Dwight Silverman

The SCW Q&A: Underwhelmed; micro/macrobursts; hurricane prep; hot summer; tornado terms; apple of our eye

If it’s almost the end of the month, that means Eric and Matt have once again scrambled to answer your most urgent questions. And given the busy weather month we’ve had in May, this edition of our Q&A is particularly timely. Got your own queries? Hit the Feedback button in the blog’s sidebar, respond here with a comment on hit us up on our many, many social network feeds: X, Facebook, Instagram, Threads, Mastodon and Bluesky. We’re everywhere, and now that includes LinkedIn!

–Dwight

Q. I feel like y’all are being TOO underwhelming. I definitely get not overhyping the weather. Which is absolutely why I started following you. But the last three storms you’ve underhyped and I was not prepared. I’d rather be over prepared than under. I didn’t at all expect the insanity that Oak Forest got on [May 16]. Thank goodness my cousin texted me to take shelter minutes before the storm hit. Please consider a middle ground.

A. This isn’t a question. Next one, please.

Just kidding. It’s a fair comment. The reality is that just as we don’t ‘over-hype’ the weather we also try not to ‘under-hype’ the forecast. Matt and I really are trying to simply be as right as we can be. You mentioned under-hyping the last three storms. That’s not true. On May 13, we predicted significant hail could accompany strong thunderstorms as they moved through the Houston area. Some areas, we said, may see hail as “large as an apple.” In reality, no one saw much, if any hail that day. I realize that pointing out how we missed on another forecast is perhaps not the best defense of our record. But my point is that we do not actively seek to under-hype storms. We are striving, always, for the middle ground you espouse. Some days, however, it’s damn hard to find.

I’m also sorry you felt unprepared for the derecho that slammed Oak Forest and other parts of Houston. We wrote about that recently, and some of the learnings we are taking away from it.

–Eric

Q: During the recent extraordinary Houston area (and beyond) weather phenomenon, is there any consideration that “microbursts” were present?

A: Yes, in our post about derechos, we noted that basically, they’re gigantic bursts of straight-line winds. In a sense, you could probably refer to a derecho event almost like a macroburst, which is wind damage on a scale greater than two and a half miles long. In reality, within this complex storm, there were probably a mix of macrobursts and smaller-scale microbursts, in addition to a couple tornadoes. We did not exactly see uniform damage across the area, but clearly some neighborhoods were harder hit than others. The more meaningful answer is that it’s all semantics in a situation like that, and the widespread damage is damage.

–Matt

Q. This storm has sobered us for what we are in for this hurricane season. How do you prepare? What do we need to keep in stock? What food should we store up?

A. Whoa, hurricane season officially starts Saturday! Fortunately, it doesn’t look like things will be insane right out of the gate. But there’s no doubt it’s going to be a busy season. The most important thing you can do right now is understand your vulnerabilities. Is your home at risk of storm surge because you live near the coast, and at a low elevation? Are you at risk of inland flooding? Is your home built to withstand hurricane-force winds, i.e. does your roof have hurricane clips? Are you willing to go without electricity for a week or three in September? All of these questions are important to determine in what circumstances you would evacuate. And after you understand when you would evacuate, you should make a plan for where you would go, what you would take, and how you will get there.

More generally, I find the preparation section on the Ready.gov website to be useful in making plans for an evacuation or to ride out the storm.

–Eric

Q: Is there any connection between the kind of intense spring weather we’ve been having and how hot the summer will be? Or are we most apt to have a drought when spring weather is severe?

A: The simple answer is not really. If you look at enough meteorological variables, you can find loose correlations among a lot of things. But correlation does not always (or often) mean causation. The best proxy to an “intense” spring may be storm reports in Harris County. If I take the five busiest years prior to this one from March through May, I can find 2007, 2019, 2020, 2023, and 2009 as my analogs. Combined, you get the map here:

Yes, active springs in Houston since 2000 have ended up with a net hot summer outcome in Texas, but correlation does not mean causation. (NOAA NCEI)

So yes, those active springs have led to hot summers on net. 2023 was our hottest summer on record, 2019 was the fifth hottest, 2009 was the seventh hottest, and 2020 was the tenth hottest. But years like 2011, 2022, and 2010 are on the top ten list as well and saw few severe reports in spring. In terms of drought, it gets a little noisier with some dry years mixed in with wetter ones. So no real solid signal.

