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May-June 2013

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Weather Front

Predicting a Dangerous Gravity Wave

Flying over the Gulf of Mexico may soon be a little safer with the development of a forecasting method to predict a lower atmospheric phenomenon called an undular bore. Until recently, there was no method available to forecast theses predominantly springtime events. A new study published in Weather and Forecasting has identified a method to accurately predict undular bores up to 48 hours out.

An undular bore is a type of gravity wave in which a frontal boundary pushes into and gently lifts a shallow, stable layer of air at the surface. As gravity pulls the layer back down, it causes smooth rolling waves. The effect is similar to that of water rippling from a pebble dropped in a pond. According to the author of the study, Phil Lutzak, by analyzing six specific parameters, his forecasting method can predict the time and location of an undular bore, and also anticipate its strength, forward speed, and horizontal wavelength. Undular bores can cause rapid, 180-degree shifts in vertical winds of more than 35 knots, and if the bore plows into a very moist environment, it can induce severe thunderstorms. Using standard operational forecasting methods to analyze wind profiles, atmospheric density, and moisture, Lutzak's forecasting tool can help pilots avoid the dangerous conditions caused by undular bores.

KIMBRA CUTLIP is a freelance writer and former assistant editor for Weatherwise.

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