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000
FXUS63 KLSX 250259
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
959 PM CDT Wed Apr 24 2024

.KEY MESSAGES...

-Multiple rounds of showers and thunderstorms can be expected
 between late Thursday and late Sunday, with widespread rainfall
 expected and at least some potential for strong/severe storms.

-Strong/severe thunderstorms will also be possible at various
 times within this timeframe, with a slight preference for Friday
 afternoon/evening, late Saturday night, and Sunday/afternoon
 evening. Confidence remains low regarding this potential.

-Well above normal temperatures can be expected Friday through
 Sunday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 235 PM CDT Wed Apr 24 2024

Quiet conditions have returned to the region in the wake of
yesterday`s cold front and associated round of showers, with
temperatures rising into the mid 60s to near 70 degrees this
afternoon and only some scattered afternoon cumulus standing in the
way of clear skies. This will largely continue through the overnight
hours, with perhaps some increasing cirrus cover towards daybreak.
Patchy fog is also likely to redevelop in Ozark valleys that can
remain sheltered from the wind, but this is not expected to be
particularly widespread.

By tomorrow morning, winds will switch to the southeast and steadily
increase in response to lee cyclogenesis across the central High
Plains. While this will be discussed in greater detail during the
long term discussion to follow, the effect on local sensible weather
during the day tomorrow will simply be slightly increasing breezy
southeast winds. Temperatures tomorrow are also expected to be
rather similar to today, ranging from the mid 60s to near 70.

BRC

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 235 PM CDT Wed Apr 24 2024

While benign conditions will persist through at least tomorrow
afternoon, a major pattern change will bring significant changes to
the area between late tomorrow and late Sunday.

The primary driver of this change will be the development of a
longwave trough across the western U.S. Thursday, which in itself
will be constructed of two distinct shortwaves that will pivot into
the central plains one after the other between late Thursday and
Sunday. These waves will each drive lee cyclogenesis across the high
plains, and the resulting low pressure systems will each move from
southwest to northeast and into the upper Midwest, the first
between Thursday night and Friday, and the second between Saturday
night and Sunday. Meanwhile, persistent southerly flow with a
largely uninterrupted trajectory from the Gulf of Mexico will
transport an increasingly moist and unstable airmass into the
central plains, setting the stage for several rounds of showers
and thunderstorms across the region.

While confidence is high that this pattern will surely produce
multiple rounds of showers and thunderstorms locally, with at least
some potential for strong or severe storms at times, confidence
remains low regarding the latter potential. On a regional scale this
pattern is almost certain to produce severe thunderstorms, but the
St. Louis forecast area remains slightly removed from what appears
to be the greatest threat area for the majority of the
Thursday/Sunday timeframe, with considerable timing uncertainties
and additional complexities inherent with multi-day events that
complicate this forecast. At this stage, it remains a bit early to
get into too much detail regarding the timing of each individual
round, but they can be roughly separated into five semi-coherent
rounds:

1. Remnant showers and a few thunderstorms traversing a stalled
front Thursday evening across the Ozarks.

2. Redeveloping showers as the stalled front lifts northward across
the area overnight Thursday and early Friday.

3. Potentially stronger surface-based thunderstorms developing
Friday afternoon and persisting through the evening and overnight
hours.

4. Additional thunderstorms late Saturday and Sunday morning, again
with the potential to be strong or severe.

5. The final round of showers and storms potentially along an
advancing cold front sometime between Sunday afternoon and evening,
again with the potential for strong or severe storms.

Each successive round will be impacted by how its predecessor
evolves, and as such, confidence in the potential for each round
steadily decreases. Specifically regarding the potential for strong
or severe storms, strong southwesterly flow aloft will maintain a
sufficiently sheared environment to produce organized thunderstorms,
particularly as stronger jet streaks move through the area. What is
less certain will be the available day-to-day instability, as the
deepest moisture will likely remain to our west until Sunday, and
highly variable cloud cover and morning showers will have a
significant impact on daytime destabilization. However, there is a
slight preference for Friday afternoon/evening and Sunday afternoon/
evening, due to the presence of stronger southwesterly flow aloft as
the primary jet streaks traverse the area. This increases the
potential ceiling during these timeframes, should we achieve
sufficient destabilization. In addition, all severe hazards will be
in play at various times, including wind, hail, and tornadoes. Not
to mention, widespread soaking rainfall can be expected between
Thursday and Sunday, regardless of whether severe thunderstorms
materialize.

Meanwhile, persistent southerly flow will maintain well above
average temperatures between Friday and Sunday, with only a modest
cold front serving as a brief speed-bump Monday before temperatures
rebound to well, above average values Tuesday onward.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 954 PM CDT Wed Apr 24 2024

VFR flight conditions are expected to prevail at least through
early to mid afternoon on Wednesday across the area. Lower clouds
will build into central and parts of northeast Missouri late
Wednesday afternoon and evening, along with widely scattered
showers, and perhaps a thunderstorm or two. Additionally,
southeast flow will likely become gusty in central and northeast
Missouri during the afternoon and evening. The rest of the area
should remain in VFR category through the remainder of the period.

Carney

&&

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

$$

WFO LSX