We expect a hot summer this year, but it’s not because of the intense spring thunderstorms. The combination of a very warm Gulf, a post El Niño warm hangover, climate change, and other factors buoy confidence in the hot summer expectation. Severe weather does not. But it does make for a fun exercise.

–Matt

Q: I’m a bit confused about the tornado warning terms used here in Texas. It seems like there is a different meaning to the terms than what I am accustomed to. Could you clarify the Texas tornado warning system in one of your posts? ( As a Midwestern Indiana girl, I learned that a tornado watch was when the conditions were likely for a tornado and a warning was when a tornado was spotted, heading your way and you needed to take cover immediately.)

A: The tornado watch vs. warning system is the same anywhere in America. A tornado watch means that conditions are favorable for possible tornadoes. A tornado warning means that forecasters have identified a likely tornado or an in-progress tornado via radar or visual observations from people in the field. In a nutshell, a watch means you should pay attention while a warning means you should take immediate action.

Every tornado warning issued in the Houston area since 2020. (Iowa State Mesonet)

We get a lot of tornado warnings in the Houston area. Since 2020, there have been 136 of them issued by the NWS Houston office. The typical tornado we get here is a little different than what you see in the Plains or Midwest. Our tornadoes here are most often quick spin ups in squall lines (what we call QLCS tornadoes) or brief south to north moving supercells in the spring or fall ahead of cold fronts. Also, tropical systems. Harvey alone in 2017 led to over 140 tornado warnings. The QLCS and tropical tornadoes are a bit like playing whack-a-mole because they usually flare up and weaken rather quickly or sometimes look like they’re about to produce a tornado and do not. In the Midwest, you often have a little time to see them coming. Here, it’s just a different reality.

That said, after the derecho this month, I think that it’s apparent that folks should take these warnings seriously, even if they are inconvenient at times.

–Matt

Q. Can you please not use an apple as a comparison tool for the size of hail possible? Is it an gala apple? Is it a red apple? Is it a green apple? Is it a honeycrisp apple? Is it a pink lady apple? Is it some random miniature apple? Or is it ping pong to baseball sized?? 1.5 to 3.5 inches wide or 3.8 to 8.9 centimeters wide is easily accessible to most people. And fun fact the National Geodetic Survey (NGS) has updated their definition of a foot as of 2022 to better match international standards. An apple is completely subjective.

A. You forgot the most important argument in favor of apples. They’re delicious.

But just like my Granny Smith, you make a good point. The next time I’m writing a post on my McIntosh computer, and we’re expecting hail, I’ll try not to be so confuji in our terminology. Honey, I’ll try to be crisp in our language. Hope you find that apeeling.

–Eric

The SCW Q&A: First, the bad news; obscured by clouds; shuttered; humidity is relative; predicting it.

Welcome to the “just in the nick of time” April edition of the SCW Q&A. Each month Eric and Matt tackle the most interesting questions you’ve thrown at them. You can leave more questions in the comments here, or hit the Feedback link in the blog’s sidebar. We’ll also scan our social media channels (Facebook, Instagram, Threads, X/Twitter, Mastodon, Bluesky) for queries. And we’ll try to get the Q&A posted sooner in May! 

– Dwight

Q. Could this be is our last front until Sept/Oct? April is coming to a close soon, and I can’t recall many pronounced cooldowns in May.

A. Let’s get the bad news out of the way first. We are very near the end of the road when it comes to cool fronts in Houston. However, it is not unheard of to see cooler nights in May. That is not to say cold. If I squint into the distance, I can see a decent chance of a front around the May 11-13 period, so a little less than two weeks from now. That’s a long way out to have some confidence, but I’m modestly hopeful we may have one final fling with drier air before sultry summer settles upon us for months on end.

–Eric

Q.  I had read before the event yesterday that clouds sometimes clear during an eclipse due to the cooldown. Is that what happened yesterday in Houston when we had a thinning of clouds enough to see the crescent?

