Why do we flood? To clarify the obvious: Too much rain … creates too much runoff … in too little time … over terrain that’s too flat. Now, dig a little deeper.
Ask a slightly different question: “Why do we experience so much flood damage?” You get slightly different, but related reasons. Based on what I’ve learned while researching more than 2,000 articles since Harvey, the reasons include:
Inaccurate predictions of future rainfall.
Conflicting development standards and building codes.
Building too close to threats.
Upstream changes that undermine our assumptions.
Difficulty of adapting downstream.
Historical unwillingness to fund flood mitigation at meaningful levels.
Many of these self-inflicted wounds have to do with self-interest and the problems we have working together. Let’s explore each in more detail.
Inaccurate Predictions of Future Rainfall
Periodically, scientists update our predictions of future rainfall. No one is omniscient. We can only guess at what might happen in the future based on what has happened in the past. So we rely on a branch of mathematics called EVA (extreme value analysis). EVA predicts the probability of future events based on the observation of extremelyrarepastevents. But that means the mathematicians work with extremely small data sets. And that, in turn, means their confidence is low. So, every time a new superstorm comes along, they get to re-evaluate assumptions.
During the past 20 years, our rainfall assumptions have officially changed at least twice: after Allison and after Harvey. Each monster storm pushed predictions higher. After Harvey, predictions increased 25-30% compared to Allison.
Atlas 14 rainfall probabilities adopted by Harris County after Harvey.
And the amount of runoff new developments must retain varies accordingly. If just one development cut corners, you’d probably never see the difference. But if hundreds or thousands of upstream developments do not retain enough rain, you will.
The casualties in this upstream/downstream conflict will include those who bought homes or built businesses near the limit of the old assumptions. If they were at the edge of the floodplain before, now they’re in it. New floodplain maps based on Atlas-14 have not yet been officially released, but…
We use these imperfect and shifting predictions of future rainfall to design margins of safety into new developments. So your safety depends on when your house was built. And where.
Conflicting Development Standards and Building Codes
Humans, both private individuals and public officials, act in their self interest. Therefore, they also disagree about the probability of future risk. This often brings private property rights and public interest into conflict. People who own cheap land in floodplains, or worse yet in floodways, often want to develop it.
But higher standards can impact developers’ profits now. And the consequences of not observing those standards may not be visible for decades.
Meanwhile, politicians are eager to attract new development. And they live in a competitive world. Higher standards and strict enforcement can cause developers to look elsewhere for more attractive opportunities. So some politicians are reluctant to adopt higher standards.
That has created a patchwork quilt of regulations in the seven-county region. After Harvey, Harris County tried to get all municipalities and counties to adopt five minimum standards. Five years later, we’ve had mixed results. See below.
Variation in shifting and conflicting standards makes it difficult for home buyers, lenders, and even engineers to assess flood risk. “Whose 100-year floodplain are you talking about?”
And when floodplain standards do change, affected home and business owners may fight them because being in a floodplain could reduce the value of their property.
Building Too Close to Threats
People normally like water. They just don’t like it four feet deep in their homes. Water is part of our DNA. We like to live close to it; aspire to own beach homes; and vacation at the shore. We even pay premiums for homes with soothing water views – despite the higher risk.
However, those same locations can turn into raging torrents of water that destroy homes, businesses, vehicles, lives, and our illusions of safety.
Many people find understanding flood risk difficult. And even if they understand it intellectually, they may repress it emotionally.
After all, who wants to think about the possibility of dying in a traffic accident every time he/she goes to the grocery store?
So most people deny and ultimately compromise. For decades, they compromised by purchasing nationally subsidized flood insurance. Until the advent of Risk Rating 2.0 last year, flood insurance didn’t reflect the true cost of payouts.
That subsidy insulated both buyers and sellers. It allowed developers to build in risky, marginal areas without fear of finding homes unsaleable.
The availability of subsidized flood insurance fueled whole industries that made money off of cheap floodplain land.
