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An optimistic late June forecast

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I love when clouds and rain give way to sunshine! My whole mood changes. This morning, I felt like I woke on the wrong side of the bed. Then suddenly around noon, I felt better! I realized that the sun had appeared and everything looked brighter. Sunshine on my shoulder really does make me happy!

I know I am not the only person whose mood can be dramatically affected by the weather. I realized how much it affected me when I lived in Minnesota for two years. Between the long, cold winters and the lack of what a southern girl would call a real summer, I spent more time than expected in a grumpy mood. That northern state is where I learned about seasonal affective disorder.

That being said, I am sure that I’m not the only one happy to see the sun today and wondering if we really have had as much rain as it feels like we’ve had this year. The answer is yes. It has been a wetter-than-normal year, so far.

6-10 day temp outlook

The 6-10 day temperature outlook from the Climate Prediction Center shows good probability of below normal temperatures during that period.

As of yesterday, Raleigh-Durham International Airport has reported 27.47 inches of rain since January 1, which is 7.86 inches above our thirty-year average. Since June 1 – just in the last three weeks – we have had 3.03 inches more rainfall than is normal.

The good news is that after the cold front moves through the state this weekend, we are in store for a drier period. High pressure will arrive behind the front on Monday, and we may even have several days of cooler-than-average air temperatures as well. With a forecast like this one, it’s easy to feel optimistic on a Friday afternoon.

Enjoy your weekend!

Weather Blog

Lightning fatalities wonderfully low so far in 2017

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We could file this post under the “no news is good news” category, but then, why would you bother reading it? Actually, I’m not sure that category exists, but maybe there’s potential in that idea. So, why am I writing about lightning fatalities? The answer is typical of a meteorologist: I want you to stay vigilant as we head into the time of the year when most occur.

As of today, there has been only one lightning fatality in the lower 48 states. It happened on May 8th in Douglas County, Colorado. A lady was riding a horse in an open field near a tree, and was struck and killed. While one is one too many, this year has a notably good track record so far. Over the last ten years, the average number of lightning deaths by the end of May is five and the average for an entire year is 30. Last year ended above average with 38.

Here are some more random lightning facts for your Front Porch conversations:

June and July tend to have the most lightning fatalities with an average of seven and ten respectively. There could be several reasons, but more people being outside during the summer months and more heat energy available to create convective storms are likely the largest contributors to those numbers.

According to statistics from the National Weather Service, “only about 10% of people who are struck by lightning are killed, leaving 90% with various degrees of disability.”

Your chances of being struck by lightning really are better than your chances of winning the jackpot in the Powerball lottery. Those odds are one in 292,201,338. Your odds of being struck by lightning in the United States over an 80-year lifetime are one in 13,000. I’m not a gambler, but I would bet on lightning over wasting two dollars on a lottery ticket.

Florida has the highest cloud-to-ground lightning flash density in the country with 20.8 flashes per square mile. Louisiana and Mississippi come in second and third, respectively. North Carolina ranks at number 20 out of 49 with an average of 8.8 flashes per square mile. Washington state has the least with 0.4. This data was collected by the Vaisala National Lightning Detection Network over the period 2007-2016.

A recent Florida Tech study confirmed that cloud-to-ground lightning strikes are more powerful over the ocean than over land. Scientists already suspected that the ocean was the more dangerous place to be during a thunderstorm. Now they have reason to believe that “people living on or near the ocean may be at greater risk for lightning damage if storms develop over oceans and move on-shore.”

Vaisala Lightning Map

Vaisala’s Lightning Detection Map shows where the most recent cloud-to-ground lightning strikes have occured.

Weather Blog

Doppler radar technology has its limits

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I love the sound of thunder. I didn’t always, though. When I was a small child, I would hide under my bed during storms, and we used to get some good ones in Paducah, Kentucky. My mother would try to calm me by telling me that thunder was just the sound of angels bowling in heaven. I’m not sure that tactic worked as well as she wanted, but I still remember it.

