062
FXUS63 KLSX 142332
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
632 PM CDT Sat Sep 14 2024

.KEY MESSAGES...

- The remnants of TC Francine will continue to erode through
  Sunday, resulting in gradual warming and drying. These
  conditions persist next week.

&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 206 PM CDT Sat Sep 14 2024

Remnant moisture and upper-level forcing from TC Francine remains
stalled across the Lower Mississippi River Valley in the absence
of any appreciable steering flow to advect it east. Further north,
a surface high over the Great Lakes is drawing easterly surface
winds and marginally-drier dew points into the forecast area. As a
result of this weak confluence in the low-levels, a narrow plume
of moisture stretches across western and central Missouri
stretching down through the Ozarks. This tropical moisture, along
with weak mid- level vorticity maxima near Francine`s remnant low,
will allow for a 15-30% chance for showers to persist along and
south of the I-44 (MO)/I-64 (IL) corridor this evening. That said,
any rain that does fall will be light and most of the night will
remain dry. Thunderstorm chances are more scarce (up to 15%) with
plenty of warm air aloft limiting instability.

The moisture axis shifts west by Sunday with high surface pressure
further impinging on the region from the east. This will not only
shunt the 15-40% shower and thunderstorm chances west of the
Mississippi River, but will also allow for more abundant sunshine
(and warmer temperatures) further east. Guidance continues to
struggle with this weakly-forced environment, producing far too much
precipitation. The rain chances were adjusted slightly lower, but
the moisture may have marginally-stronger forcing with which to work
and precluded greatly reducing or removing the chances. While the
gradual warming trend is most certain, exact temperatures are still
unclear since they will greatly hinge on could cover and the
location of the upper-level low. That said, those along and east of
the river have the best chances of reaching the mid/upper 80s during
the afternoon with slightly cooler temperatures further west.
Temperatures stay seasonably warm overnight Sunday into Monday with
clouds overhead, but rain chances will be next to zero with the
upper-level wave disintegrating.

MRB


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 206 PM CDT Sat Sep 14 2024

Remnant moisture and upper-level forcing from TC Francine remains
stalled across the Lower Mississippi River Valley in the absence
of any appreciable steering flow to advect it east. Further north,
a surface high over the Great Lakes is drawing easterly surface
winds and marginally-drier dew points into the forecast area. As a
result of this weak confluence in the low-levels, a narrow plume
of moisture stretches across western and central Missouri
stretching down through the Ozarks. This tropical moisture, along
with weak mid- level vorticity maxima near Francine`s remnant low,
will allow for a 15-30% chance for showers to persist along and
south of the I-44 (MO)/I-64 (IL) corridor this evening. That said,
any rain that does fall will be light and most of the night will
remain dry. Thunderstorm chances are more scarce (up to 15%) with
plenty of warm air aloft limiting instability.

The moisture axis shifts west by Sunday with high surface pressure
further impinging on the region from the east. This will not only
shunt the 15-40% shower and thunderstorm chances west of the
Mississippi River, but will also allow for more abundant sunshine
(and warmer temperatures) further east. Guidance continues to
struggle with this weakly-forced environment, producing far too much
precipitation. The rain chances were adjusted slightly lower, but
the moisture may have marginally-stronger forcing with which to work
and precluded greatly reducing or removing the chances. While the
gradual warming trend is most certain, exact temperatures are still
unclear since they will greatly hinge on could cover and the
location of the upper-level low. That said, those along and east of
the river have the best chances of reaching the mid/upper 80s during
the afternoon with slightly cooler temperatures further west.
Temperatures stay seasonably warm overnight Sunday into Monday with
clouds overhead, but rain chances will be next to zero with the
upper-level wave disintegrating.

MRB

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 206 PM CDT Sat Sep 14 2024

While broad upper-level ridging will persist throughout most of
the CONUS to start the work week, which overall favors warmer and
drier weather, there is one feature that has the outside chance
throw a curveball at this forecast. An organizing area of
convection off the Carolina coastline has potential to form a
tropical cyclone over the next few days (see the NHC Tropical
Weather Outlook for more information). Regardless of whether it
strengthens into a TC, this wave will drift west onshore along the
southern periphery of the upper-level ridge and gradually weaken
amidst this feature. What happens from here will factor into how
warm we get mid-week and beyond. A sizable majority of global
ensemble members keep the upper-level wave far from the Mid-
Mississippi Valley, which would allow for uninhibited warming (as
high as the upper 80s to low 90s) for the latter half of the work
week. If the second solution, which features the wave getting
close to the forecast area, comes to fruition, we`d see
temperatures a little bit cooler. That said, the difference is
pretty minor (as much a 5 degrees) and largely inconsequential.

What the ensemble guidance seems quite certain of is that we will be
entering a several-day period of dry weather under the strong ridge
established over the eastern two-thirds of the CONUS. Even if the
wave mentioned earlier manages to reach us, it will be very weak and
moisture-starved, making it very unlikely to produce much rain at
all. While the dry weather this week is preferred for outdoor
activities, this forecast does not bode well for relief from the
gradually-worsening drought. Coupled with warm temperatures
promoting stronger evapotranspiration, and our climatologically-
driest part of the year approaching, drought conditions are likely
to either remain steady state or continue gradually deteriorating
through the week. A strong upper-level trough will gradually expand
and drift east next weekend, which forces a frontal boundary into
the region. This feature, which doesn`t actually reach us in the
forecast period, presents our next shot for widespread rain.

MRB

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 626 PM CDT Sat Sep 14 2024

Current shower/thunderstorm activity is expected to
weaken/dissipate over the next few hours. Some light rain will
linger across parts of southeast Missouri tonight, but stay well
south of the terminals. Scattered showers and thunderstorms are
forecast once again on Sunday, again mainly across parts of
southeast Missouri. Overnight fog is once again possible, but the
setup is not nearly as favorable as yesterday. That being said,
some river valley fog is possible, most likely at KSUS.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX