338
FXUS63 KLSX 031949
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
249 PM CDT Wed Jun 3 2026

.KEY MESSAGES...

- Predominantly dry conditions will continue through Thursday.
  Near daily chances of showers and thunderstorms are expected
  Friday into next week.

- Seasonably warm temperatures will prevail through next week
  along with increasing humidity.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 248 PM CDT Wed Jun 3 2026

An upper-level ridge, over the Mid-Mississippi River Valley this
afternoon, will shift eastward away from the region through Thursday
leading to the departure of a surface anticyclone and increasingly
southwesterly low-level flow that becomes established on Thursday.
With increasing surface winds and thin upper-level clouds, low
temperatures will be several degrees warmer tonight than last night
and in the mid-50s to low-60s F. Patchy river valley fog is also
possible in the Ozarks if clouds remain thin enough through day
break Thursday. The strengthening and veering low-level flow will
more importantly begin to advect a warmer and more moist airmass
northeastward into the CWA with enough instability and decreasing
influence from the ridge to potentially yield isolated showers and
thunderstorms in central and northeastern MO during late
afternoon/evening. But the highest probabilities of showers and
thunderstorms reside just west and northwest of the CWA.
Accordingly, high temperatures on Thursday will be several degrees
warmer than today and further into the 80s F.

Pfahler

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 248 PM CDT Wed Jun 3 2026

Between late Thursday night and Friday morning, an upper-level
trough and nocturnal, veering LLJ will result in showers and
thunderstorms tracking eastward across IA and northern MO, with 50
to 70 percent of ensemble model membership having these showers and
thunderstorms reaching northeastern MO/west-central IL during the
morning into early afternoon. Similar probabilities expand across a
larger portion of the CWA along/northwest of I-44 (MO) and I-55 (IL)
during the afternoon and evening, but greater coverage of showers
and thunderstorms at that point in the day would seemingly require a
slower passage of the trough with lingering large-scale ascent.
Diurnal instability and a weak capping inversion, however, suggests
at least isolated development during peak heating in the afternoon
and evening. High temperatures on Friday are forecast to be similar
to Thursday but will depend on cloud debris and the amount of shower
and thunderstorm development during the afternoon. A similar
evolution of showers and thunderstorms is expected on Saturday
morning with the passage of another upper-level trough, but
indications point to the trough and highest probabilities of showers
and thunderstorms passing a little further to the north of the CWA.

Daily opportunities for showers and thunderstorms will persist
through early next week as the warm and moist airmass further
entrenches the CWA with the most favored times for showers and
thunderstorms generally during each afternoon and evening when
(weakly capped) instability is maximized, but overall ensemble model
probabilities of measurable rainfall are highest (60 to 80 percent)
when an upper-level low/trough lifts northward through the Central
Plains and Mid-Mississippi River Valley Sunday and Monday. With
little change in airmass, seasonably warm high temperatures in the
80s F are still supported, but scenarios with greater precipitation
and associated cloud cover would result in cooler temperatures.
Unsurprisingly, the largest NBM high temperature interquartile
ranges (5 to 7 F) are on Sunday and Monday when shower and
thunderstorm chances are greatest.

Overall, this relatively wet and active period looks to feature
predominantly innocuous, poorly organized thunderstorms with a lack
of appreciable vertical wind shear. However, environmental
parameters could still support isolated gusty winds from microbursts
as well as locally heavy rainfall with precipitable water near the
95 to 99th climatological percentile and deep warm cloud depths
resulting in very efficient rainfall processes, especially Sunday
onward. That being said, the details of any part of this pattern are
difficult to discern.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1236 PM CDT Wed Jun 3 2026

Dry and VFR flight conditions are likely to prevail into Thursday
afternoon across the region along with light winds. The only
exception is the potential for patchy river valley fog early
Thursday morning, but confidence is low that river valley terminals
will be impacted.

Pfahler

&&

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

$$

WFO LSX