River Flood Warning 141, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
526 AM CST Mon Nov 4 2024

.KEY MESSAGES...

- On and off rain, heavy at times, continues today into tonight.
  One final round of thunderstorms is expected to move in from
  the west this evening and cross the region tonight.

- Thunderstorms tonight will have the potential to produce
  damaging winds and tornadoes, mainly in the evening hours.
  It's unclear how quickly these storms will weaken as they move
  east overnight.

- We will get at least a couple of days break from the rain this
  week with dry conditions and seasonable temperatures through
  midweek. The next rain chances come this weekend.

&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 249 AM CST Mon Nov 4 2024

Early this morning we continue to be underneath a deep southwesterly
flow aloft between a deep trough over the Southwest US and a high
amplitude ridge over the East Coast. Wave after wave of
thunderstorms have been developing over the Southern Plains the last
few days where moisture continues to be fed northward on a low level
southerly flow. From there, the moisture advects northeastward with
the mid level flow in the form of showers and embedded
thunderstorms. This morning the southerly flow is riding up and over
a surface warm front stretching from southern Oklahoma through
northern Arkansas, serving as the primary focusing mechanism for
storm initiation. This puts much of our area downstream with a
near continuous area of moderate rainfall.

PWATs over 1.6 inches, near the max for this time of year,
indicate a very moisture-rich environment leading to heavy
rainfall totals. Thankfully, though, so far this rain has been
coming down at a steady pace (0.25 to 0.5 per hour) onto dry
ground that is able to quickly absorb it. The best potential for
flash flooding would be with any more intense convection which can
develop and produce heavier rainfall rates (1 to 2 inches per
hour). This has thus far been limited by weak instability.
However, the low level warm front does extend northeastward into
southeast Missouri and will serve as a focus for new shower and
thunderstorm development for the next several hours. If a bit more
instability develops then rainfall rates could quickly ramp up
and a greater flash flood threat could develop. While this
potential does exist through this morning across southeast
Missouri, confidence is fairly low that we will get the
instability needed to produce the rainfall rates necessary for
flash flooding.

Convective initiation along the warm front tapers off around mid to
late morning which may lead to a relative break in the rainfall from
midday into the afternoon. Although the moist southwest flow does
continue while the warm front lifts north so some on and off showers
remain possible through the day. The upper trough begins to move out
of the southern Rockies and into the Plains today. As it does so,
greater synoptic scale forcing will lead to a more focused area of
lift along and ahead of a Pacific style cold front. This will
initiate a line of thunderstorms over Oklahoma and Kansas which will
move steadily eastward this evening and through the overnight hours.

The environment ahead of the front is characterized by very strong
shear, including low level directional shear, but with more limited
surface based instability. Instability is greatest across Kansas and
Oklahoma and into western Missouri late this afternoon and this
evening, and it's this area that has the greatest severe weather
threat. Damaging winds and tornadoes are the primary severe weather
hazards, but extreme PWATs suggest heavy rainfall rates will also
accompany these storms. There is some potential for training
especially toward the more northern portion of the line where the
warm front may also play a role in convective initiation. Here the
line may move more slowly, allowing greater residence time in the
heavier downpours and thus greater overall rainfall amounts. This
will come with at least some threat for flash flooding, although we
continue to think that threat is low due to a lack of overlap with
the more significant rainfall this morning.

Instability decreases with eastward extent, and the broader
convective line will be entering our area after 6PM tonight when
surface based instability will be becoming diurnally limited. So
we expect the line to weaken as it moves east this evening,
although just how quickly it does so is a bit unclear. Considering
the strong synoptic forces at work, it's possible that more
surface based instability remains into the evening even as the
line reaches the Mississippi River near or after midnight. While
the convective line is the dominant feature, it is also possible
that more discrete thunderstorms develop ahead of the line in the
mid afternoon. If this occurs, the storms will quickly develop
into supercells with the potential for tornadoes in the highly
sheared environment. Storms along the dominant line are more
likely to be multicellular with the potential for QLCS tornadoes
and damaging winds.

