putting out heat headlines but
will highlight on social media.

Main question tonight will be if any convection from the looming
upstream MCS will make it into central Indiana. The CAMs and models
are divided on this but with strong instability, 35 plus knot bulk
shear and abnormally seasonably strong 50 knot low level jet feeding
the thunderstorm complex, believe this system will propagate forward
efficiently with a good chance it lays out a decent outflow boundary
over northern parts of central Indiana prior to dawn Thursday. Mixed
layer CAPEs even at 12z Thursday still 1000-1500 J/kg over north
central parts of central Indiana. With all this in mind, chance PoPs
and SPC Day1 Marginal Risk look good after 08z or so for areas near
and north of a Shadeland to Cicero to Anderson line.

Moving into Thursday proper, there are more considerations such as
will the convection from the MCS hang around long during the morning
and limit the potential for strong or severe thunderstorms during
the afternoon as a cold front approaches and moves through late
Thursday and Thursday evening. Also, what effect will this have on
the heat and humidity along and ahead of the front. Thus, timing and
convective coverage along with precise temperatures are not clear
cut. Regarding the heat and humidity, could see the heat index
exceed 105 degrees over the Wabash Valley Thursday afternoon, but
not confident enough for a Heat Advisory.

The Day2 SPC Marginal Risk looks good for now, but potential for a
higher risk if the morning convection ends earlier in the day and
sufficient sunshine breaks out prior to afternoon re-development.
This is especially true over east central Indiana where the shear
will be a bit more conducive. Potential for Mixed Layer CAPEs
greater than 2500 J/kg to go along with 25-35 knot deep layer bulk
shear, streamwise helicity pooled in the vicinity of the cold front,
curved hodographs and low level veering. This combination would
certainly to sufficient to trigger a few severe storms with all
severe weather types on the table.

Look for the convection to end from north to south Thursday night as
the cold front moves through. The cold front will usher in much
cooler temperatures for the long term and overnight lows in the 60s
Thursday night.

&&

.Long Term...(Friday through Tuesday)
Issued at 308 AM EDT Wed Jul 28 2021

Cooler temperatures will settle in and stay throughout the long term
period. After a cold front pushes south through central Indiana,
cooler, northerly air will drop the high temperatures to near 80 in
the northern portion of the forecast area and to the mid 80s in the
south, near where the front will stall for a day or two. PoPs will
still be present in the south Friday near the boundary where some
lift will remain. Surface high pressure on its backside will lead to
dry weather for the rest of central Indiana.

The upper trough will continue to push southward from Saturrday on
and a couple of short waves will act to push moisture along the
boundary. This will lead to some additional PoPs for the area this
weekend. The upper trough will continue to amplify into next week
which will continue to bring N to NW flow to the region, prolonging
the cooler stretch. It should be noted that this cooler stretch of
highs in the 80s and lows in the 60s and even 50s at times, is
really only slightly below normal, it will just be a welcome change
to the 90s we have been experiencing. At the surface, high pressure
will settle in, prompting subsidence and dry weather for the start
of next week.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1146 PM EDT Tue Jul 27 2021

IMPACTS:
- mainly VFR conditions through the period
- outside chance for patchy ground fog at outlying sites
- winds less than 4 kts through the overnight

DISCUSSION: High pressure will continue across central Indiana
through the rest of the night and much of Wednesday. Leftover mid
and high level clouds from convective complexes over the upper
Midwest may occasionally drift across the sites into Wednesday. With
ample low level moisture could see some patchy ground fog, but don`t
expect it to be prevailing and too low of confidence in
location/timing to include. Should see few to scattered cu develop
Wednesday afternoon AOA 4kft. Winds will largely be light and
variable through the overnight hours, but could have a westerly
component. Winds should be less than 10 kts out of 270 to 290 from
midmorning Wednesday through Wednesday evening. Could see some
convection move in from the northwest late Wednesday night, but low
enough confidence to leave out at this time.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

Short Term...MK
Long Term...KH
Aviation...CP


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