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Weather service predicting dry winter
Special to The Independent 01/03/2006
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This Fall Season (12th driest since records began in 1898) has been dominated by a stagnant weather pattern with a dominant ridge of high pressure over much of the southwestern United States.
This stagnant weather pattern has been due, in part, to persistent tropical thunderstorm activity in the western Pacific Ocean.
Persistent thunderstorm activity in the tropical Pacific can affect the location and strength of the jet stream over the mid-latitudes, which is the steering current for storms.
With the majority of thunderstorm activity located over the western Pacific Ocean, the jet stream has been strengthened over the west and central parts of the Pacific Ocean, with a ridge of high pressure over the eastern Pacific and the western United States.
Sea surface temperatures (SSTs) over the eastern Pacific Ocean are below normal, and weak La Nina conditions are expected to develop over the next few months.
La Nina represents a state of the eastern and central Pacific Ocean where SSTs are 0.50C or greater below normal (i.e. colder).
The combination of enhanced thunderstorm activity in the western Pacific, along with the likely development of a weak La Nina favors less storm activity over the southern United States due to a more northerly displaced jet stream.
SSTs in the northern Atlantic Ocean, which research has shown to be correlated to drought conditions in the western United States, are currently warmer than normal. This, combined with the current conditions in the Pacific, also signals a higher likelihood of drier than normal conditions over the western United States, especially the southwest.
Current models forecast that the jet stream has strengthened to the point that it will overcome the ridge in the western United States for the short-term, with some opportunities for storms during the next week to 10 days. Based on conditions in the Pacific however, it is likely the ridge of high pressure will rebuild after this period for a return to drier than normal conditions.
Longer range forecasts for the January through March period call for much greater chances (55 percent chance) for above normal temperatures along with slightly greater chances (40 percent chance) for below normal precipitation during that same period across northern Arizona. Random chance would lead to a 33 percent chance for either above, near, or below normal conditions.
Because of the very dry fall season, and the anticipated drier than normal winter, it is unlikely that we will recover and have a normal or above normal snow season. Thus, drought conditions are expected to worsen over the next three months.
While there may be fewer opportunities for storms this season due to the conditions mentioned above, there will still be periods with colder than normal temperatures along with periods of stormy weather with accumulating precipitation. Keep up on weather conditions at
http://www.weather.gov/Flagstaff.
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This story was provided by the National Weather Service - Flagstaff.