From: Roger Greenway, ENN
Published October 28, 2013 06:49 AM

Forecasting heat waves far in advance

Heat waves create unpleasant, sometimes deadly conditions. They also create serious problems for farmers who can suffer serious crop losses. Forecasting heat waves more than a few days in advance would enable more time to prepare for them.


Scientists have fingerprinted a distinctive atmospheric wave pattern high above the Northern Hemisphere that can foreshadow the emergence of summertime heat waves in the United States more than two weeks in advance.
The new research, led by scientists at the National Center for Atmospheric Research (NCAR), could potentially enable probability forecasts of U.S. heat waves 15-20 days out, giving society more time to prepare for these often-deadly events.

The research team discerned the pattern by analyzing a 12,000-year simulation of the atmosphere over the Northern Hemisphere. During those times when a distinctive "wavenumber-5" pattern emerged, a major summertime heat wave became more likely to subsequently build over the United States.

"It may be useful to monitor the atmosphere, looking for this pattern, if we find that it precedes heat waves in a predictable way," says NCAR scientist Haiyan Teng, the lead author. "This gives us a potential source to predict heat waves beyond the typical range of weather forecasts."

The wavenumber-5 pattern refers to a sequence of alternating high- and low-pressure systems (five of each) that form a ring circling the northern midlatitudes, several miles above the surface. This pattern can lend itself to slow-moving weather features, raising the odds for stagnant conditions often associated with prolonged heat spells.

The study is being published next week in Nature Geoscience. It was funded by the U.S. Department of Energy, NASA, and the National Science Foundation, which is NCAR's sponsor. NASA scientists helped guide the project and are involved in broader research in this area.

This map of air flow a few miles above ground level in the Northern Hemisphere shows the type of wavenumber-5 pattern associated with U.S. drought. This pattern includes alternating troughs (blue contours) and ridges (red contours), with an "H" symbol (for high pressure) shown at the center of each of the five ridges. High pressure tends to cause sinking air and suppress precipitation, which can allow a heat wave to develop and intensify over land areas. (Image courtesy Haiyan Teng.)

Read more at NCAR/UCAR.

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