A. This is a great question. The answer is yes. During the eclipse in Houston, we had an issue with various sorts of clouds. We had higher level cirrus clouds, mid-level clouds, and low-level clouds. Most of the low-level clouds were cumulus clouds. What usually causes cumulus clouds to form? Heating. You heat the ground during the daytime, the heated air parcels rise, cool, condense, and you get clouds. Well, as you begin to block out the sun during an eclipse, you begin to reduce that heating mechanism. And in time, a lot of those cumulus clouds (or what we often call “fair weather clouds”) will dissipate. The animation below is from the 2017 eclipse, and you can see how the cumulus cloud field over Missouri and Illinois really dissipated as the eclipse unfolded.

A satellite loop of the 2017 total eclipse over Missouri and Illinois. (University of Wisconsin CIMSS)

This is likely what “saved” much of Texas this year. There were still plenty of clouds higher up, which are less impacted by daytime heating and more driven by physical storm systems. But by virtually eliminating a layer of lower cumulus clouds, you had one less obstruction to view the sun, which periodically broke through the higher clouds.

–Matt

Q. How far inland would you recommend having hurricane shutters to board up if a storm comes inland? I find myself trying to calculate what would be the strongest type of hurricane that we could feel in order to decide if I want to invest in shutters, but can’t find any info. Would you guys know?

A. We’re not storm damage experts, but whether you should have hurricane shutters depends upon several factors. First of all, the most important factor is whether you’re close to the coast, as winds do die down significantly as a storm moves inland and encounters friction with trees, homes, high rises, and other structures.. The second factor is the proximity of stuff, like trees and unattended deck chairs and you name it. The most common reason windows break is due to flying debris. So if there’s lots of things around that you can imagine flying into your windows, that’s a risk factor.

Maximum sustained winds from Hurricane Ike in 2008. (NOAA)

I’ll be honest with you. I’ve lived through flood storms in Houston. I’ve lived through surge storms. But I’ve not really experienced a wind storm. Hurricane Ike was the closest thing, but it barely brought Category 1 winds to parts of Houston. This was bad enough, knocking power out to the city for up to two weeks. At the time I lived in Clear Lake and we had to get a new roof. I guess what I’m saying is that it’s not just your windows, it’s also your roof. And a prolonged period without power.

I guess what I would advise is that, if you live south of Interstate 10, and can afford it, hurricane shutters are not a bad idea. You will probably never need them, but if it proves peace of mind, that is not a bad investment in an uncertain world. Make sure they’re easy to put up on short notice.

–Eric

Q. On your weather app I notice that the humidity (sorry I mean HOUmidity) can be low in the evening and then go way up in the morning, coming back down again as the day goes on. Why?

A. Relative humidity (RH) is just that, relative. Dewpoint temperature is the temperature to which you’d need to cool the air to saturate it. In other words, the higher the dewpoint, the damper the air is. Dewpoint can fluctuate, but it’s usually more stable than temperature. So, let’s say you have a dewpoint of 72°. The morning low is 75° in this example. That means your morning relative humidity at 75/72 would be 90 percent. Obviously, you warm up during the day, so with a high of 88 degrees but a steady dewpoint still sitting at 72, your RH at 88/72 has dropped to 59 percent. As the air cools around sunset bringing the temperature relatively closer to the dewpoint, the humidity rises again. It limits the usefulness of RH. This is why we flout other metrics like dewpoint to drive home how humid it actually feels.

–Matt

Q. After your earlier answer, I’m confused by the description of what “percent chance of rain” represents. I was taught in my meteorology classes that probability of precipitation in weather forecasts means the probabilistic chance that it will rain at the point specified in a given time period. For example, if I enter my zip code to get a National Weather Service forecast for my area today, a 40 percent chance of rain means each point within my zip code has a 40 percent chance of seeing rain, not that 40 percent of the land area within my zip has a chance of seeing rain. Insights? Or is this just splitting hairs?

A. It’s more or less splitting hairs. But this is a fun topic so why don’t we dive a little deeper. Let’s go directly to the National Weather Service, where we find this delightful introduction to its “probability of precipitation” explainer:

The probability of precipitation forecast is one of the most least understood elements of the
weather forecast.

I just love the “most least” phrasing. A perfectly confusing introduction to a confusing topic. Anyway, fundamentally you are correct that it is a point forecast rather than an areal forecast. But it is a point forecast based on an areal forecast. If that makes sense. Which it probably doesn’t. And that’s ok.

