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For the second year in a row, the climate pattern known as La Niña has evolved in the Pacific Ocean, and it will likely take longer. severe drought While this winter brings some relief to Northern California and the Pacific Northwest across much of the western United States, government forecasters said on Thursday.
In La Niña, lower normal sea surface temperatures in the equatorial Pacific lead to changes in the jet stream, a high-altitude wind river that can affect weather elsewhere in the world.
Over North America, La Niña usually, but not always, shifts the jet stream north, bringing more storms to that part of the continent and fewer to the south.
This typical pattern is reflected in the National Oceanic and Atmospheric Administration outlook for coming winter, released Thursday.
With the development of La Niña, which is expected to continue into the spring, wetter-than-normal conditions are predicted in the Pacific Northwest and northern Rocky Mountains, Jon Gottschalck, head of the operational forecasting branch of NOAA’s Climate Prediction Center, said. and in the Great Lakes and Ohio Valley regions. Below-normal precipitation is expected in much of the south.
In terms of temperatures, the outlook calls for cooler conditions in the Pacific Northwest as far as the Northern Plains, and warmer-than-normal conditions almost everywhere: a wide area from Central and Southern California to the central Rockies to Minnesota and the entire Midwest. and East.
“A major area of concern this winter remains the Southwest,” Gottschalck said. The region is more or less submerged in drought. for the last two yearsDespite heavy monsoons in Arizona and elsewhere, there has been only a slight improvement this summer.
Mr Gottschalck said that with La Niña, drought is expected to continue in the Southwest and develop in the Southern Plains.
But Mr Gottschalck said the forecast for more precipitation for the Pacific Northwest bodes well for improving and in some cases eliminating drought conditions. Recovery can also be seen in Northern California; That’s good news for a region that has suffered a severe wildfire season this year, in part due to continued heat and dryness.
La Niña is the opposite phase of El Niño, where higher-than-normal sea surface temperatures in the Pacific tend to shift the jet stream south, bringing wetter conditions to Southern California and elsewhere to the south.
After last year’s La Niña, Pacific Ocean temperatures rose slightly, but not enough for an El Niño to develop. Temperatures have now dropped again, leading to the second La Niña. But Mr Gottschalck said such a “double immersion” La Niña is not unheard of.
For now, the forecast said this La Niña will be moderate, meaning sea surface temperatures will be about 1 to 1.4 degrees Celsius (1.8 to 2.5 degrees Fahrenheit) below normal. But Mr. Gottschalck did not rule out that temperatures could drop further, leading to a strong La Niña.
In general, with a stronger La Niña, the response of the jet stream is also greater.
Mr Gottschalck said with La Niña, the likelihood of blizzards or other strong winter storms in the Northeast has decreased because the shift of the jet stream has shifted winter storms west of the Appalachian Mountains.
But Mr Gottschalck said that as with every La Niña and El Niño, typical conditions don’t always happen. He noted that NOAA’s winter outlook is a probabilistic forecast, meaning it reflects the probability of what will happen and is not certain.
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