Katabatic and Anabatic Winds:

Local Surface winds are sometimes more a function of Temperature Differences between mountain tops and lower elevations than overriding Synoptic winds. These winds are sometimes called Mountain Winds as they occur most frequently in mountainous areas, meteorologist call them Katabatic or Anabatic Winds

Anabatic Winds are upslope winds driven by warmer surface temperatures on a mountain slope than the surrounding air column. Katabatic winds are downslope winds created when the mountain surface is colder than the surrounding air and creates a down slope wind. Katabatic wind may range over fairly large areas as in the case of the Santa Anna winds experienced throughout southern California during certain times of the year. They can produce winds to 80 miles per hour and dominate local weather patterns for extended periods of time (weeks). As shown in figure 2.4 below, they are initiated when cold air atop higher land masses begins to flow down hill (remember cold air is heavier than warm air) displacing the warm air below it and warming adiabatically and often gaining speed in the process. When the lower elevations are hot desert areas the temperature differences can be quite substantial on the order of 60 to 70 degrees F. The greater the temperature difference the stronger the wind. They are often so well-known that they are given names like California' Santa Anna as mentioned above, the Chinook of the pacific northwest or the Fohn in Switzerland.

Winds can be derived from a number of different meteorological phenomena that are either caused by large scale synoptic pressure and temperature differences or by local temperature and pressure differences. Once generated, however, there are many small scale surface structures that can modify the wind direction and speed and distort the accuracy of the observing instrumentation. We call these wind modifiers and will talk about them in future blogs.

Mature Thunderstorm Wind:

Thunderstorms are primarily local thermal weather phenomena (usually less than 5 miles to sometimes more than 30 miles in diameter), that are caused by either local surface heating , Air Mass Thunderstorms , or by weather systems such as fronts, converging winds, or troughs aloft that force upward motion of the surrounding air. From a surface wind perspective, thunderstorms, regardless of their cause can quickly and substantially modify wind direction and speed. As shown in figure 2.3 below, the wind outflow from the base of a thunderstorm tends to hit the ground a radiate axially from the storm center. This out flow can and often does exceed 50 mph and may contain gusts in front of the storm and opposing winds aloft that create wind shear (wind flowing in opposite directions) near the surface. As thunderstorms move from their initial formation, through the mature stage (as shown) surface wind surrounding the storm changes from updrafts and inflow (at the initial stages) to down flow and outflow at the mature stage. Local thunderstorm generated winds easily overcome most synoptic surface winds as the local temperature/pressure differences often are greater than the larger scale synoptic differences.

Points to Ponder: What happens to accuracy of wind measurement at an airport with a thunderstorm sitting over the middle of airport? How do you measure wind shear?

January 17, 2009 copyrighted.

The Airlines' Eyes on the Skies By Del Quentin Wilber The Washington (DC) Post

FORT WORTH -- Airline meteorologist Mark Mabey stares at four computer screens on his desk. They are filled with data, charts and radar images. All seem to suggest a different potential for thunderstorms -- the airlines' enemy during the hectic summer travel season.

He rubs his chin and sighs, then walks to a large bank of windows. His eyes scan a mass of menacing clouds in the distance. He is thinking about the forecast he is trying to generate for his carrier, American Airlines.

"This isn't an easy call," says Mabey, lost in thought as he looks back toward his computers. "I might have to rely on intuition."

On this particular Monday last month, Mabey was worried about more than nasty letters or phone calls of the kind television or radio meteorologists get for predicting a sunny weekend that turns out to be a washout. The quiet, little-noticed work that Mabey and dozens of other airline meteorologists perform has huge financial and operational consequences and can affect the travel plans of thousands of passengers.

Relying on computer models, government forecasts and radar images, Mabey's predictions will dictate how American executes its schedule, files flight plans for aircraft arriving from as far away as India and loads fuel on each jet. A good forecast will save the airline cash and grief. A bad one could lead to an operational and public relations debacle -- just ask executives at American and JetBlue Airways, which have endured recent weather-related mishaps that left hundreds of passengers trapped on planes for hours.

As Mabey walks about his office, he mulls his options.

A forecast of a decent chance of thunderstorms will force dispatchers to add fuel to planes so that they might be able to circle until the weather clears. That helps the carrier prevent costly diversions to alternate airports.

But that extra fuel is heavy, requiring more of it to be burned to keep a plane airborne. With oil prices at all-time highs, airlines are doing everything they can to cut back on their use of fuel.

It's a difficult balancing act, especially in an industry that has razor-thin profit margins after years of billion-dollar losses. And during the busy and congested summer travel season, the stakes are even higher: Planes are packed, and airlines are battling record delays at airports across the country.