There are two factors that go into making a “probability of precipitation” forecast. First there is the forecaster’s certainty that precipitation will form or move into the area, and this is multiplied by the areal coverage of the precipitation that is expected. Here are two examples for how one might derive a 40 percent chance of rain:

(1) If the forecaster was 80 percent certain that rain would develop but only expected to cover 50% of the forecast area, then the forecast would read “a 40 percent chance of rain” for any given location.

(2) If the forecaster expected a widespread area of precipitation with 100 percent coverage to approach, but he/she was only 40 percent certain that it would reach the forecast area, this would, as well, result in a “40 percent chance of rain” at any given location in the forecast area.

Does that clear things up? Probably not.

But given the general inaccuracy of precipitation forecasts, I think it’s fine to think of a “40 percent chance of rain” as either a point forecast or, more generally, that about 40 percent of an area will receive rainfall during a given period of time. This is not an exact science, it’s just a forecaster making a most best guess of things.

– Eric

The SCW Q&A: Eclipsing, hurricane vs. typhoon, climate changed, thunder calc, bad forecasts!

In this second edition of our new Q&A feature, Eric and Matt tackle an excellent set of questions from you, our most excellent readers.

We do this monthly, and if you’re dying to know something weather- or SCW-related, leave us a comment here or on our many, many social channels – Facebook, Instagram, Threads, X/Twitter, Mastodon, Bluesky (we’re everywhere!) – or hit the Feedback button in the blog’s sidebar.

Let’s get to it.

Q: What does the forecast look like for the solar eclipse on April 8?

A. We have received more questions about the total solar eclipse next month than almost anything that I can remember. And for good reason, it is going to be spectacular—very likely the most dramatic celestial event that most all of us will see in our lifetimes. I cannot wait.

However, in regard the forecast we need to exercise a little bit of patience. Unless we see a very strong signal for high pressure over the state of Texas, confidently forecasting clear or partially clear skies is not something that can be done too far in advance. I plan to make an initial forecast next Thursday, and then we’ll provide regular guidance after that.

– Eric

A preview of things to come: The 2017 total solar eclipse as seen from Casper, Wyoming, by a team of European Space Agency astronomers. (Credit: ESA)

Q: I’ve been noticing that the term hurricane and typhoon are being used interchangeably and frequently by weather forecasters – both on tv and in the paper. I don’t recall this happening in the recent past. Why is this happening and do the terms mean the same thing?

A: The answer depends on where they’re talking about. No, really. Both terms describe the same phenomenon: What we call a hurricane, folks in East Asia call a typhoon. According to the American Meteorological Society’s Glossary of Meteorology, the word “typhoon” originates either from Cantonese (t’ai fung: “great wind”), Arabic (tufan: “smoke”), or Greek (typhon: “monster”). Aristotle described it as such in his text Meteorologica to mean a wind-containing cloud. You can read more about the etymology (and debate) of “typhoon’s” origins on the Wiki page.

Meanwhile, “hurricane” probably derives from “Hurakan,” the Mayan god of wind, storm, and fire. The thought is that the indigenous Taino peoples told Columbus and other Spaniards of this deity, and the name became associated and stuck to what we call hurricanes today.

If you travel to the Indian Ocean or Australia, these storms will be referenced as “cyclones.” I was taught in grade school that Aussies referred to them as “willy willys.” That is not the case. “Willy willy” actually refers to a dust devil which is like a miniature tornado that can form in clear weather (another topic for another day).

But, the bottom line: Hurricane, typhoon, cyclone, tropical cyclone, cyclonic storm are all basically interchangeable at the highest level. Hearing it called one of those names can narrow down for you where it actually occurred. There are occasionally other regional references you may hear, such as “Medicane,” which is essentially a Mediterranean version of a hurricane.

– Matt

Q. In southeast Texas, how has the climate changed over the last 10,000 years? Was this area drier, wetter, more trees, more prairie? How did this effect how people lived?

A. The Texas State Historical Association has a great website with answers to questions like this. I encourage you to visit there for the full details. But the big picture is that 10,000 years ago Texas (and the rest of the present-day United States) were emerging from the last great ice age. At that time, when glaciers reached their greatest extent, average temperatures were 10 to 15 degrees cooler than today. But by 10,000 years ago things were getting back closer to what conditions were like today, although Texas has steadily gotten a bit warmer and drier over recent millennia.

