River Flood Warning 81, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 PM CDT Wed Jun 10 2026

.KEY MESSAGES...

- Showers and thunderstorms are expected this afternoon and
  evening, in northeast MO and west-central Illinois, posing a
  threat of flash flooding, damaging winds, and a few tornadoes.

- A cold front will drive another round of strong to severe
  thunderstorms through most of the area tomorrow evening and
  overnight, with damaging winds and tornadoes as the most likely
  hazards.

- Another round of similar early-season heat is expected tomorrow
  with heat index values of 95-105 degrees, although breezy winds
  will mitigate this slightly.

- Additional strong to severe thunderstorms are possible in some
  areas Saturday, but confidence in these storms is much lower.

&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 247 PM CDT Wed Jun 10 2026

An active 48 hours of weather is in store for the region, with
multiple opportunities for thunderstorms capable of damaging winds,
flash flooding, and even tornadoes. The first of these rounds of
storms is already ongoing in northeast Missouri thanks to a passing
shortwave, which triggered the development of early morning
elevated storms in northwest Missouri several hours ago. These
storms have steadily strengthened and moved east, and are now
slowly moving through northeast Missouri and west-central Illinois
as of 1:00 PM. For this initial round, the primary concern is
heavy rain, although the potential for damaging downburst winds
may also slowly increase as surface-based instability increases.
SPC mesoanalysis indicates that a corridor of 2-2.2 inches of
precipitable water has developed along the nose of a relatively
robust low level jet, and this is feeding directly into the
ongoing storms. While they are steadily moving east, they are not
doing so particularly quickly, and when combined with likely 1 to
2 inch per hour rain rates, localized flash flooding will be
possible. Fortunately these areas have not seen quite as much rain
as other areas over the past few days, but this is likely not
enough of a mitigating factor to eliminate this threat.

This initial round is likely to last another couple of hours, and
move east of the area by roughly 3 to 4 PM. Even if we manage to
escape widespread flash flooding issues with this initial round
though, it likely will act to saturate some areas in advance of the
next round of thunderstorms later this evening. While these storms
are acting to stabilize the lower levels in the immediate vicinity,
satellite imagery reveals plenty of clearing behind this round, and
mesoanalysis also indicates that a very unstable airmass
(3000-3500 J/kg MLCAPE) is being quickly reinforced just to the
west across northwest Missouri. This is likely due to the presence
of the aforementioned low level jet, which is drawing warm and
humid air quickly in to replace the shallow cold pool behind these
storms. Not to mention, 2+ inch PWAT values also extend well to
the west and even into far northeast Kansas, so there will be
plenty of fuel for more heavy rain with the next round. As storms
arrive from the west, confidence is growing that a line of storms
will slowly pivot into our area and become oriented almost
parallel to the mean flow, potentially leading to training cells
with very heavy rain rates. This also may occur over the same
areas that are seeing heavy rain now, exacerbating the threat. All
told, totals of 3 to 6 inches of rain will be possible between
this afternoon and early tomorrow morning, primarily across
northeast Missouri and west-central Illinois. A Flash Flood Watch
has been issued in these areas until 6 AM tomorrow to account for
this.

Not only this, but there is also amble effective bulk shear
collocated with all of this instability (40-50kt), which will also
support organized convection capable of severe thunderstorm hazards.
Current shear parameters and initially clockwise-turning hodographs
suggest that while supercells may develop to our west, as discussed
previously these storms are very likely to grow upscale into a
linear complex of storms. As such, damaging straight line winds (60-
75mph) will be the most likely (non-water) hazard in our area,
although considering the 30-35kt 0-3km shear and likely presence of
a lingering outflow boundary, QLCS tornadoes will be possible as
well. Hail does not appear to be a significant hazard, unless a
stray supercell manages to remain isolated long enough to reach our
area. The most significant hazards for the second round are most
likely locally between about 7 PM and 11 PM, with a gradual
weakening as storms move east-southeast through the night. Storms
are expected to exit the area or diminish prior to sunrise, laying
down an outflow boundary somewhere across our area in the morning.
This will set the stage for tomorrow's threat, which will be
discussed in more detail in the Long Term discussion below.

