914
FXUS63 KLSX 290954
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
454 AM CDT Wed May 29 2024

.KEY MESSAGES...

- Mild and dry conditions will persist today and tomorrow.

- Widespread showers and a few thunderstorms are expected sometime
  between Friday afternoon and Saturday evening. Some showers may
  produce locally heavy rain.

- Additional waves of showers and thunderstorms will be possible
  Sunday onward, with warmer temperatures expected.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 315 AM CDT Wed May 29 2024

Quiet conditions have settled into the area this morning
behind yesterday`s cold front, thanks to high pressure and a dry
airmass. While a few mid level clouds continue to percolate across
the southern half of Missouri and far southern Illinois, possibly
even producing a few instances of virga, this activity will continue
to move south through the morning, and measurable precipitation is
not expected. Otherwise, while surface winds have weakened, the
presence of this mid-level cloud cover is likely to limit fog
formation early this morning across Ozark valleys, and as a result
we do not expect this to be as widespread in these areas as it was
yesterday.

During the day, high pressure and dry northwest flow will persist,
leading to a mild day with plenty of sun. Temperatures this
afternoon are likely to reach only the mid 70s to perhaps near 80
degrees in the southern Ozarks, with light winds as well. This will
continue into Thursday as well, with a chilly morning followed by a
barely noticeable warmup as a transient ridge aloft builds overhead.
This slight boost in temperatures will likely bring afternoon
temperatures closer to 80 degrees, but easterly low level flow will
prevent most areas from climbing much higher than this.

Meanwhile, the potential for precipitation overnight Thursday has
diminished, which will be discussed in greater detail in the
following Long Term discussion.

BRC

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 315 AM CDT Wed May 29 2024

Attention turns to the arrival of a shortwave/vorticity maximum
Friday and Saturday, which continues to trend a bit slower in recent
model projections. This is the primary reason that precipitation
chances have waned overnight Thursday, although a few ensemble
members and the deterministic GFS continue to produce a few elevated
showers very late at night, likely due to modest mid-level warm air
advection and isentropic ascent ahead of the main wave. This
possibility is now within the minority of possible solutions,
though.

Rather, the best chances for precipitation have shifted to sometime
between Friday afternoon and Saturday evening, although enough
timing variance remains among ensemble members to preclude
increasing precipitation chances to greater than 60% at any specific
time. However, at least some rain is expected to fall at some point
in that time window in most areas.

As for the potential for thunderstorms, instability projections
continue to be rather marginal ahead of this wave (~250-750 J/kg
MUCAPE) due to very poor mid-level lapse rates, and forecast
profiles appear almost tropical in nature with high humidity
throughout the column. Bulk shear parameters are also marginal
overall owing to weak mid-upper flow and a displacement from the
primary polar jet to the north. However, there will likely be an
enhanced low level jet, which may lead to locally higher low-level
wind shear but is not expected to significantly increase severe
weather chances given the other factors. As such, the potential for
strong or severe storms remains rather low, although some convective
cells could be reasonably efficient rain producers, with
precipitable water projections ranging from roughly the 75th to 90th
percentile and some outliers exceeding this range as well.

From Sunday onward, weak zonal flow aloft will develop across the
CONUS, with additional weak shortwaves/vorticity maxima passing
through it. There remains very little specificity regarding the
timing of these waves, but this will maintain an unsettled pattern
heading into next week with multiple opportunities for
showers/thunderstorms. While these features may have some
similarities to this weekend`s system, it does appear that
temperatures and moisture will be steadily rise early next week,
along with instability, which increases the potential for
thunderstorms whenever precipitation does develop. However, the
persistence of modest mid and upper level flow will continue to
limit the ceiling of severe weather overall.

BRC

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 451 AM CDT Wed May 29 2024

VFR conditions are expected throughout the 12Z TAF cycle. Very
light north winds will gradually veer to easterly tomorrow
morning, with minimal cloud cover aside from a few mid level
clouds lingering near I-70 terminals. Otherwise, no weather
hazards are expected.

BRC

&&

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

$$

WFO LSX