This round of storms was due to an outflow boundary from earlier activity. As it moved east through the afternoon hours it interacted with a rather unstable air mass with surface based CAPE in excess of 3000 J/kg.
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The episode as NWS LSX wrote it up.
This round of storms was due to an outflow boundary from earlier activity. As it moved east through the afternoon hours it interacted with a rather unstable air mass with surface based CAPE in excess of 3000 J/kg. The main threat from these storms was damaging winds.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS St. Louis, MO wrote its last area forecast discussion before the first event at Jul 16, 11:41 AM CST, 1 hour 8 minutes earlier.
Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1241 PM CDT Sun Jul 16 2023 .SHORT TERM... (Through Late Monday Afternoon) Issued at 416 AM CDT Sun Jul 16 2023 1) The chances for showers and thunderstorms will increase over northern sections of Missouri late this morning into the early afternoon. A few of the thunderstorms could be strong to severe. 2) Thunderstorms and associated cloud cover will have an influence on high temperatures. Confidence in warmer temperatures (90s) is highest south of I-70. 3) The approaching cold front may not entirely clear the area, offering additional chances for thunderstorms Monday. Aside from stray mid-level clouds passing through the region, skies have cleared with light and variable surface flow. The only other obstruction to account for is the thin haze/smoke from Canadian wildfires streaming in on northwest flow aloft. This is mostly impacting the northeastern one-third of the CWA. Otherwise, surface temperatures have ranged from the mid-60s to low-70s. The cooler sub- urban and rural areas, especially those in low-lying valleys and riverbeds that recently received rainfall, have observed occasional visibility reductions with dewpoint depressions of 1-3 degrees. Some of the smoke/haze will persist over the same areas today up until precipitation chances are introduced from west to east over northern sections of the CWA. This is where forecast confidence begins to fall off, largely due uncertainty in the evolution of convection. RAP guidance depicts the mid-level shortwave traversing the northern end of a mid-level ridge and running almost due west to east over northern sections of Missouri. This runs ahead of the approaching cold front, where 40-50 percent of the grand ensemble supports 1500-2000 J/kg of SBCAPE. RAP guidance is among the more bullish with a narrow corridor of MUCAPE building to 2000-2500 J/kg between 18z-20z. While bulk shear is a respectable 35-40 knots, the region is largely absent of mid-level lapse rates (sub-7C), though low level lapse rates approach 9C, coinciding with surface dewpoints in the mid-60s to near 70 degrees. CAMs advertise a variety of scenarios, though one feature in the HRRR has been rather consistent. Over the last 24 hours, it has played off outflow, from what is expected to be a decaying MCS, running into instability over northern Missouri. This may invigorate scattered development in this region with HREF reflectivity paintball plots showing a smattering of activity as early as 18z, spreading east-southeast. With the front lagging to the north, addition development further south will likely be driven by competing outflow from scattered thunderstorms. The real struggle is then pinpoint any severe potential. While there is a broad SPC marginal risk area, severe potential continues to look conditional on the evolution of the MCS - whether is maintains intensity or decays as expected - and any downstream behavior. Severe potential looks to be isolated this far east as SBCAPE peeks in the early afternoon and steep low level lapse rates help drive initial updrafts. Marginally severe hail is possible, but the window is short as the threat transition to localized wind gusts resulting from outflow. Initially, cloud cover will help keep northern sections of the CWA slightly cooler. The overall spread of thunderstorms and their southward extent will be key in making or breaking current forecast highs. Highs in the 90s are more probable with HREF probabilities of 60 percent or higher lining up along and south of I-70. The cold front slowly drifts south Monday evening into Monday night with the focus for scattered thunderstorms sinking southeast along with the track of the mid/upper shortwave features. Much of the support is driven by the mid/upper ascent with surface based instability waning through the late evening and especially overnight. As mentioned in prior discussions, thunderstorms are likely elevated by this time, which will make it difficult to realize the wind potential at the surface. While a few strong storms are certainly possible, the confidence in severe is low with localized damaging wind gusts being isolated to the strongest thunderstorms. The southward progress of the cold front will slow, if not stall Monday. Current projections line up somewhere along or just south of the I-70 corridor. By this time, the region is in a relative void of mid/upper ascent, though surface dewpoints remain well into the 60s along and south of the front. HREF ensembles show roughly 40-50 percent of members destabilization over southern Missouri and Illinois on the order of 2000 J/kg of SBCAPE. Isolated to perhaps scattered thunderstorms are possible Monday afternoon, but largely favored over south/southeast sections of the forecast area. By Monday night, much of it will weaken and fade with loss of diurnal heating. Highs will be notably cooler with most of the area in the 80s. Maples .LONG TERM... (Monday Night through Saturday) Issued at 416 AM CDT Sun Jul 16 2023 The upcoming week continues to look active, particularly Tuesday morning into Tuesday afternoon and again Tuesday night into early Wednesday. Thunderstorms potential continues to make temperatures trends difficult to nail down. Long range guidance has been consistent in the slight eastward shift of the upper level