889
FXUS63 KLSX 270351
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1051 PM CDT Wed Mar 26 2025

.KEY MESSAGES...

- Moisture return begins tonight, bringing showers and
  thunderstorms back into the forecast through Sunday.

- The greatest threat for severe thunderstorms is on Sunday,
  although confidence remains low on where this threat will
  materialize.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 226 PM CDT Wed Mar 26 2025

Our stretch of dry weather is about to come to an end. Moisture
return has already begun across Texas where dewpoints have already
risen into the mid 60s, a stark difference from the mid 20s
currently observed in parts of our area. Surface winds have begun to
turn southerly across the Plains which has begun pulling this
moisture northward.

A shortwave trough traversing the top of the ridge will enhance the
northward pull of moisture tonight, with this moist advection being
driven primarily in the 850-925MB layer. The low level moist
advection triggers some showers and a few thunderstorms late tonight
into tomorrow morning, initially to our west, but then spreading
eastward into our area through the day on Thursday. Clouds
associated with this moisture keep the temperature at ground level
cooler, setting up an inverted low level profile. Any convection
will be elevated in nature above that inversion. That low level
stable layer will limit any severe weather threat with this
convection on Thursday to just hail. Guidance is still pretty
variable on how much instability is available, but it remains
possible that a few stronger storms could produce marginally severe
hail. This threat is reflected in the SPC Day 2 outlook. High
resolution guidance is also very variable on the timing of when
convective activity will be most likely or most intense, but it
appears there`s a general shift northeastward with time as the
subtle warm front aloft will likely be the primary focusing
mechanism for convection. This front shifts further northeast
Thursday night, likely shifting the convective threat north of our
forecast area.

While the incoming warm front does bring warmer air as well, the
expected cloud cover on Thursday will limit how much of this warmth
will be felt at the surface. NBM interquartile range for Max
temperatures is generally 5 to 8 degrees, fairly high for such a
short range forecast, reflecting uncertainty in cloud cover. If it
stays cloudy all day, the temperature will likely hold in the low to
mid 60s, but where the sun breaks out it could warm into the 80s.
Clouds and cooler weather are more likely to the north and east
while the best chance of seeing sun and the warm temperatures is
further to the west and south.

With the warm front lifting north of our area, the whole area gets
in on the warmth on Friday. Building heights aloft associated with
the arrival of the ridge should also suppress convection, making
Friday the driest (and warmest) day of the next several.

Kimble

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 226 PM CDT Wed Mar 26 2025

As the ridge shifts east and troughing takes over to our west, flow
aloft becomes more southwesterly Saturday and Sunday. While warm air
aloft should continue to suppress convection on Saturday, there is a
separate shortwave trough tracking east from the coast of Texas
through the lower Mississippi Valley Friday into Saturday. Renewed
moist advection associated with this trough may be enough to spread
some light rain showers into parts of our area on Saturday. This is
most likely in the southern and eastern portions of the forecast
area. The clouds and showers will also hold temperatures back
several degrees from Friday`s warmth, though areas that don`t see
rain may warm into the 80s.

An initial wave tracks to our north Saturday night, sending a cold
front southward behind it. A second wave tracks along this front on
Sunday as troughing moves out of the western US and into the Plains.
It`s this trough and frontal passage that represent our best
opportunity for severe thunderstorms as our low level moisture will
be maximizing (leading to greater instability) while winds aloft
will also be strengthening with the approaching trough (greater
shear). The timing and track of this wave will be important in
determining where the severe weather threat will be greatest. North
of the front much cooler air will be moving in, ending the threat
for any surface based instability. However in the warm sector ahead
of the front surface based instability will be maximizing and may
become uncapped, leading to the development of supercell
thunderstorms with a threat for all severe weather hazards including
tornadoes. However, the timing of that front and where it will be
when Sunday`s wave arrives is still uncertain. Southern areas stand
the best chance of still being in the warm sector and thus seeing
the severe weather threat mainly from the late morning into the
early evening.

The wave moves east Sunday night, fully shoving the cold front south
of our forecast area. This drops temperatures some 20-30 degrees
from the prefrontal warmth, holding only in the 40s and 50s on
Monday. It`s unclear how much precipitation will develop on the back
side of the wave, but we`ll have at least some precipitation chances
linger into late Sunday night.

Beyond Sunday there remains a good deal of spread in the guidance on
how to handle the overall upper flow pattern and thus the resulting
temperature and precipitation forecast across the region. It seems
clear that we`ll have at least one day of cooler and drier
conditions, possibly lasting into Tuesday. At least brief ridging
returns in the wake of the trough, though, so a warm up will be in
store by mid week. Precipitation chances will depend on whether
another trough can develop out west and track toward our area, but
there should at least be some access to Gulf moisture which would
enable rain chances should another wave move through the region.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1036 PM CDT Wed Mar 26 2025

A northwest to southeast oriented narrow band of showers is
expected to develop very early this morning, however, its exact
placement relative to the terminals remains uncertain. Confidence
has increased enough though in a shift in its general position
that now places all of the local terminals in play for potential
impacts. These impacts are expected to be reductions in
visibility due to passing showers, with drier low-level air
keeping ceilings VFR. Rain looks to become more persistent later
in the morning before tapering off around mid-day. Given the
narrow nature of this band of showers, it can`t be ruled out that
some of the local terminals see little no rain through the
morning. Shower chances may return during the afternoon at any to
all of the local terminals, however, confidence is very low on
the timing and placement of this activity relative to the local
terminals. While this potential second round has the greatest
chance of thunderstorms occurring, there is very low chance of
thunderstorms this morning, particularly at KJEF and KCOU.

Elmore

&&

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

$$

WFO LSX