806
FXUS63 KLSX 281721
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1221 PM CDT Sat Jun 28 2025

.KEY MESSAGES...

- The chance for showers and thunderstorms will continue through Monday,
  with the best chances (70-80%) being Sunday and Monday.

- Warm and humid conditions will continue through Sunday before a
  cold front on Monday brings seasonable temperatures to the area
  through mid next week.


&&

.SHORT TERM... (Through Sunday Night)
Issued at 247 AM CDT Sat Jun 28 2025

Quasi-zonal to southwesterly flow stretches over much of the Plains
and Midwest as the upper-level ridge struggles to maintain its hold
over the CONUS. Weak convergence over southeastern Missouri and
southwestern Illinois continues to produce low probabilities (around
20%) for isolated showers and possibly a thunderstorm across this
portion of the CWA this morning. Patchy fog can`t be ruled out
through the remaining pre-dawn hours thanks to minimal dew point
depressions and recent rainfall. However, persistent light winds are
expected to mostly mitigate this threat.

Subtle disturbances riding the periphery of the ridge will keep a
continuous stream of mid to upper-level clouds feeding into the CWA
through the day, mainly along and south of I-70. This will keep
temperatures subdued in this portion of the CWA compared to as of
late, with values struggling to warm out of the 80s where cloud
cover is more persistent and dense. Where sunlight can be more
consistent - mainly north of I-70 - afternoon highs around 90 and
into the low 90s are expected.

What this means for the chance for showers and thunderstorms today
is uncertain, as CAMs have been fluctuating in the occurrence and
coverage of convection. Reasons for this are likely the
aforementioned cloud cover limiting heating, as well as subtle
height rises seen in some guidance. Where instability can build,
SBCAPE will be similar to yesterday, with 2,500 J/kg or higher
forecast. However, bulk shear is weaker among the majority of
guidance, with only 5-10 kts expected. All this leads to lower
chances for scattered showers and thunderstorms this afternoon
compared to yesterday, with chances (30%) being maximized over
southeastern Missouri where a weak front and subtle boundaries from
previous convection will exist.

Sunday is similarly forecast, though the chance for showers and
thunderstorms greater (60-80%). This is due to falling heights as an
upper-level trough digs into the Midwest, an approaching cold front,
and subtle disturbances rippling through the flow over the Midwest.
We`ll have to keep our eye on a complex of storms that guidance has
consistently been dropping southward out of Iowa Sunday evening and
overnight. The most favorable track for this system is just west of
the CWA where instability is maximized, but these weakly forced
systems are notorious for changing trajectory as lead time decreases
and subtle features become increasingly resolved.

Elmore

&&

.LONG TERM... (Monday through Friday)
Issued at 247 AM CDT Sat Jun 28 2025

At the start of the workweek, a trough will be digging southeastward
into the Midwest per deterministic and ensemble guidance, pushing
Sunday`s cold front further southward. This front will serve as the
focus for showers and thunderstorms as the lift from the trough
increases, though guidance still varies on the front`s placement on
Monday. While it is generally expected to be stretched from the Ohio
Valley into the Mid South, if it is too far south of the CWA, much
of the area will be dry on Monday. If the front is further north and
closer to the CWA, portions of the CWA will see showers and
thunderstorms. With this solution, the most likely (60-80%) areas
for rainfall are southeastern Missouri and southwestern Illinois,
and this is supported by a majority of guidance.

The more notable story with this front is the post-frontal airmass.
As northwesterly flow aloft ushers in an area of high pressure at
the surface, temperatures Tuesday through Thursday will be more
seasonable than they have been as of late. Guidance has actually
trended a couple of degrees cooler over the last couple of
initializations, with ensemble means favoring highs in the mid to
upper 80s for much of the CWA.

This relative cool down will be short lived, as guidance continues
to converge on a solution favoring an upper-level ridge building
back into the Midwest Friday into next weekend. While the timing and
amplitude of this ridge vary notably among guidance, the general
pattern favors warming temperatures and a return of more widespread
low rain chances.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1218 PM CDT Sat Jun 28 2025

Mostly VFR conditions with light winds are expected today and
tonight outside of thunderstorms. The primary threat area for
thunderstorms this afternoon is across southern Missouri. This has
the best chance of reaching toward JEF in the next few hours,
though there`s an outside chance of a storm reaching up into the
St Louis metro as well. This activity is expected to die down
around sunset. Additional storms may develop overnight associated
with a weak convective vortex drifting across southern Missouri.
There`s a bit more confidence in this round of storms owing to the
more clear forcing associated with it, however there remains
uncertainty on the location and timing of its impact. These have a
slightly better chance of reaching into the St Louis metro Sunday
morning and this has been included via the PROB30 designation for
now.

Kimble

&&

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

$$

WFO LSX