907
FXUS63 KPAH 242226
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
526 PM CDT Tue Sep 24 2024

.KEY MESSAGES...

- A brief period of relatively dry weather is expected this
  evening through Wednesday following the passage of a cold
  front.

- Chances for widespread heavy rain will ramp up Thursday night
  through Sunday as the remnants of Hurricane Helene interact
  with an upper-level disturbance.

- The heaviest rain looks to fall Thursday night through
  Saturday night, though lighter rain showers may linger
  through early next week.

- Event total rainfall amounts of two to three inches are likely
  across the region, with areas of higher totals possible.

&&

.UPDATE...
Issued at 522 PM CDT Tue Sep 24 2024

Updated Aviation discussion for 00Z TAF Issuance.

&&

.DISCUSSION...
Issued at 247 PM CDT Tue Sep 24 2024

Tonight through Wednesday night...Isolated to widely scattered
showers and thunderstorm are occurring across western KY this
afternoon ahead of a surface cold front that is pushing eastward
through the region. These storms have been rather benign, with
the better environment for organized convection located east of
the region.

Tonight, an upper-level low centered over the Upper Midwest
will shift southward towards the region. This will bring
continued cloud cover, and perhaps some light rain showers or
drizzle overnight along the I-64 corridor. However, confidence
was too low to include in the forecast at this time. Where we do
have breaks in the clouds, fog development is likely,
especially over areas that saw heavy rain yesterday. Overnight
lows will fall into the lower to middle 60s.

The upper-level low will become centered over the region during
the day Wednesday. Most of the area will be dry, but isolated
showers/sprinkles are possible during the afternoon hours.
Plentiful cloud cover will keep high temperatures confined to
the middle to upper 70s.

Thursday through Monday night...The forecast for this period is
about as complex as you will see in this region. There are two
players, and how they interact will determine how the weather
shakes out. The first player is the aforementioned upper-low.
This feature will become cut off from the main synoptic-level
flow and remain stalled over the region. The other player is
the remnants of Tropical Storm Helene, which is forecast to make
landfall on the FL Panhandle late Thursday as a major
hurricane.

Most model guidance takes Helen`s surface circulation through
the southern Appalachian Mountains and eastern TN River Valley
through Friday and into central TN/KY by Saturday. The wrinkle
in this setup is that the upper- level low over our region will
begin to siphon Helene`s tropical moisture, developing a
deformation-band like swath of heavy rain around the upper-level
low. Assuming all the pieces line up, the heaviest rains should
fall during the Thursday night through Saturday night period,
with a gradual diminishment in rainfall coverage and intensity
Sunday and Monday.

The latest WPC QPF forecast for the Thursday-Sunday period is
very aggressive, perhaps a bit too aggressive, with a broad
brush of 3 to 6 inches of rain falling during this time. This is
higher than what most global model ensembles are showing, which
is more like 2 to 4 inches. Furthermore, NAEFS ensemble
guidance is not bullish on extreme precipitable water or
specific humidly levels during this time, a signal that
rainfall processes may not be very efficient as usually observed
in tropical rainfall events. A third wrinkle to consider will
be the presence of dry pockets of air that will be absorbed
into the upper-level low from the north. These dry slots could
cut off the rainfall activity for several hours at a time,
limiting rainfall totals significantly. Either scenario will
include at least a minor flooding risk, but given the 72 hour
time frame for this rainfall and below normal soil moisture,
much of this rain may percolate into the soil rather than
running off and causing flooding issues. Will need to watch
closely how things trend over the next 24 hours for the need for
an ESF or Flood Watch.

Gradient winds will pick as the remnant tropical low
approaches, but gusts should remain well below advisory levels,
peaking around 20-25 kts on Friday. Clouds and rain chances will
keep temperatures rather uniform as well, with highs in the
middle to upper 70s and overnight lows in the lower to middle
60s.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 522 PM CDT Tue Sep 24 2024

Dew points have fallen into the lower 60s at the TAF sites after
a cold fropa. Bases are SCT-BKN VFR, but patchy fog/low cloud
may offer restrictions late tonight. Diurnal cu tmrw will rise
into low VFR with daytime heating CIGS potential.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.

&&

$$