225
FXUS63 KIND 220251
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1051 PM EDT Sat Sep 21 2024

.KEY MESSAGES...

- Rain and storms possible Sunday

- Turning cooler and more active with additional rain chances early
  next week

&&

.FORECAST UPDATE...
Issued at 943 PM EDT Sat Sep 21 2024

Isolated showers near Knox County have moved out of the area.
Meanwhile, the extensive cloud deck from the now dissipated Illinois
convection is breaking up some across central Indiana.

Adjusted sky forecast into the early overnight based on latest
trends. Also updated hourly temperature forecast based on latest
observations.

Latest guidance continues to slow down arrival of showers and
embedded thunderstorms late tonight into Sunday morning. Thus, have
slowed down the increase in PoPs late tonight into the early
daylight hours of Sunday morning. More refining will be done
overnight when additional data arrives and trends upstream can be
observed.

Low temperatures look good so only made some minor tweaks.

&&

.SHORT TERM (This evening through Sunday)...
Issued at 253 PM EDT Sat Sep 21 2024

The last of the hot days in this recent stretch ongoing as multiple
sites across central Indiana have already hit 90 this afternoon...
including KIND. Mostly sunny skies currently but clouds are
expanding in from the west ahead of a cold front moving into Iowa
and Missouri.

As mentioned above...today will do it for the hot weather of late as
the approach and arrival of the aforementioned cold front into the
Ohio Valley on Sunday will usher in a pattern shift to cooler
temperatures and an increased risk for rain and storms that will
last into the upcoming week.

The rest of the afternoon and most of tonight will be quiet. As
expected...the airmass has drier out substantially since this
morning as deeper subsidence and drier air aloft have been pulled
down to the surface. Dewpoints have tumbled into the lower and mid
50s across the northern half of the forecast area. This will be an
issue with respect to maintaining ongoing convection over western
Illinois as it moves east into the evening. With such a hostile
environment over much of the forecast area and little to no
instability available...expect the convection to our west will
diminish before getting to the Wabash Valley by early evening. Main
focus into the evening will be to gradually increase clouds from the
west.

Convection is not likely to advance into the Wabash Valley until the
predawn hours at the earliest and perhaps not until closer to
daybreak as the deeper plume of moisture spreads back into the
region ahead of a warm front. Convection will spread east across the
forecast area through the morning but will likely diminish in
coverage as it shifts east and interacts with the residual drier air
present. Regardless...this will bring the best threat for widespread
rain to the forecast area in a few weeks.
 and intensity Surface flow will veer to the S/SW during the
afternoon with convective coverage likely diminishing as subtle
ridging aloft builds in before additional showers and storms expand
in from the west by late day in advance of the cold front.

Temps...should see lows fall into the lower 60s over northeast
counties where the drier air will linger the longest with mid and
upper 60s elsewhere. The abundance of clouds and threat for rain
will keep temperatures down and closer to normal on Sunday... mainly
in the upper 70s and lower 80s.

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 253 PM EDT Sat Sep 21 2024

Summer-like heat comes to an end around the start of the long
range period. Strong ridging will gradually be replaced by
troughing this weekend, which will bring about multiple chances
for rain and thunderstorms...the first decent chance of widespread
rain in a few weeks. The best chance of rain looks to be Monday
into Tuesday as an embedded vort max lifts northeastward around
the base of the trough.

Amounts, including what falls in the short term period, could be up
to an inch or two in places...but most will see less than an inch.
This, unfortunately, is likely not enough to put a major dent in the
moderate drought most of central Indiana is currently seeing.

Heading into next week, guidance struggles a bit with how the large-
scale pattern develops. The aforementioned troughing looks to become
positively tilted, stretching from the Great Lakes into the
southern Plains. Various models are now starting to hint at the
trough pinching off into a cut-off low. If and where this happens is
a major factor in how our weather plays out over the coming week.

While all this is going on, a disturbance currently in the western
Caribbean Sea may develop into a tropical cyclone by mid-week. As
this system lifts northward, the position of the trough / cut-off
low should dictate where it and its associated impacts end up.

Forecast confidence decreases quickly by mid-week since, as
mentioned before, guidance begins to struggle. Run-to-run and model-
to-model differences are quite large once the cut-off low process
begins to take shape. The addition of a yet-to-form tropical system
adds to the complexity of the situation.

Still, some points we are confident in are as follows: well-above-
average warmth is coming to an end. Temperatures will drop to normal
values for late September (mid 70s / mid 50s). Most locations will
see rainfall to some extent, but likely not enough to significantly
dent the drought.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1051 PM EDT Sat Sep 21 2024

Impacts:

- Convection including embedded thunderstorms will spread across
  the terminals after 12z before briefly diminishing after 18z

- MVFR and briefly worse flying conditions in convection and also
  after 18z away from convection

Discussion:

A warm front will move across the terminals this morning followed by
a cold front tonight. These fronts will interact with deep moisture
and sufficient instability to result in scattered to widespread
convection through the TAF period. MVFR and briefly worse flying
conditions are possible in and away from convection.

Winds will be less than 10 knots and shift from southwest to
northwest in the wake of a cold front prior to daybreak Monday.

&&

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

$$

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