New NWS storm surge flooding maps help you run from the water and hide from the wind - Blue Skies Meteorological Services

New NWS storm surge flooding maps help you run from the water and hide from the wind

Hurricane Dennis brought strong winds and dangerous storm surge inundation to the Florida panhandle in 2005. Credit: USGS

Hurricane Dennis brought strong winds and dangerous storm surge inundation to the Florida panhandle in 2005. Credit: USGS


“Run from the water. Hide from the wind.” This adage speaks to a truth long known among meteorologists and emergency management officials: it’s generally not the wind that’ll kill you – it’s the water.

Between 1963 and 2012, only 11% of tropical cyclone (hurricane and tropical storm) deaths were due directly to the wind. Yes, hurricane-force winds can be frighteningly destructive and frankly awe-inspiring, but when the numbers are tallied, water is undeniably the deadlier threat. Combined, storm surge, inland flooding due to heavy rains, and high surf are responsible for 88% of tropical cyclone deaths. The storm surge alone kills nearly half of all people who lose their lives during these events.

The reasons for this are simple but not necessarily obvious.

Cause  of  death  in  the  United  States  directly   attributable to Atlantic tropical cyclones, 1963–2012. Credit: Rappaport 2014

Cause of death in the United States directly attributable to Atlantic tropical cyclones, 1963–2012. Credit: Rappaport 2014

Why Water Not Wind

Especially in areas with modern building codes and construction, structures can withstand long duration strong winds. Even when structures are significantly damaged by debris or the wind itself, they continue to offer some shelter and protection from the wind. This is why people in the path of a tornado are advised not to jump in their car and drive away but rather to shelter in place in an interior room on the lowest floor. The roof can be ripped off a building and the exterior walls toppled, yet a tiny bathroom or closet often remains intact and offers a pocket of safety amidst the chaos.

Water is different. It rises inexorably, under doors and through windows. No room is safe. Entire neighborhoods are engulfed at once – there is no accessible safe haven once the water begins to rise. Storm surge water seethes with debris, from toxic waste to power lines to floating vehicles. And unlike the wind, which weakens quickly as a storm departs, storm surge and inland floodwaters can engulf a region for days to weeks. Those who don’t drown during the storm are often trapped without water or food until rescue personnel arrive, and when the impacted area is large and damage is extensive, rescue can be slow coming.

Hurricane Matthew

If you were watching news coverage as Hurricane Matthew marched menacingly up the east coast of Florida earlier this month, you probably noticed that meteorologists and local officials were focusing far more on the potential for unprecedented storm surge than on the storm’s maximum winds, despite Matthew being a Category 3 or 4 storm with winds up to 145 mph at times. Major Florida cities along the Atlantic coast and along the St. John’s River (which empties into the Atlantic Ocean just east of Jacksonville, FL) were threatened by a storm surge unseen for at least a century.

Small closets remain intact after a tornado ravaged this neighborhood. Credit: Alabama Wx Blog

Small closets remained intact after a tornado ravaged this neighborhood. Credit: Alabama Wx Blog

Matthew was a major hurricane with destructive winds, but it was the water, not the wind, that led governors, mayors, meteorologists, and emergency managers alike to issue impassioned pleas for those in the path of the storm to evacuate. Like hurricanes Sandy, Ike, and Katrina before it, Matthew testified to the fact wind tells only part of the story of a cyclone’s destructive power.

The rest of that story, and the far deadlier chapters, are told by water.

And starting this year, emergency managers, public officials, and the general public have another tool to evaluate the impact of that water on their communities. Developed by the National Weather Service and made operational for the 2016 hurricane season, Potential Storm Surge Flooding Maps are specific to each tropical cyclone and show a reasonable worst-case scenario for storm surge inundation at the neighborhood level. In other words, it shows the storm surge heights that a person should prepare for before a storm, given the uncertainties in the meteorological forecast.

Potential Storm Surge Flooding Maps

The Potential Storm Surge Flooding Maps are based on the existing National Weather Service (NWS) Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. (Modeling involves a dizzying and inescapable array of acronyms.) The SLOSH model takes into account forecast uncertainty and, when run as an ensemble, provides an envelope of possible storm surge outcomes based on the current forecast.

An entire neighborhood is engulfed by water due to inland flooding associated with Hurricane Matthew in early October 2016. Credit: Quavas Hart.

An entire neighborhood is engulfed by water due to inland flooding associated with Hurricane Matthew in early October 2016. Credit: Quavas Hart.

Ensemble modeling involves running a model (or group of models) many different times, each time with small differences in the initial conditions or model assumptions. For the SLOSH model, these differences represent plausible futures for the track and intensity of the hurricane given current observations and historical forecast errors. The result is a set of possible storm surge scenarios, with each member of the set representing a slightly different hurricane track and intensity.

Once this set – or “ensemble” – is assembled, it is analyzed statistically to determine a reasonable worst-case storm surge scenario at each location, and the depth of that storm surge is displayed on the Potential Storm Surge Flooding Maps. In this instance, “reasonable worst-case” is defined as that storm surge depth which has a 1-in-10 chance of being exceeded at each location. (In other words, at any given location, there is a 90% chance that the actual storm surge will be less than or equal to what is displayed on the map, given the current forecast.)

How They’re Created

The Potential Storm Surge Flooding Maps are based on the existing National Weather Service (NWS) Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. (Modeling involves a dizzying and inescapable array of acronyms.) The SLOSH model takes into account forecast uncertainty and, when run as an ensemble, provides an envelope of possible storm surge outcomes based on the current forecast.

October 6, 2016 Potential Storm Surge Flooding Map for northeastern Florida. At the time this map was created, Hurricane Matthew was passing near the Bahamas. Credit: NWS

October 6, 2016 Potential Storm Surge Flooding Map for northeastern Florida. At the time this map was created, Hurricane Matthew was passing near the Bahamas. Credit: NWS

Ensemble modeling involves running a model (or group of models) many different times, each time with small differences in the initial conditions or model assumptions. For the SLOSH model, these differences represent plausible futures for the track and intensity of the hurricane given current observations and historical forecast errors. The result is a set of possible storm surge scenarios, with each member of the set representing a slightly different hurricane track and intensity.

Once this set – or “ensemble” – is assembled, it is analyzed statistically to determine a reasonable worst-case storm surge scenario at each location, and the depth of that storm surge is displayed on the Potential Storm Surge Flooding Maps. In this instance, “reasonable worst-case” is defined as that storm surge depth which has a 1-in-10 chance of being exceeded at each location. (In other words, at any given location, there is a 90% chance that the actual storm surge will be less than or equal to what is displayed on the map, given the current forecast.)

Official National Hurricane Center forecast for Hurricane Matthew as of October 6, 2016, with the storm's wind field marked. Credit: NWS Jacksonville

Official National Hurricane Center forecast for Hurricane Matthew as of October 6, 2016, with the storm’s wind field marked. Credit: NWS Jacksonville

Utility and Limitations

The Potential Storm Surge Flooding Maps are a valuable visual tool to assess storm surge risk as a tropical cyclone approaches land. The SLOSH model that forms the basis of the maps takes into account the factors most critical in determining storm surge:

  • The hurricane’s forward speed, angle of approach to the coast, and landfall location
  • Forecast uncertainty in the hurricane’s track, intensity, and wind field
  • Astronomical tides
  • The specific topography of the coast
  • Artificial features like roads and levees

However, the potential storm surge flooding map does not take into account a number of factors that do not impact storm surge directly but that nonetheless greatly impact overall flooding and water damage. The maps do not account for:

  • Wave action (i.e. waves that occur on top of the storm surge)
  • Freshwater flooding from rainfall
  • Riverine discharge (i.e. river flooding)
  • Flooding resulting from levee failures
  • For mapped leveed areas – flooding inside levees, overtopping of levees

Wave action
Wave action can significantly increase the impact of storm surge along the immediate coast, overtopping seawalls and sandbags where the storm surge alone would not. The potential storm surge flooding maps show only the potential storm surge – they do not provide any information about expected wave height. In many cases, the height of waves riding atop the storm surge can exceed the height of the storm surge itself.

The anatomy of the storm surge. NWS Potential Storm Surge Flooding Maps display the storm tide (storm surge + astronomical tide), but do not address the impact of waves on top of the storm tide.

The anatomy of the storm surge. NWS Potential Storm Surge Flooding Maps display the storm tide (storm surge + astronomical tide), but do not address the impact of waves on top of the storm tide.

Information about expected wave height and wave action impacts can be found in hurricane-related text products from the National Weather Service, including the local area forecast discussions and hazards and impacts statements. Interests along the coast and in areas protected by levees should pay particular attention to the impacts of wave action and weigh those impacts in addition to the direct impacts of the storm surge when making hurricane preparations.

Freshwater and Inland Flooding
Flash flooding, areal flooding, and river flooding due to excessive rainfall are responsible for over one quarter of all tropical cyclone-related deaths and can impact areas far inland and outside of the storm surge risk area. Hurricanes and tropical storms can dump tremendous amounts of rain in a short period of time. Even weak tropical systems can produce devastating amounts of rain. For example, the remnants of Tropical Storm Amelia in 1978 flooded central Texas with four feet of rain. Interests in low-lying areas prone to flooding and along creeks and rivers expected to be impacted by a tropical system should pay careful attention to rainfall forecasts and expected impacts.

Levees
Forecasting the protection offered by levees during a tropical cyclone is complex and difficult, as Hurricane Katrina tragically demonstrated in 2005. Wave action, the depth and speed of the storm surge, and the strength and construction of the levees all influence the amount of protection they provide. Interests living in leveed areas need to remain especially vigilant as a tropical cyclone approaches, and consider all relevant risks, not just those posed by the storm surge.

Application during Hurricane Matthew

The potential storm surge flooding maps issued during Hurricane Matthew’s approach of Florida’s east coast offered a clear and dire assessment of the risk for unprecedentedly severe storm surge inundation.

A briefing from the NWS Jacksonville forecast office on the expected local impacts from Hurricane Matthew. Note that storm surge was the primary concern. Credit: NWS Jacksonville

An October 6th briefing from the NWS Jacksonville forecast office on the expected local impacts from Hurricane Matthew. Note the emphasis on storm surge-related dangers. Credit: NWS Jacksonville

The maps for Hurricane Matthew were so dire because the worst-case scenario was squarely within the cone of uncertainty. It wasn’t just possible. It was likely that locations along the east coast and the St. John’s River would be under several feet or more of water if the hurricane continued to hug the coast or made landfall in northeast Florida or southeast Georgia.

More than just the beaches were under threat. The potential storm surge flooding maps showed areas along the St. Johns River — inland regions that don’t typically think of themselves as vulnerable to storm surge –- under up to 6 feet of water as Matthew pushed a wall of water at the coast and up the mouth of the St. Johns. Although the worst-case scenario fortunately did not materialize, reports were still received of the St. Johns River flowing backwards on the morning of Saturday, October 8th, as storm surge and hurricane-force onshore winds pushed the sea inland.

“Fortunately” is the correct word in this situation, because it was nothing more or less than luck that prevented a truly worst-case scenario from actualizing. Had Matthew drifted 20 miles farther the west, the Atlantic coast of Florida, and inland river cities like Jacksonville and Palatka would have experienced truly devastating flooding.

The Bottom Line

The National Weather Service’s new potential storm surge flooding maps provide a graphical, easy-to-understand, quantitative assessment of storm surge risk along the U.S. Gulf and Atlantic coasts. By displaying a reasonable worst-case scenario at each location, they show both local officials and the general public the storm surge depth for which they should prepare themselves, enabling well-informed preparation and evacuation decisions.

However, these maps are not intended to offer a complete picture of water-related risks associated with tropical cyclones. They do not take into account wave action (i.e. waves riding atop the storm surge), rainfall-induced flooding, or potential levee failures. These impacts must be considered separately when assessing the impact of a hurricane or tropical storm in a given area.

And, as always, the output of any model is only as good as its input.

Ultimately, the accuracy of the potential storm surge flooding maps depends on the accuracy of the hurricane track and intensity forecast. Those forecasts – and the storm surge inundation maps derived from them – are continually refined as new data from in-situ and remote sensing platforms (like hurricane hunter aircraft measurements and satellite imagery, respectively) as well as new model guidance become available.