As for how people lived in Houston, how did they do it without air conditioning?

– Eric

Q: When you hear thunder, sometimes it sounds like it is right over you and other times it seems far away. As a meteorologist, are you able to point/pinpoint a specific area in the sky where the thunder is coming from?

A: So the first question to ask is “what is thunder?” Thunder is the audible response you hear when lightning heats and expands the air around the bolt. Remember, lightning is hot, with a temperature in the bolt of up to 50,000°F, almost as hot as last summer in Houston. Just kidding. Sort of. One reason the thunder sounds like it may be right over you is because it could literally be right over you, or at least nearby. In that case, you’re hearing the thunder “right over you” because the lightning strike occurred within a mile or less of your location. I’ve found that usually the loudest thunder I hear is when lightning hits within about a half-mile or so of where I am.

Now, there are other possible reasons for really loud thunder when lightning is nowhere near you. If we have an inversion in place in the atmosphere, or when it’s actually warmer above our heads than at the ground, sometimes those sound waves from the thunder can propagate farther along or just have more impact. So lightning can strike miles away, yet you still hear loud thunder.

Map of lightning strikes on July 28, 2020, in the Houston area. Yikes! (Lightningmaps.org)

So, like anything, it’s complicated! Everything from the air temperature at the ground to the air temperature a few thousand feet up can impact the sound of thunder. Fortunately, we are blanketed with lightning detection sensors today, so we almost always know where lightning strikes or comes from in near-real time. And there’s always the Lightning Distance Calculator. But just remember, if you can hear thunder, it’s time to get inside!

– Matt

Q. Why are models and meteorologists so bad at predicting rain? Apps always say its going to rain and not a drop. This has been happening in the past three years. Something is off.

A. And I took that personally. Seriously, I share your frustrations. A big part of it is that rain can be a very localized phenomenon. Pure misery is watching a radar app during a drought and hopefully seeing heavy showers in the next neighborhood over, but they stop half a mile from your location. Well, guess what, a forecast for rain showers verified for that neighborhood, but failed for yours. Imagine the challenge for us when we must forecast rain chances for a metro area 100 miles across, with varied climates from the coast the piney woods. And all you want to know is whether it will rain at your house.

That’s why you’ll often see a 30 percent chance of rain or a 50 percent chance, or whatever. That means that, for a given forecast area, the percentage of that area expected to see rain—it could be a sprinkle or a deluge—is 30 or 50. It’s a probabilistic answer because we cannot tell you definitively that it will rain. (Except during Hurricane Harvey, of course. One could confidently predict a 100 percent chance of rain at that time).

There are other factors: Even high resolution models cannot account for the physical processes that occur on a small scale, of a few miles or less, that determine whether rain showers develop or dissipate. Finally, it does not help that there are no regular, local weather balloons in Houston.

– Eric

The SCW Q&A: Frost, pollen, predictions, blue skies, and swag!

One of the best things about Space City Weather is the people who read it. Anyone who writes regularly wants to feel like the audience is paying attention – and it’s even sweeter when they’re talking back. SCW is more than just Eric and Matt: It’s you, too.

And you have questions. Lots of them. We enjoy turning your queries into posts, which happens a lot. Now, it’s going to happen more. We’re starting a monthly SCW Q&A feature, in which Eric and Matt will tackle a handful of questions you’ve asked them recently.

Got a question of you want answered? Leave it as a comment here or on one of our many social channels (we’re everywhere!), or hit the Feedback button on the blog’s home page.

Q. Do you think we’ve seen the last chance of frost? I’m itching to get plants in the ground.

A. We received a couple of questions along these lines. We are now past the “average” date of the final freeze for pretty much all of the Houston metro region, except for a few outlying areas like Conroe and Montgomery. So historically the city’s odds of seeing another freeze are below 50 percent.

But I think they’re far lower than this. We’ve clearly entered a more spring-like pattern, and there is no sign of a super-strong front in the next 10 to 14 days. So I’d say our chances of seeing another freeze in the Houston area this season are 10 percent, or less. It could happen. The city has recorded freezes in early April before. But it’s very unlikely.

