River Flood Warning 102, NWS St. Louis, MO

Area Forecast Discussion
National Weather Service St Louis MO
1050 PM CDT Thu Jul 9 2026

.KEY MESSAGES...

- A flash flood watch is in effect through Friday night in
  southeast Missouri and southwest Illinois, with multiple
  rounds of showers and thunderstorms expected.

- Some storms this evening and again Friday afternoon/evening
  may be strong to severe with damaging winds the primary
  threat each day.

- Dry weather along with above normal temperatures are forecast
  Sunday through the middle of next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 237 PM CDT Thu Jul 9 2026

GOES-19 visible satellite imagery shows 3, maybe 4 MCVs across
the region all moving eastward. One is near K3LF and the other
near KUIN. Both of these features has recently led to convective
initiation just east/southeast of each of these in west central
and south-central Illinois. One or two of these storms may be
on the stronger side with damaging winds the primary threat.
More convective development is expected by early this evening as
the low-level jet strengthens. Moisture convergence associated
with the low-level jet will also increase, and this combined
with an uptick in midlevel ascent downstream of the upstream
MCVs (one near OK-KS border and another possible MCV near KSTJ)
should lead to more widespread showers and thunderstorms. This
activity is expected to focus mainly across southeast Missouri.
Concern for flash flooding is increasing, as training is
expected through the early overnight hours in an environment
that is supportive of high rainfall rates (deep warm cloud
depths, anomalous precipitable water values). New cells should
develop on the west/northwest flank of the activity through the
early overnight hours as the low-level jet veers from the
southwest to the west. Past events with these setups tend to
have a narrow west/northwest to east/southeast axis of very
heavy rainfall on the west/southwest edge of the precipitation
shield. That may indeed occur again tonight, and if so, may
heavily impact a portion of a few counties in southeast
Missouri. The LPMM of the HREF has a narrow axis of 3-4" whereas
the REFS has almost double those totals. If training occurs
long enough, I would not rule out the higher-end potential of
the REFS LPMM. Due to this threat for significant rainfall
amounts and flash flood potential, a flash flood watch is now in
effect beginning this afternoon through Friday night across
southeast Missouri and a small part of southwest Illinois.

The heavy rain threat overnight tonight should end around dawn with
the stronger low-level moisture convergence shifting to the
east/southeast more toward the lower Ohio Valley. Mostly dry
conditions are then forecast through the remainder of the morning
hours across the area. Attention will then look to the west again.
Another MCV(s?) is likely to be moving across eastern Kansas by
midday. The exact track/timing of this feature is not certain,
nor is the environment ahead of it due to the morning showers
and thunderstorms. The effective front may be to our south,
though at least some sunshine should allow for instability to
climb ahead of the approaching MCV. Scattered showers and
thunderstorms are forecast across the area, though there may be
a bit more focus from central-southeast Missouri during the late
afternoon/evening time frame. Similar to today, damaging winds
should be the primary threat. Locally heavy rainfall will also
be possible as there will be little/no change in the environment
so efficient warm rain processes are expected. Areas that get
hit hardest tonight would be the main concern as soils may be
very saturated and any additional (even brief) heavy rainfall
could cause renewed hydrological issues.

The low-level jet increases again Friday night, though it does not
look as strong as tonight. Therefore, I think there will be another
uptick in the coverage of showers and thunderstorms, but the overall
threat for flash flooding likely will stay mostly confined to areas
that are hardest hit tonight as alluded to in the paragraph above.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 237 PM CDT Thu Jul 9 2026

(Saturday - Saturday Night)

Uncertainty on Saturday increases, in part due to the 2-3 rounds of
showers and thunderstorms anticipated before this time period.
Deterministic guidance though does show a midlevel shortwave trough
moving south/southwest almost beneath the amplifying mid/upper level
ridge to the west. Showers and thunderstorms are again possible
Saturday/Saturday night, mainly across southeast
Missouri/southwest Illinois, which should be closer to the
effective frontal boundary. If confidence increases in the
threat for showers and thunderstorms on Saturday, the existing
flash flood watch may need to be extended in time.

(Sunday - Next Thursday)

Not a lot has changed over the past 24 hours, with a historic record-
breaking mid/upper level ridge expected across the northern
Plains/Upper Midwest. Our area will be within deep northeasterly
flow aloft, so dry weather is expected. The low-level thermal ridge
is also forecast to stay well to our north, so 850-hPa temperatures
are actually pretty close normal (+16 to +20C). Nighttime lows are
forecast to be near seasonal averages, with daytime highs likely a
bit above normal due to plenty of sunshine expected each day.
Relative humidity (dewpoint) values also should tick down early next
week, aided by continued deep northeasterly flow. This means heat
index values should not be too much higher than the ambient air
temperature, and the chances of heat advisory duration criteria
(100+ for 4+ days) seem very small attm.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1048 PM CDT Thu Jul 9 2026

Main concern with the TAFs is the potential for thunderstorms,
as otherwise conditions should remain VFR with light winds. This
evening's batch of thunderstorms is expected to remain south of
the TAF sites and ends shortly after 06Z anyway. Another round
of storms is possible in the afternoon on Friday, arriving from
the west and pushing eastward through the evening. Confidence
remains somewhat low on the timing and track of the wave
triggering this, but for now we have included PROB30 remarks for
the time period where storms are most likely at each site.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Saturday morning for MOZ072>075-084-085-
     099.
IL...Flood Watch through Saturday morning for ILZ079.

&&

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Kimble