911
FXUS63 KIND 271017
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
617 AM EDT Fri Sep 27 2024

.KEY MESSAGES...

- Strong northeast winds with gusts of 45-60 MPH expected this
  afternoon and evening

- Sporadic gusts above 60 mph possible late afternoon into the
  evening

- Widespread rainfall expected into the weekend with rainfall totals
  around 1-3 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 (Today and Tonight)...
Issued at 258 AM EDT Fri Sep 27 2024

Rain continues to gradually overspread the forecast area from the
south early this morning...especially along and south of I-70.
Northeast wind gusts have been steady peaking at around 25mph.
Temperatures at 06Z were generally in the mid and upper 60s.

The remnants of Helene and the specific impacts locally are the
primary focus for the short term. Helene made landfall in the Big
Bend of Florida late Thursday evening and is now moving through
southern Georgia. The remnant center of the system will lift into
eastern Kentucky by this afternoon then retrograde along the Ohio
River into western Kentucky tonight as it interacts then becomes
absorbed by an upper low currently centered over western Tennessee.
Heavy rain and strong to potentially damaging wind gusts will be the
main threats across the forecast area and will discuss both below.

Wind Threat

As mentioned above...gusts have been steady around 25mph so far
early this morning. With Helene onshore and plowing N/NW...expect
surface winds to steadily increase through daybreak with peak gusts
pushing above 30mph and then towards 40mph by midday.

The approach of the remnant surface low this afternoon...likely to
still be near 980mb...will create a pressure gradient that tightens
rapidly across the Ohio Valley by late afternoon. CAMs remain
consistent on an intense low level jet at 70-75kts rotating around
the northern flank of the surface low and across the southern half
of central Indiana late this afternoon into the evening. Lapse rates
will be poor with a deeply saturated tropical airmass over the
region...which will limit the strongest winds from being pulled
fully to the surface. That being said...the signal for a swath of
gusts approaching 60mph pivoting W/NW across parts of the area has
grown in tandem with the low level jet late today.

After collaboration with our neighboring offices...we will be
upgrading the southern half of the forecast area from near the I-70
corridor south to a High Wind Warning with a particular focus in the
19Z to 02Z timeframe as the core of the strongest winds shifts west
across the area and where confidence is highest in warning criteria
being met. Plan on including the entire Indy metro into the High
Wind Warning. Sustained winds at 30-35mph with 60mph gusts are on
the table and cannot rule out an isolated gust at 65mph.

The Wind Advisory will continue further north but will bump up peak
wind gusts to 50-55mph. The dayshift will need to monitor trends to
determine if an expansion in the High Wind Warning is needed for
later. Also plan on extending the wind headlines out by a few hours
tonight to account for the higher winds. Wind gusts will drop back
quickly overnight tonight as the low level jet moves off to the
west.

Rain Threat

General trends as the 00Z model suite has come in is to expand the
higher rainfall amounts further north across the forecast area.
While rainfall currently is generally light to moderate...the faster
onset to precip this morning lends support to increasing rainfall
amounts across the southern half of the forecast area.

Current mesoanalysis shows higher precip water values are steadily
expanding across the forecast area with most locations above 1.50
inches. This will only increase further through the day...peaking at
above 2 inches by late this afternoon as the core of the tropical
moisture associated with Helene lifts into the region. The highest
rainfall rates will come at this point with the band of moisture
that lifts into the area in tandem with the strong low level jet and
an accompanying deep layer of convergence. Expect a sharp gradient
in rainfall amounts south to north across the forecast area with
high pressure over the northern Great Lakes influencing how far
north the widespread rain shield will make it.

Expect amounts by Saturday morning to be less than an inch over far
N/NW counties...1 to 2 inches along and just south of the I-70
corridor including the Indy metro...and 2 to 3 inches in far
southern portions of the forecast area. These amounts falling over a
24 to 36 hour period with the antecedent dry conditions in recent
weeks will keep the flood threat generally low. The primary concern
for any localized flooding will come with the heaviest rainfall
slated for late afternoon into the evening as it is entirely
possible that rainfall rates may briefly overwhelm small streams and
areas with poor drainage. Main stem rivers should be fine going into
next week as levels have been low over the last several weeks due to
the dry conditions.