Among those industries – engineering. Houston has hundreds of engineering companies that study ways to build “safely” near water. The vast majority are highly ethical. But what if you live downstream from a project with an engineering firm that wasn’t? Life can change in an instant.
Upstream Changes that Undermine Downstream Assumptions
Upstream changes cause downstream consequences. I once owned a home in the Dallas/Fort Worth area overlooking a creek. Engineers and surveyors certified that the home was two feet above the 100-year floodplain when built.
But Plano, just upstream from us, was the fastest growing city in America at the time. A new shopping mall with 80+ acres of parking changed things quickly. On small rains, water started coming up to our back door. One day, after a moderate rain, I saw a pickup floating down the creek.
After I complained to our City engineer, he requested the Army Corps to resurvey the creek. The Corps found that the upstream development had changed the floodplain.
Instead of being two feet above the 100-year floodplain, we were now 10 feet below it.
Unwilling to live with that risk, we sold our house, took a loss on it, and moved to Kingwood – two miles from the San Jacinto West Fork on one of the highest points in Harris County.
But soon Conroe became the fastest growing city in America! And Montgomery County became the second fastest growing county in the region. During my 40 years here, I’ve watched floods get higher and higher until, during Harvey, the Cajun Navy launched rescue boats from our driveway.
If all those new upstream developments really had “no adverse impact,” how did that happen? Was Harvey just a freak, monster storm? Yes. But manmade changes upstream also exacerbated the flooding. Engineering firms eager to deliver cost-effective answers for clients pushed the envelope. For instance, I could cite examples where engineers:
Used obsolete rainfall probability statistics to minimize the amount of stormwater detention needed. That increased the number of salable lots and the developer’s profitability.
Mischaracterized soil types to overestimate the rate of infiltration. That virtually eliminated the need for floodwater detention basins.
Tried to build 50-story high rises on land soon to be reclassified as floodway.
Accelerated water flowing into rivers during floods rather than retaining it. To justify this, they used a questionable type of study allowed by Montgomery County but outlawed in Harris County because it makes floods peak higher and faster downstream.
If enough companies push the envelope as these did, gradually flood peaks change, as shown in the graph below.
Red line shows how Brays Bayou watershed would have handled Tropical Storm Allison in 1915 before development. Blue line shows time of accumulation in 2000. Note faster, higher flood peak.
Does anyone really know how all that new impervious cover upstream affects flood peaks downstream? Some areas still use flood data from the 1980s.
Difficulty of Adapting Downstream
Lack of upstream regulation and enforcement saveupstream residents money. But they costdownstream residents. The burden of mitigation costs falls on Harris County residents, not our surrounding counties. And mitigation costs billions of dollars!
It’s easy to build a floodwater detention basin or widen a channel before development, but a Herculean task afterwards.
Another aspect of the difficulty: political conflict. Scarcity of funds has pitted neighborhoods and races against each other, as each vies for funding. Harvey united us in our resolve to finally do something about flooding. But recovery has torn us apart.
Historical Unwillingness to Fund Flood Mitigation at Meaningful Levels
Until Harvey, we have consistently underfunded flood mitigation efforts at the State, county and local levels. Unless we’re dealing with a flood disaster, it seems we have more pressing issues. Even after Harvey, we are now spending more money on bike trails in Harris County than on flood mitigation in the Lake Houston Area.
Harris County Flood Control’s budget before Harvey was so small that the District often had to save up multiple years to build one detention pond.
During the 2011 drought, State Representative Dan Huberty went to City of Houston Mayor Annise Parker. Lake Houston was so far down, the West Fork was a trickle between Humble and Kingwood. Huberty suggested that that would be a great time to get sediment buildups out of the river. You could have done it with trucks, restored the river’s conveyance, protected people from flooding and avoided water quality issues associated with dredging in our water supply. Parker declined.
So why do we flood? It’s not just the rainfall. Many of our wounds are self inflicted.
