In brief: After a few mostly cloudy days we’ll see increasingly clear skies and this will help temperatures march upwards. We’ll go from highs in the low-90s today, to mid-90s this weekend to upper-90s by Memorial Day. After that a weak front will provide some modest relief.

Thursday

After a cloudy start we should see partly sunny skies this afternoon, and this should help to push high temperatures into the low-90s. Winds will blow from the south at 10 to 15 mph, with occasionally higher gusts. Once again, we should see some fairly strong storms develop in central Texas to the north of Austin. While these will propagate eastward, I expect them to remain north of Highway 105 once again, with no impact on the greater Houston metro area. Low temperatures tonight will only drop into the upper 70s.

Friday

A day very similar to Thursday, although high temperatures are likely to be a degree or two higher.

Saturday and Sunday

We’ll see mostly sunny skies this weekend, with high temperatures solidly in the mid-90s. We will be hitting our first highs above 95 degrees nearly three weeks earlier than normal, in case you were wondering whether this is typical weather for late May. It’s not. Nighttime lows remain sultry, around 80 degrees.

Memorial Day

Everything comes together on Monday, sunny skies and the characteristic jump in temperatures associated with an approaching front, to push our highs into the upper 90s. If we look at wet bulb globe temperatures—a measure of heat stress in direct sunlight that takes into account air temperature, humidity, wind speed, sun angle, and cloud cover—we see the potential for an ‘extreme’ day in terms of heat. Please bear this in mind if you have outdoor activities planned.

Tuesday and beyond

We’ll see a slight chance of rain on Monday evening as the front approaches and moves through, but for now I don’t expect anything more than a dusting of showers. Highs next week look more reasonable, in the low 90s, with overnight lows perhaps in the mid-70s. We’ll also see some daily rain chances in the Wednesday through Saturday period, although they may be of the 20 percent daily variety. I’m not sure yet. In any case, the very end of May should see a bit of a return to normalcy.

In brief: This post explains what a derecho is, where the term came from, and talks a bit about some past thunderstorms of note in Houston.

What is a derecho?

The National Weather Service has concluded that Thursday’s severe storms in Houston constituted a derecho. So what does that mean?

First off, it’s pronounced “deh-REY-cho.” Meteorologists have debated what the definition of one of these things actually is for years. And we still don’t have a concrete, universally accepted definition. However, progress was made after a 2011 storm that hit the Southeast and a 2012 derecho that ravaged the Mid-Atlantic and Midwest to work toward something more widely accepted. Ultimately, NOAA/NWS defines a derecho as a continuous or intermittent path of wind damage from a squall line of thunderstorms, bow echo, or quasi-linear convective system (QLCS) that extends at least 400 miles and is at least 60 miles wide. In other words: It’s a swath of wind damage from mostly non-tornadic thunderstorms that extends for 400+ miles and is at least 60 miles wide.

What makes it different than typical severe thunderstorms?

A derecho, as noted above can be a squall line, bow echo, or QLCS. We get several of those types of events every year in Houston. What sets a derecho apart is the wind damage. It’s not normal. It’s not a couple trees on power lines. It’s a lot of wind damage over a long path.

Are all derechos the same?

No! Derecho events are broken down into three categories: Serial, progressive, and hybrid. A serial derecho is basically where you have one giant squall line that is hundreds of miles long with multiple embedded bow echoes producing widespread wind damage. A progressive derecho is the one we experienced in Houston last week that is typically no more than about 250 miles wide. You also have hybrid outcomes, which basically share characteristics of the two others.

Why is it called a derecho?

According to NOAA, Dr. Gustavus Hinrichs, who was a professor at the University of Iowa coined the term in 1888. The literal Spanish translation of derecho is “straight ahead” or “direct” or even “right.” Here’s where the etymology gets kind of fun. “Tornado” derives from the Spanish “tronada,” which literally means thunderstorm. But there is also a Spanish word “tornado” which essentially means “twisted,” and it derives from the Spanish verb “tornar,” which means “to twist.” So essentially, Hinrichs took the “opposite” of twisted and decided that derecho (or “straight”) would be a good way to distinguish tornado-like wind damage that was not caused by a tornado.

Are derechos common?

The short answer is: Kind of. The most recent derecho prior to Thursday’s in Houston occurred back on April 1-2 from just west of Missouri through West Virginia. A storm that almost met derecho criteria occurred just this past weekend in Kansas and Missouri. There were derechos in 2023, 2022 in Canada, 2021, and so on. In fact, the quad-state area around Kansas, Missouri, Arkansas, and Oklahoma northeast of Tulsa averages more than one derecho per year.

Derechos are most common in May, June, and July. Keep in mind that a lot of the areas that see derechos every 1 to 2 years are more rural, so it’s likely you hear less about them than when they hit places like Chicago or DC or Houston directly, causing billions in damage.

