Flash Flood Warning 36, NWS St. Louis, MO

775 
WGUS73 KLSX 121005
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
505 AM CDT Sat Aug 12 2023

MOC163-121130-
/O.CON.KLSX.FF.W.0036.000000T0000Z-230812T1130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Pike MO-
505 AM CDT Sat Aug 12 2023

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 630 AM CDT THIS 
MORNING FOR CENTRAL PIKE COUNTY IN NORTHEASTERN MISSOURI...

At 505 AM CDT, Doppler radar indicated thunderstorms producing heavy 
rain across the warned area. Between 3 and 4 inches of rain have 
fallen. Flash flooding is ongoing or expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Bowling Green, Eolia, Clarksville, Curryville, Tarrants, Hamburg, 
  Paynesville, Annada, Cyrene, Edgewood, St. Clement and Ashley.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

In hilly terrain there are hundreds of low water crossings which are 
potentially dangerous in heavy rain. Do not attempt to cross flooded 
roads. Find an alternate route.

&&

LAT...LON 3923 9118 3927 9143 3942 9145 3940 9094
      3939 9093 3938 9091 3931 9079 3927 9075
      3926 9073 3922 9072

FLASH FLOOD...RADAR INDICATED

$$

MRB

510 
WGUS73 KLSX 121055
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
555 AM CDT Sat Aug 12 2023

MOC163-121105-
/O.CAN.KLSX.FF.W.0036.000000T0000Z-230812T1130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Pike MO-
555 AM CDT Sat Aug 12 2023

...FLASH FLOOD WARNING IS CANCELLED FOR CENTRAL PIKE COUNTY IN 
NORTHEASTERN MISSOURI...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Please continue to heed remaining road closures.

LAT...LON 3923 9118 3927 9143 3942 9145 3940 9094
      3939 9093 3938 9091 3931 9079 3927 9075
      3926 9073 3922 9072

$$

MRB

Area Forecast Discussion
National Weather Service Saint Louis MO
329 AM CDT Sat Aug 12 2023

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 329 AM CDT Sat Aug 12 2023

As of 08z this morning, thunderstorms across central MO into south-
central IL have become organized into a mixed multicell thunderstorm
mode including small bowing line segments and embedded supercells.
With MLCAPE of 2500 to 3500 J/kg and deep-layer wind shear of 35 to
45 kt, these thunderstorms will likely maintain much of their
intensity through much of the early morning hours as they move
southeastward through most of the rest of the CWA at the nose of a
veering southwesterly LLJ. Although these thunderstorms may be
slightly elevated atop a nocturnally stabilized BL, the strongest
ones should still be able to produce damaging winds with plentiful
DCAPE and 25 to 35 kt of 0 to 3 km wind shear. Additionally, any
supercell thunderstorms could produce large hail. A brief tornado
cannot be ruled out with mesovortex generation accompanying any
bowing segments. It is still unclear how much upscale aggregation of
thunderstorms into a larger MCS will occur as CAMs have offered
little assistance given their poor performances with thunderstorm
evolution thus far. With backbuilding and training of thunderstorms
at the western flank of any clusters of thunderstorms, locally heavy
rainfall and perhaps an isolated instance of flash flooding is
possible. These thunderstorms are anticipated to exit the CWA to the
southeast during the 13 to 15z timeframe.

An approaching cold front, lagging behind most thunderstorms this
morning, is forecast to move southward into the CWA and reach along
and south of I-70 by the afternoon. It is questionable if and how
much redevelopment of any thunderstorms take place this afternoon
through evening due to weak frontal moisture convergence, rising mid-
level heights, and a weak capping inversion. However, any
thunderstorm that does develop could become strong to severe with
localized large hail and damaging microburst winds, given model
guidance projections of 2500 to 4000 J/kg of MLCAPE. But weaker deep-
layer wind shear (15 to 25 kt) would limit longevity and
organization. Along and south of the front's afternoon position,
temps are forecast to warm into the upper 80 and low-90s F with
dewpoints in the 70s F supporting heat index values around 100 F for
some areas. To the north, drier and cooler air will provide more
comfortable temps in the mid to upper 80s F.

The cold front should drift slowly southward through this evening,
making it south of the CWA. Enough overlap of calm/light winds,
residual BL moisture, and bouts of efficient radiational cooling may
be sufficient for development of patchy fog across east-central,
southeastern MO and southwestern IL late tonight, especially in
river valleys. However, fog development will be largely dependent on
how much of the night has mostly clear skies. Low temps tonight
should fall into the mid-60s to low-70s F.