As I got older, my fear turned into fascination. When I was in elementary school living in Mississippi, I thought that a tornado watch meant that I should run from window to window in the house watching for tornadoes. I’m not kidding. I took it that literally. I guess it gave me something to do on a summer day when I couldn’t play outside.

Now thunder gives me a strange joy – a combination of excitement over the power of the storm and an odd sense of peace that Nature is working the way she should. After all, thunderstorms are as much a part of our environment as sunny days are. We need the rain just like we need the sun.

I guess my attitude toward storms has changed since I was a child as much as our technology has.

The type of Doppler radar the National Weather Service uses was first designed in 1988 and went into wide usage in the 1990s as a means to track storms. There are currently 155 WSR-88D Doppler radars in the country and its territories. Improvements to the technology continue as scientists and engineers come up with new ways to listen to various aspects of storms using radar.

I say “listen” because radar stands for “Radio Detection And Ranging.” At the risk of over-simplification, the WSR-88D sends out radio pulses and listens for how much of them return and how quickly. Using specific algorithms, those signals are translated into a visual image for users to interpret as precipitation types, storm directions, wind speed, etc. It is quite the useful tool!

Credit: National Weather Service Jetstream.
At increasing distance, the radar is viewing higher and higher in storms and the beam may overshoot the most intense parts

As much as meteorologists depend on it for nowcasting – meaning seeing what a storm is doing at the moment and projecting its path and strength into the extremely near future (minutes to a few hours) – Doppler Radar still has its limitations. Probably the most glaring one is how it is limited by the curvature of the earth’s surface. A radar’s beam is emitted in a straight line. While it will take several scans at multiple elevations above the earth, each scan is still a straight line. Imagine the lowest scan being directly out from the radar and basically parallel to the ground at the radar location. As the beam continues moving directly out along that path, the earth curves away from it. The effect is that the radar beam’s path goes higher in elevation as it gets farther from the radar site.

If you are in a location relatively close to the radar, the increase in altitude won’t matter much to you. If you happen to be in a place that is farther from the radar, it can make a big difference. While the radar is seeing what is happening in the top of the storm cloud, it could be missing what is going on at the bottom of the cloud.

For example, when I was a broadcast meteorologist on a network of radio stations in the middle third of the country, I once covered a tornadic storm in rural South Dakota. The cloud was so far away from the radar that it looked like there was just a little rain. I could not see any evidence of rotation on the velocity returns. I knew that it existed because the local National Weather Service office’s tornado warning stated that a trained spotter called in a tornado on the ground at a location under that cell. If it had not been for that ground-truth, that NWS office might have completely missed the severity of that storm and no warning would have been issued. Not only was that event an example of a rotation happening in the lower levels of a storm while not clearly indicated in the higher levels on radar, but it’s also a great example of how important trained Skywarn spotters are to our warning system.

Another more recent, relatively local example is what happened last week in Sampson County when straight-line winds up to 90 miles per hour hit an area hard. Below is the official word the NWS office in Raleigh gave on their Facebook page the following day:

Good morning, all. We appreciate all of your comments and questions regarding the results of yesterday’s storm survey in Sampson County. This was a very rare event for central North Carolina; we tend to not get straight-line winds of this magnitude, though they are more common in other parts of the country. Most of our damaging wind events are spotty and relatively less impactful, and with that consideration, this was indeed not a “normal” event for our area. However, this shows the potential power of significantly severe straight-line winds.

We understand your concern, particularly given that this area was hit twice in the last week with damaging storms. However, please know that our assessment that straight-line winds led to this damage was determined based only upon the damage present. The magnitude of damage was indeed consistent with wind speeds of a weak tornado; however, the direction in which debris was scattered suggested straight-line winds were the culprit.

