315 
FXUS63 KIND 271330
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
930 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

&&

.FORECAST UPDATE...
Issued at 930 AM EDT Fri Sep 27 2024

Forecast is in good shape this morning, with only tweaks needed to 
hourly forecasts based on latest trends.

Models remain consistent that a band of over 50 mph wind gusts will 
move through central Indiana from mid-afternoon into the early 
evening hours, with the strongest winds across the southern 2/3 of 
the area. 

Coverage of rain looks to diminish midday, and during this period 
clouds may thin some. If enough thinning occurs, stronger winds 
could start to mix down earlier. This thinning could also impact 
high temperatures a bit. Will continue to watch closely. 

Given the above, current headlines look on track so no changes were 
made at this time.

&&

.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 until 1 AM EDT Saturday for INZ021-028>031-035-038-
043.

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

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

Wind Advisory until 11 PM EDT this evening for INZ040>042.

&&

$$

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