Extreme Temperature Diary- Wednesday July 27th, 2021/ Main Topic: When Heat Domes Relent Watch Out for Severe Flooding

The main purpose of this ongoing blog will be to track planetary extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: When Heat Domes Relent Watch Out for Severe Flooding

Dear Diary. Early on Tuesday July 26th yet another major metropolitan area experienced a climate change related weather event. The St. Louis experience over eight inches of rain in a short amount of time from a mesoscale convective complex (or big clump of thunderstorms) shortly after seeing a very toasty max of 103°F on the 24th.

Mainly outside of the Far West, large tracks of the United States are susceptible to flooding when heat domes weaken or break down, causing severe flooding. Here is the 500 millibar pattern we saw the morning of the 26th:

Portions of the southern Midwest into West Virginia remain susceptible to flooding this week because of a weak front that is located just to the north of a strong heat dome’s influence, as depicted on the above Pivotal Weather chart. Back when I was forecasting at The Weather Channel, my colleagues and I would call such rainy systems “ridge runner storms” in association with a “ring of fire” moving around heat domes. One such ridge runner released havoc on St. Louis this week.

Heat domes can hold a lot of moisture. When weak summer fronts interact with heat domes, they squeeze out this moisture in the form of heavy rain. We see a lot of flooding potential on the periphery of nearly stationary heat domes, which produce drought underneath them but copious rain on the edges. As our planet warms, we will see more flooding when heat waves break causing misery and death with billions of dollars’ worth of damage.

Here is Dr. Jeff Master’s and Bob Henson’s summary of the devastating flooding that unfolded in St. Louis:

EYE ON THE STORM

Record rain in St. Louis is what climate change looks like

As the stormy pattern that inundated St. Louis shifts east, a multi-day flash flood threat targets the central Appalachians.

Bob HensonJeff Masters

by BOB HENSON and JEFF MASTERS JULY 26, 2022

A motorist is rescued from a stalled-out vehicle in Jennings, Missouri, just north of St. Louis, Missouri, early Tuesday morning, July 26, 2022. Dozens of water rescues were carried out across the St. Louis metro area during record-setting rainfall. (Image credit: St. Louis County Police Department)

Torrents of rain that began before dawn on Tuesday, July 26, gave St. Louis, Missouri, its highest calendar-day total since records began in 1873. And the deadly event is just the latest example of a well-established trend of intensifying downpours in many places across the globe.

The official reporting site at Lambert International Airport received 8.6 inches of rain from midnight to 11 a.m. Central Standard Time on Tuesday. (Standard time is used year-round to separate calendar days for meteorological data purposes.) Another 0.46 inch had been recorded just before midnight CST on Monday, bringing the total for July 25-26 to 9.04 inches as of 11 a.m. CST Tuesday.

The predawn onset of the storms meant that many residents were startled awake by floodwaters or caught on highways during early commutes. Dozens of water rescues were carried out across the area. The storm closed Interstate 70 and many other key roads across the St. Louis area throughout the morning, according to the St. Louis Post-Dispatch. At least one death has been reported as of Tuesday evening, a person pulled from an inundated vehicle.

More heavy rain is possible early Wednesday, although the storms in that round are expected to keep moving rather than stalling out.

Below are several records set in Tuesday’s brief but intense deluge. We’ll update this information after final data for Tuesday are in.

  • Heaviest rainfall in a 24-hour period, including periods that straddle calendar days: at least 9.04 inches (old record 7.02 inches on August 19-20, 1915, from the remnants of the 1915 Galveston hurricane)
  • Heaviest calendar-day rainfall: at least 8.60 inches (old record 6.85 inches on August 20, 1915).
  • Second-heaviest total for two calendar days: at least 9.04 inches (old record 9.54 inches on May 16-17, 1995)

Figure 1 rainfall totalsFigure 1. The 24-hour total of just over 9 inches in St. Louis would be expected to occur about once every 200 to 300 years if the climate were “stationary,” based on the NOAA Atlas 14 catalog of recurrence intervals. Atlas 14 is based on past observed rainfall, so it does not take ongoing climate change into account. Recurrence intervals are most likely getting shorter in many locations. (Image credit: NOAA Atlas 14)

