The U.S. government released its national winter forecast last week, and it doesn’t look good for drought-stricken California and states across the South.
The forecast “favors below-average precipitation across the entire southern tier of the [United States],” said meteorologist Mike Halpert at a 20 October press conference. Halpert directs the Climate Prediction Center (CPC) of the National Oceanic and Atmospheric Administration (NOAA) in College Park, Md. The CPC forecasts climate trends for the United States on weekly and monthly timescales.
At the press conference, Halpert and other officials discussed NOAA’s latest Winter Outlook, a forecast the agency publishes each fall, which predicts large-scale trends for winter weather across the United States. A key factor of that outlook is a weak La Niña, which brings dry air to much of the southern United States.
El Niño Wasn’t Enough
Many were hoping that the recent El Niño, a period of warm and wet conditions that began in the spring of 2015 and ended last May, would ease California’s drought, which now has lasted 5 years. In June 2016, California’s snowpack amounted to just 6% of what it normally is, according to the U.S. Geological Survey. The drought has threatened water supplies for farmers and cities and raised the risk of wildfires. Other parts of the United States, like Georgia and Alabama, as well as New England states, have been experiencing their own droughts.
This past El Niño didn’t dump as much rain and snow as many Californians had wished. That window of opportunity has now closed, and the outlook released this week doesn’t provide much hope for relief in the near future for California or elsewhere.
Multiyear Wetness Needed
For the country’s middle latitudes, including most of California, NOAA is predicting equal chances of a wetter or drier than normal season between December and February.
However, dry areas of the country need more than that. “It’s probably going to take a couple of wet winters in a row to really put a big dent into this drought,” said NOAA meteorologist David Miskus, also with the CPC. He explained that not only are the topsoil dry and the reservoirs low, but even wells now are running dry. Water levels at only one third of California’s major reservoirs measure at or near their historic averages.
Weak La Niña Coming
Now that El Niño is over, enter La Niña. That’s the cyclical weather pattern caused by low pressure over the western Pacific Ocean that drives cool, dry air down into the eastern Pacific and to southwestern states. La Niña typically follows El Niño conditions.
Although La Niña delivers dry air to southern California, it is usually associated with wetter conditions in the Pacific Northwest. However, NOAA forecasters are saying that this La Niña should be a weak one, meaning a lower chance of big storms in the north that could find their way into northern California and replenish the snowpack in the Sierra Nevada mountains. The NOAA forecast does call for a wetter than average winter in the northern Rocky Mountains.
Hurricane Matthew Gave Some Drought Relief
NOAA is forecasting that the drought will get worse for the southern states that will get the dry La Niña weather, like those along the Gulf Coast. Halpert said that the drought may even expand north into the Southern Plains states like Oklahoma and Kansas. The only parts of the southeast not looking at a worsening drought are areas of the Eastern Seaboard that are still drying out after Hurricane Matthew.
Parts of New England are also enduring drought this year. NOAA forecasters see that dry spell ending this winter for the northern parts of those states, helped, in part, by the Great Lakes. The upper Midwest had a hot summer, and Miskus says that a cold blast of air across that warm lake water could produce a big dump of so-called lake-effect snow early in the winter before the lakes ice over.
Halpert noted at the press conference that the outlook will be updated once more before winter starts, on 17 November.
—Sam Lemonick, Freelance Science Journalist; email: email@example.com