Temps...the diurnal range will be minimized over the next 24 hours
courtesy of the deep tropical moisture...thick cloud cover and
rains. Highs today will hold mainly in the lower 70s with lows
tonight in the low to mid 60s.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 258 AM EDT Fri Sep 27 2024

The remnants of Hurricane Helene will dictate our weather through
the first half of the long range period. Currently, Hurricane Helene
is located over southern Georgia and is still a powerful hurricane
as of 3am. Steady weakening is anticipated as the system heads
northward away from the warm waters of the Gulf. However, a potent
mid to upper-level low situated over southeastern Missouri will give
the system a baroclinic assist. The hurricane will race
northwestward towards the upper-level low and quickly phase with it.
The resulting system should then meander to our south for a couple
of days since the overall steering flow aloft is quite weak. Rain
showers are expected to continue at times until the system spins
down. By the middle of the week, a trough and associated cold front
should sweep down and kick what remains of Helene out of the region.

In terms of sensible weather, rain is the primary concern through
the majority of the weekend and into early next week. Saturday and
Sunday will feature the greatest likelihood of rainfall over a
quarter of an inch, with the highest amounts generally south of I-
70. Lingering showers are possible on Monday as well, but by this
point the system should be an ill-defined remnant low. The
aforementioned cold front arrives late Tuesday or early Wednesday
with little fanfare. Even though Helene`s remnants may still be
nearby, the bulk of its moisture will likely be east of Indiana by
the time the front gets here. That, combined with weak forcing,
should limit rainfall potential with the frontal passage.

Temperatures through the period are expected to be near average for
the most part. Cloud cover and rain associated with Helene should
keep temperatures down a bit through Sunday. Then, a brief warm up
before the cold front nudges temps downward again by Wednesday.
Temperatures gradually moderate towards the end of the week as the
trough departs. Averages at Indianapolis are 74/52.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 617 AM EDT Fri Sep 27 2024

Impacts:

- MVFR ceilings expanding this morning, IFR possible at times

- Rain through this evening

- Significant aviation impacts from mid afternoon into the evening
with heavier rainfall and wind gusts in excess of 40-50kts

Discussion:

Rain has now overspread most of central Indiana with MVFR
stratus expanding northwest through the region as well. Northeast
wind gusts remain steady at 20-25kts but seeing higher gusts to the
southeast of the region. Expect gusts to increase later this
morning. Rain may briefly diminish in coverage midday. Occasional
IFR ceilings are likely at KBMG throughout the morning.

The greatest impacts to aviators will come by mid afternoon into the
evening as the main remnants of Helene lift up into the region.
Model guidance remains consistent on bring a swath of 70kt winds at
850mb around the northern flank of the remnant low and across the
southern half of central Indiana. Despite poor lapse rates...this
will likely translate to a 3-5 hour period with wind gusts in excess
of 40kts and potentially approaching 50kts for brief periods at
KBMG...KHUF and KIND. The heaviest rain in the forecast period will
occur during this timeframe as well with IFR conditions
likely. There is potential for a brief period of low level wind
shear considering the very strong winds within the boundary layer.

Wind gusts will begin to drop back by mid to late evening with rain
lightening up as well. Gusts will drop further tonight into early
Saturday. MVFR ceilings will persist through Saturday morning.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from noon today to 1 AM EDT Saturday for INZ021-
028>031-035-038-043.

High Wind Warning from noon today to 1 AM EDT Saturday for
INZ036-044-045-051>053-060-061-067>069.

High Wind Warning from noon today to 11 PM EDT this evening for
INZ037-039-046>049-054>057-062>065-070>072.

Wind Advisory from noon today to 11 PM EDT this evening for
INZ040>042.

&&

$$

SHORT TERM...Ryan
LONG TERM...Eckhoff
AVIATION...Ryan