BRC

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 247 PM CDT Wed Jun 10 2026

In the wake of tonight's storms, persistent south-southwest return
flow is likely to maintain a hot and humid airmass across our area,
although the distribution of greatest instability may be impacted
by outflow from morning activity if it persists later than
currently expected. In the afternoon and evening, a shortwave will
drive a sharp cold front southeast through Missouri and
eventually Illinois, which is expected to overturn this unstable
airmass and produce another round of strong to severe
thunderstorms across much of the area.

While most of the early part of the day should be dry, temperatures
in the low to mid 90s coupled with low to mid 70s dewpoints should
yield 3000-4000+ J/kg of surface-based CAPE by mid to late
afternoon. Initial storms are expected to develop along the boundary
to our west in northwest Missouri during the early to mid afternoon,
grow upscale into another line, and steadily move through our area
during the evening hours. As it does so, damaging straight line
winds appear to be the most likely hazard with these storms,
followed closely by QLCS tornadoes thanks to continued southwesterly
30-40kt 0-3km shear and perhaps the presence of another lingering
outflow boundary. What separates tomorrow's severe threat from
tonight's is most coverage, as stronger storms are likely to spread
further southeast and impact a larger portion of the forecast area.
These storms likely will also feature heavy rain rates but will be
more progressive than tonight's storms, which should mitigate the
threat of another round of flash flooding. The most likely window
for severe hazards will be between 6 to 11 pm, although this may
linger a little bit later into the night. Thunderstorms, severe or
not, should exit the area to the southeast prior to sunrise.

Lastly, tomorrow is also expected to be the third day in a row
featuring early season heat, with heat index values ranging from
generally 95 to 105 degrees (highest in the St. Louis metro area).
This still falls just a bit short of Heat Advisory levels, but may
cause problems for those sensitive to heat or otherwise unprepared
for these conditions this early in the season.

While Friday will feature largely dry conditions and milder
temperatures in the wake of the passing cold front, an active, quasi-
zonal flow regime will maintain an active pattern over the weekend
and potentially into next week. In particular, Saturday may see
another round of strong to severe thunderstorms, although with
multiple rounds of strong to severe storms just over the next 24-36
hours, most forecast attention was given to the shorter-term
hazards for this forecast package.

BRC

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1125 PM CDT Wed Jun 10 2026

Area of showers and thunderstorms across northeast Missouri and
west central Illinois will continue to bring MVFR conditions to
UIN through 08Z as it moves southeast. I now expect this area to
stay out of the COU/JEF, but it may still affect the St. Louis
area terminals, so have kept a PROB30 group going until 08Z. Then
mainly dry weather and VFR conditions are expected through 18Z
tomorrow with an increasing chance for showers and thunderstorms
along a cold front tomorrow afternoon and evening that will move
from northwest to southeast across the area. The best timing for
thunderstorms at UIN/COU/JEF will be between 21-01Z and at the
STL/SUS/CPS between 00-04Z on Thursday evening. The strongest
storms will reduce visibilities and ceilings to MVFR/IFR
conditions and will also have the potential to produce hail and
wind gusts to 35 knots. Winds will gust into the 25 to 30 knot
range on Thursday afternoon outside of thunderstorms.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 7 AM CDT Thursday for Knox MO-Lewis MO-Marion
     MO-Shelby MO.

IL...Flood Watch until 7 AM CDT Thursday for Adams IL-Brown IL-Pike
     IL.

&&

WFO LSX

Preliminary Local Storm Report
National Weather Service St Louis MO
959 PM CDT Wed Jun 10 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0956 PM     Flash Flood      2 N Edina               40.20N 92.18W
06/10/2026                   Knox               MO   911 Call Center

            State highway 15 just north of Edina closed
            due to high water.

&&

JPG

Preliminary Local Storm Report
National Weather Service St Louis MO
1015 PM CDT Wed Jun 10 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1006 PM     Flash Flood      7 E Colony              40.24N 91.84W
06/10/2026                   Lewis              MO   911 Call Center

            Water over road at State Route E and 160th
            Avenue.

&&

JPG