January 3, 2013
By Benét J. Wilson
Weather Services International (WSI) is forecasting that the December-February period will be colder than normal across much of the northern half of the United States, especially the northern Rockies and northern Plains, according to its latest longer-term report. Above-normal temperatures will be common across the southern United States, especially in the Southwest.
“After an extended spell of above-normal temperatures across much of the U.S. during the past 18 months, the last few months have been characterized by below-normal temperatures across much of the eastern U.S., as a weak El Nino event has tried to emerge,” said Dr. Todd Crawford WSI Chief Meteorologist.
“While this El Nino event now appears to be a dud, most of our more skillful climate indicators suggest that very cold air will be in plentiful supply across western and central Canada this winter, with frequent border crossings into the northern U.S. Currently, we do not expect the kind of frequent atmospheric blocking in the North Atlantic that would result in more extreme and more widespread cold in the eastern U.S.,” he continued. “However, trends in some of the long-lead indicators suggest that this assumption may be challenged, and that the risk to the forecast in the eastern U.S. is towards the colder side.”
If the jet stream and prevailing westerly winds weaken, colder air will sink more deeply into the U.S., while allowing warmer air to move northward, said Kristen Seaman, a meteorologist and communications coordinator at AOPA. “The mixing of these air masses will not only lead to colder temperatures in the northern part of the U.S., but more severe winter storms in the areas where they collide, namely the Rockies and the Mid-Atlantic region,” she added.
Dan Leonard, a senior WSI meteorologist, said his organization provides these updates because the markets want to position themselves on weather conditions.
WSI uses different models to create its forecasts, said Leonard. “We use a few from the National Oceanic and Atmospheric Administration (NOAA), along with a few others run by other countries in the world like Canada and England,” he said. “We use their data, plus we use models that we run in house. We also look at models from winters past to see if there are any similarities.”
WSI then gets an overall picture of what it thinks the weather patterns will be, said Leonard. “I like to say the models are the science and forecasting is the art,” he said.
Longer term forecasting for aviation is harder to do, said Leonard. “With things like convection, icing, turbulence, and thunderstorms, you can only forecast them on a one-to two-day basis. It’s impossible to do these types of forecasts in the long term,” he said. “But looking at what we’ve done, pilots can look and see that in February, we’ll have stronger than usual west-to-east jetstreams, which means there will be quicker flights from San Francisco to Washington, D.C.”
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