Future Posts in Harvey-Anniversary Series
My next post in this series will focus on a Harvey-Mitigation 5-Year Report Card. Another will focus on why some Harvey survivors still experience PTSD, and how it could affect them well into their seventies.
Posted by Bob Rehak on 8/25/22
1822 days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2022/07/20210520-RJR_6978.jpg?fit=1200%2C800&ssl=18001200adminadmin2022-08-25 19:21:162022-08-26 09:55:48Why Do We Flood?
In their 8/23/22 meeting, Harris County Commissioners discussed proposed budget priorities for the next fiscal year. Dr. Tina Petersen, PhD, PE, Harris County Flood Control District’s Executive Director, presented her goals for next year. And once again, they revolved around “equity.” See page 64 of the proposed budget for Petersen’s priorities or the summary below. The inequities of the “equity plan” are getting too hard to ignore.
Goal
Petersen wants to “reduce flood risk and strengthen resiliency.” Not much to quibble with there!
However, she also described how she wants to do it: “…through … equitable … strategies.”
The emphasis on “equitable” raises concerns about when HCFCD will start addressing the needs of the Lake Houston Area.
The outcomes associated with reducing flood risk? Harris County is targeting year-over-year reduction in the number of structures susceptible to damage from a 1% ATLAS 14 event. HCFCD also wants to reduce the number of structures susceptible to flooding in any flood. Both of those are admirable outcomes.
Having been burned once, though, I wish they would take it two steps further. Tell me: a) how many structures and b) where they are. Their wording leaves things too open ended and generic for my taste. The district could save a handful of homes and declare victory.
To achieve the not-so-specific outcomes articulated, the District wants to increase its budget for:
Sediment removal by $5 million, due to inflationary costs totaling 35%
Maintenance by $790,000, due to increased contract and material costs.
Mowing by $760,000, due to increased contract costs.
Building costs, professional services, and money paid to other departments, such as IT, by $1.7 million due to inflation.
Desired Outcome #2
Petersen also wants to: “invest in flood control equitably, where the most people are at risk of flooding.” I read that as, “Not the most people with the most risk; just the most people with any risk.”
Her strategy: “…increase alignment of flood control investment to areas of greatest need.” What does she mean by “greatest need”?
The deepest flooding?
The most damage to infrastructure?
The highest frequency of flooding?
Schools, grocery stores, and hospitals underwater?
Loss of critical bridges that cut off whole communities?
The southbound lanes of the I-69 bridge were knocked out by Harvey for approximately a year, causing massive delays and detours.Harvey flooding forced Humble ISD to close Kingwood High School for almost a year and bus 4000 students elsewhere.Chart showing feet above flood stage at 33 gages. Highest flooding was at 59 between Humble and Kingwood on the West Fork.
Thus, the money would go to the most densely populated areas, not necessarily those that suffered the most or worst damage. And the “revised prioritization framework” emphasizes the social vulnerability index (SVI). Ooops. There’s the “tell” again.
At least she’s telling you what you need to know when you go to the polls this fall. If you live in the Lake Houston Area, I wouldn’t count on seeing any benefit from the flood bond next year. Or the Flood Resilience Trust. The Trust contains money diverted from tollroads. That will now likely go to fix neighborhood drainage long ignored by Precincts One and Two, and the City..
Blocked street drainage in Kashmere and Trinity Garden subdivisions.
Commissioners discussed the budget for 90 minutes Tuesday. A vote on it will come in September. More to follow before then.
Posted by Bob Rehak on 8/23/22
1820 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/01/KHS-e1702338318946.jpg?fit=1100%2C616&ssl=16161100adminadmin2022-08-23 21:59:122022-08-24 10:41:55Flood Control Lists Budget Priorities for Fiscal ’23
Last week, I posted about the possibility of heavy rain early this week. Last night, Dallas experienced torrential rains and they’re headed this way. One amateur weather gage on Londonderry Lane reported more than 14″ of rain! Dallas/Fort Worth officially received 9.46 inches of rainfall in 6 hours and 7.8 inches in 3-hours. Significant flash flooding has resulted. A 1-hour storm total of 3.01 inches was recorded at DFW with a storm total of 6.54 inches. That wiped out 67% of the area’s 2022 rainfall deficit in a few hours.
