River Flood Warning 107, NWS St. Louis, MO

Area Forecast Discussion
National Weather Service St Louis MO
652 PM CDT Fri Jul 31 2026

.KEY MESSAGES...

- Showers and thunderstorms are expected this afternoon and
  evening. A few severe thunderstorms are possible. Damaging
  winds will be the primary threat, though a brief, weak tornado
  is possible.

- Much cooler air arrives tonight and extends through the
  weekend. High temperatures will be hard pressed to reach 80
  degrees at most locations.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 452 PM CDT Fri Jul 31 2026

Showers and thunderstorms remain possible this afternoon into late
this evening. A few thunderstorms may become strong to severe with
damaging winds being the primary threat. There is also a threat for
brief, weak tornadoes. This threat is largely confined to portions
of central, east-central, and southeast Missouri. Thunderstorm
potential is highest from 4PM to 10PM.

Latest radar and visible satellite imagery shows clouds breaking
west of the departing precipitation, which extends through interior
sections of Illinois near 19z. Clearing over central sections of
Missouri, where SBCAPE values have climbed as high as 2500 J/kg.
These value quickly drop from west to east and zero out along and
east of the Mississippi River. Where CAPE values drop off, a strong
capping inversion remains in place, which keeps the focus for
additional development to the west.

Surface observations show the cold front currently (19z) extending
roughtly from KIRK through Topeka, KS. Ahead of the front, surface
temperatures have warmed into 80s with a few low-90s and dewpoints
well into the 70s. Ample moisture and warmth resides ahead of the
front, along with a broad area of 35-40kts of 0-6km bulk shear. A
narrow corridor of 200-300 SRH extend north/south over the eastern
third of Missouri with impressive curvature to the hodographs. Aside
from the uncertainty in the eastward extent of SBCAPE, mid-level
lapse rates under 6C are also a limiting factor, though SPC
mesoanalysis indicates a brief resurgence of 6C rates over southeast
Missouri late this afternoon into early evening. Therefore, if
thunderstorms are able to develop, become surface-based, and lapse
rates recover enough, brief, weak tornadoes will be possible. These
conditions are most favored from parts of central Missouri through
southeast Missouri through this evening, where winds are become
backed with persistent southerly flow. Otherwise, the main threat
will be damaging winds. Probabilities for hail are low given the
lack of strong mid-level lapse rates and increasingly narrow CAPE.
Any thunderstorm will be capable of very heavy rainfall with rates
approaching 2in./hr. in the stronger thunderstorms. Localized
flooding is also possible, but there enough progression and lack of
a training setup to be too concerned with extensive flash flooding.

The upper level wave very slowly pivots east/southeast through the
weekend, though at times, may look stationary. This will keep rain
potential in the area through Saturday, primarily through peak
heating, when scattered showers will be supported. CAPE values under
1000 J/kg and mid-level lapse rates under 6C should limit
thunderstorm potential, though a low-topped thunderstorm can't be
ruled out. PWATs of 1.5-1.75 inches will support brief bouts of
effecient rainfall through the afternoon. Much of the same is
possible Sunday, though the chances will be limited to along and
east of the Mississippi River.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 452 PM CDT Fri Jul 31 2026

There isn't much to address in the long term period as long range
guidance is in fairly decent agreement, indicating that high
pressure settles into the Mid-Mississippi Valley Monday, Tuesday,
and possibly through Wednesday. Temperatures gradually warm through
the week, rising back to near/above normal.

The upper level trough that is giving rise to showers and
thunderstorms today into the weekend will slowly meander through the
Tennessee/Ohio Valley Regions as elongated ridging builds in behind
the system. NBM blends have been a little generous with rain
chances, skirting portions of the CWA Monday and Tuesday. Global
guidance isn't favoring this as we get onto the anticyclonic side of
the upper level trough late Sunday into early Monday. This pattern
seems to hold pretty well through Tuesday and even potentially into
Wednesday with surface high pressure parked under northwesterly mid
and upper level flow. Monday and Tuesday look quite pleasant by
August standards with highs in the 80s each afternoon.

Warmth and moisture continue to slowly climb through late week with
increasing chance for rainfall sometime between late Wednesday and
into Thursday. Global guidance isn't too dispersed with subtle
differences in the evolution of the upper level trough to the east
and an approaching cold front from the north. Front timing is likely
to adjust provided in extends well south of a Canadian low and
interacts with another surface low ejecting from the Plains. These
type of boundaries can often be influenced by increasing southerly
push, causing it to slow or even wash out, depending on the
aggressiveness (or lack thereof) the warm push. Rain chances are most
favored at the tail end of the period, though specifics with timing
and placement are likely to be fine tuned through the course of the
week.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 652 PM CDT Fri Jul 31 2026

A cold front, that is currently positioned from northeast to central
Missouri, has initiated several broken segments of showers and
thunderstorms, a few of which have been strong to severe. This
convection will continue to slide east along and ahead of the cold
front into this evening, with the main impacts expected to be low
MVFR/brief IFR visibilites/ceilings from thunderstorms. Widespread
low MVFR/IFR stratus is forecast to move in from the northwest
tonight with impacts expected at all terminals. Additionally,
scattered showers are expected on the backside of the system through
the late morning to afternoon tomorrow with potential visibility
impacts related to showers. Low MVFR/IFR stratus is forecast to
continue at all terminals through tomorrow evening with low
confidence on how quickly ceilings improve beyond the TAF. Lastly,
southerly surface winds around 10kts ahead of the cold front quickly
veer westerly behind the front. Northwesterly surface winds prevail
tomorrow increasing in magnitude throughout the day with sustained
winds 10-15kts gusting to 20-25kts into tomorrow evening.

&&

.CLIMATE...
Issued at 221 PM CDT Fri Jul 31 2026

Unseasonably cool temperatures are expected Saturday. High
temperatures will flirt with record min max (coolest high
temperature) for August 1st. Below are the record min max values
for each climate site:

Site		Record (Year)	Forecast

St. Louis   73 (1985)		76
Columbia 	71 (1985)		76
Quincy		73 (1973)		75

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

&&

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

&&

SHORT TERM...Maples
LONG TERM...Maples
AVIATION...Peine
CLIMATE...Maples