Prioritize...
When you've completed this page, you should be able to retrieve monthly summary wind statistics from Local Climatology Data documents, interpret key tendencies from wind roses (most / least common wind directions and directions most / least likely to produce fast winds), and analyze important regional terrain features (elevation changes and bodies of water) that may impact a location's climatology, as well as their impacts based on local wind direction.
Read...
The temperature and precipitation statistics that we covered in the last section are a big piece of a particular location's climatological puzzle, but they don't paint the whole picture. A location's wind climatology also provides important clues about typical / atypical weather, and perhaps more importantly, when coupled with knowledge of the surrounding terrain like bodies of water and elevation changes, can help forecasters understand local influences that winds can have on other weather variables (like temperatures and precipitation).
First off, however, it's important to gauge what constitutes "windy" conditions at your forecast location. Perhaps you've never dug into wind data before, but your experience has probably told you that some locations are typically windier than others. Unfortunately, climatological wind data can be somewhat hard to come by because of a relative lack of properly sited observation stations (many privately owned and home weather observing equipment is not set up to measure wind speed at a standard height of 10 meters). Furthermore, publicly available wind data from ASOS sites is generally limited to hourly observations and some summary statistics for stations at larger airports (anything more typically requires some data mining).
Still, we can get a sense for what constitutes a windy day at select forecast locations by viewing summary statistics compiled by the National Centers for Environmental Information. For larger airports in the U.S., they produce "Local Climatological Data" documents, which contain a wealth of statistics, including mean and record wind speeds (sustained and gusts) for each month. For example, compare the historical wind data at Cold Bay, Alaska and Seattle, Washington. Cold Bay is clearly a windier place, with monthly mean wind speeds that are roughly twice those in Seattle. Furthermore, the monthly record sustained wind speeds in Cold Bay are significantly higher, as are the record gusts (multiple months have had gusts of over 80 miles per hour in Cold Bay). The data for monthly record sustained wind speeds and gusts can be particularly helpful for gauging what constitutes unusually fast winds at a particular location during various times of the year.
Key Data Resource
Local Climatology Data documents from NCDC/NCEI contain a wealth of climatological statistics and other useful information. In addition to the monthly summaries of wind data described above, they also contain the exact location (latitude / longitude coordinates) and elevation of major airport stations. They also include a brief, but informative climatology discussion toward the end of the document that can really help forecasters get their local bearings.
A very common visualization for studying a location's wind climatology is a wind rose, which is a plot that displays historical wind direction and speed information. You encountered wind roses during your previous studies, and if you need a refresher on how to interpret them, I recommend this quick discussion on the basics (keep in mind, however, that display conventions can vary from website to website). Ultimately, wind roses are a great way to quickly assess from which directions winds most and least commonly blow, and assess which directions are more (or less) prone to particularly speedy winds.
Recurrent patterns in winds may become apparent at a particular location because of regional terrain (winds being channeled through mountains or valleys, for example), persistent mesoscale circulations (like sea breezes or mountain-valley circulations), or persistent storm tracks, and these patterns may change throughout the year. For example, check out the wind roses for Miami, Florida (above) from January and July.
Note that the Miami wind roses for January and July look very different. The most frequent wind direction (marked by the longest spoke) is from the north-northwest in January (blowing from that direction nearly 14 percent of the time). Winds from the east and southeast are also fairly common in January, but not quite as common as north-northwest winds. In July, however, east-southeast winds are the most common (occurring nearly 19 percent of the time), and winds from the north-northwest are much less frequent. It's not even close! In fact, if we sum the percentages of winds from the east, east-southeast, and southeast (the three longest spokes), winds from those directions occur nearly 50 percent of the time combined!