Figure 2 satellite imageFigure 2. The cold, high tops of an intense mesoscale convective system that tracked across the St. Louis metropolitan area on July 26, 2022, can be seen in this infrared satellite image from 0800Z (3 a.m. CDT) Tuesday, with a particularly intense core (dark red) stretching from west to east across the St. Louis area. (Image credit: RAMMB/CIRA/CSU)

The culprit behind the early-morning deluge was a mesoscale convective system — a large, highly organized complex of showers and thunderstorms — that moved across the area in a “training” fashion from west-northwest to east-southeast, with cells regenerating and tracking along a constant path while the complex itself moves much more slowly. The system included one band of intense rainfall passing directly over St. Louis, with a secondary band roughly 60-70 miles to the north. Some areas just northwest of St. Louis may have seen as much as 14 inches of rain.

Figure 3. Hydrograph for Dardenne Creek near I-70 in St. Louis. In the seven hours beginning at 12:30 a.m. July 26, the creek rose 21 feet, and peaked just 1.36 feet below the all-time record set on September 15, 2008. (Image credit: NOAA)

The Midwest is getting more rain — and more extreme rain events

Although the Midwest climate is naturally drought-prone, recent decades have trended more toward the wet side of the spectrum. “Annual precipitation in the Midwest has increased by 5% to 15% from the first half of the last century (1901–1960) compared to present day (1986–2015),” the Fourth National Climate Assessment observed in 2018.

There’s a well-established trend in many parts of the globe for the heaviest short-term rainfall events to become more intense, consistent with a human-warmed atmosphere allowing more moisture to evaporate from warmer oceans and to flow into rainmaking systems. Over the past 120 years, the Midwest has seen a 42% increase in the amount of rain falling in top-end short-term rainfall events (the heaviest 1% of events). That was larger than any other region of the country for the period 1901-2016, although it was surpassed by the Northeast in the period 1958-2016 (see tweet below, which includes a National Assessment analysis).

Read: Why is it raining so hard? Global warming is delivering heavier downpours

“Storm water management systems and other critical infrastructure in the Midwest are already experiencing impacts from changing precipitation patterns and elevated flood risks,” the National Climate Assessment, a sweeping government report on the impacts of climate change in the United States, noted in 2018.

As one of the 10 biggest U.S. cities between 1850 and 1960 — but only the 70th-largest as of 2020 — St. Louis joins other venerable but now-smaller U.S. cities in having to adapt major century-old infrastructure to the evolving climate of the 21st century. As noted in the National Climate Assessment, the Metropolitan Sewer District in St. Louis had embarked upon a $100 million “rainscaping” project designed to divert storm water runoff in the northern portion of the city of St. Louis and adjacent north St. Louis County, including areas where the July 26 storm tracked.

Significant flood threat for Kentucky and West Virginia this week

The stalled frontal boundary that brought St. Louis its record flooding will be draped over the Ohio River Valley through Friday, bringing an elevated threat of flash flooding across portions of Kentucky and West Virginia. On Tuesday evening, this area was been placed under a moderate-risk threat of excessive rain leading to flash flooding. The threat extended across a 48-hour period from Wednesday through Friday morning by the National Weather Service, which is predicting widespread rainfall amounts of 2-4 inches on Wednesday and 1-3 inches on Thursday. This area has already seen significant flash flooding during the past few weeks from extreme rainfall; however, soil moisture levels are currently near average.

As detailed in the tweets below by Alex Lamers, this region, which is highly mountainous, is particularly prone to deadly flash floods.

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TAGGED: Bob Henson Jeff Masters

Bob Henson

BOB HENSON

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance… More by Bob Henson

Jeff Masters

JEFF MASTERS

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a… More by Jeff Masters

Dr. Jeff Master’s and Bob Henson’s Record rain in St. Louis is what climate change looks like was first published on Yale Climate Connections, a program of the Yale School of the Environment, available at: http://yaleclimateconnections.org. This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 2.5 license (CC BY-NC-ND 2.5).

Here are more “ET’s” recorded from around the planet the last couple of days, their consequences, and some extreme temperature outlooks:

Here is more climate and weather news from Wednesday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)

(If you like these posts and my work please contribute via this site’s PayPal widget. Thanks in advance for any support.) 

Guy Walton “The Climate Guy”

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