139
FXUS61 KILN 270156
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
956 PM EDT Thu Sep 26 2024

.SYNOPSIS...
As the remnants of Helene track north, rain will spread into the
area. In addition, it will become breezy on Friday. Low pressure
will then linger in the Ohio Valley through the weekend keeping
conditions unsettled.

&&

.NEAR TERM /UNTIL 7 AM THIS MORNING/...
Upper low in the lower Ohio Valley will continue to meander
around its current location. As Hurricane Helene makes landfall
overnight and begins to track northward over land, will begin to
observe an influx of anomalously high moisture values in our
CWA. While the rainfall won`t be heavy overnight tonight, we
will observe a gradual increase in light rain coverage across
our counties from south to north.

Northeasterly winds will also begin to increase overnight, but
only expecting gusts of 20-25 mph before daybreak. The more
notable increase in winds will arrive during the late morning
and afternoon hours on Friday.

&&

.SHORT TERM /7 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Key Messages...
1. As Helene remnants approach the Ohio Valley, confidence is
increasing that a low pressure between 980 and 985 mb will slide
through Kentucky/Tennessee Friday afternoon. Depending on the
exact track of the low pressure, a period of strong winds,
potentially resulting in scattered damage and power outages is
forecast to occur through the afternoon and early evening.

2. Period of moderate to heavy rain will result in rainfall
amounts of 1 to 3 inches, generally focused over southeast
Indiana, northern Kentucky, and southwest Ohio. While drought
has persisted for many months, continuous rainfall may result in
scattered flooding in certain area. Riverland flooding can`t be
ruled out, depending on the rainfall amounts. This would be more
likely into the long term period as additional rain falls.

Details:
Wind/wind gusts... In collaboration with surrounding offices, a
wind advisory has been issued from 10 am to midnight, for winds
of 25 to 35 mph and gusts between 45 and 55 mph. The 12Z suite
of guidance increased in wind values, as the remnants of Helene
are expected to approach the Ohio Valley Friday morning. The
pressure gradient will drive strong northeasterly to easterly
winds beginning in the morning, intensifying into the early and
late afternoon. As Helene continues to gradually strengthen in
the eastern Gulf, there is still some uncertainty as to the
overall low pressure value as it enters the Ohio Valley. There
is certainly the potential for lower and higher wind values
depending on the magnitude of the low pressure and the exact
track. However, enough confidence was in place to start with a
wind advisory focused over a large portion of southwest Ohio,
southeast Indiana, and northern Kentucky. The advisory could be
expanded or potentially upgraded to a High Wind Warning if
necessary.

While the track is important, another one of the primary
reasons for the uncertainty is because a saturated low-level
atmosphere mixes boundary layer winds less efficiently. This
would limit the ability for the higher end winds at 1500-2000
feet mixing to the surface. There may be period of dry air where
stronger winds are able to mix more efficiently to the surface.
These details are yet to be ironed out.

Rainfall...PWAT anomalies 200-250% will be present over the Ohio
Valley as the remnants move through Friday. While thunderstorm
driven rain bands aren`t expected, sustained moderate rainfall
rates within the tropical air mass will put down decent amounts
of rain during the 3 to 6 hr period. This may result in
localized areas of flooding, primarily in the south and
southwest portions of the area where terrain may also play an
important role. A flood watch was not issued given the lack of
sustained rates over a high confidence area. The ongoing drought
was also considered. Riverland flooding could become more of an
issue in the long term period.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
On Saturday, a vertically stacked low pressure system will be
located over western Kentucky. The low will move ever so slowly
into central Kentucky by Sunday morning. Dynamics and lift will
be maximized across the Tri-State during this period, trailing
off as one heads north. Showers are in the forecast, with some
locally moderate to heavy rain possible for the Tri-State. The
period of heaviest rain will be during the day Saturday.
Temperatures will be held down on Saturday due to clouds and
pcpn, but remaining warm at night. Highs will range from the
upper 60s across the Tri-State to the lower to mid 70s in our
northern and eastern periphery of the forecast area. Lows will
bottom out in the lower to mid 60s.

The period Sunday through Tuesday will feature a slow process
of the vertically stacked low weakening and shearing over time
as it lifts northeast across the Great Lakes and Ohio Valley.
Best chance for showers, perhaps a thunderstorm, will be highest
on Sunday, with lingering chances of pcpn into Monday. By
Monday night into Tuesday, the system will eject northeast as a
digging mid level trough and associated cold front move into
southeast Canada and the northern Great Lakes.

The cold front is forecast to pass through the region Tuesday
into Tuesday night. This front will be followed by surface high
pressure on Wednesday which will move east of the area on
Thursday.

Highs on Sunday will once again be held down by clouds/pcpn, in
the lower 70s. Highs warm Monday into Tuesday, especially
Tuesday ahead of the cold front (75 to 80), with temperatures
then cooling some by Wednesday (upper 60s/lower 70s). A rebound
in highs will occur on Thursday with sunshine. Lows will
initially start out in the 60s with the coolest night on tap for
Thursday morning (mid 40s/lower 50s)

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Anticipating more VFR conditions to start the overnight period
before categorical reductions become more prominent. Several
aviation impacts expected from the remnants of Helene. Light
rain will gradually increase in coverage overnight tonight,
becoming more steady (and heavier, especially for our southern
terminals) throughout the day Friday. Anticipating mainly MVFR
reductions from rainfall.

CIGs will reduce to MVFR tonight across our KCVG/KLUK terminals
first, gradually progressing northward towards our northern
terminals by early Friday morning. CIGs expected to be less
than 2000 ft AGL majority of Friday, and while IFR CIGs are
certainly possible, not confident enough to include in the tafs
yet.

Winds will certainly be impactful as a gradual increase in
winds is expected overnight into Friday. Strongest winds still
expected across our southern terminals, particularly KCVG/KLUK.
Could see a slight increase in forecast wind speeds (especially
sustained winds) if the Helene tracks more northeasterly, so
will have to monitor trends and adjust accordingly. For now,
also put a mention of LLWS for every terminal given the fact
that several models are suggesting potential for 50-60+ kt winds
2000 ft AGL, mainly during the afternoon hours Friday.


OUTLOOK....MVFR ceilings likely Friday night and possible again
Saturday through Monday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Wind Advisory from 10 AM Friday to midnight EDT Friday night
     for OHZ042-051>054-060>063-070>072-077>081.
KY...Wind Advisory from 10 AM Friday to midnight EDT Friday night
     for KYZ089>100.
IN...Wind Advisory from 10 AM Friday to midnight EDT Friday night
     for INZ050-058-059-066-073>075-080.

&&

$$
SYNOPSIS...McGinnis
NEAR TERM...Clark
SHORT TERM...McGinnis
LONG TERM...Hickman
AVIATION...Clark