Not all straight-line wind events are created equally, and they certainly do not conform to conceptual models very well. A couple of additional items to note, addressing comments from yesterday: 1) straight-line winds can also sound like a freight train when they are the strength of a tornado and 2) in terms of changes in air pressure, tornadoes are associated with low pressure, while straight-line winds are associated with high pressure.

Our thoughts are with those of you affected by the recent storms in Sampson County. We are here to serve you. This was, unfortunately, the combination of a rare event with poor radar coverage in that area. While we were keeping an eye on the storm and thought wind gusts to 50 mph were possible, data available to us did not indicate a severe threat. We continue to strive to improve upon our warning service for all of central NC.

~US National Weather Service Raleigh NC, May 31 at 10:33am

I added the italics in the last paragraph for emphasis.

Many commented on the post that we need an additional radar for better coverage in that area. Perhaps we do. Radars are expensive to site, establish, man, and maintain. There are other regions of the country with less radar coverage than rural North Carolina has. Of course, those regions also tend to be pretty sparsely populated, but I bet the people living there would like improved coverage for their families and properties.

Using technology like the WSR-88D, the National Weather Service provides a unique service to all residents of the United States. Its goal is the protection of lives and property, and it strives to reach that goal using (among other things) forecast models, satellite data, Doppler radar, trained volunteer Skywarn spotters and cooperative weather observers, and talented, well-educated, and passionate employees. It is a necessary expense line on any federal budget – something to consider if you are calling for additional radars.

Personally, I would love to see that particular improvement in the system nationwide. No one likes to be taken by surprise by severe weather, and I can’t imagine living some place where that could be the case. Or maybe I can – maybe I would feel more like the four-year-old me that feared every thunder clap because I was unsure of just how bad or benign each storm might be.

Weather Blog

Reader Question: What determines the size of raindrops?

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You might have noticed that raindrops are bigger in the warmer months and feel like tiny ice daggers in the winter months. The difference in size really boils down to how much heat is available in the atmosphere.

summer storm cloud

A summertime thunderstorm with a tall updraft like this one photographed by Niki M. allows raindrops time to grow.

Heat causes air to rise. The layer of the atmosphere closest to earth’s surface, the troposphere, typically gets cooler with height. As the air cools, it loses the ability to hold as much water vapor.  The excess water vapor in the air eventually condenses into liquid water droplets. Those water droplets fall, and on the way down bump into other water droplets. Liquid and frozen water has this cool ability to grow by accretion – meaning that when droplets hit each other, they form one larger water droplet. If the droplets get too big, they may split again, but they’ll still be pretty large relative to the size they would be in winter.

The farther the droplets have to fall back to earth, the more time they have to grow. In the warmer months, there is more heat available to cause air to rise, which means there is more energy available to create large updrafts and taller clouds. Winter air tends to breed weaker updrafts and shorter clouds, so the water droplets have much less time to grow before reaching the ground.

Weather Blog

Will planting more trees stop global warming?

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I have always preferred to exercise outside. I walk on the sidewalks and greenways and hike in the woods. The fresh air and nature’s music – the sounds of the wind through the trees, the birds, running water, etc. – keep me grounded and happy.

Reedy Creek

Trees line a muddy Reedy Creek running through Umstead State Park in Raleigh, NC.

This weekend while walking with my friend at Umstead State Park, I heard a loud, unmistakable popping and cracking, and I looked to our right just in time to see an old, dead tree come crashing down. Believe it or not, that was the second time in a year we have witnessed a tree fall in the woods. If we see one more, I might start to think it has something to do with us.

That moment was a reminder that trees don’t live forever. It was also just part of a thread of tree-themed conversation items that has run through my life in the last month. A larger part is a question I have been asked a few times in recent weeks: will planting more trees stop global warming?

The answer seems simple. After all, we learned in grade school that trees turn carbon dioxide into oxygen, right? Unfortunately, the issue is really not simple at all.