Any ideas why winds from those three directions are so common in July? A big part of it is the regular occurrence of sea breezes as the Florida peninsula warms up during the day and a mesoscale sea-breeze circulation develops, resulting in onshore flow at Miami. During the summer, this onshore flow ushers in slightly cooler, moist air into south Florida. The reliable sea breeze is a big reason why temperatures have only hit 100 degrees in Miami once since records began in 1895 (per the ThreadEx data). Daily record highs in Miami during the summer are typically in the middle and upper 90s, which is comparable to or even lower than many locations that are much farther north in the U.S. So, wind direction, and the trajectory of the air as it approaches your forecast location are important considerations!
Given the forecasting impacts that air trajectories can have, getting the lay of the land around your forecast site and the surrounding region is critical. Large bodies of water and elevation changes are particularly influential. To get a feel for the lay of the land around your forecast location, it's always a good idea to study a detailed topographic map of the local area, in order to judge the local elevation changes and distance from your forecast site. I'll use Los Angeles International Airport (KLAX) as an example. As you can see from the Google map below, the terrain around Los Angeles is complicated! Many terrain features influence the weather at KLAX!
For starters, the Pacific Ocean is just west of the airport, and the coastline wraps around such that the ocean also lies about 15 miles to the south. Therefore, any time low-level winds blow onshore (having a large westerly or southerly component), they'll bring a substantial maritime influence, which during certain times of year can lead to fog or low cloud development. But, given the substantially higher elevations that are located around the Los Angeles Basin (KLAX sits at an elevation of 97 feet), considerable downsloping occurs when low-level winds blow from the northwest all the way around to the southeast.
Such downsloping brings a warming and drying influence (from compressional warming), with the greatest downsloping occurring on northeast and east-northeast flow since that's where the highest elevations are locally. Indeed, within 30 to 40 miles northeast of KLAX, multiple elevations in excess of 7,000 feet can be found! That's a lot of downsloping! Even downsloping from smaller ranges of hills and mountains (like the Hollywood Hills about 12 miles north of the site, or the Palos Verdes Hills about 12 miles south) is considerable. If air parcels descended the Palos Verdes Hills dry adiabatically (warming at a rate of 5.5 degrees Fahrenheit per 1,000 feet), that's worth almost 8 degrees Fahrenheit of compressional warming between the hills and the airport (assuming a starting elevation of 1,500 feet)! So, it pays to study the terrain surrounding your forecast location even for fairly subtle elevation changes. It's worth considering the impacts for even elevation changes of a few hundred feet or more within several miles.
The farther you go from your forecast site, it takes a more significant topographic feature (body of water or elevation change) to make a significant contribution to a location's climatology. In general, it's wise to assess the terrain within several hundred miles for major bodies of water or elevation changes. And, sometimes, the elevation changes don't take the form of well-defined, obvious hills or mountains. To get an idea of how a forecaster might assess the larger-scale terrain around a forecast location, check out the short video below (4:16), which contains a few examples.
Click here for a transcript of the video.
Each forecast location can have its own unique topographic influences that are an integral part of its weather and climate, and it’s important to look at both local factors, which may be within only a few miles or tens of miles, and larger-scale regional factors. In this video, I’ll show some examples of the types of larger-scale regional factors that forecasters need to consider. Some of the factors and their influences are fairly obvious, while others might be more surprising. To start, imagine that you’re forecasting for Omaha, Nebraska. Nebraska is located in the Central Plains of the United States, so it’s easy to think that the terrain in the state is flat, but it’s not.
A closer look at a topographic map of Nebraska shows Omaha over here in extreme eastern Nebraska. The official observation site at the airport sits at an elevation of 982 feet, but elevation steadily increases toward western Nebraska. In fact, the town of Scottsbluff, Nebraska sits at an elevation of nearly 4,000 feet! So, there’s an elevation difference of about 3,000 feet between these two cities across the supposedly flat plains, and there are even some higher elevations to the south of Scottsbluff. The elevation changes are very gradual – the distance between Omaha and Scottsbluff is about 400 miles, but they’re elevation changes are still significant. Any wind with a large westerly component will downslope across Nebraska toward Omaha. Of course, farther to the west, just off the map is the Rocky Mountains, so forecasters have to think about downsloping anytime low-level wind flow has a large westerly component across Nebraska toward Omaha. Downsloping causes warming and drying, so if there’s no cold advection occurring, such wind flow can have a considerable warming influence. Even if cold advection is occurring, downslope warming can counteract some or all of it, depending on the speed of the wind and the strength of the advection.
Now, imagine you’re forecasting for Philadelphia, Pennsylvania. Philadelphia International Airport sits at an elevation of 10 feet above Mean Sea Level. But, there are a number of hills west and northwest of the city, so elevations of 300-500 feet are common even within 20 miles of the airport. Back in Central and Northern Pennsylvania, numerous ridge tops in the Appalachians are between 1,000 and 2,000 feet and we’re still less than 200 miles from the airport. The Poconos are less than 100 miles north of Philadelphia, with some elevations exceeding 2,000 feet. So, winds with a notable northerly or westerly component will downslope toward Philadelphia, bringing a warming and drying influence. Off the map to the east, the Atlantic Ocean sits a little more than 50 miles to the east, and Delaware Bay sits less than 50 miles to the south. So, winds from the south or with notable easterly components will bring a maritime influence, which may moderate temperatures and bring moisture.
Finally, let’s look at Portland, Oregon. The airport lies at a low elevation of 19 feet above mean sea level. About 65 miles to the west is the Pacific Ocean, but in between the ocean and Portland is the coastal range, with numerous elevations between 2,000 and 3,000 feet within 40 miles of Portland. So, winds with large westerly components bring a moderating, maritime influence from the Pacific, but they also downslope considerably between the coastal range and Portland. The drying influence makes the airport one of the drier locations in the area, on average. About 30 miles to the east, we get up into the Cascades, with numerous elevations in excess of 4,000 feet, and Mount Hood in excess of 11,000 feet. So, winds with a significant easterly component will downslope significantly from the Cascades toward Portland, also bringing a warming, drying influence.
As I mentioned, each location can have its own unique topographic influences, so forecasters must take the time to get to know the lay of the land, and think through what impacts changes in elevation and bodies of water have on local weather and climate.
From the video, take note that quantitatively estimating elevation changes and the distance of a particular feature from your forecast location is important, as it gives context for how significant a particular feature may be. Performing these types of analyses also helps forecasters understand the influences that various wind directions may have on the weather at their forecast location in terms upsloping (which brings cooling and potential cloud / precipitation development) or downsloping (warming and drying), or a potential maritime influence.
Ultimately, each location can have its own unique topographic influences that are an integral part of its weather and climate, and it's up to the forecaster to analyze the location's surroundings and determine the relevant features and impacts. I hope the sampling of examples gives you an idea of the types of features and influences that forecasters need to look for, and with your fundamental knowledge from your previous studies, you should be able to perform basic analyses like these on your own. If you want a little practice in making these kinds of assessments for yourself, check out the Quiz Yourself section below for a few more examples. In the next section, I'll show you a Case Study detailing how a forecaster might compile relevant climatology information for a particular city.
Key Data Resources
- Wind Roses: The Natural Resources Conservation Service has a selection of wind roses for many larger U.S. airports. The wind roses are broken down by month and each shows a 30-year climatology for a particular month.
- Topographic Maps: Turning the terrain layer on Google Maps can be a good way to analyze local terrain around your forecast site. For larger-scale state maps, the topographic maps from Johns Hopkins University are a good source, although you may find others you like around the Internet.
Quiz Yourself...
Question #1
Imagine that you are forecasting for KMAF in Midland, Texas (elevation 2,862 feet). Given these local-scale and state-level terrain maps (here's the elevation key), describe the important topographical features (including reference elevations and distances) and the impacts of wind direction on local weather based on the terrain. Feel free to explore the area around Midland International Air and Space Port in Google Maps, if you wish.
