NWS St. Louis, MO wrote its last area forecast discussion before the first event at Jun 11, 1:43 PM CST, 2 hours 27 minutes earlier. Its key messages:
Area forecast discussion, Jun 11, 1:43 PM CST, 2 hours 27 minutes before
Area Forecast Discussion
National Weather Service Saint Louis MO
243 PM CDT Thu Jun 11 2026
.KEY MESSAGES...
- Another round of strong to severe storms is expected in most of
our area between late this afternoon and evening. Damaging
straight line winds and tornadoes are the most likely hazards,
with a more limited potential for large hail.
- Seasonable and dry conditions are expected tomorrow, but showers
and thunderstorms will again be possible at various times
between late tomorrow night and early Sunday. Some strong to
severe storms are possible, but forecast confidence is low.
&&
.SHORT TERM... (Through Late Friday Night)
Issued at 238 PM CDT Thu Jun 11 2026
After an early round of thunderstorms moved through portions of
northeast Missouri and west-central Illinois this morning, the
forecast remains on track for a more widespread round of strong to
severe thunderstorms this afternoon and evening. Damaging straight
line winds and tornadoes will be the most probable hazards
associated with these storms, with a more limited hail threat and
also the potential to worsen ongoing flooding mainly in northeast
Missouri.
While early morning storms have exited the area, allowing us to
cancel the previous Tornado Watch early, satellite and radar
observations indicate that the atmosphere is destabilizing quickly
behind it and ahead of an advancing cold front in northwest
Missouri. According to SPC mesoanalysis, as much as 3000-3500 J/kg
of largely uncapped MLCAPE is already in place, thanks to very rich
low level moisture featuring low to mid 70s dewpoints. As such, new
updrafts are already beginning to develop along the cold front in
northwest Missouri, and these storms are expected to continue to
expand and strengthen as the front overturns this extremely unstable
airmass.
Meanwhile, effective shear parameters across especially the
northern third of Missouri are more than sufficient to support
organized updrafts, ranging from 40 to 50 kt. Low level shear is
also relatively abundant (0-3km of 30-40kt, 0-1km of 20-30kt)
thanks again to a strong southwesterly low level jet. In spite of
the southwesterly surface winds, there is still at least some
clockwise curvature in the hodographs, although perhaps not as
enlarged as those further northwest. Finally, there appears to be
some semblance of an outflow boundary remnant from this morning's
round of storms, which may also add some additional low level
helicity if storms can manage to interact with it at the right
orientation.
All of this is to say that organized severe storms are very likely
this afternoon and evening, with all hazards on the table. Large
hail and tornadoes will be most likely with any supercells that
develop initially, although these storm modes are likely to occur
primarily to our west. Eventually, supercells are expected to grow
upscale into an expansive linear complex with embedded bowing
segments, possibly very quickly due to the strong forcing along the
front. Given the above parameters and a high probability of linear
storm modes, damaging straight line winds and QLCS tornadoes appear
the be the highest probability hazards. The latter threat appears
to be maximized across northern Missouri and west-central
Illinois where shear parameters are most favorable. Large hail in
the 1-2 inch range will also be possible, particularly with
isolated cells, but this potential will become more limited as
storms transition into a line. Finally, while these storms will be
progressive, we do expect brief heavy rain rates to occur given
the very rich moisture in place, and this may exacerbate ongoing
flooding issues in northeast Missouri and west-central Illinois.
Even an hour or two of heavy rain may be enough to cause flooding
in these areas, and considering that we had another round of rain
this morning, a Flash Flood Watch has also been issued through 7
PM to account for this.
Storms will steadily move southeast through the evening, and
eventually exit the area to the southeast sometime between 11 pm and
1 am. Severe storms will be possible at any time between roughly 4
PM and then, but will likely be maximized before roughly 10 pm when
instability is expected to be highest...which also places the
greatest threat area along and north of I-44.
BRC
&&
.LONG TERM... (Saturday through Next Thursday)
Issued at 238 PM CDT Thu Jun 11 2026
Overnight tonight, a cold front will move through the area, which
will usher in a more seasonable and mild airmass for early summer.
Clearing skies and light winds may also allow for some river valley
fog overnight as well, particularly in central/northeast Missouri
where skies will clear faster, and also in areas that have more
lingering surface moisture. Expect near average temperatures
tomorrow, with mostly clear skies and more comfortable humidity
levels.
While we will have Friday to provide a bit of a lull in our active
pattern, additional rounds of showers and thunderstorms are expected
Saturday and again Sunday as we enter a zonal flow pattern aloft.
Saturday in particular has a lot of moving pieces, including the
potential for early morning convection along the nose of a
strengthening low level jet, followed by possibly additional showers
and storms later in the day and again overnight/Sunday morning. Much
will depend on how each round evolves, and also on the passage of
subtle shortwaves through the day and overnight. While very little
confidence exists in the coverage or timing of strong or severe
storms, bulk parameters support the potential for this to occur at
some point during this window, and this threat will be evaluated
more closely in subsequent forecast packages. Beyond Sunday,
confidence is increasing that we will enter a relatively cool
pattern as a trough digs into the central U.S., although there may
be a few opportunities for showers periodically.
BRC
&&
.AVIATION... (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1218 PM CDT Thu Jun 11 2026
VFR conditions are in place early this afternoon, but widespread
MVFR cumulus clouds exist throughout the area and will remain so
until a round of showers and thunderstorms sweeps through late
this afternoon and evening. This round of storms will be brief,
but is expected to impact all local terminals at some point
between 21 and 02Z, first at COU/JEF/UIN, and later at
STL/SUS/CPS. Strong surface winds and brief heavy rain can be
expected with these storms, with a more limited potential for
hail. Brief visibility and ceiling reductions are both expected
as storms impact terminals.
Skies will clear behind these storms and a cold front will switch
breezy south-southwest winds to the northwest. Winds will weaken
overnight, and patchy fog is likely in some river valleys. This
has been included at the SUS and JEF TAFs as these sites are fog
prone in these conditions.
BRC
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 7 PM CDT this evening for Knox MO-Lewis MO-
Marion MO-Shelby MO.
IL...Flood Watch until 7 PM CDT this evening for Adams IL-Brown IL.
&&
WFO LSX