National Weather Service map as of 12:41 pm Houston time. Purple boxes represent flash flood warnings. Bright green = Flood warnings. Dark green = flood watch.
Threat Will Increase From North to South During Next 24 Hours
According to Jeff Lindner, Harris County Meteorologist, the frontal boundary over north Texas will slowly move southward today and approach the northern portions of southeast Texas by mid- to late afternoon. Numerous showers and thunderstorms will develop along the boundary along with scattered showers developing northward along the seabreeze and Gulf inflow.
The air mass will become extremely moist and unstable. When combined with slow moving/stalled boundaries, excessive rainfall can result. Lindner says areas north of HWY 105 have the first potential for heavy rainfall in early afternoon. Then the front will slowly sink southward toward I-10 tonight into early Tuesday. Expect slow storm motions, cell training, and back-building of cells to the west and northwest. Everything points to heavy rainfall.
While grounds are dry, the local air mass will be capable of some impressive short duration rainfall amounts of 2-4 inches in an hour.
Jeff Lindner, Harris County Meteorologist
This was clearly seen overnight in north Texas. The local air mass will not be much different over southeast Texas. Especially N of I-10. These rainfall rates can lead to rapid flash flooding especially in urban areas.
Widespread rainfall amounts of 2-4 inches are expected over much of southeast Texas through mid week. But Lindner also expects isolated higher totals of 6+ inches. And where these higher totals occur, flash flooding will be possible, he says.
Confidence in rainfall is high. But confidence in rainfall amounts and location of the heaviest rainfall is low.
Street flooding will be the primary threat with the heavy rainfall rates. Rises on area creeks and bayous will be possible if some of the heavier storms train or move slowly over any watershed.
Overall, this wet pattern will linger into late week. But a slightly drier air mass will eventually push through and we should transition back toward a more “normal” cycle of showers and thunderstorms driven mostly by the seabreeze front.
See the National Weather Services predictions below.
Posted by Bob Rehak on 8/22/22 based on information from HCFCD and NWS
Why Do We Flood?
Why do we flood? To clarify the obvious: Too much rain … creates too much runoff … in too little time … over terrain that’s too flat. Now, dig a little deeper.
Ask a slightly different question: “Why do we experience so much flood damage?” You get slightly different, but related reasons. Based on what I’ve learned while researching more than 2,000 articles since Harvey, the reasons include:
Many of these self-inflicted wounds have to do with self-interest and the problems we have working together. Let’s explore each in more detail.
Inaccurate Predictions of Future Rainfall
Periodically, scientists update our predictions of future rainfall. No one is omniscient. We can only guess at what might happen in the future based on what has happened in the past. So we rely on a branch of mathematics called EVA (extreme value analysis). EVA predicts the probability of future events based on the observation of extremely rare past events. But that means the mathematicians work with extremely small data sets. And that, in turn, means their confidence is low. So, every time a new superstorm comes along, they get to re-evaluate assumptions.
During the past 20 years, our rainfall assumptions have officially changed at least twice: after Allison and after Harvey. Each monster storm pushed predictions higher. After Harvey, predictions increased 25-30% compared to Allison.
Unfortunately, the differences are even greater for those who live near county lines where upstream rainfall standards may be based on data from the 1980s. For instance, the difference between official rainfall probabilities in Harris and Montgomery Counties approaches 40%.
And the amount of runoff new developments must retain varies accordingly. If just one development cut corners, you’d probably never see the difference. But if hundreds or thousands of upstream developments do not retain enough rain, you will.