During Hurricane Isaac, a storm surge causes tides to quickly rise while rough waves pound the concrete seawall along the shores of Lake Pontchartrain.

During Hurricane Isaac, a storm surge causes tides to quickly rise while rough waves pound the concrete seawall along the shores of Lake Pontchartrain.

Automated Hail Tracks: The Dark Side of Dual Pol

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Last spring we wrote about the capabilities of dual-polarization radar to identify and distinguish between regions of different types of precipitation within thunderstorms and winter weather events (see “Seeing in the Dark”). This powerful technology provides valuable information to operational meteorologists deciding whether to issue a warning for damaging weather and to forensic meteorologists reconstructing that weather and its impact.

It is also used by the dozens of online hail track products marketed to both construction contractors and insurance claims investigators. These automated hail track products can provide a useful first estimate of hail impact, but they are far from perfectly accurate.

Megan Walker Radtke, chief meteorologist and climatologist here at Blue Skies, recently published an article in Claims Magazine discussing the use of hail track products for insurance claims investigation, including when they should be used with caution.

Check out the article in Claims Magazine’s July digital edition.

It’s That Time of Year Again: Get Storm Ready

tornado approaching homestead

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 Weather Season

tornado season by month

The progression of “tornado season” northward across the country from early spring to mid-summer. Original source: NWS SPC

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.

The structure of a classic supercell. Source: NWS

The structure of a classic supercell. Source: NWS

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.

Preparing for Severe Weather

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).

Tree Trimming

source: The Davey Tree Expert Company

source: The Davey Tree Expert Company

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.

Insurance Policy

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?

Photo by John Williams, courtesy of The Valley Reporter

Photo by John Williams, courtesy of The Valley Reporter

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.

Storm Alert System

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.

source: Alabama Wx Weather Blog

source: Alabama Wx Weather Blog

When comparing weather radios, look for those that:

  • play a loud, obnoxious tone/alarm when an alert is issued, even if the radio sound is turned off – remember, you want it to wake you out of your soundest slumber if a tornado is barreling toward your house.
  • allow you to specify the particular area for which you want to receive alerts – called SAME (specific alert message encoding) technology, radios with this feature will alarm only if the county or region you’ve pre-selected is included in the warning. You probably don’t want to be woken up from your soundest slumber if the tornado is barreling toward somebody else’s house three counties away.
  • allow you to choose which types of weather alerts will trigger an alarm. If you live in a coastal county, for instance, but not near the beach, you probably don’t want to receive coastal flood warnings. Or you may want to be alerted only to the most extreme events, like tornado warnings, but not all severe thunderstorm warnings.
  • have a battery back-up to ensure you’re able to continue using it if/when the electricity goes out
  • receive AM and FM radio bands so you can also listen to weather information from your local radio station
  • if you live in a rural area, you may also want to consider a radio with an external antenna jack so you can attach a larger antenna for better reception

cell phone weather alerts

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.

Storm Plan

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?

Basic Storm Preparedness Kit

source: Weather Underground

source: Weather Underground

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.

Wind Damage: Reconstructing Chaos and Variability

Chaos

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.

A rare rogue wave caught on camera as it passes a large ship on otherwise calm seas. Credit: NOAA.

A rare rogue wave caught on camera as it passes a large ship on otherwise calm seas. Credit: NOAA.

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.

Variability

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).

A bolt from the blue.

A bolt from the blue.

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.

An urban dweller struggles against strong, gusty winds. Credit: The Guardian.

An urban dweller struggles with strong, gusty winds. Credit: The Guardian.

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.

Reconstructing Damaging Conditions – It’s More Than Just Reading the Station Data

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.

A microburst is caught on camera near the airport. Microbursts affect a small area but can produce winds greater than 100 mph. Credit: Las Vegas Review Journal

A microburst is caught on camera near the airport. Microbursts affect a small area but can produce winds greater than 100 mph. Credit: Las Vegas Review Journal

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.

Megan Walker Radtke Awarded AMS Certified Consulting Meteorologist Designation

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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.