I don’t claim to be a forestry expert or a climatologist. I’m an operational and broadcast type of meteorologist. Still, that doesn’t mean I don’t enjoy reading and researching answers to questions like this one. Over the last couple of days, I have done just that, and trying to find a succinct answer has lead me down rabbit hole after rabbit hole.

It seems – like so many other aspects of weather, climate, environment, and nature – not only is the answer complicated, but all the things we need to consider to be able to answer it are not necessarily completely understood.

If you ask the Arbor Day Foundation, planting trees fights climate change. Period. Its website even tells you which side of your house to plant trees for the biggest benefit if your goal is an energy-efficient home. It says that neighborhoods with tree-lined streets are several degrees cooler than neighborhoods without, and it lists other reasons to plant trees. Of course, what else would you expect from an organization with the goal of planting trees?

An article by Thinkprogress titled “Reforestation Doesn’t Fight Climate Change Unless It’s Done Right,” inspires a bit more deep thought on the subject. The author points out that while reforestation is generally a good idea, planting in the wrong places may actually do more harm than good.  For example, planting more trees in areas that tend to have a good deal of snow such as Canada’s boreal forests, will decrease the earth’s albedo, which is a measure of a planet’s reflectivity. Snow reflects more of the sun’s radiation – earth’s largest source of heat – back to space than trees do. Decreasing the amount of solar radiation reflected would lead to more warming.

An article on Eos, the news website of the American Geophysical Union, makes the same point and talks about afforestation, which is planting forests where none have existed. There’s another interesting idea that has its own pros and cons and if undertaken, must be done so in an intelligent, thoughtful, and well-researched manner. One point to consider is the trees planted should be native to the area and helpful in creating and protecting biodiversity.

One last article that I read was from the International Union for Conservation of Nature. By looking at three case studies in the American Northwest, it explains a little further how reforestation isn’t just about planting trees. I’ll admit, there isn’t much about climate change in this one, but it was interesting nonetheless.

NASA is currently assimilating satellite data into computer models to show how carbon dioxide moves in the atmosphere and changes seasonally. The better those models are, the better we will understand where the carbon dioxide in the atmosphere comes from and goes to, and in the long run, that may help determine just how much planting the right kinds of trees in the right places might help mitigate a warming climate.

 

I really do suggest reading the following linked articles if you want more detail.

Arbor Day Foundation

https://www.arborday.org/trees/climatechange/treeshelp.cfm

Think Progress

https://thinkprogress.org/planting-trees-climate-change-solution-3e5b6979561f

American Geophysical Union

https://eos.org/research-spotlights/can-tree-planting-really-help-mitigate-climate-change

International Union for Conservation of Nature

https://www.iucn.org/content/forest-landscape-restoration-more-planting-trees-three-case-studies-united-states

NASA carbon cycle video and story

https://www.nasa.gov/feature/goddard/2016/eye-popping-view-of-co2-critical-step-for-carbon-cycle-science

Weather Blog

Long wait to see weather heroes worth it

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Hundreds of people of all ages stood for hours in a line queued around and inside the General Aviation Terminal at RDU International Airport Wednesday afternoon. Looking at it and listening to the chatter of the people in it, I was reminded of waiting to experience a popular ride at Disney World on a high traffic day. The afternoon heat combined with concrete helped create that memory as well, but RDU had something Disney would never offer — free bottles of water being handed out by Red Cross volunteers and RDU police officers.

Like Disney, with the exception of a few grumpy toddlers, everyone was in good spirits and quite friendly. Unlike Disney, we weren’t in line for a thrill ride in a theme park. Instead, we were patiently waiting to meet service men and women who get to live the ultimate thrill ride every year – the NOAA Hurricane Hunters!

With the exception of a few broadcast meteorologists, very few weather geeks receive the recognition and heroic welcome that these guys do. Part of it is the excitement of meeting the select few who pilot planes that fly through the eye wall of hurricanes, the specialists who drop meteorological instruments into the storms, and the mechanics that keep the planes in top condition for their important missions. The other part is the fact that they bring the planes for the public to see up close and in person.