The casualties in this upstream/downstream conflict will include those who bought homes or built businesses near the limit of the old assumptions. If they were at the edge of the floodplain before, now they’re in it. New floodplain maps based on Atlas-14 have not yet been officially released, but…
We use these imperfect and shifting predictions of future rainfall to design margins of safety into new developments. So your safety depends on when your house was built. And where.
Conflicting Development Standards and Building Codes
Humans, both private individuals and public officials, act in their self interest. Therefore, they also disagree about the probability of future risk. This often brings private property rights and public interest into conflict. People who own cheap land in floodplains, or worse yet in floodways, often want to develop it.
Big floods, by their very definition, happen rarely. This often fuels arguments between developers and regulators. John Blount, Harris County’s former head of engineering showed that higher development standards and building codes reduced flood damage 20X.
But higher standards can impact developers’ profits now. And the consequences of not observing those standards may not be visible for decades.
Meanwhile, politicians are eager to attract new development. And they live in a competitive world. Higher standards and strict enforcement can cause developers to look elsewhere for more attractive opportunities. So some politicians are reluctant to adopt higher standards.
That has created a patchwork quilt of regulations in the seven-county region. After Harvey, Harris County tried to get all municipalities and counties to adopt five minimum standards. Five years later, we’ve had mixed results. See below.
Variation in shifting and conflicting standards makes it difficult for home buyers, lenders, and even engineers to assess flood risk. “Whose 100-year floodplain are you talking about?”
And when floodplain standards do change, affected home and business owners may fight them because being in a floodplain could reduce the value of their property.
Building Too Close to Threats
People normally like water. They just don’t like it four feet deep in their homes. Water is part of our DNA. We like to live close to it; aspire to own beach homes; and vacation at the shore. We even pay premiums for homes with soothing water views – despite the higher risk.
However, those same locations can turn into raging torrents of water that destroy homes, businesses, vehicles, lives, and our illusions of safety.
After all, who wants to think about the possibility of dying in a traffic accident every time he/she goes to the grocery store?
So most people deny and ultimately compromise. For decades, they compromised by purchasing nationally subsidized flood insurance. Until the advent of Risk Rating 2.0 last year, flood insurance didn’t reflect the true cost of payouts.
That subsidy insulated both buyers and sellers. It allowed developers to build in risky, marginal areas without fear of finding homes unsaleable.
The availability of subsidized flood insurance fueled whole industries that made money off of cheap floodplain land.
Among those industries – engineering. Houston has hundreds of engineering companies that study ways to build “safely” near water. The vast majority are highly ethical. But what if you live downstream from a project with an engineering firm that wasn’t? Life can change in an instant.
Upstream Changes that Undermine Downstream Assumptions
Upstream changes cause downstream consequences. I once owned a home in the Dallas/Fort Worth area overlooking a creek. Engineers and surveyors certified that the home was two feet above the 100-year floodplain when built.
But Plano, just upstream from us, was the fastest growing city in America at the time. A new shopping mall with 80+ acres of parking changed things quickly. On small rains, water started coming up to our back door. One day, after a moderate rain, I saw a pickup floating down the creek.
After I complained to our City engineer, he requested the Army Corps to resurvey the creek. The Corps found that the upstream development had changed the floodplain.
Unwilling to live with that risk, we sold our house, took a loss on it, and moved to Kingwood – two miles from the San Jacinto West Fork on one of the highest points in Harris County.
But soon Conroe became the fastest growing city in America! And Montgomery County became the second fastest growing county in the region. During my 40 years here, I’ve watched floods get higher and higher until, during Harvey, the Cajun Navy launched rescue boats from our driveway.
If all those new upstream developments really had “no adverse impact,” how did that happen? Was Harvey just a freak, monster storm? Yes. But manmade changes upstream also exacerbated the flooding. Engineering firms eager to deliver cost-effective answers for clients pushed the envelope. For instance, I could cite examples where engineers:
If enough companies push the envelope as these did, gradually flood peaks change, as shown in the graph below.