Answer: Midland is located about 500 miles northwest of the Gulf of Mexico on the Plains of Texas. Elevations near the city don't change very much, but there is a gradual decrease in elevation toward the northeast, east, and southeast, such that elevations fall below 2,000 feet less than 100 miles from the site and continue decreasing from there. Toward the southwest, west, and northwest, elevations gradually increase toward the mountains of West Texas and New Mexico, where elevations exceed 5,000 feet less than 200 miles from the site.
Flow from the southeast would import moisture from the Gulf of Mexico, which combined with gradual upsloping (a cooling mechanism) can sometimes lead to low clouds, fog, and/or drizzle. Some upsloping occurs on any wind with a substantial easterly component. Flow with a large westerly component downslopes from higher terrain in Mexico, West Texas, and New Mexico, which favors compressional warming and drying.
Note that the exact elevation references and distances that you chose may differ from the ones mentioned here, but a good description needed to reference the Gulf of Mexico and the elevation changes to the east and west (along with upsloping and downsloping impacts).
Question #2
Imagine that you are forecasting for KALB in Albany, New York (elevation 280 feet). Given these local-scale and state-level terrain maps (here's the elevation key), describe the important topographical features (including reference elevations and distances) and the impacts of wind direction on local weather based on the terrain. Feel free to explore the area around Albany International Airport in Google Maps, if you wish.
Answer: KALB is located in the Hudson River Valley, with rolling hills generally ranging from 200-500 feet near the station (lower elevations are near the river, about 6 miles east). The Helderberg escarpment rises to about 1800 feet 11 miles to the west, while about 12 miles to the east, terrain rises up near 2000 feet. Even higher elevations (3000-4000 ft+) lie about 40+ miles northwest and northeast of the site in the Adirondacks and Green Mountains, respectively. The Atlantic Ocean lies about 120 miles south and east of KALB, while Lake Ontario is about 100 miles northwest.
Winds from most directions downslope into Albany, which has a warming and drying influence, with the greatest downsloping occurring on northwest, southwest, and east/east-northeast winds,. This largely inhibits lake-effect precip (and to a lesser extent, clouds) on northwesterly flow. Long-duration southerly – easterly flow brings maritime, moderating influences from the Atlantic, but they are mitigated somewhat (primarily on easterly flow) by downsloping.
A good description needed to reference Albany's valley location, rolling hills nearby, and the higher elevations surrounding it (along with distance and elevation references), as well as the major bodies of water in the region (Atlantic Ocean and Lake Ontario) and potential downsloping and maritime influences.
Question #3
Imagine that you are forecasting for KRDU in the Raleigh-Durham Metropolitan Area in North Carolina (elevation 416 feet). Given these local-scale and state-level terrain maps (here's the elevation key), describe the important topographical features and the impacts of wind direction on local weather based on the terrain. Feel free to explore the area around Raleigh-Durham International Airport in Google Maps, if you wish.
Answer: Terrain in the Raleigh-Durham metro area is generally rolling with elevations within 100-200 feet of the station elevation of KRDU. Higher elevations start about 10-20 miles west of the area on the Piedmont Plateau (generally 500-1000 feet). Higher elevations in the Appalachian Mountains are located about 150 miles to the west, up to 3000-6000 ft+. The Atlantic Ocean lies about 150 miles east and south of Raleigh, with lower elevations on the coastal plain in the eastern part of North Carolina.
Northwest to west-southwest winds will downslope from the Appalachians and Piedmont Plateau toward KRDU (a warming, drying influence). Winds from the south and those with a large easterly component will have a maritime influence from the Atlantic, with slight upsloping (a slight cooling influence, which combined with moisture from the Atlantic could lead to low cloudiness and precipitation depending on the large-scale weather situation).
A good description needed to reference rolling hills near KRDU, and the higher elevations to the west (along with distance and elevation references), as well as the Atlantic Ocean and resulting downsloping, upsloping, and maritime influences on specific wind directions.