I would never profess being an aviation geek. I am not even a fan of flying; although, I am a fan of traveling to far-off places and that often requires boarding a plane. Thinking about the job the Hurricane Hunters do from the perspective of someone who suffers motion sickness creates an even greater element of awe for them. I heard them asked by several people whether they have ever been ill during a mission, and all said “no.” Impressive.

big plane

From outside the terminal, a glimpse of the big plane hinted at just how big it really was.

For being the rock stars of the military and scientific research worlds, they were very approachable and friendly. They seemed to enjoy chatting about their lives and careers with perfect strangers.  A few even walked up and down the line soliciting questions from those patiently awaiting their chance to see the inside of the big plane.

Pilot Shannon Hailes stopped to chat with my section of line on the tarmac and offered to have his photo taken with us. I opted to just have him in the picture (the album is posted on my Facebook page), and asked him a few questions about his career and why he chose to be a Hurricane Hunter. Hailes told us that he has been in the Air Force since 1991 and used to fly combat missions. This week is his 26th anniversary of active duty. He chose to join the Hurricane Hunters for three reasons: they are based close to his home in Mississippi, he gets to help people by providing necessary data used to improve hurricane forecasts, and he was “tired of getting shot at.” We thanked him for his service — past and present — as he moved down the line.

After nearly two hours of waiting, I finally got to see the inside of the big plane, which is a WC-130J that has a few customizations specific to its mission including a radiometer pod on the left wing and two external fuel tanks that give it a longer flight range. I was impressed despite not really knowing much about planes. I could see where the crew sits, and I could see where the weather equipment lives. That is really all I wanted to see.

More interestingly to me was meeting the man whose job it is to deploy Dropsondes from the big plane. His name was Chris Beckvar, and he was inside the big plane answering questions. He told us that he has been doing it for six years. He used to be a carpenter and wanted to do something different. He enjoys helping to get information about the storm to the National Hurricane Center so that our Hurricane forecasts can be more accurate. Beckvar explained that he deploys 12 to 14 Dropsondes on a mission, three of four of which are deployed while flying through the eye wall, inside the eye, and back through the eye wall. They also drop the instruments outside of the hurricane in areas around it to find the steering currents to help forecast the direction of the storm.

I could probably spend all day writing more about the experience, but I have other work to do. Feel free to look at the album of photos from the afternoon on my professional Facebook page. For now, I will leave you with a few final thoughts:

  • If you have the chance to see the Hurricane Hunters in person, take it, but bring your patience. The experience is truly worth the wait.
  • While some of the day focused on educating school children, the real goal was to educate the public about this special group’s important mission.
  • The next time you hear or read a hurricane forecast, remember the brave people who fly through and around those storms in order to collect data that is absolutely necessary to making that forecast.

A few links for more information on the NOAA Hurricane Hunters:
https://www.omao.noaa.gov/learn/aircraft-operations/about/hurricane-hunters
http://www.hurricanehunters.com/
http://www.hurricanehunters.com/mission.html (Dropsonde information)
https://www.facebook.com/NOAAHurricaneHunters/ (Like them!)

Weather Blog

Things that make you say “ugh”

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Most weather forecasters like a good challenge. When you live in the Piedmont of North Carolina, challenges abound.

We have the mountains, foothills, and ocean. We have all four seasons — sometimes all in one week, as the joke goes. Our latitude and our geography both play a role in our weather for better or worse.

This week, our challenge is a stationary front. The boundary between cool air and warm air is just draped across the state from northwest to southeast creating a headache for meteorologists who are trying to publish forecasts for the Triangle area — yours truly included.

forecast high temp map

The NAM model’s forecast high temperatures across the country for Thursday, May 10, 2017

I think I said “ugh” at least 10 times this morning while writing the forecast for the Wake Forest Weekly and the Butner-Creedmoor News. While the towns aren’t very far apart, the forecast could be quite different in a case like the one we have this week. I settled on similar expected temperatures for both, but reality could play out differently than the virtual computer models are showing.

