878
FXUS63 KLSX 261944
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
244 PM CDT Sat Apr 26 2025

.KEY MESSAGES...

- There is a 50 to 80 percent chance of showers, a few weak
  thunderstorms late tonight into Sunday morning, mainly
  along/south of I-70 and west of the Mississippi River.

- Near-record high temperatures are forecast Monday, in the 80s
  to near 90 F.

- There is a 15 to 30 percent chance of strong to severe
  thunderstorms late Monday night and Tuesday afternoon and
  evening, with large hail and damaging winds the primary hazards.
  Tornado potential is low but non-zero.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 242 PM CDT Sat Apr 26 2025

Stratocumulus continues to erode and scatter from northeast to
southwest this afternoon upon drier air infiltrating the area within
low-level northeasterly flow, resulting in some sunshine before
additional upper-level clouds arrive ahead of an approaching
convectively induced mid-level trough or MCV. This MCV, associated
with ongoing showers and thunderstorms across OK and KS, is progged
to advance eastward into the Mid-Mississippi River Valley overnight
with 40 to 70 percent of HREF membership depicting scattered to
numerous showers accompanying the feature, mainly along and south of
I-70 and west of the Mississippi River late tonight into Sunday
morning. MUCAPE will generally be less than 100 or 200 J/kg but
enough to support a weak thunderstorm or two.

Isolated showers and thunderstorms could linger into Sunday
afternoon as low-level WAA persists and strengthens; however, mid-
level height rises in the wake of the MCV suggest a significant
decrease in coverage. Morning precipitation and clouds through most
of the day will offset the WAA and keep temperatures on Sunday
similar to today, perhaps slightly cooler where clouds remain most
prevalent.

Pfahler

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 242 PM CDT Sat Apr 26 2025

Southerly low-level WAA will persist through Monday with 850-hPa
temperatures exceeding the 90th climatological percentile, yielding
high temperatures well into the 80s F and flirting with near 90 F
and daily records (see CLIMATE section) with periods of stronger
insolation ahead of increasing upper/mid-level clouds later in the
day. Additionally, 10 to 20 percent of ensemble membership does
depict some mid-level/high-based showers and thunderstorms across
northeastern MO/west-central IL during late afternoon/evening.
However, more robust development of showers and thunderstorms,
including severe thunderstorms, will be to the west of the CWA
Monday evening along/ahead of a cold front and dry line. These
showers and thunderstorms will have the potential to track into
central and northeastern MO and west-central IL after midnight
Monday night with support from nocturnal strengthening of a
southwesterly LLJ; however, there is disagreement in shower and
thunderstorm coverage. Instability will be decreasing overnight but
around 1000 J/kg of MLCAPE and 40 to 50 kt of deep-layer wind shear
indicated by much of short-term model guidance supports a few
thunderstorms being strong to severe across those areas late Monday
night/early Tuesday morning, capable of large hail and damaging
winds, perhaps a tornado depending on how much the BL stabilizes.

Showers and thunderstorms from Monday night may still be ongoing on
Tuesday morning, but additional development is expected during the
afternoon near the cold front bisecting the CWA with an increasingly
unstable warm sector and broad large-scale ascent from an
equatorward upper-level jet entrance region along with mixed signal
for a passing MCV. The afternoon position of this front is not
completely clear with some potential augmentation by morning
thunderstorms, but a general increase in thunderstorms is expected
along and south of I-70 during the afternoon. Model guidance
advertise between 1000 and 3000 J/kg of MLCAPE and 35 to 45 kt of
deep-layer wind shear but with relatively straight hodographs and
weak low-level wind shear. Therefore, a mixed mode of splitting
supercells and multicell clusters is expected with large hail and
damaging winds the main hazards during the afternoon and evening,
mainly along/south of I-70. The tornado potential appears low given
veered surface winds, unless a locally more favorable environment
can emerge with thunderstorm outflows and a potential MCV.

Rounds of showers and thunderstorms will persist Tuesday night
through Thursday as the front wavers near and/or across the CWA and
mid-level perturbations/MCVs track along it within southwesterly
flow. A more substantial upper-level trough will traverse the region
sometime around Thursday, coinciding with when ensemble model
guidance has the highest probabilities (70 to 90 percent) of showers
and thunderstorms and the largest footprint. With multiple rounds of
thunderstorms, the NBM probability of total rainfall Tuesday through
Thursday exceeding 2" is 30 to 50 percent near the I-44 and I-70
corridors. NBM interquartile temperature ranges span 5 to 7 F
Tuesday through Thursday as well, but most of the distribution is
near to slightly above average.

Behind Thursday`s trough, upper-level northwesterly flow will favor
drier and slightly cooler conditions, albeit still close to average
per the NBM.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1232 PM CDT Sat Apr 26 2025

MVFR ceilings will continue to erode from northeast to southwest
early this afternoon with improvement to VFR flight conditions
becoming prevalent at all terminals. Late tonight through Sunday
morning scattered to numerous showers are expected to reach the
area, especially across central and southeastern MO. Therefore,
confidence is greatest in showers occurring at KCOU and KJEF with
relatively lower confidence at St. Louis metro terminals. MVFR
flight conditions could accompany some showers, with MVFR stratus
also developing at KCOU and KJEF through the morning. IFR ceilings
cannot be ruled out but confidence is too low for inclusion at this
point. Winds will gradually veer throughout the period from
northeasterly this afternoon to southeasterly Sunday morning.

Pfahler

&&

.CLIMATE...
Issued at 218 AM CDT Wed Apr 23 2025

Unseasonably warm temperatures are expected on Monday, nearing
daily records for late April. Here are the daily record highs
for April 28.

LOCATION        RECORD
ST LOUIS    92 set in 1970
COLUMBIA    88 set in 1970
QUINCY      88 set in 1970


&&

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

$$

WFO LSX