pattern from early to midweek. The eastward translation in the upper ridge over the southwest CONUS and the broader cyclonic flow over Canada keep the upper level shortwave track concentrated over the central U.S. As the upper ridge shifts east, a northwest-to-southeast oriented warm front will become the focus for thunderstorm development late Monday night into Tuesday. The nocturnal jet intensifies over the central Plains with the nose of the jet directed at at the Kansas/Nebraska border. Meanwhile, an upper level shortwave ejects from the northern Rockies in the Plains, providing a broad area of ascent. Medium range guidance, (namely the NAM) shows a couple of mid-level shortwaves running along the front. One is position over southwest Missouri, while the other near the Nebraska/Iowa border by Tuesday morning. Thunderstorms should ignite along the boundary, and track southeast along the northeastern periphery of the ridge and in conjunction with a CAPE gradient that set up somewhere between the eastern Plains and over western sections of Missouri. Depending on where this all initiates and how it evolves will not only determine thunderstorm potential, but the layout of temperatures through the day Tuesday. Another wave is expected to develop Tuesday night into early Wednesday in a similar manner. This may be the better potential with a continued eastward shift in the upper level pattern. ECM/GFS are pretty close in their orientation of the low level jet. Forcing is focused in the vicinity of the Mississippi River, where convective potential increases late Tuesday evening into Tuesday night. This time development could be right overhead, running nearly parallel to the river through Wednesday morning. While the exact positions and timing will still need to be worked on in coming days, there has been some consistency with guidance placing development in the region between late Monday night and Wednesday morning. Temperatures will be heavily reliant on convective trends. Therefore, some of the higher temperatures south of I-70 (upper 90s to near 100) from the NBM are likely at the mercy of thunderstorm evolution. The active track remains focused over the central sections of the country, but the western ridge begins to flatten from mid to late week as a broad upper trough sink southward over the eastern CONUS. Thunderstorm potential beyond Wednesday may be suspect as a cold front drops south of the region and surface high pressure builds in from the northern Plains. Maples && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1230 PM CDT Sun Jul 16 2023 Showers and thunderstorms will develop along a boundary moving into central MO early this afternoon impacting KCOU and KJEF. At this time I have flight conditions with the storms lowering to MVFR but they could certainly be lower at times along with stronger winds. This boundary will continue to move east and may generate additional scattered storms impacting KUIN and KSTL/KSUS/KCPS between 20-23z. The evolution is less certain for these terminals and thus I just have VCTS at this time. Another round of showers and storms is expected from central MO through the St. Louis area from 02-03z through 07-09z prompting 6SM -SHRA VCTS in the terminals, however flight conditions could certainly be lower at times. Some of the terminals may also see visibility restrictions to MVFR at times outside of any showers and storms due to haze/smoke. Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && WFO LSX
Hazardous Weather Outlook National Weather Service St Louis MO 354 AM CDT Sun Jul 16 2023 ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027- 034>036-041-042-047>052-059>065-072>075-084-085-099-170900- 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- 354 AM CDT Sun Jul 16 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. There is a chance of thunderstorms this afternoon through tonight. Isolated strong to severe thunderstorms are possible this afternoon mainly north of I-70. .DAYS TWO THROUGH SEVEN...Monday through Saturday. There is a chance of thunderstorms Monday through Saturday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. Jaja
Preliminary Local Storm Report
National Weather Service St Louis MO
1202 PM CDT Sun Jul 16 2023
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0610 PM Tstm Wnd Dmg Taos 38.51N 92.07W
07/14/2023 Cole MO Public
Trees and tree limbs blown down.
&&
CarneyThe St Louis radar (KLSX), 79 km away, was scanning. The volume nearest the first event began at 18:47 UTC.
15 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds blew down two trees, a flag pole and numerous tree limbs around town.
Thunderstorm winds blew a tree onto power lines at Highway EE and Wild Flower Lane.
Thunderstorm winds blew down power lines in Marthasville as well as a couple of trees and numerous tree limbs. In Dutzow, numerous trees and power lines were blown down.
Thunderstorm winds blew down a few large tree limbs.
Thunderstorm winds blew down a tree near the intersection of Highway 94 and Highway DD.
Thunderstorm winds blew down numerous tree limbs. In St. Charles, a business sign was blown down onto an unoccupied car causing moderate damage to the vehicle.
Thunderstorm winds blew down several large tree limbs.
Thunderstorm winds blew down a large tree limb.
Thunderstorm winds snapped off a power pole with the transformer landing in a nearby tree.
Thunderstorm winds blew down several large tree limbs just northwest of Blackwell.
Thunderstorm winds blew down numerous tree limbs between DeSoto and Olympian Village.
Thunderstorm winds blew down several large tree limbs in Oakville.
Thunderstorm winds blew down several large trees and numerous tree limbs in the Pevely, Herculaneum, and Festus areas.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Missouri in 2023Every state in 2023This day in weather historyWarnings in Missouri, July 2023
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1128536, 1128537, 1128540, 1128543, 1128550, 1128551, 1128552, 1128546, 1128547, 1128553, 1128555, 1128557, 1128554, 1128560, 1128561.