Does anyone really know how all that new impervious cover upstream affects flood peaks downstream? Some areas still use flood data from the 1980s.
Difficulty of Adapting Downstream
Lack of upstream regulation and enforcement save upstream residents money. But they cost downstream residents. The burden of mitigation costs falls on Harris County residents, not our surrounding counties. And mitigation costs billions of dollars!
More than one third of that goes to right-of-way acquisition, in large part, because people built too close to bayous.
To implement new mitigation projects, HCFCD must buy-out whole subdivisions and move entire neighborhoods, as it did along Halls Bayou. That’s a difficult, expensive, time-consuming process. And that exposes people to risk longer than would otherwise be necessary.
It’s easy to build a floodwater detention basin or widen a channel before development, but a Herculean task afterwards.
Another aspect of the difficulty: political conflict. Scarcity of funds has pitted neighborhoods and races against each other, as each vies for funding. Harvey united us in our resolve to finally do something about flooding. But recovery has torn us apart.
Historical Unwillingness to Fund Flood Mitigation at Meaningful Levels
Until Harvey, we have consistently underfunded flood mitigation efforts at the State, county and local levels. Unless we’re dealing with a flood disaster, it seems we have more pressing issues. Even after Harvey, we are now spending more money on bike trails in Harris County than on flood mitigation in the Lake Houston Area.
Harris County Flood Control’s budget before Harvey was so small that the District often had to save up multiple years to build one detention pond.
During the 2011 drought, State Representative Dan Huberty went to City of Houston Mayor Annise Parker. Lake Houston was so far down, the West Fork was a trickle between Humble and Kingwood. Huberty suggested that that would be a great time to get sediment buildups out of the river. You could have done it with trucks, restored the river’s conveyance, protected people from flooding and avoided water quality issues associated with dredging in our water supply. Parker declined.
So why do we flood? It’s not just the rainfall. Many of our wounds are self inflicted.
Future Posts in Harvey-Anniversary Series
My next post in this series will focus on a Harvey-Mitigation 5-Year Report Card. Another will focus on why some Harvey survivors still experience PTSD, and how it could affect them well into their seventies.
Posted by Bob Rehak on 8/25/22
1822 days since Hurricane Harvey
Flood Control Lists Budget Priorities for Fiscal ’23
In their 8/23/22 meeting, Harris County Commissioners discussed proposed budget priorities for the next fiscal year. Dr. Tina Petersen, PhD, PE, Harris County Flood Control District’s Executive Director, presented her goals for next year. And once again, they revolved around “equity.” See page 64 of the proposed budget for Petersen’s priorities or the summary below. The inequities of the “equity plan” are getting too hard to ignore.
Goal
Petersen wants to “reduce flood risk and strengthen resiliency.” Not much to quibble with there!
However, she also described how she wants to do it: “…through … equitable … strategies.”
Desired Outcome #1
“Equitable” might cause people in outlying areas concern, considering that Judge Hidalgo, Commissioner Ellis and Commissioner Garcia redefined that term after voters approved the 2018 Flood Bond. Equitable no longer means “fair and impartial” as most dictionaries would define it. Equitable now means prioritizing projects in watersheds with a majority of Low-to-Median Income (LMI) households and a high social-vulnerability index.
Since being blindsided in 2019, taxpayers in more affluent watersheds have largely been put on hold. For instance, out of $236 million dollars in active construction projects at the end of July 2022, the heavily flood-damaged Lake Houston Area has only $2000. That’s less than one-thousandth of one percent – 0.0008% to be precise. So…
The outcomes associated with reducing flood risk? Harris County is targeting year-over-year reduction in the number of structures susceptible to damage from a 1% ATLAS 14 event. HCFCD also wants to reduce the number of structures susceptible to flooding in any flood. Both of those are admirable outcomes.
Having been burned once, though, I wish they would take it two steps further. Tell me: a) how many structures and b) where they are. Their wording leaves things too open ended and generic for my taste. The district could save a handful of homes and declare victory.
