837
FXUS63 KLSX 121938
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
238 PM CDT Sun May 12 2024

.KEY MESSAGES...

- Widespread showers and a few thunderstorms are expected
  tomorrow, with some breaks expected in the afternoon. A strong
  thunderstorm or two will be possible in the southern half of the
  Ozarks late in the afternoon and evening, with strong wind
  being the primary threat.

- Lighter showers are likely to continue through Tuesday afternoon.

- The next opportunity for rainfall will be Thursday and Friday.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 237 PM CDT Sun May 12 2024

Quiet weather continues this afternoon as surface high pressure
remains in place, albeit temporarily. Meanwhile, temperatures have
climbed into the low 80s as of 1 PM, thanks to a combination of
mostly clear skies, warm southerly flow, and a passing upper level
ridge. Later this afternoon and evening, patchy high level cloud
cover will begin to spread into the area, the first hint of the next
storm system approaching from the west. Otherwise though, weather
for the remainder of the evening will remain uneventful.

Changes are on the horizon, though, as a slow-moving low pressure
system currently located across the Central Plains will move into
the western Missouri. Ahead of this low, modest southerly low level
flow will gradually advect Gulf moisture northward overnight tonight
through early tomorrow morning, with PWAT values climbing to between
1.2 and 1.5 inches. This will set the stage for widespread
precipitation between tomorrow morning and Tuesday afternoon.

The first round of widespread rainfall is expected to move through
the area between early morning and mid afternoon, as a subtle
vorticity maximum pivots around the approaching trough. As this
occurs, a wave of showers is expected to move from southwest to
northeast, and almost all areas are expected to see at least some
rainfall. Meanwhile, modest MUCAPE ranging from 100 to as much as
500 J/kg will support at least a few thunderstorms during this
timeframe, although strong/severe storms are not anticipated with
this initial round. Overall, rainfall rates are expected to be light
to moderate outside of a few embedded convective cores, as forcing
is not expected to be particularly strong. This initial wave of rain
will also be progressive, and and training storms are not expected.
As such, while a soaking rain can be expected for most areas,
flooding is not a significant concern locally.

By late afternoon, most of this rain is expected to exit the area to
the northeast, with a relative lull in precipitation expected in
many areas for a few hours. From here, attention turns to the
possibility of redeveloping showers and thunderstorms during the mid
to late afternoon, with a limited potential for a few stronger
storms as well. As the first round of showers moves off to the
northeast, varying levels of clearing may allow for some afternoon
destabilization, particularly across central and southern Missouri.
How much so will likely be limited by cloud cover and poor lapse
rates, but between 1000 and 2000 J/kg of CAPE may be attainable.
Meanwhile, mid level winds will increase across southern Missouri as
the shortwave approaches from the west, with favorable jet dynamics
underneath the left exit region of a modest 500 mb jet. With around
30-40kt of 0-6km shear to work with, it wouldn`t be out of the
question to see a some more organized convection late Tuesday
afternoon and evening capable of producing strong wind gusts across
the southernmost parts of our area, or roughly the southern half of
the Missouri Ozarks. This is highly conditional, but will be worth
watching over the next 24 hours.

Between Monday night and Tuesday afternoon, the low pressure system
will continue its slow eastward march, and a cold front will sink
into the area. Meanwhile, light showers along and behind the cold
front will slowly spread into the area from the northwest, although
there is some model disagreement regarding just how vigorous
Tuesday`s shower activity will be. However, this activity will
likely be less convective in nature save for perhaps parts of the
southern Ozarks and southern Illinois, with lower rain rates
and perhaps some drizzle mixed in later in the day as well.

Once all is said and done late Tuesday, most areas will likely
observe somewhere between .5 and 1.5 inches of rain, with forecast
amounts dropping slightly from previous forecasts. Temperatures both
days will also likely top out only in the low 70s, and perhaps not
even out of the 60s in northern areas.

BRC

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 237 PM CDT Sun May 12 2024

A break in the rain is expected Wednesday as the cold front surges
south and another transient upper ridge moves in overhead. However,
this will not persist for long, as rain chances will increase yet
again Thursday through Friday. Model guidance continues to suggest
that a positively tilted upper trough will move through the area,
providing just enough forcing to produce widespread but perhaps not
particularly heavy precipitation. Moisture content will be
sufficient to support this, but not anomalously high, and forcing
from the upper trough and perhaps a diffuse surface cold front do
not appear to be particularly noteworthy. As such, the potential for
heavy rain appears to be low, but there is a consistent signal among
a majority of ensemble members for at least some precipitation in
most areas late in the work week. Meanwhile, seasonable, if not
slightly below average temperatures are likely to persist through
the end of the week.

BRC

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1246 PM CDT Sun May 12 2024

VFR conditions are expected to prevail for the remainder of the
day and well into the evening. Overnight, ceilings will gradually
lower as precipitation arrives from the west. Ceilings will likely
remain at VFR levels until early tomorrow morning, but will fall
to at least MVFR, possibly IFR throughout the morning and through
the end of the TAF period. Showers are also expected to impact
all local terminals during this time frame, with at least some
potential for a thunderstorm or two. Confidence in widespread
precipitation is high, but low regarding the potential for
thunderstorms. Visibility reductions to MVFR levels will be
possible due to this precipitation, potentially lower within
stronger convective cores.

BRC

&&

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

$$

WFO LSX