There is a strong signal in model guidance that an MCS/MCV
originating this evening across eastern CO and northeastern AZ will
be maintained by a nocturnal LLJ and pool of downstream instability,
allowing it to track through the CWA late tonight into Sunday
morning. There are differences in the strength of associated
thunderstorms and timing of this feature. However, enough
instability could be present across southeastern MO (closer to the
cold front) to support a strong to severe thunderstorm or two with
damaging winds and large hail late tonight/Sunday morning.
Rain/showers and cloud cover could be quite extensive through Sunday
morning, perhaps into the afternoon. This early day MCS/MCV
complicates the potential for strong to severe thunderstorms Sunday
evening into night as a potent mid-level shortwave trough and
accompanying cold front reach the region, especially in terms of
instability. Confidence is higher in destabilization occurring to
the west and southwest of the CWA, per the HREF, but the combination
of strengthening low-level southwesterly flow/LLJ ahead of an
approaching cold front could advect more unstable air into the CWA
Sunday evening even if in-situ generated instability is modest.
Instability aside, 40 to 50-kt mid-level flow should be favorable
for organized strong to severe thunderstorms along and ahead of the
cold front. Currently, confidence is highest in strong to severe
thunderstorms Sunday evening into night across central and
southeastern MO, where destabilization is most likely to be
greatest. All severe hazards appear possible at this juncture.

Pfahler

.LONG TERM...  (Sunday Night through Friday)
Issued at 329 AM CDT Sat Aug 12 2023

Most of the attention was given to the short term forecast, but more
quiet and drier weather is favored during the upcoming weak. Time-
mean upper/mid-level flow is progged to be northwesterly, with a
period of low-level CAA and dry air transport into the Mid-
Mississippi River Valley behind Sunday's cold front supporting below
average temps through mid-week.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1048 PM CDT Fri Aug 11 2023

Thunderstorms have rapidly developed in northwest Missouri moving
east-southeast. These currently discrete thunderstorms are expected
to congeal into a line with bowing segments and move southeast
through our forecast area, impacting all terminals tonight into
Saturday morning. These thunderstorms have a history of producing
severe conditions, and are expected to continue to do so overnight.
If a thunderstorm directly impacts a terminal, expect reduced flight
conditions as well as the potential for heavy rain, large hail, and
damaging winds. These thunderstorms and lingering showers behind the
system are expected to exit the terminals by 10z to 14z from
northwest to southeast. After this, southwesterly winds will turn to
northwesterly, and dry, VFR conditions are expected to persist
through the end of the TAF period.

Jaja

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
255 AM CDT Sat Aug 12 2023

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-130800-
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-
255 AM CDT Sat Aug 12 2023

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.

Storms will continue through this morning. Some of the storms could
be severe and capable of producing damaging winds, large hail, and
locally heavy rain. A tornado or two is also possible.

There is a low chance for scattered storms late this afternoon and
evening across portions of southeastern Missouri and southwestern
Illinois.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

There is a chance of thunderstorms across much of the area Sunday
into early Monday. Some of the storms could be severe Sunday
afternoon through Sunday night.

.SPOTTER INFORMATION STATEMENT...

Spotters are to report hail occurrences and size as well as storm
damage to the St. Louis NWS.

Elmore

Preliminary Local Storm Report
National Weather Service St Louis MO
131 AM CDT Sat Aug 12 2023

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

0117 AM     Tstm Wnd Dmg     Palmyra                 39.80N 91.53W
08/12/2023                   Marion             MO   Law Enforcement

            10inch diameter tree has fallen. location is
            approximate on New Street. time is
            approximate.

&&

MMG

Preliminary Local Storm Report
National Weather Service St Louis MO
226 AM CDT Sat Aug 12 2023

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

0200 AM     Tstm Wnd Dmg     Summer Hill             39.55N 90.92W
08/12/2023                   Pike               IL   Law Enforcement

            report of a tree down in Summer Hill, IL.
            time is approximate.

&&

MMG

Preliminary Local Storm Report
National Weather Service St Louis MO
232 AM CDT Sat Aug 12 2023

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

0157 AM     Tstm Wnd Dmg     1 ENE Atlas             39.52N 90.95W
08/12/2023                   Pike               IL   Law Enforcement

            tree down northeast of Atlas, IL on Route
            54. time is approximate.

&&

MMG

Preliminary Local Storm Report
National Weather Service St Louis MO
233 AM CDT Sat Aug 12 2023

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

0203 AM     Tstm Wnd Dmg     Pleasant Hill           39.44N 90.87W
08/12/2023                   Pike               IL   Broadcast Media

            Tree down over a road in Pleasant Hill. Time
            estimated from radar.

&&

AE

Preliminary Local Storm Report
National Weather Service St Louis MO
243 AM CDT Sat Aug 12 2023

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

0203 AM     Tstm Wnd Dmg     Pleasant Hill           39.44N 90.88W
08/12/2023                   Pike               IL   Law Enforcement

            Power lines down. Time is approximate.

&&

MMG

Preliminary Local Storm Report
National Weather Service St Louis MO
319 AM CDT Sat Aug 12 2023

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

0316 AM     Tstm Wnd Gst     1 E Vandiver            39.16N 91.82W
08/12/2023  M61 MPH          Audrain            MO   AWOS

            Measured at KMYJ.

&&

MRB