The line of thunderstorms, and the cold front, continue pushing
eastward overnight and into Tuesday. The rainfall ends with the
passage of the front, so rain chances decrease from west to east
through the day Tuesday. The air mass behind this front is not
particularly cold, but it is drier. Temperatures Tuesday will be
seasonable, in the 60s.

Kimble

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 249 AM CST Mon Nov 4 2024

The trough heads off to the northeast, so the low level front loses
its push eastward not long after it exits our area on Tuesday. This
means our area will get into the drier air, but the low level
moist air mass does remain lurking not too far away over the Deep
South and the Ohio Valley. We'll have at least a couple days break
from the rain with seasonable temperatures, near 60 for highs,
and some cooler nights in the drier air (40s).

Meanwhile, the next trough is moving onshore into the Pacific
Northwest today and will dig toward the Four Corners by midweek
helping to perpetuate the southwesterly flow through the middle
of the country. The low level moisture will begin to ooze back to
the west and north later in the week just in time for this trough
to exit the Rockies and into the Plains. This sets up our next
round of rainfall which should be of shorter duration this time.
Model guidance varies on how quickly the trough exits, so there
is some timing uncertainty on the rain. NBM PoP maxes out at 50-60
percent on Saturday as this is when the majority of the guidance
brings the trough through our area. However, our confidence in
rain is considerably higher than that (near 100 percent), we're
just not sure if we'll see that on Friday, Saturday, or Sunday.
The result is the PoP gets spread out over each of those periods
due to that timing uncertainty even though we know it won't be
raining all 3 days. At this time it's unclear whether we will get
into the warm sector ahead of this wave. If we do, then there will
be a greater threat for thunderstorms and more significant
rainfall.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 521 AM CST Mon Nov 4 2024

This morning an area of rain with embedded thunder continues to
push northeast across parts of the area, including the St Louis
metro. Ceilings within this are mostly VFR, although some MVFR and
IFR ceilings have developed further west across central Missouri.
Expect the area of rain to continue through mid to late morning
before finally exiting to the northeast. Cannot rule out thunder
during this time period, but confidence is too low to include it
in a TAF. MVFR ceilings are likely to develop as the rain ends.
Later this afternoon into the evening, another round of
thunderstorms is expected to move slowly from west to east with
enough confidence in the timing of this round to include it in the
TAF. Some of these storms may have strong winds in central
Missouri, although the chances of strong winds decreases as the
storms move east overnight. Ceilings will mostly hover around MVFR
although IFR at times is possible before some clearing begins on
Tuesday.

Kimble

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
305 AM CST Mon Nov 4 2024

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-050915-
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL-
Calhoun IL-Jersey IL-Madison IL-Saint Clair IL-Monroe IL-Knox MO-
Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO-
Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO-
Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO-
Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO-
Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
305 AM CST Mon Nov 4 2024

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...Today and tonight.

Thunderstorms are expected today and tonight. Some could be severe,
mainly in central Missouri this evening. The primary threats are
damaging winds and a few tornadoes, along with locally heavy
rainfall.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Thunderstorms end Tuesday morning. Otherwise no hazardous weather is
expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Kimble

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Preliminary Local Storm Report
National Weather Service St Louis MO
814 AM CST Mon Nov 4 2024

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

0753 AM     Flash Flood      4 SSE Black             37.48N 90.90W
11/04/2024                   Reynolds           MO   Law Enforcement

            Water over the road at intersection of
            Highway 21 and Highway 49.

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
815 AM CST Mon Nov 4 2024

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

0758 AM     Flash Flood      6 SSW Belleview         37.60N 90.79W
11/04/2024                   Reynolds           MO   Law Enforcement

            8 inches of swift moving water over the
            roadway at Highway N near the Reynolds
            county border.

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
830 AM CST Mon Nov 4 2024

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

0752 AM     Flash Flood      1 WSW Iron Mountain     37.69N 90.66W
11/04/2024                   Iron               MO   Law Enforcement

            At State Highway U and County Road 31 water
            over the bridge along the St. Francios River
            pushed a car over the bridge.

&&

Delia