183
FXUS63 KIND 262214
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
614 PM EDT Thu Sep 26 2024

.KEY MESSAGES...

- Strong northeast winds with gusts of 40-55 MPH expected late
  Friday morning through Friday evening.

- Sporadic gusts above 55 mph possible Friday evening.

- Widespread rainfall expected late tonight into the weekend with
  rainfall totals around 1-2 inches south of I-70. Locally higher
  amounts possible.

- River flooding is not expected due to abnormally dry soil, but
  efficient rainfall rates may lead to localized flash flooding.

&&

.SHORT TERM (This evening through Friday)...
Issued at 258 PM EDT Thu Sep 26 2024

Strong winds and heavy rain from the remnants of Hurricane Helene
expected much of the day Friday for Central Indiana. Latest
satellite imagery shows Hurricane Helene pushing northward toward
the Big Bend of Florida while clouds and deep moisture advection
advect northward up the Appalachians and to the Canadian border. The
earliest effects of the hurricane will begin to be felt across
central Indiana as early as tonight as the potent tropical cyclone
makes landfall along the Big Bend Coast of Florida. Helene will
rapidly proceeds inland toward north Georgia and the Tennessee
Valley by daybreak tomorrow. As Helene interacts with the large
upper low over the Mid Mississippi Valley tomorrow, it will
retrograde into the Ohio Valley. As this occurs, warm air advection
aloft, strong winds, deeper moisture and more expansive cloud cover
will push northwestward into the area tonight and through the day
tomorrow.

Wind Threat: The most impactful threat from the remnants of Helene
locally will be strong winds across the state of Indiana. As
Hurricane Helene transitions into an extratropical system and pushes
toward the Ohio Valley, a strong 60-75kt low level jet develops on
the northwest side of the system and moves overhead by Friday
afternoon. In addition to this, pressure falls from around 1008mb to
near 996mb through the day and an increasing pressure gradient will
result in strong northeast winds Friday morning through Friday
evening. Winds should steadily increase tonight with gusts at or
above 40 mph increasing from SE to NW late morning. Strongest winds
are expected within the 3pm-8pm timeframe where sporadic gusts to 60
mph will be possible. One caveat to the forecast is that the
atmospheric profile will be largely saturated with weaker low level
lapse rates, inhibiting much stronger LLJ winds from mixing down to
the surface. For this reason, a Wind Advisory has been issued for
all of Central Indiana with frequent gusts of 40-55mph expected.
With how strong and dynamic this system is, gusts over 60 mph are
not out of the question and still could happen; however they should
be sporadic in nature. Another thing to note, strong winds out of
the NE are not very common, potentially resulting in more impacts
and down trees than one would expect from winds of this strength.

Rainfall: Strong moisture advection will overspread the region as
the Hurricane makes its way northward toward the region tonight.
While the main area of low pressure is expected to remain south of
the Ohio River, an expanding precipitation shield is expected to
develop as the system becomes extratropical bringing heavy rain to
portions of the state. Greatest moisture advection and PW will be
further south with a sharp S-N gradient across the state. Best
chance for rainfall amounts at or above 1 inch will be along and
south of I-70 with lower values further north. Despite a long
duration rainfall event, recent dry conditions and low river levels
should prevent a widespread flooding event across the region.
Localized flooding is possible, mainly across Southern portions of
Indiana where heaviest rain rates and higher amounts are expected,
but again, flooding is not a huge concern due to ongoing drought
conditions.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 258 PM EDT Thu Sep 26 2024

The main concern in the extended will be early in the period as the
remnants of Helene linger near central Indiana. The strong wind gust
and heavy rain threat mentioned in the short term is expected to
continue through Friday evening before diminishing overnight. The
remnant surface low from Helene should phase with an upper low and
continue to gradually weaken through the weekend. Sufficient forcing
and moisture will likely still be in place to support numerous
showers through Sunday. Flash flooding appears unlikely over the
weekend due to less efficient rainfall rates so the additional
rainfall is welcomed news given the active drought conditions.
However, a low end threat for localized flooding continuing into
Saturday cannot be ruled out depending on the evolution or location
of the system.

The remnant disturbance begins to depart sometime late Sunday into
Monday as mid-upper level ridging builds in ahead of an approaching
trough. In the low-levels, lingering moisture will keep the
potential for some diurnal showers in the forecast to start the work
week. Weaker forcing and less available moisture may tend to limit
the coverage of showers.

By Tuesday, diverging model solutions leads to some uncertainty
though ensemble guidance generally shows a deep trough and
associated cold front approaching central Indiana. Limited moisture
ahead of the front and weak overall forcing will once again limit
chances for precipitation with only isolated showers expected. High
pressure should then build in behind the front midweek providing
quiet weather.

Precipitation and clouds will limit diurnal temperature swings over
the weekend with near seasonal highs. Temperatures remain near
seasonal into next week, but a slight cooldown is likely behind the
cold front. Look for highs in the upper 60s to low 70s by Wednesday
and lows around the upper 40s to near 50F.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 614 PM EDT Thu Sep 26 2024

Impacts:

- NE winds picking up and MVFR flying conditions developing in
  showers after 04z-06z

- Gusts to 40 plus knots after 18z

Discussion:

VFR flying conditions will continue the remainder of the evening but
flying conditions will be deteriorating to MVFR in both ceilings and
visibilities overnight as showers move in from southwest to
northeast marking the arrival of the remnants of Helene.

A strong 50-75 knot low level jet will move in Friday afternoon with
widespread gusts to 40+ knots and gusts also to over 47 knots are
possible at times. Wind gusts will gradually decrease Friday night.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 1 PM to 11 PM EDT Friday for INZ021-028>031-
035>038-043-044.

Wind Advisory from 10 AM to 9 PM EDT Friday for INZ039>042-
045>049-051>057-060>065-067>072.

&&

$$

SHORT TERM...CM
LONG TERM...Melo
AVIATION...MK