You can read about a bunch of pre-2012 events across the country here. Some even occur out West. I was introduced to derechos when I worked in Upstate New York early in my career. The memories of the 1998 Syracuse derecho were still incredibly sharp, much like Houstonians will remember last week’s. That was followed up by a second derecho event that moved from Michigan to New York City. The 1995 Adirondack derecho (or Adirondack blowdown) was responsible for knocking over more than half the trees in 100,000 acres of Adirondack Park.

The Houston area’s history with derechos and thunderstorm wind events

There are a few thunderstorm wind events and derechos that have stood the test of time in this area. First and foremost was just last summer when a squall line delivered a 97 mph wind gust to Bush Airport.

That storm on June 21st was one in a series last June that caused damage across the area. It was not a derecho, but it certainly caused severe damage north of downtown Houston.

A storm system in 2002 did a good bit of damage, including to the I-10/Gessner area, according to the Houston Chronicle’s archives. Just shy of $1 million in damage was reported with fortunately no injuries.

In early May 1993, a powerful squall line knocked out power to 200,000 homes in Harris County and went on to rampage Galveston County, causing at least $50 million in damage and delivering a 98 mph wind gust to Scholes Field in Galveston.

There was also an event the year after this in March that brought 100 mph winds to the less populous western end of Galveston Island.

Texas Boaters’ Derecho (May 1986)

While not Houston, the “Texas Boaters’ Derecho” of May 1986 makes the list of memorable derecho events in the United States. You can read a full summary of the event on page 20 of the May 1986 NOAA StormData publication.

It’s tough to find a lot of good information on how this particular event impacted Houston specifically, but it is infamous due to the fact that it drowned six. There was a fishing tournament and boat race on Lake Livingston that day when the storm hit, bringing winds estimated to be 90 mph and waves of 10 feet on the lake. Much like we see with the damage from this year’s derecho, there were pockets of more significant damage within a broad damage field during the 1986 storm.

May 1983 storms

Thanks to Bill Read for pointing this one out to us last week. Three years prior to the ’86 derecho, a particularly bad thunderstorm event impacted much of the Houston area.

According to NOAA’s May 1983 StormData, approximately four downburst events, including one over the city of Houston, combined with eight tornadoes for a deadly severe outbreak in our area. Winds were estimated at 75 mph or stronger in spots, with several transmission towers crumpled over, much like in this month’s event.

Over 300,000 customers were left without power in that storm, which would have been a bit less proportionally to this year’s storm. Winds were measured as strong as 110 mph during a tornado in Nederland, near Beaumont with this one. According to a Houston Chronicle recap of this event at the time, the spokesman for the Houston-Harris County Civil Defense stated that the damage was worse than in Hurricane Carla in 1961.

Approximately 10 people died with over 100 injured from this storm. Arguably, this was the previous worst non-hurricane wind storm in Houston until last week’s. It’s tough to find an official estimate on the damage caused by the May 1983 event, but it was likely in the tens of millions of dollars at the time.

Other events that seemed to garner some attention were a combination of severe storms and tornadoes on May 2, 1979, which primarily impacted western and northwestern parts of the area. On May 7 of 1976, significant wind damage occurred east and southeast of Houston, along with a few tornadoes nearby. The Exxon facility in Baytown apparently observed winds of 90 to 95 mph with considerable damage in that community. Back on June 4, 1962, a torrential squall line of storms seems to have had something of a similar impact on parts of the city as the recent derecho. Many people lost power, wind gusts hit at least 75 mph, and some windows were blown out downtown.

While last week’s derecho was extreme by any real definition of Houston thunderstorms, I think we can assume that perhaps the return period on such a storm may be less than we might have thought. And Houston can now add destructive thunderstorm winds to a litany of periodic weather disasters including freezes, floods, hurricanes, extreme heat, and drought.

In brief: A dying front brings a chance of storms well to the north of Houston tonight, but for most of us the story remains one of heat. Temperatures will peak over the weekend, with Memorial Day looking especially hot.

Wednesday

Expect another warm day in Houston, with highs of around 90 degrees due to mostly cloudy skies. It will be a little windier than Tuesday, with southeasterly gusts up to about 20 mph. With the humidity, it will feel plenty hot outside during the daytime hours before lows drop to about 80 degrees tonight.

For areas north of Houston, and by this we are probably talking about locations north of Highway 105 in Montgomery County, there is a chance of storms later this evening and during the overnight hours as a dying frontal boundary pushes a line of storms through northern Texas. There is some question as to how far south these storms will get. It is possible that locations such as College Station and Huntsville could see some thunderstorms tonight. There is even a slight chance that locations further south, including The Woodlands, could see some of this action. However, I think a capping inversion will probably prevent such activity for most of the Houston metro area, including at least the southern half of Montgomery County.