The map above shows one model’s forecast high temperatures for Thursday. The northeastern corner of North Carolina could have high temperatures in the 50s, while the southern portion of the state might see a high in the upper 80s. That’s a 30 degree temperature spread over just one state!

Any little waver in that frontal boundary could make a huge change in the forecast. If it moves a little to the north, we could see warmer temperatures. If it moves a little to the south, it could be much cooler.

Disturbances in the atmosphere are riding along the boundary from northwest to southeast bringing rain and the chance for strong to severe storms over the next couple of days as well. The timing of those showers and storms changes a little with each model run, so a forecaster really has to play it safe and just say “chance of showers and storms” for the whole 24-hour period.

QPF Map

Quantitative Precipitation Forecast map for May 10 – May 15, 2017

The amount of precipitation each location receives over the next few days also depends upon the position of the front. The QPF (Quantitative Precipitation Forecast) map shows a pretty wide range from south to north. The southern tip of the state may only receive a quarter of an inch while the northeastern corner  of North Carolina could get nearly two inches.

Happily, the last disturbance and the frontal boundary will finally exit late Saturday as a low pressure system develops off the Atlantic Coast and moves toward New England, leaving us sunshine and a chance to warm up and dry out on Sunday.

Weather Blog

Severe storm forecasts are improving, but could be better.

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With the system that brought us rain Monday night, there were 215 filtered reports of severe winds (58+ mph) from South Carolina up to the New York/Canada border, as well as seven tornado touchdowns and three hail reports. You could say that our area dodged a bullet since all of the storm reports in North Carolina happened in the western Piedmont.

SPC storm reports

Storm Prediction Center’s map of Monday’s filtered storm reports

Improvements in our computer models over recent years have made forecasting severe weather days in advance possible. As with any weather forecast, the resolution improves as the time period gets closer. In other words, there is some confidence several days out about the timing and geographic area of an event. There is usually more confidence with each model run closing in on the event — two days out, one day out, within hours, etc.

If you watch the progression of the models’ output, you will see slight changes in space and time with each run. It’s normal, and it’s why the forecast for Friday published on Tuesday afternoon may look different from the forecast for Friday published on Thursday afternoon.

Metorologists have many computer model options available to use when forecasting. The most popular three include the GFS, which is a long-range model with course resolution used to see up to 16 days out. The NAM-HIRES is used to forecast for a period within 3 days. The RAP and HRRR are used for forecasting within hours. As the time gets closer, the resolution for the models gets finer.

There is also more reliable initial data and fewer assumptions with the higher resolution models. Imagine looking 16 days into the future and trying to predict what the stock market will do. A lot can change in 16 days. Politicians can make rash decisions, gas pipelines can develop leaks, iconic corporations can announce massive layoffs or take-overs, or a natural disaster could bring transportation to a complete stop. Any one of those things can change the economic forecast.

The same is true for weather forecasting. We can look two-plus weeks out and see what we think may happen giving what is happening around the globe right now combined with mathematical theory and basic assumptions, but there are likely smaller details that we are not taking into account because we don’t see them yet. At one week closer to the date, we can see more details and have more confidence in the way things are shaping up. By the time the date is tomorrow, we have a pretty good idea of what will happen, where it will happen, and when it will happen. Still, occasionally, we don’t get it exactly right, but by the day of the event, we’re pretty sure we know what’s going on.

Going back to Monday’s system:

On Friday, we could tell there would be thunderstorms on the east coast on Monday, and that it would likely be during the second half of the twenty-four hour period. By Sunday, we could see the ingredients for severe weather lining up from northern North Carolina all the way to the Canadian border with New York. By Monday morning, we could tell that the rain should hit the Triangle late in the evening and clear by early morning. By Monday afternoon we could tell that the tornado threat would remain north of the Virginia/North Carolina border, but there was still the potential for severe level winds across North Carolina.

