592 
FXUS63 KLSX 301137
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
637 AM CDT Thu Jul 30 2026

.KEY MESSAGES...

- Temperatures will remain a few degrees below normal today,
  mainly in the low to mid 80s with low humidity.

- The chance for precipitation increases tonight, and showers
  and thunderstorms will be likely across much of the area on
  Friday. A few storms could produce locally heavy rain late
  tonight and Friday. Additionally, a few of the strongest
  storms could produce large hail, damaging winds, and perhaps a
  brief tornado Friday afternoon and evening.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 335 AM CDT Thu Jul 30 2026

High pressure centered over northern Illinois will shift east into 
the Ohio VAlley over the next 24-36 hours.  A relatively cool, 
easterly breeze will keep temperatures in the mid to upper 80s in 
most locations, which is 2-3 degrees below normal for the end of 
July.  The air mass associated with the high is also relatively dry, 
with dew point temperatures as low as the mid 50s, and the easterly 
flow around the high will continue to push this drier air into the 
Mid Mississippi Valley today.

Winds will turn back to the south tonight as the high moves east and 
low pressure develops over the central Plains.  The short wave 
driving this low will move into the Upper Midwest overnight tonight, 
and should be centered over Minnesota by 12Z Friday.  The wave then 
moves slowly southeast Friday through Friday night with the low 
level reflection drifting from the eastern Plains to near or just 
east of the Mississippi River in Illinois by 12Z Saturday.  Low 
level southerly flow ahead of the system will bring moisture from 
the southeast Plains back to the region, and increasing chances for 
precipitation late tonight into Friday.  Precipitable water increases 
to 2-2.25 inches ahead of the cold front by Friday morning  This 
is around the 99th percentile of climatology making storms 
capable of heavy rain.  However, current indications are that 
convection will be progressive, so widespread flooding does not look 
very likely at this time.

Models are also showing CAPE values exceeding 2000 J/Kg Friday 
afternoon coinciding with around 30kts of deep-layer shear, mainly 
over central Missouri.  Forecast soundings show a decent amount of 
this CAPE in the hail growth zone, as well as an "inverted-v" in the 
low levels.  Large hail and damaging winds will are therefore the 
primary threats from thunderstorms Friday afternoon if clouds and 
precip from earlier in the day doesn't limit afternoon heating. 
There is also some low level directional shear, although it mostly 
moves along ahead of the greatest instability rather than coincident 
with it through the afternoon. Still, a few brief tornadoes will be
possible.  Storms should weaken through Friday the evening as 
daytime instability wanes, although scattered convection will 
continue through the night ahead of the short wave.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 335 AM CDT Thu Jul 30 2026

The surface low moves into eastern Illinois by Saturday afternoon. 
Cold advection on the west side of the low along with continuing 
showers and clouds should produce a cool day with highs struggling 
to reach the upper 70s.  This will likely be the coolest day of the 
next 7, although the latest model runs keep temperatures below 
normal at least through Monday.  High pressure moves into the 
Midwest on Sunday as the short wave continues digging and amplifies 
the long wave trough over the eastern U.S.  This should put an end 
to most of the precip, although some isolated showers remain 
possible Sunday afternoon over southern Illinois and southeast 
Missouri as moisture wraps around the western side of the low level 
wave over the lower Ohio Valley.  Medium range guidance shows the 
long wave pattern shifting eastward through midweek with the upper 
level ridge stretching into the Mid Mississippi Valley. Temperatures 
gradually warm up, finally reaching the upper 80s to around 90 by 
Wednesday. Dew point temperatures also rise gradually, and heat 
index values could be back to around 100 degrees Wednesday afternoon.

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 632 AM CDT Thu Jul 30 2026

VFR flight conditions and light east to southeast flow will
prevail across the area through this evening. Scattered showers
and thunderstorms are expected to move into central and
northeast Missouri as well as west central Illinois before 12Z.
The precipitation will continue moving east Friday, likely 
reaching east central Missouri between 14Z and 18Z.


&&

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

&&

$$

SHORT TERM...Carney
LONG TERM...Carney
AVIATION...Carney