Other than this, we should be rain-free through the weekend.

Thursday

Expect partly sunny skies and a high of about 90 degrees with plenty of humidity. Another warm night.

Friday

As skies turn mostly sunny, expect highs to nudge up into the low 90s with plenty of humidity.

Saturday, Sunday, and Monday

The holiday weekend looks hot and sultry. Highs will rise from the low 90s on Saturday to the mid- to upper-90s by Memorial Day with mostly sunny skies. Folks, it’s going to be Houston hot this weekend, so take all appropriate heat precautions. That includes sunscreen during the daytime with the Sun reaching an angle of 80 degrees during the early afternoon hours.

Next week

So what happens after Memorial Day? It still looks like some sort of weak front arrives on Monday night or Tuesday. It’s late May, so your expectations should be for slightly cooler weather, and slightly drier air, and not much more. Still, beggars cannot be choosers at this time of year. Rain chances look a little bit improved later next week, but we’ll have to see about that. I don’t have much confidence in such a prediction.

Last week’s storms

Check back later this morning as Matt has a post on last week’s storms, and where they share some commonality with Houston’s history of similar events. It’s a great article with a lot of historical context.

In brief: Today’s post talks about the arrival of summer-like weather in Houston, and breaks down the four phases of summer. We also discuss a new offering from the National Weather Service called “HeatRisk.” Finally, we look ahead to a hot and sunny Memorial Day Weekend.

We’re starting to see 90-degree days on the regular which, in my mind, signals the start of summer in Houston. Long-time readers will know that I like to break summer down into four phases. Why? Because “summer” season lasts so long, nearly five months. This is contrast to meteorological summer, which runs from June through August, and “solstice” summer, which runs from June 20 through September 22 this year. For me, Houston’s summer typically runs from about mid-May through mid-October. Here are the four phases:

• Early summer: When we first start to see 90-degree temperatures with regularity, but some nights in the 60s are still possible, and there’s still the thinnest hope of a weak front
• Mid summer: When highs run from 90 to 95 degrees, and nights are sultry, but you know it could still get worse
• High summer: Somewhere between late July and early September there’s a period where temperatures reach the upper 90s to mid-100s and you realize, “Ok, this really is the worst.”
• Late summer: This is the period in September and early October when days grow shorter and we usually see the first front or two of the season. But most of the time it’s still hot.

Early summer began this week in Houston, and we have a chance to bump into Mid summer early next week before we drop back into early summer. You may think it’s crazy to have gradations of heat during summer, as Houston is invariably hot and humid during the summer months. But as we found out last year, there is heat and there is heat. Last summer we used the “wet bulb globe temperature”to measure how hot it really felt outside, and we’ll continue to use this tool. However there’s now another way to assess the heat.

This year the National Weather Service is introducing a “HeatRisk” color-based scale that takes into account the following factors to provide guidance for outdoor activities:

• How unusual the heat is for the time of the year
• The duration of the heat, including both daytime and nighttime temperatures
• If those temperatures pose an elevated risk of heat-related impacts

The scale ranges from green (little or no risk) to magenta (extreme). If we look at the risk for Memorial Day we can already see a few areas of Houston reaching an ‘extreme’ level of risk. This is due to temperatures likely in the mid- to upper-90s and the time of year, late May, as we’ve not re-accustomed ourselves to the heat yet.

In any case, feel free to use this planning tool as we go through the summer.

Tuesday

We’ll see a few more clouds today than we saw on Monday, and this should help hold temperatures to about 90 degrees. Winds will be from the south, at 10 mph or so, with gusts up to 20 mph. Aside from that it’s going to be another humid day, with a warm night in the mid- to upper-70s.

Wednesday

Skies should be partly to mostly cloudy on Wednesday, and this should allow some parts of Houston to stay in the upper 80s. However, if we get a bit of sunshine during the afternoon hours, highs in the low 90s are possible. Still warm. Still humid.

Thursday and Friday

These days will probably bring mostly sunny skies, so temperatures from 90 to the low 90s are likely. Nights remain warm.

Saturday, Sunday, and Monday

Hot and mostly sunny. Highs this weekend are likely to reach the mid-90s, with upper-90s possible on Memorial Day. By Monday it looks like a weak front will approach the area, bringing a chance of rain with it. However I don’t believe this front will arrive in time to modify conditions during the daytime on Monday.

Next week

The front should arrive on Monday night or Tuesday, and at this point it does appear as though the boundary will indeed push all the way to the coast. Don’t expect miracles in late May, but we might see some slightly drier air and highs in the upper 80s, with modestly cooler nights. It isn’t much, but it’s the best we can reasonably hope for at least the next three months, and probably longer.