That’s pretty good considering how far the science of meteorology has come in the last century! Still, as with all technology, there is room for improvement.

For example, Monday morning’s outlook for severe weather that evening showed more of the state having the potential for severe, damaging winds. By the time the storms reached the Triangle, the wind threat had greatly diminished, so narrowing down that geographic area  farther in advance is a potential improvement in our forecasting.

Why would that help? Any advances in our accuracy helps meteorologists’ credibility when we predict severe weather days in advance. Higher reliability gives the public more reason to prepare ahead of time to protect life and property when a threat exists. Perception being reality — if you buy into that idea — means that we have to change the public’s view of how trustworthy a weather forecast is. The best way to do that is to continue to improve the technology we use every day.

Weather Blog

Heavy rain caused localized flooding

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The sun is shining! After the amount of rain that has fallen across the area since Saturday, it will take a while to dry things out across the state. While this particular rain event wasn’t historic or record-breaking, it was serious and damaging to many low-lying spots around the Triangle.

satellite image

Satellite image of low pressure circulating over North Carolina the morning of April 25, 2017

I was asked what caused such massive amounts of precipitation over the last few days, and here is the simple, short-term answer: Saturday through Sunday, we saw a frontal system pass bringing the first round of rain. Almost right on its heels, a slow-moving low pressure system that developed over the Deep South arrived and creeped across North Carolina. Drawing moisture from the ocean, it had a large amount available to dump on much of the state.

This isn’t the first time a situation like this has occurred, and it won’t be the last. In fact, we should probably be grateful that it’s not January — at least, those of us who aren’t fans of snow. Instead of snow drifts, we are dealing with the aftermath of localized flooding. Maybe that’s not much better, but the higher elevations recover and get back to business quicker after a heavy rain than after a heavy snow. The lower elevations may take a bit more time.

One infamous low-lying area in Wake County is Crabtree Creek near Highway 70/Glenwood Avenue, which is home to Crabtree Valley Mall. Anyone who has lived around here for any length of time knows that when we see four-plus inches of rain fall in a short period, Crabtree Valley is probably going to flood.

Crabtree Creek water level

Graph of water level of Crabtree Creek at Highway 70 in Raleigh during April 22-24 extreme rain event

The mall opened in 1972, and the first historic peak discharge listed at the Crabtree Creek and Highway 70 gauge operated by the U.S. Geological Survey is listed as June 29, 1973. I found it odd that the next peak flow listed wasn’t until 1996, so I inquired about the history of that station.

According to Doug Smith at the USGS Raleigh office, that gauging station “was operated as a partial record site and a few flow measurements were made at the site beginning in 1972. There were no continuous data collected at that site before February 1988.” There have been at least 10 flood-level or above-peak stream flow events at that gauge since September 6, 1996 (Hurricane Fran).

What contributes to Crabtree’s flooding issues? First and most obviously is that it is a low point in the geography of Raleigh. Second, the amount of urban development surrounding it has grown exponentially over the decades. The more impervious the surfaces created around the creek, the faster precipitation flows directly into the creek leading to faster water level rise and flash flooding. Concrete, asphalt, and buildings surrounding a creek with very little open green space and absorbant soil to slow the flow are a major cause of Crabtree Valley’s troubles.

Another potential factor there and elsewhere is storm drain blockages. When you see areas that don’t often flood, or those that do, flood more quickly, it’s quite possible that nearby storm drains are unable to do their jobs. Storm drains should divert the flow of water away from roads and into locations where the water can safely collect and eventually disperse. Precipitation that falls too fast for the storm drains to do their jobs is a possibility, but another is blockages caused by debris and litter. A simple rule of living with storm drains: don’t put anything down there except storm water. That water flows to streams which flow to rivers which flow to the ocean. Those drains need to be kept clean for that reason at the very least.

Some people would attribute rain events like this one to climate change, and they might be partially right. I have written here before about studies that point to a warming climate as a cause for extreme rain events. Below are links to a couple of relatively recent stories about two such studies. There is no question that climate models predict dramatic warming and related weather events such as heavy single-day rainfall, prolonged drought, and temperature extremes. I would be remiss if I did not acknowledge the documented questions about the accuracy of the climate models and such predictions and their potential fallacies.

Whether flooding is caused by poor choices in urban development, blocked storm drains, slow moving low pressure systems, or climate change, we need do what we can to mitigate the risk. There are some things we have no control over such as the weather. Other things we have pretty good control over include storm drains and choosing to use pervious materials in and around urban development. Considering storm water runoff when deciding where to build both residential and commercial developments can help avoid issues like those faced by our neighbors along Crabtree Creek in Raleigh.

We can’t go back in time and rethink where to put that mall, but we can avoid repeating that developer’s mistake.

 

Additonal reading not included in the hyperlinks above:

“Study finds more extreme storms ahead for California”

“Extreme downpours could increase fivefold across parts of the U.S.”

Weather Blog

Wow! What happened with that forecast?

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My print forecast in the Wake Weekly made a lot of sense on Wednesday morning when I wrote it. I thought I might have been a little optimistic about Sunday’s forecast high in the mid to upper 70s. I know my personal bias is caused by my preference for warmer temperatures. However, I didn’t expect my forecast and that of the models I used for it on Wednesday morning to be so drastically different from reality.

The forecast for Saturday was for partly to mostly cloudy skies, a high in the upper 70s, and a chance for showers and thunderstorms with the possibilty that a few storms could be strong to severe. It looked to me like the cold front and its rain would approach early Saturday evening and bring those storms with it.

rain total map

Map of the 24-hour rain totals over central North Carolina from 8am, April 23, to 8am, April 24, 2017 courtesy of the National Weather Service Raleigh Office.

What happened Saturday was a bit surprising – the front stalled in Virginia, the sun shone here, and the temperature at RDU International Airport reached 87 degrees! I doubt anyone was too angry over a sunnier reality on a Saturday filled with outdoor events across the area. I know I wasn’t. Well, I was not thrilled that the forecast busted, but I was happy with the nicer weather.

The severe weather Saturday evening was mostly constrained to just north of the Virgina border where the stalled frontal boundary sat. By the time it started moving south, the atmosphere had cooled and lost its instability, which led to more rain and less thunder.

My forecast busted on the cool side yesterday. I had predicted a rainy day, but the rain and the winds from the east kept the temperature 20 degrees cooler than it looked like it would be several days before.

As I beat myself up a bit over the way my printed forecast did not verify, a friend pointed out to me, “Most people don’t expect weather people to be right. They just want some guidance on what to expect for the next few days.” He told me that he appreciated my personal need to be accurate, but he didn’t think accuracy was all that expected.

While I appreciate his sympathetic thoughs, I disagree. Accuracy should be expected. Maybe not on a weekend like this recent one — when the speed of a cold front’s movements ultimately determined the temperatures over two days and there was not a huge amount of confidence in the models three days in advance — but it should be expected.

Meteorologists’ accuracy over the long term is what gains the public’s trust. Without that trust, we can’t expect them to take us seriously when we forecast a chance for severe weather or a winter storm or a hurricane making landfall several days out. While most of the time we are actually right, it’s those times that we are not that the public seems to recall most. It’s human nature, and it is something we have to work hard to overcome — both as forecasters and as humans.

The best way for a forecaster to improve is to spend time picking apart a forecast that didn’t verify and figuring out what happened. Sometimes, there is not much to blame other than the very models we rely on to make the forecasts. Other times, we can see trends in hindsight that we should have recognized in advance. So, that is why this morning, I asked myself the question that I expected to receive from my readers. “What happened with the forecast?”