421
FXUS63 KIND 130534
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
134 AM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Fog possible again tonight, with locally dense fog
- Periodic shower and thunderstorm chances through Wednesday, some
  uncertain potential for strong to severe storms
- Hot and humid from Sunday through Tuesday, possibly nearing
  Advisory criteria

&&

.FORECAST UPDATE...
Issued at 945 PM EDT Fri Jul 12 2024

Stubborn isolated showers continue this evening from Indy to the
east, under an upper trough where some deeper moisture resides.
These should diminish within a couple of hours as instability
weakens diurnally, but will keep an eye on it in case they remain
stubborn and continue.

Otherwise just mainly made some tweaks to the hourly forecasts based
on latest observational trends. Still believe fog will develop as
clouds diminish overnight.

&&

.SHORT TERM (This evening through Saturday)...
Issued at 304 PM EDT Fri Jul 12 2024

Scattered convection so far today has been confined to far eastern
portions of the forecast area near the apex of a weak upper wave
passing through. ACARS sounding from KIND shows less moisture in the
low levels versus Thursday afternoon and with weaker forcing aloft,
convective coverage has been much lower this afternoon. 18Z
temperatures were in the mid and upper 80s most areas within a muggy
airmass.

The upper level transition is beginning from the progressive flow of
weak waves to more of a stronger influence from ridging aloft with
mid level heights set to rise for Saturday. While the presence of
instability and low level moisture supports at least isolated mainly
afternoon and early evening convection, the focus through Saturday
will shift to warmer and mainly dry conditions as the upper ridge
builds in.

Isolated to scattered convection will remain focused especially
across eastern counties through the afternoon with a gradual
eastward shift into Ohio as the upper wave moves away from the
region. Convective mode will again be disorganized, pulse intensity
multicellular storms with locally heavy rainfall and lightning as
the main hazards with gusty winds possible within any collapsing
downdraft. Expect any storms to wrap up by early evening leaving a
muggy evening and overnight. Mid and high level clouds will drift
across the region through daybreak. Similar to this morning, suspect
fog development will commence once again with locally dense a
possibility as well with light winds and a shallow layer of moisture
in the near surface layer lingering. Focus for best chances of fog
will be across the northern half of the forecast area which saw some
of the highest rainfall totals over the last 3-4 days.

Fog will diminish by mid morning Saturday as mixing gets going
within the boundary layer and just based on model soundings, the fog
may diminish more quickly than it did this morning. Expect diurnal
cu formation again by Saturday afternoon but coverage should be less
than what we have seen over the last few afternoon with the
increased mid level heights and a greater amount of dry air and
subsidence present above the boundary layer. Once again, an unstable
airmass will be conducive for isolated convection favored during the
afternoon and early evening, but a decrease in low level moisture
and little to no forcing aloft under the expanding ridge will limit
overall development. Localized downpours will be most common with
slow moving. and disorganized storms but most will remain dry
throughout the day Saturday.

Temps - lows tonight will remain in the mid and upper 60s throughout
the forecast area. Low level thermals are supportive of highs a few
degrees warmer than today in most locations, with upper 80s to
around 90 expected.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 304 PM EDT Fri Jul 12 2024

A fairly typical midsummer pattern is expected over the weekend into
early next week, characterized by broad, strong upper level ridging
centered over the Four Corners region, and a strong subtropical
ridge over the western Atlantic nudging back into the southeastern
CONUS. This will leave the region under quasizonal or weakly
northwesterly flow aloft, with prolonged southerly or southwesterly
flow at the surface setting the stage for maintenance of a hot and
steamy airmass, and possibly multiple rounds of convection,
primarily late days into the overnights with (still fairly low)
chances highest to the north as possible storms developing and
traversing the periphery of the ridge may get into the area.

As the week wears on, the upper level pattern will amplify as shifts
in location and intensity of the mean ridges allows for an anomalous
upper level trough to swing into the Great Lakes and drive a surface
boundary southward into the area. This will allow for some heat
relief, but also may produce higher chances for thunderstorms on
multiple days as the tail end of the frontal zone sags through the
region.

Gradual height reduction aloft and the approach of this
aforementioned frontal zone by mid week, along with the ridge riding
convection early in the week, may offer one or more opportunities
for strong to severe storms, though predictability is fairly low at
this time given the dependence of convection in such patterns on
preceding rounds of thunderstorms. There is some signal in
experimental machine learning guidance for this, which will bear
watching. The primary concern with these storms would be damaging
winds, along with heavy downpours and localized flooding given
recent significant rainfall and seasonably high wet bulb zero
heights promoting highly efficient warm rain processes.

Temperatures early in the week will again be quite warm, with high
humidity promoting a possible heat threat, primarily Sunday through
Tuesday, though convective potential will increase uncertainty in
this regard. Significant relief from the heat appears likely late in
the week as the front passes.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 134 AM EDT Sat Jul 13 2024

Impacts:

- MVFR/areas of IFR conditions redeveloping overnight tonight into
  daybreak Saturday.

Discussion:

Surface high pressure will allow for mainly clear skies and light
winds through morning. With high moisture levels, we`re expecting
fog to develop by morning with MVFR/IFR conditions possible.

Fog should mix out within a few hours after sunrise. Diurnal cumulus
growth will be quick, with periods of SCT or perhaps BKN possible.

Winds gain a southwesterly component during the day, becoming more
southerly Saturday night.

&&

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

&&

$$

UPDATE...50
SHORT TERM...Ryan
LONG TERM...Nield
AVIATION...Eckhoff