What are the chances that the U.S. would experience yet anotherwarmer-than-normal winter after just having two in a row?Apparently they’re pretty good right now, according to a new winterweather forecast released last week by the National Oceanic andAtmospheric Administration. One thing is certain: the La Ninatropical Pacific sea temperature event, which is expected toinfluence this winter’s weather, will throw a monkey wrench intoregional weather forecasting models.

NOAA’s new winter outlook, which focuses on cooling equatorialPacific sea surface temperatures, called La Nina, was partly toblame for a 26-cent price drop in gas futures last Thursday,according to some analysts. On Oct. 26, NOAA released its officialwinter weather forecast, calling for another unusual winter.

“Once again, La Nina will have a pronounced effect on winterweather in the United States and, consequently, manyclimate-sensitive businesses and industries,” said D. James Baker,under secretary of commerce for oceans and atmosphere and NOAAadministrator. “While we can’t put a price tag on this year’s LaNina cycle, we can forecast with confidence how it will steer thenation’s winter weather.”

The 1997-98 El Nino winter, which brought a mild winter to thenorthern Midwest and heavy rains to the Southwest and West Coast,caused U.S. energy consumers to spend $2.2 billion less on oil andgas for heating, but then cost consumers and farmers $3 billion inlost crops and agricultural production, Baker said. A La Ninawinter preceded it in 1997-98, causing 10% warmer than normaltemperatures on average throughout the U.S.

“La Nina will alter the strength and pattern of the Pacific jetstream over North America to give us a warm and dry winter in thesouthern half of the nation, but more snow and rain to the PacificNorthwest and the Great Lakes,” he said. “We expect considerablemonth-to-month variation in temperature, rainfall and storminess inthe central, northern and eastern states, which means days ofwarmer than normal temperatures followed by bouts of bitter cold.As with every winter, it’s too early to predict just how the jetstream will affect the weather in many north central states and fornorthern New England.”

La Nina winters are characterized by temperature variability, orchanges in the weekly mean temperatures as the season progresses. Aseason with little variability would have mean temperatures thatchanged little from week to week. A season with high variability,like this La Nina, will have some very warm weeks interspersed withsome very cold ones.

“La Nina years are characterized by a tendency for blocking highpressure systems to form in the North Pacific Ocean,” said LouisUccellini, director of the National Weather Service’s NationalCenters for Environmental Protection. “These blocks tend to persistfor a week or two at a time. Depending on the exact location, whichis variable, the weather can alternate from very warm to very coldconditions that persist for a while, then change. This causes thelarge amount of temperature variability in the northern UnitedStates.”

NOAA’s winter temperature breakdown is as follows: