Ah, springtime – the season when life, greenery, and sandals return to the land and towering storms return to the sky.
Severe weather is already visiting parts of the southern Plains this year (including Oklahoma and Texas), and it will soon begin its annual march northward across the country as winter gives way to spring and summer.
Severe storms are fueled by the tremendous energy of an unstable atmosphere, where cold air vies with warm in a perennial battle for territory. Storms fire up and ride along the front lines – sentinels flashing, booming, blowing, and occasionally swirling their way across the landscape. For this reason, there really is no true, nationwide severe storm season – that clash of warm and cold air masses occurs at different times of year across different regions of the country, resulting in regionally variable storm climatologies.
Typically, storm season ramps up first in the South, where warm air returns earliest (or never really leaves): the Gulf Coast states experience severe storms, including hail and tornadoes, every month of the year. During late winter and early spring, severe storms in the South are usually triggered by strong cold fronts that also bring heavy snow and ice to more northern latitudes.
As March slides into April and May, the southern Plains see the annual resurgence of supercell severe storms, fed by warm Gulf moisture pulled northward on southerly spring breezes and triggered by strong midlatitude storm systems that sweep out of the Rockies. Supercells – a specific type of thunderstorm that is highly organized, long-lived, and characterized by a persistent region of rotation (the mesocyclone) – are responsible for some of the world’s most damaging severe weather, including almost all significant tornadoes (EF2 or greater) and most giant hail.
During June and July, the jet stream shifts northward, steering storm systems (and their accompanying entourage of thunderstorms) into the northern Plains and upper Midwest, where storm season peaks in mid-summer.
But don’t get too attached to the timeline – severe weather doesn’t respect the notion of a “season” and can strike well outside the boundaries of what’s considered the climatological norm, as winter tornado outbreaks so destructively illustrate.
Because of that variability in when severe weather strikes, it’s an excellent idea to remain storm ready throughout the year. However, that first window-rattling rumble of thunder in the spring can certainly provide a little extra motivation and a helpful sense of urgency. Below are some essential storm preparations to ensure that you and your family are ready to weather the storm (pun intended).
Trees are beautiful, stately, and attract a wonderful diversity of wildlife. Deciduous trees are also great for your utility bill: providing leafy shade in the summer and allowing the sun to warm your home unimpeded during winter. But if not properly cared for, they can become highly efficient house- and car-crushers during wind storms.
Before the howling winds of spring start blowing across your newly leafed-out trees, call in a reputable arborist or tree trimming company to remove unhealthy limbs and trees and to shape healthy trees to be more wind-resistant. Services typically cost a couple hundred dollars (for basic limb removal) to a couple thousand dollars (for removal of entire trees), and are ideally performed every 3-5 years. A few hundred bucks in preventative maintenance now can save you not only your insurance deductible but also the hassle of major car and home repair.
Speaking of insurance, now is the perfect time to make sure you have enough and the right type of insurance. Dust off your insurance policy documentation – or better yet, call your insurance agent for a comprehensive review of your policy. Is your deductible affordable in your current financial situation? The purpose of having insurance is to use it when you need it, so make sure your deductible is an amount you can afford to pay should your home or vehicle sustain damage.
Review your coverage amounts for the structure and its contents – if the worst happens, will your insurance policy pay enough for you to repair or replace your house and belongings? Know whether you have replacement coverage (i.e. the insurance policy will pay for a brand new item equivalent to what was lost) or whether your policy covers only the depreciated value (i.e. the value of a used item equivalent in age, wear and tear to what was lost). Is the type of coverage you have what you need? Have you recently purchased any high-value items that might need to be insured separately as valuable personal property?
Consider purchasing flood insurance if you haven’t already. Standard homeowners’ policies do not cover flooding, whether from severe storms (flash flooding), prolonged rain (areal flooding), snowmelt, hurricanes, or even sewer back-ups. With an average flood insurance claim of $42,000, that’s not a check you’re going to want to write.
You don’t have to live in a designated floodplain to experience flooding – a third of all federal disaster assistance for flooding goes to people outside of mapped high-risk areas. In fact, if you don’t live in a flood plain, you’re likely to get a preferred rate on your flood insurance policy ($35/mo is the average premium for low-to-moderate risk properties). Flood insurance is offered through the federal National Flood Insurance Program (NFIP) and can be purchased through your insurance agent.
What you don’t know can, in fact, hurt you. This is especially true when it comes to severe weather. As technology becomes ever more sophisticated, the channels through which we can receive about information about wicked weather headed our way has rapidly expanded.
Despite the myriad new options, a NOAA weather radio is still an easy, relatively inexpensive, and extremely reliable means of receiving weather alerts even when you’re not by your TV, phone, or computer. There isn’t one brand of weather radio – instead, NOAA maintains a network of radio stations broadcasting information directly from the nearest National Weather Service office, including forecasts and weather warnings. These stations broadcast on a fixed set of frequency channels, and any commercially-available emergency radio worth buying will come pre-programmed with them.
When comparing weather radios, look for those that:
For those whose cell phones have become a fifth appendage, Wireless Emergency Alerts (WEA) put critical information right in the palm of your hand. WEA messages are overseen by the FCC and include Amber alerts, presidential messages, and weather warnings. Many if not most newer cell phones are already capable of receiving them. Participation in the WEA program is voluntary but also widespread among mobile carriers. If your phone is WEA-capable, you can choose which WEA messages you receive (with the exception of presidential messages, which are mandatory), so check for instructions specific to your phone make/model to ensure that WEA weather alerts are enabled.
Another mobile device solution is the use of apps. A wide variety of apps will send you a text or alert you through the app itself if hazardous weather is headed your way. The National Weather Service maintains a list of apps, and you can check around for other options. Be aware, though, that cell phone service can be interrupted during and after a major storm – it’s wise to have a back-up means of receiving weather information in case cell service is disrupted.
Once you know a storm is coming, what are you going to do? The National Weather Service’s Weather-Ready Nation campaign and The Department of Homeland Security’s ready.gov have resources for a number of specific weather hazards, including thunderstorms, tornadoes, floods, and hurricanes. Read through the information for the weather hazards that can impact your area, and formalize a storm plan for each. Make sure everyone in your family knows what the plans are, and practice the plans, especially if you have small children. Some things to consider: where will you go during a severe thunderstorm or tornado, when a hurricane threatens, when floodwaters rise? How are you going to get information as the weather unfolds? Where do you keep your storm kit?
Speaking of storm kits – it’s a really good idea to have one and to keep it in or near your storm shelter (i.e. basement; lowest-level interior, windowless room; or safe room). If you already have a storm kit: excellent! Time to check and refresh the supplies. If you don’t already have a storm kit, it’s time to put one together. Ready.gov and Weather Underground both have thorough checklists for building a basic storm/disaster kit.
At a minimum, storm kits should include food and water, a first aid kit, medicine, sanitation products, supplies to shelter in place (tarps, duct tape, etc), gloves, basic tools for turning off utilities, flashlights, a portable radio, extra batteries, signals for help (whistle, flare, etc), and infant and pet supplies if applicable. You can expand your kit to include other useful but not necessarily critical supplies based on your own needs.
We know it’s a lot to think about, but preparing now — before severe weather strikes — will save time, money, and heartache down the line. At a minimum, you’ll have peace of mind knowing you’ve mitigated against preventable damage, planned how you’ll ride out the storm and its aftermath, and insured your property against loss. And if storm season happens not to spare you this year, you’ll have much more than just peace of mind. You’ll have the tools needed to weather the storm.
A bolt from the blue. A rogue wave.
As anyone who has lived on planet Earth for more than a few seasons can attest, nature is full of surprises.
Lightning usually strikes near the core of a thunderstorm, but occasionally it will strike more than 20 miles away, arcing across an otherwise peaceful sky. Ocean swells on a placid sea tend to be of a similar height, but rarely, a rogue wave many times the average height can appear suddenly, damaging or devouring any ship unlucky enough to be in its path.
Bolts from the blue and freak waves are just two examples of variability and chaos in nature. Here chaos describes a sensitive dependence on initial conditions – the proverbial butterfly flapping its wings in Africa that leads to a hurricane over the Bahamas. If the surface temperature had been just slightly cooler, that bolt from the blue would have sliced the air directly under the storm. If winds over the ocean had been just a tad bit different, that rogue wave would never have formed.
It is due to this chaos that atmospheric scientists so often speak in terms of probabilities and distributions (as frustrating as that can be to folks who just want to know whether a rain shower will or will not do the work of watering their lawn this weekend – I promise if we knew, we’d tell you).
The chaotic nature of the weather leads to variability both between events and within a single event. Thunderstorms are a perfect example: no two thunderstorms are alike, and each storm changes from moment to moment.
To describe such variability, we typically speak of averages and deviations from that average. For thunderstorms, we can describe the average peak thunderstorm wind for an area – say 40 mph for summer afternoon thunderstorms in north-central Florida. However, peak winds in exceptionally strong thunderstorms have been recorded at over 70 mph in this region, while winds in weaker storms may not exceed 25 mph. And within a storm that produces a 70 mph gust, winds are not sustained at that speed throughout the event. The sustained wind speed within such a storm averaged over a 2-minute period may only be 45 mph.
Building codes typically ensure that structures and infrastructure are built to withstand expected conditions for a given area – roofs in snowy areas must be able to withstand a higher load than in areas without snow; structures in hurricane-prone regions must be able to withstand higher winds; structures in seismically active areas must be able to withstand earthquakes. It’s generally not average conditions that cause damage – it’s the exceptions, those events that vary greatly from what is normal and expected.
In the case of thunderstorm wind damage, it’s the gusts. How gusty winds are during a given event depends on a number of factors, but mostly on the surrounding terrain: the rougher the terrain, the gustier the winds. Winds are far gustier in the center of a city, surrounded by skyscrapers and densely packed buildings of many sizes than in a smooth, open farm field.
To illustrate, given a weather station measurement of the 1-minute average wind speed, we would expect peak 3-second wind gusts in the heart of a major city to be nearly 250% higher than that average speed, while peak wind gusts over open farmland would be less than 50% higher.
The orientation of landscape features to the wind direction also impacts wind speed and gustiness. For coastal areas, this is particularly noticeable. Onshore winds – those that have blown unimpeded over a lake or ocean – tend to be stronger and steadier, all else being equal, than winds that have blown over a rough landscape (say, across a large metropolitan area). Similarly, winds blowing parallel to city streets tend to be felt more strongly than those blowing perpendicular.
When evaluating weather station data to determine the peak wind speed associated with a given event, we must consider the location of the weather station. Is it a rural site or an urban site? What is the terrain like surrounding the station? Are there certain directions from which the wind would be more impeded or would be blowing over rougher terrain?
How does the weather station site compare to the site at which damage was reported? Is the surrounding terrain similar? Was damage reported at an elevated location – for example, the roof of a high-rise building, where winds tend to be stronger? Differences in both roughness and height must be considered.
Also of obvious importance in the evaluation of winds associated with tropical cyclones and thunderstorms is estimation of the relative strength of the system when it impacted the weather station versus the damage site. If the damage site was directly impacted by the core of a severe thunderstorm while the nearest weather station experienced only a glancing blow, we would expect the winds experienced at the damage site to be stronger than those recorded at the weather station.
Evaluation of these considerations – location, orientation, height, and roughness – allows forensic meteorologists to estimate peak wind speeds from measured average wind speeds and to evaluate the extent to which a given weather station is an accurate proxy for the site at which damage was reported. The weather station data is just the beginning.
“The devil is in the details.” Nowhere is this truer than in the beautifully chaotic weather, where details determine outcomes.
If you or a client experienced wind damage and need an estimate of the wind speed associated with that weather event, call or email Blue Skies Meteorological Services for a free consultation.
Blue Skies Meteorological Services congratulates Megan Walker Radtke on earning her Certified Consulting Meteorologist designation from the American Meteorological Society (AMS)!
From the American Meteorological Society:
GAINESVILLE, FL: Megan Walker Radtke of Blue Skies Meteorological Services has earned the nationally recognized Certified Consulting Meteorologist (CCM) designation by the AMS.
The CCM designation is issued by the Society to highly qualified meteorologists providing research and services to a wide variety of users of weather information, including agriculture, business, industry, and various sectors of government. These services extend beyond the traditional public service functions and statutory responsibilities of the National Weather Service.
To earn the CCM credential, a meteorologist must make application for the designation, be recommended by three associates, pass a stringent written examination, and pass an oral examination before a national board of examiners. The CCM designation is granted only to those who demonstrate a broad background in meteorology together with detailed knowledge in a particular field of specialization. CCMs must demonstrate exemplary qualities of character and devotion to high professional standards.
CCMs are highly regarded by their peers in meteorology. They are considered experts in the application of weather information to a host of practical challenges ranging from specialized forecasts to engineering design support and expert testimony on weather-related court cases. Certification enables users of meteorological services to select consultants or employees with greater confidence in the quality and reliability of the products or services they will receive.
The AMS promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, students, and weather enthusiasts. AMS publishes 11 atmospheric and related oceanic and hydrologic journals—in print and online, sponsors more than 12 conferences annually, and offers numerous programs and services.
Full press release available here.
What does a birthday mean? A major birthday – the type that warrants a card declaring your exact new age, possibly by spelling it out in macabre black balloons – what does it mean? Why do we care?
It’s not like you wake up on the morning of your birthday feeling dramatically older than when you went to bed. A decade’s worth of wrinkles don’t suddenly appear on your face. Yet you are older, and on your birthday, you are acutely aware of that fact.
A major birthday reminds you that life is short and you don’t have forever to act. It reminds you of all you’ve done and all you have left to do. Then it starts playing the Final Jeopardy countdown music in your ear. Time is ticking. Better get busy.
Reaching a global average carbon dioxide (CO2) concentration of 400 ppm is that type of milestone, and we passed it in March. To put 400 ppm in perspective, consider that maximum pre-industrial CO2 levels were 280 ppm and that 350 ppm is widely considered the upper limit to avoid truly dramatic climate change. Consider that CO2 levels haven’t been as high as 400 ppm in several million years, when the world was much hotter and the oceans much higher than they are today.
Yet, besides the climate scientists who marked the passing of 400 ppm with a mixture of dismay, anger, and sad resignation, few others seem to have noticed (well, besides the United States military who consider climate change a national security risk and key business and insurance leaders who are already taking action to adapt). Nationally and internationally, we’re certainly not getting busy.
It’s as if we believe that if we don’t acknowledge what’s happening, it won’t happen. As if staying in bed with your eyes closed on your birthday somehow stays the hands of time.
But time doesn’t stand still just because we avoid clocks and mirrors – just as CO2 concentrations continue to increase whether we acknowledge it broadly and publicly or not. Of course, the critical difference between the inexorable forward march of time and the increasing concentration of greenhouse gases in Earth’s atmosphere is that we can actually do something about greenhouse gas concentrations.
We very likely can’t undo what we’ve already done (the technology just doesn’t exist to capture and indefinitely store vast quantities of atmospheric CO2). But we can slow down and eventually stop emitting new greenhouse gases, if only we muster the foresight to recognize and the willpower to address a large, costly, complex, global problem that will only get larger, more costly, and more complex with each year of procrastinated action.
Failing to even acknowledge the passage of the 400 ppm milestone doesn’t bode well, though.
So what does 400 ppm mean? What is this new world we’ve created for ourselves and our progeny?
Well, for one thing, 400 ppm means we’ve committed to major climate change – to what we’re already experiencing and more. The average residence time of carbon dioxide in Earth’s atmosphere is hundreds to thousands of years, so even if we stopped emitting CO2 tomorrow, our climate would continue to warm toward a 400 ppm equilibrium.
Of course, we can’t put the brakes on instantaneously. If you’re traveling 100 mph down the highway and slam on the breaks, you keep traveling forward as you slow to a stop. A shift to renewable energy and carbon-neutral fuels, like stopping a speeding car, takes time, and the concentration of CO2 in the atmosphere will continue to increase during that shift.
Right now, though, we’re mashing on the accelerator rather than the brakes. With the exception of 1990-2000, each decade has seen an increase in the rate of CO2 emissions. Not only are we continuing to emit carbon dioxide – we’re emitting it faster and faster each year. If we continue along our current trajectory, we’re on pace for greater than 3° C warming, and that’s just the increase in average temperature. Extremes in both temperature and precipitation tend to increase more dramatically than their respective averages.
Such climatic changes would decrease crop yields and alter agricultural zones, decrease water availability while simultaneously increasing demand, inundate coastal areas with rising seas, extend the season and range of numerous pests and insect-borne diseases, increase heat stress and heat-related illness, and increase the frequency and intensity of flooding rainfall, among many other impacts.
400 ppm means that aspects of our environment that have been our touchstones for thousands of years – food and water availability, weather and climate – will shift in unprecedented ways. The ideal locations for cities, farmland, roads, factories, homes, and military assets will modify. Processes and procedures that have been reliable will become uncertain.
In short: the assumptions upon which we have built our societies may cease to be valid.
Although some progress toward mitigation (emissions reduction) and adaptation has been made on the local level both domestically and internationally, the sort of global-scale agreement and action required to alter our current emissions trajectory remains elusive. Emissions will therefore continue to rise, and the climate will continue to shift. Governments, industries, and individuals will be increasingly impacted by a variable and changing climate, and given the lack of coordinated effort to date, the unfortunate reality is that we must prepare to protect our own interests, assets, and welfare.
Businesses and insurers looking to take the long view of their investments, infrastructure, supply chains, and insured properties need to be aware of climatic changes that impact vulnerability. Blue Skies Meteorological Services is here to help these clients understand and mitigate their climate-related risk and exposure. Contact us at email@example.com for more information.
Weather radar works by emitting microwave radiation into the sky and then listening for the signal that’s reflected back. It’s a meteorological game of Marco Polo.
All sorts of targets reflect the microwaves – raindrops, snowflakes, hailstones, bats, airplanes, and even swarms of insects. How well a given target reflects microwaves depends on its composition, size, and shape. For instance, liquid water is a better reflector of radar energy than ice.
When a meteorologist looks at a radar display, she’s seeing the reflected signal from all those targets in a given slice of sky. The radar doesn’t “know” which piece of reflected energy came from a bird and which piece came from the hailstone that moments later cracked your car windshield. The radar simply aggregates the reflected signal. It’s up to the meteorologist to interpret the results.
Until just a few years ago, the National Weather Service’s network of weather radars collected information about only two quantities: the reflected energy from a given section of sky (reflectivity) and the velocity of the targets within that section (mean radial velocity and spectrum width). In complex meteorological situations like winter weather events or severe storms, these two pieces of information provide only an incomplete picture of the type of precipitation that’s falling. When you’re just looking at reflectivity and velocity data, for instance, it can be difficult to tell the difference between hail and heavy rain. Yet on the ground, knowing the difference can be critical.
Enter dual-polarization radar technology. If you’ve ever owned polarized sunglasses, you’re already familiar with the principle of polarization. The short-n-sweet version is that electromagnetic waves (like radio waves emitted by radar or visible light waves emitted by the sun) can be oriented along a certain axis.
