451
FXUS63 KPAH 221721 AAA
AFDPAH

Area Forecast Discussion...UPDATED
National Weather Service Paducah KY
1221 PM CDT Sun Sep 22 2024

.KEY MESSAGES...

- A cold front remains on track to brings waves of showers and
  storms this morning through Monday night. The risk for severe
  storms is marginal for today and Monday. The main concern is
  for isolated damaging winds and perhaps some large hail during
  peak heating. Between 0.5 to 2.0 inches, with locally 3.0
  inches of rainfall along the I-64 corridor remains possible.

- Behind the cold front, cooler and less humid conditions are
  expected for the rest of the week with highs only in the mid
  70s to low 80s.

- Returning rain shower chances are becoming more likely
  towards the second half of the week into next weekend.
  Forecast confidence is below average in how a potential
  tropical system down in the Gulf of Mexico may interact with a
  disturbance in the vicinity of the region and anything that
  would be more impactful.

&&

.DISCUSSION...
Issued at 319 AM CDT Sun Sep 22 2024

An unsettled period of weather remains on track as a 500 mb trough
over Colorado lags behind a cold front slowly transversing
southeast across Missouri. Increasing height falls will mean
ample rain chances along with cooler temps as potentially 4
waves of pcpn will impact the FA through Monday night. The
first round of convection is currently moving downstream from
central Missouri and is on track to bring a round of showers and
storms later this morning, mainly across southern Illinois and
southwest Indiana. These storms should be mainly elevated with
heavy downpours and lightning being the main concern. It is
worth nothing that enhanced cloud cover will likely mean temps
struggle to reach 90 today across most of the FA. For this
reason, leaned below the NBM as highs are now likely to range
from the lower 80s to upper 80s from north to south.

After the initial wave pushes east by the afternoon, isolated
activity still remains possible at any given time; however, CI
associated with the second wave likely occurs late this afternoon
into the evening as the aformentioned cold front approaches
from the west. These storms are likely to be more scattered
versus what will be a cluster of storms this morning, but will
pose a marginal risk of severe weather as indicated in SPCs D1
convective outlook. The risk will be contingent on how much
destabilization occurs this afternoon as it will depend on how
much cloud cover debris there is from the morning convection.
Should the parameters come together, the general consensus is
for about 1500-2000 J/kg of MLCAPE and 30-35 kts of effective
bulk shear combined with 7.0-7.5 C/km sfc-3km lapse rates. This
would support mainly a isolated damaging wind risk and large
hail. The severe risk should quickly wane after sunset with the
loss of heating, but additional isolated to scattered storms
remain possible through the overnight.

As the cold front stalls over the FA Monday morning, increased sfc
convergence and mid level forcing will support a third round of
showers and storms, followed by the final round late Monday
afternoon into Monday night. The last round will once again pose
a similar marginal severe risk to today, but again is
contingent on how much destabilization is able to occur due to
cloud cover. Given that the forcing will be more robust, the
risk has the potential to be slightly greater on Monday if all
the ingredients are able to come together. Otherwise, a few rain
showers may linger into Tuesday as the cold front pushes
southeast of the FA. Total rainfall amounts through Tuesday
generally look to be between 0.5 to 2.0 inches, with localized
higher amounts near 3.0 inches favored along the I-64 corridor.
Given that the rainfall will occur over a long duration, any
flash flooding concerns should be limited to mainly runoff on
roadways where heavy downpours occur.

Behind the front, highs are now progged to range from the mid
70s to low 80s through the end of the week. The synoptic flow
turns highly amplified with a deep 500 mb trough that will begin
to dig into the lower Ohio Valley on Wednesday. This is when
the forecast challenges begin as there is more support from the
latest 0z model guidance for conditions to turn rather wet to
end the week, while some guidance still would support mainly dry
weather.

The deterministic ECMWF/CMC are in decent agreement in showing
a 500 mb cutoff low developing in the vicinity of the FA by
Wednesday morning, and remaining nearly stationary with robust
cyclonic flow through the weekend. This scenario would result in
daily rain chances returning quickly in the middle of the week
and continuing right through the weekend. The one caveat is how
the potential Gulf of Mexico tropical system eventually
interacts as this scenario would also potentially mean quite a
bit of heavy rainfall and possibly some wind. Meanwhile, the
GFS is much more progressive with the evolution of the 500 mb
low and would mean mainly dry weather into the weekend.

It is worth noting the ECMWF/CMC have much stronger support for
the 500 mb low by its ensembles, similar to what the ECMWF AIFS
has been showing. Meanwhile, the GFS lacks much support from
the GEFS, and is why the deterministic runs have been very
inconsistent. Given the latest trends, would lean towards there
being at least returning rain shower chances later in the week.
Until the tropical system develops in the northwest Caribbean,
substantial changes are still likely to occur for anything that
would be more impactful. For this reason, forecast confidence
remains below average.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1221 PM CDT Sun Sep 22 2024

High MVFR ceilings will slowly rise over parts of southeast
Missouri as convective clouds begin forming. Thunderstorm
development is expected over the region later this afternoon and
through early evening. A decrease in activity is then expected
after sunset. After midnight increased influence from an
approaching storm system is expected to lead to lower ceilings
with rain showers and embedded thunderstorms possible from about
08-15z. The new forecast calls for low MVFR ceilings although
IFR ceilings are possible. Below VFR ceilings are expected
through midday Monday with areas of rain and a few thunderstorms
remaining possible.


&&

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

&&

$$

DISCUSSION...DW
AVIATION...JGG