To achieve the not-so-specific outcomes articulated, the District wants to increase its budget for:
Desired Outcome #2
Petersen also wants to: “invest in flood control equitably, where the most people are at risk of flooding.” I read that as, “Not the most people with the most risk; just the most people with any risk.”
Her strategy: “…increase alignment of flood control investment to areas of greatest need.” What does she mean by “greatest need”?
Apparently, Petersen means none of those things when she talks about greatest need. She wants to “Use the revised Prioritization Framework that emphasizes people, not structures.”
Thus, the money would go to the most densely populated areas, not necessarily those that suffered the most or worst damage. And the “revised prioritization framework” emphasizes the social vulnerability index (SVI). Ooops. There’s the “tell” again.
Petersen wants to spend her budget in the most highly populated neighborhoods with a high SVI. Translation: mostly inside the Beltway where the vast majority of funding for the last 22 years has already gone.
I’ll give Petersen one thing. She’s open about her priorities. No secrets there, unlike the trick Commissioner Ellis played on voters in 2018 with the bond language.
At least she’s telling you what you need to know when you go to the polls this fall. If you live in the Lake Houston Area, I wouldn’t count on seeing any benefit from the flood bond next year. Or the Flood Resilience Trust. The Trust contains money diverted from tollroads. That will now likely go to fix neighborhood drainage long ignored by Precincts One and Two, and the City..
Commissioners discussed the budget for 90 minutes Tuesday. A vote on it will come in September. More to follow before then.
Posted by Bob Rehak on 8/23/22
1820 Days since Hurricane Harvey
Heavy Rainfall Threat Approaching
Last week, I posted about the possibility of heavy rain early this week. Last night, Dallas experienced torrential rains and they’re headed this way. One amateur weather gage on Londonderry Lane reported more than 14″ of rain! Dallas/Fort Worth officially received 9.46 inches of rainfall in 6 hours and 7.8 inches in 3-hours. Significant flash flooding has resulted. A 1-hour storm total of 3.01 inches was recorded at DFW with a storm total of 6.54 inches. That wiped out 67% of the area’s 2022 rainfall deficit in a few hours.
Threat Will Increase From North to South During Next 24 Hours
According to Jeff Lindner, Harris County Meteorologist, the frontal boundary over north Texas will slowly move southward today and approach the northern portions of southeast Texas by mid- to late afternoon. Numerous showers and thunderstorms will develop along the boundary along with scattered showers developing northward along the seabreeze and Gulf inflow.
The air mass will become extremely moist and unstable. When combined with slow moving/stalled boundaries, excessive rainfall can result. Lindner says areas north of HWY 105 have the first potential for heavy rainfall in early afternoon. Then the front will slowly sink southward toward I-10 tonight into early Tuesday. Expect slow storm motions, cell training, and back-building of cells to the west and northwest. Everything points to heavy rainfall.
This was clearly seen overnight in north Texas. The local air mass will not be much different over southeast Texas. Especially N of I-10. These rainfall rates can lead to rapid flash flooding especially in urban areas.
Widespread rainfall amounts of 2-4 inches are expected over much of southeast Texas through mid week. But Lindner also expects isolated higher totals of 6+ inches. And where these higher totals occur, flash flooding will be possible, he says.
Confidence in rainfall is high. But confidence in rainfall amounts and location of the heaviest rainfall is low.
Street flooding will be the primary threat with the heavy rainfall rates. Rises on area creeks and bayous will be possible if some of the heavier storms train or move slowly over any watershed.
Overall, this wet pattern will linger into late week. But a slightly drier air mass will eventually push through and we should transition back toward a more “normal” cycle of showers and thunderstorms driven mostly by the seabreeze front.
See the National Weather Services predictions below.
Posted by Bob Rehak on 8/22/22 based on information from HCFCD and NWS
1819 Days since Hurricane Harvey