–Eric

Q. When do you expect that the yellow pollen will be back in Houston again? Thanks!

A. It’s baaaaaack! Allergy season is now in full swing. Usually, we’ll see little bumps in pollen through January and February as we get periodic milder weather. But we never see the full force of pollen arrive until usually the last week of February. It appears that began last Friday. In fact, if you look historically, you can see this in the City of Houston’s tree pollen count. The chart’s a bit messy because data is not taken on weekends or holidays. But you can see the general trend.

The daily tree pollen count in Houston from 2017 through last week shows that allergy season typically peaks around mid-March here. 2022 was a notable exception with a massive peak in late March.

Since 2017, Houston’s peak pollen day has occurred in March, varying between the 6th and the 31st and averaging around St. Patrick’s Day. Pollen typically builds in the first half of March, peaks, and then slowly tails off before a more dramatic drop heading into April. Notice how on the chart above 2021 stands out for how short pollen season was, thanks in part to the mid-February freeze. With a potentially extended spring this year, we probably won’t get so lucky. Whatever the case, the next three to five weeks will probably be rough for those with pollen allergies.

–Matt

Q. You’ve talked about how it’s silly to predict hurricanes too early. But at what point does a season prediction start to become credible, in terms of timing?

A. This is a really good question. Seasonal forecasting for hurricanes is a challenge, whether you do it in January, March or May. This is part of my day job in the energy industry, and it remains the most elusive in terms of consistency, particularly when you get into other variables like temperature or rainfall for a season. But from the standpoint of hurricanes, seasonal forecasting is actually not half bad when you begin to see outlooks emerge in March. Colorado State University issues one of the most publicized hurricane outlooks, and this year’s first iteration comes out on April 4th. Anything prior to that can be hit or miss.

Raw modeling of hurricane season forecasts is occasionally good, occasionally bad. For humans, trying to predict El Niño vs. La Niña and the amplitude can be a challenge this time of year because of the inherent “spring predictability barrier.” That’s one of our best signals for determining directionality of a hurricane season (busier or quieter). But some years are easier than others. The current thought among most meteorologists I know and follow, as well as my own independent thinking, is that we are almost certainly heading into a La Niña this summer. That, combined with continued exceptionally warm oceans globally (a global marine heat wave) seems to imply that virtually no one should be forecasting a quiet hurricane season this year. We wrote about this in detail last week at our companion site The Eyewall.

But as far as firm concrete numbers? Late March and early April offers a viable first guess, with some adjustments in May and even June. That said, what no one is really, consistently good at on a seasonal scale is predicting where storms will go. So regardless of forecasts, it’s important to remember to prepare for every hurricane season as if it will be the one that impacts you.

–Matt

Q. I have a question regarding how clear Houston appears following a cold front. I imagine it’s because the wind blows the smog and pollution away. But what’s the science behind that? Does it also have something to do with our humid climate? 

Well, you have pretty much answered your own question!

First let’s characterize the haze that typically makes for less clear air. Haze is caused when sunlight encounters tiny pollution particles in the air. Some of this light is absorbed by particles, and some is scattered away before it reaches you. More pollutants mean more absorption and scattering of light. In Houston we have plenty of pollutants in the air, which increases the likelihood of haze. But weather plays a role as well.

Fronts typically bring blustery conditions, and these winds clear out air pollution at the surface. In addition, warmer air in Houston tends to be more humid. So think about a warm, summer day in Houston: It’s humid, winds are typically light and its partly to mostly sunny. These are ideal conditions for the formation of haze. Conditions in the wake of a good front: cooler and drier air, and windy conditions, are kryptonite for haze.

–Eric

Haze is caused when sunlight encounters tiny pollution particles in the air. (US EPA)

Q. I love the site and love the new(-ish?) logo! Any chance you’ll get that on a coffee cup at some point?

A. I’m glad you like the new design! It was time for a refresh. The original design, depicting the space shuttle carrier aircraft flying over the city of Houston, dates to October 2015. At the time I was in a rush to create the site in a couple of hours. I grabbed the image because it was a free NASA photo and it captured both the elements of “Space City” and “Weather.” But it wasn’t professionally done. I love the new look, and especially because it features the International Space Station, which is flown right here from Houston.

As for coffee cups, that’s a great suggestion. We’ll be sure and add those to our annual fundraiser. That takes place in November when we encourage people to buy merchandise and donate to support the website and our app.

–Eric