Tilt your head from side to side while wearing polarized sunglasses, and you’ll notice that the image you see changes – the color of the sky darkens and lightens, glare off the pavement appears and disappears. As you tilt your head, you’re actually changing the polarization of the light that’s being let through your sunglasses, and that gives you additional information about the world around you.
The same is true with weather radar. Conventional radar sends out radio pulses polarized only in the horizontal direction, so the reflected signal carries only 1-dimensional information. Dual-polarization (or “dual-pol”) radar, on the other hand, sends out both horizontally polarized pulses and vertically polarized pulses, so the reflected signal carries 2-dimensional data.
This may seem rather trivial until you consider that precipitation types have characteristic shapes. Small raindrops are spherical, while big raindrops flatten out like a Frisbee. Hailstones are roughly spherical when they’re dry but can become oblong as their outer layers melt. The two-dimensional data provides invaluable insight into what types of precipitation are present within a storm.
Here in Florida, we don’t have to worry too much about winter weather, but hail is another matter. In the lightning capital of the United States, thunderstorms are part of the scenery for much of the year, and most thunderstorms, if they are strong enough and reach high enough into the atmosphere, produce hail.
But that hail doesn’t always reach the ground. In warm, moist atmospheres, hail melts as it falls toward the ground. If the hail starts out small or if the freezing level is high in the atmosphere, hail can melt completely before reaching the ground. Dual-pol radar data can reveal whether a storm is producing hail aloft, and by examining radar data at different heights within the storm, meteorologists can determine whether and how much that hail is melting before it reaches the surface (and people’s cars and houses).
Dual-pol radar adds three more tools to the meteorologist’s kit. Each of these tools provides unique information about the size, shape, and mixture of precipitation types within a storm.
Correlation Coefficient (CC)
Correlation coefficient measures how similarly the returned horizontal and vertical pulses are behaving. It’s like looking at the world under a strobe light. From one flash to the next, how much does the image change? When the targets within a given region are of the same shape and type (for example, all medium-sized raindrops), one pulse will look much like the next, and the correlation coefficient will be high. If, on the other hand, precipitation types are mixed (like rain and hail swirling together), correlation coefficient values will be lower. Generally, the larger the hail, the lower the correlation coefficient.
Differential Reflectivity (ZDR)
Differential reflectivity compares the reflectivity values returned in the horizontal and vertical directions, like comparing how much the image through your polarized sunglasses changes as you tilt your head. Targets that are wider than they are tall (like large raindrops) have higher differential reflectivity – they reflect more horizontally polarized energy than vertically polarized energy. Hailstones, on the other hand, are more spherical and tend to tumble as they fall, reflecting roughly equal amounts of horizontally and vertically polarized energy. Hail typically has low to near-zero ZDR values.
Specific Differential Phase (KDP)
Specific differential phase is a bit more complicated than correlation coefficient and differential reflectivity. Physically, KDP measures the phase shift of the returned horizontal and vertical signals. In practice, this means that specific differential phase responds to both the shape and the density of liquid water targets. Frozen precipitation, like dry hail and snow, do not contribute to KDP – KDP “ignores” frozen precipitation and sees only liquid precipitation. Specific differential phase is therefore useful for determining rainfall rate.
As part of the dual-polarization upgrade, National Weather Service weather radars now incorporate an algorithm that estimates precipitation type from the dual-pol variables discussed above. Numerous automated hail report websites use the National Weather Service algorithm or a custom one to identify regions of hail. While such algorithms provide a useful first-pass to identify regions within a storm where hail is likely being produced aloft, they do not provide information about whether that hail is reaching the ground and at what size.
When Blue Skies Meteorological Services investigates the presence of hail for a forensic meteorology case, we don’t just run an algorithm and depend on the radar to “know” what was happening in the storm and to assume what was happening on the ground. We examine official storm reports, severe weather warnings and advisories, the atmospheric profile, and dual-polarization radar data at multiple heights and throughout the lifetime of the storm to reconstruct a comprehensive picture of the weather situation – both high in the storm and on the ground, where it matters.