850
FXUS63 KPAH 251752
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1252 PM CDT Wed Sep 25 2024

.KEY MESSAGES...

- A few showers or storms will be possible over the southern
  half of the Quad State this afternoon. Then dry weather is
  expected tonight, and possibly through the day Thursday.

- Chances for widespread heavy rain will ramp up Thursday night
  through Sunday, as the remnants of Tropical Storm Helene
  interact with an upper-level storm system.

- The heaviest rain is expected from late Thursday night through
  Friday evening. Forecast rainfall in this period currently
  ranges from around 2 inches along I-64 to 3.5 inches in far
  southern portions of the region. The rains will become lighter
  and more isolated through the weekend.

- The Quad State will begin to dry out on Tuesday as a cold
  front passes. Cool, fall-like conditions are forecast for
  next Wednesday.

&&

.DISCUSSION...
Issued at 335 AM CDT Wed Sep 25 2024

An upper low will move south through the Quad State today, as
surface high pressure builds in. With remnant low-level
moisture and the cold pool aloft associated with the upper low,
widely scattered showers and thunderstorms will be possible over
the southern half of the region this afternoon. As is the case
with any convection under upper lows, some cold air funnels
cannot be ruled out this afternoon. No severe weather is
expected. Brief heavy downpours, and lightning will be the
primary concerns.

Tonight should be dry throughout the Quad State, and guidance
has trended slower with the onset of rains with the approach of
the remnants of Tropical Storm Helene. Much of the region will
be dry through Thursday morning, and possibly the afternoon,
especially over southeast Missouri and southern Illinois.

The upper low will drift south or southwest to a position
somewhere between Memphis and Little Rock on Thursday, as
Helene makes landfall in northern Florida. These two systems
will then begin to dance with Helene heading north through
Georgia and eventually northwest toward the Quad State. Current
guidance has the two systems totally merged somewhere in our
vicinity by Saturday morning. Confidence in the details of this
interaction is still quite low, as this is a rare occurrence
and the models are not likely to get it right this far out,
especially with how fast this occurs (from landfall to merger in
48 hours).

WPC QPF has storm total rainfall through Sunday ranging from
2.5" along I-64 to 3.5-4" over the southern half of the region.
The bulk of this rainfall is expected in the 24 hour period from
late Thursday night through Friday evening. The 00Z GEFS and
ECENS are not very bullish for this magnitude of rainfall. They
indicate no more than a 50% chance of reaching 2" in this 24
hour period over far southern portions of the region, and little
to no chance of reaching 2" over the northern half of the
region.

The ensemble SA tables indicate highly anomalous moisture at
500mb, but have minimal positive anomalies in the low-levels. It
is highly likely that Helene will suffer mightily crossing the
southern Appalachians on its way here. This should severely
weaken the low-level circulation/winds and much of the tropical
moisture is likely to be rained out on the east side of the
mountains. NBM surface dewpoints never get any higher than the
middle 60s across the Quad State which is not exactly tropical
(we had dewpoints in the lower 70s just last weekend). All of
this is evidence for taking the current QPF with a grain of
salt, and tempering expectations. In general, the heaviest rains
should be over west Kentucky with the lightest amounts in the
far northwest portions of the Quad State.

In other news, the 00Z ECENS has a 50% chance of 35kt wind
gusts over the northern half of the region Friday afternoon and
evening. Given the concern for the weakening of the system as it
comes through the Appalachians, it would seem unlikely we will
see gusts this strong, but confidence in the merging of the two
systems is low, so it bears watching the trends over the coming
days. Regardless of the intensity, the strongest winds will be
Friday afternoon and evening, which in addition to the wet
conditions expected, will make for some challenging conditions
for Friday night football games and any other outdoor
activities. At least at this time, the NBM does not have any
lightning forecast Friday afternoon or evening.

As the merged storm system spins down over the region this
weekend, showers will become more scattered with the greatest
coverage each afternoon. The coverage and intensity will both
decrease for Sunday and moreso on Monday. The consensus of
guidance now has the system east of the area by Tuesday, with
northwest flow aloft over our region. This will bring a surge
of cool surface high pressure through the Quad State Tuesday.
High temperatures next Wednesday will be rather fall-like in the
upper 60s to lower 70s, and there will be a healthy north
breeze.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1237 PM CDT Wed Sep 25 2024

Mostly a VFR forecast expected today and tonight. 5kft ceiling
this afternoon will eventually erode away this evening with FEW-
SCT upper level clouds passing through at times. Winds today and
tonight will be light. Fog potential tonight is a bit uncertain
given the potential for some drier air working its way in.
There is a higher signal in the guidance for CGI and did include
a mention of it in the TAF. Easterly winds increase Thursday
between 5 and 10 knots.

&&

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

&&

$$

DISCUSSION...DRS
AVIATION...AD