"Meteorologists start everything around here," said Monte E. Ford, a senior vice president and the chief information officer at American. He said the first question he asks his assistants each morning is about the day's weather outlook. "A big part of what we do is dependent on weather."

Mabey, a laid-back 48-year-old Texas native who wears glasses and short-sleeved shirts, dreamed of being an airline meteorologist when he was a little boy and kept detailed records about rainfall and temperatures in his back yard. He realized his goal in 1986, getting a job with American after spending several years bouncing around other meteorological jobs and chasing tornadoes in Texas and Oklahoma.

In 2003, American eliminated its 21-person meteorological team and hired outside contractors. Several of the airline's meteorologists, including Mabey, eventually got jobs with Weather Services International, the firm American ultimately hired to generate its forecasts.

To keep close contact with American's flight dispatchers and operations workers, Weather Services International stationed its meteorologists in the same office they had occupied as American employees. It has six full- or part-time meteorologists assigned to American's operations center; other meteorologists work out of another office to help with forecasts for American and the firm's other clients.

Other airlines have made similar cuts, saying they have reduced costs and that they get better forecasts from third parties. United Airlines got rid of its 19-person team in 2005 and hired Ensco, which is headquartered in Falls Church, to generate its forecasts. Low-cost carriers such as JetBlue have generally shied away from the expense of employing in-house weather staffs.

At least two carriers, Delta Air Lines and Northwest Airlines, have kept their teams despite going through recent bankruptcy reorganizations.

The work of airline meteorologists, whether as airline employees or at contractors, has historically generated little public attention. But recent incidents have put them in the spotlight. American's meteorologists -- not including Mabey -- didn't predict the duration of thunderstorms that whacked the carrier's hub here in December and April, forcing American to divert nearly as many flights each day as it did on Sept. 11, 2001, American executives said.

The highest-profile airline weather fiasco occurred on Feb. 14, when JetBlue's executives thought government and contractor forecasts indicated that an ice storm would relent over New York. It didn't. Scores of flights were canceled, and hundreds of passengers were trapped on planes for as long as 10 hours. Mabey said he doesn't worry too much about making a mistake -- it's all part of a job that sometimes relies more on gut instincts than on computer models.

On Thanksgiving Day 1993, he predicted little chance of an ice storm because he did not believe the temperature would drop low enough to turn the rain to ice. He was wrong, and American was caught off-guard. Ice strangled its Texas hub, stranding jets all over the tarmac. He still remembers his disappointment.

"It was so close, 32 to 33 degrees, and I thought it would be rain," Mabey recalled. "It was a disaster. It was real ice storm. It killed our operations. Thank goodness it was a holiday and there were fewer flights."

He has also saved the carrier money and operational snarls. Before a recent wind and dust storm, Mabey was checking government forecasts and computer models and thought they weren't predicting high enough winds. He decided to forecast gusts up to 50 mph, a speed that would prevent many planes from safely taking off or landing. It was a gutsy call because the forecast would force American's executives to begin to cancel flights in advance of the storm.

The high winds did develop -- starting and diminishing within a half-hour of Mabey's predictions.

"The meteorologists really hit that one right on the mark," said Robert W. Reding, senior vice president of technical operations for American.

On the iffy Monday last month, Mabey had been wrestling with the forecast since he started his shift at 6:30 a.m. His computer models predicted various outcomes: no chance of thunderstorms, a risk of thunderstorms, a 40 to 60 percent chance of thunderstorms and a near guarantee of scattered to severe thunderstorms. Radar images hinted at potential thunderstorms east of Dallas, and government forecasts put the chance at about 30 percent.

Mabey said he didn't want to simply report that there was a good chance of thunderstorms. He wasn't convinced they would show up, thinking it would not get hot enough "to set them off."

"You don't want to be too pessimistic because then you burn fuel," he said. "But if you are too optimistic, you can get burned, too. The tough part about today is that you don't see anything now, really. But you have to plan for two, three, four hours down the road."

Then, about noon, just as he was about to finish his forecast, he looked at another computer model and radar images of rain east of Dallas. He heard a computer beep behind him. He turned and watched as the computer's monitor began to map lightning strikes near Dallas. "Hmm," he said several times before heading to the windows to take a peek at the building storm clouds. "This is the kind of torture you put yourself through."

By 1:30 p.m., he decided to parse the forecast carefully, writing that the storms should remain near Dallas but that he "can't rule out" that they might pop up around American's hub at nearby Dallas-Fort Worth International Airport.

That afternoon and evening, as thunderstorms rattled Dallas, only a few small ones developed close to the airport. Lightning forced workers to shut the ramp for about half an hour.

There were no diversions.

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