937
FXUS63 KLSX 200745
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
245 AM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Tranquil weather continues today with increasing cloud cover and highs
  in the upper 70s and low 80s.

- There is a chance of showers and thunderstorms each day from
  Sunday through late next week. There will be plenty of dry time,
  and severe weather is not expected.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 244 AM CDT Sat Jul 20 2024

Another tranquil day is in store today as surface high pressure
releases its last breath of influence on our region before exiting
east. The greatest difference we`ll see today from days past will be
the arrival of mid and high cloud cover ahead of our next system.
Otherwise, expect high temperatures to reach the upper 70s to low
80s, warmest in areas that receive the most sun exposure.

The first potential for precipitation will arrive early Sunday
morning as mid-level ascent and moisture increase with a weak
passing shortwave. Most deterministic guidance has some semblance of
light showers in the pre-dawn hours. However, sounding data shows a
stout dry layer in the low-levels. With weak lift and a respectable
dry sub-cloud layer, confidence is low in light rain reaching the
ground. Therefore, opted to maintain sub-15% PoPs.

The chance for showers and thunderstorms increases during the day
Sunday, but plenty of dry time is expected. Despite the arrival of
another shortwave and more low-level moisture, ascent, shear, and
instability will still be incredibly low and not conducive for
the development or maintenance of updrafts.

Jaja

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 244 AM CDT Sat Jul 20 2024

The potential for thunderstorms increases beginning Monday as low-
level moisture continues to filter into the region and instability
rises accordingly. By Monday morning, a stationary front will be
settled in the Mid-Mississippi/Ohio River Valleys as well, serving
as a focus for shower and thunderstorm development as shortwaves
rotate through the larger scale mid-level trough. The greatest
chance for showers and thunderstorms will exist Monday and Tuesday
afternoon as a more pronounced shortwave ejects into the Ohio Valley
from the south central Plains. This feature will provide increased
ascent and moisture to the southern CWA, closer to its track.
Dewpoints these days will reach the upper 60s and 70s, and SBCAPE
will climb closer to the 750 to 1000 J/kg range each afternoon.
Although the potential for convective development will be highest
these afternoons, severe weather probabilities still remain low. The
increased parameters are still weak, and a lack of bulk shear will
keep thunderstorms from organizing. Pulse type thunderstorms are the
expected mode.

The potential for showers and thunderstorms is expected to continue
for as long as the mid-level trough and stationary front are present
to interact with each other. There is uncertainty regarding when
these features move on and regarding the pattern overall.
Deterministic models are showing an earlier dissipation of the front
than in previous runs, and as a result the latest NBM has cut PoPs
by up to 20% late next week. However, guidance is consistent in
another mid-level trough dipping into the Great Lakes during the
middle of the week. This may potentially lay another boundary down
somewhere in the Midwest that could act as a focus for additional
showers and thunderstorms late in the week. If this does occur, weak
ascent and shear will again limit the potential for severe weather.
In short, uncertainty in mid-level pattern make it difficult to
pinpoint exactly how long active weather will continue.

For the temperature forecast, there is high confidence in below
average temperatures lasting until late this week. However, upper
60s/low 70s dewpoints will remind us that it`s still July.

Jaja

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1035 PM CDT Fri Jul 19 2024

A majority of the forecast period will be dry and VFR at all local
terminals. Fog may develop tonight, particularly in the river
vallies. However, the signal for fog development is weak, so
confidence is low. The most likely terminal for impacts is KSUS,
but impacts due to fog can`t be ruled out at KCPS too. Any fog
that develops tonight will dissipate with the rising sun Saturday
morning.

Elmore

&&

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

$$

WFO LSX