873
FXUS63 KLSX 051725
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1225 PM CDT Fri Jun 5 2026

.KEY MESSAGES...

- There are daily chances for showers and thunderstorms through early
  next week.

- Heat and humidity will build through next week. The coolest days
  of the week will be Sunday and Monday.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 310 AM CDT Fri Jun 5 2026

Thunderstorms in northwestern Missouri continue to very slowly push
east through the state. A strengthening low-level jet will cause
coverage to increase through sunrise, but a lack of abundant surface
based instability and bulk shear will keep these thunderstorms sub-
severe. Convection will continue to peter out through the morning
and early afternoon as pushes east into increasingly strong mid-
level subsidence. Despite ample SBCAPE on the scale of 2000 - 3000+
J/kg expected this afternoon, a lack of any lift or forcing
mechanisms and a stout capping inversion (for some) will stave off
redevelopment. The only possible exception to this will be in
northeast Missouri and west-central Illinois, areas closest to
marginally stronger mid-level lift, but confidence is low in this
occurring. Tonight, remnant convection is expected to dive south out
of Iowa, weakening and dissipating as it nears our border around
sunrise Saturday. If any thunderstorms remain strong to severe as
they arrive, brief and isolated 1" diameter hail and damaging winds
would be the primary threats. As confidence in this happening is
low, we will not be messaging the SWODY1 Slight Risk.

By Saturday afternoon, a mid-level closed low will be pushing
northeast through the Southern Plains as it ejects vorticity lobes
into the Mid-Mississippi Valley. This nebulous lift and 2000+ J/kg
of SBCAPE will allow for isolated to scattered thunderstorms during
the afternoon, and <15 kts of effective bulk shear will keep
convection disorganized. Perhaps more notable will be the heat and
humidity. REFS probabilities of dewpoints >69 degrees reach 80% for
the majority of the CWA Saturday afternoon. With highs hovering in
the 85 to 90 degree range, this translates to heat index values in
the low to mid-90s. It will definitely feel like summer.

Jaja

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 310 AM CDT Fri Jun 5 2026

The aforementioned mid-level closed low will weaken as it passes
through the Mid-Mississippi Valley Sunday and Monday. This feature
will bring with it additional chances for showers and thunderstorms
these days, but continued scarce shear (<20 kts) will limit the
potential for organized, and by extension, severe convection. The
cloud cover and precipitation will keep temperatures relatively cool
on Sunday and Monday, but to what extent will depend on the duration
of precipitation at any given location. Those that see less(more)
rain will be able to warm more(less).

Mid-level ridging is forecast to dominate the eastern 2/3 of the
CONUS by midweek. With no fronts to sweep the accumulated low-level
moisture from the area, humidity will only continue to increase
within an ever-heating airmass atop the region. Conditions will
become more oppressive over time. Confidence is high in temperatures
reaching the 90s each afternoon by Wednesday, as even the NBM 10th
percentile at KSTL reads 89 degrees. How far into the 90s we get is
uncertain, but with a 60-70% chance of dewpoints reaching 75+
degrees from Wednesday onward, the air will feel like a weight on
your back regardless.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1225 PM CDT Fri Jun 5 2026

Showers and thunderstorms continue to gradually wane as they reach
east-central MO and south-central IL early this afternoon, likely
before reaching St. Louis metro terminals. Otherwise, MVFR ceilings
will also lift early this afternoon with areawide VFR and
predominantly dry flight conditions through most of the rest of the
TAF period. That being said, there are low chances (20 percent or
less) of showers and thunderstorms at KUIN this evening through
overnight and then Saturday afternoon across much of the region.
However, confidence is very low in any impacts at the terminals.
Additionally, a period of MVFR ceilings is favored at KCOU, KJEF,
and KUIN Saturday morning. Winds will vary between southwesterly and
southerly with gusts diminishing this evening.

Pfahler

&&

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

$$

WFO LSX