Believe it or not, cooler-than-normal waters in the Pacific Ocean and the eruption of an underwater volcano may determine if Delaware has a mild or harsh winter.
AccuWeather senior meteorologist Paul Pastelok said the Pacific waters are one of the leading indicators about weather in the U.S., while the volcanic eruption is a “wild card” with effects that haven’t been determined.
He also said, as most Delawareans know, the weather can differ considerably from New Castle County to Sussex County and from the west to the coast, with some areas receiving snow while others receive rain or a mix.
What’s the bottom line?
“Overall, it will be milder, we feel at this point, with less snow than normal,” Pastelok said. “In general, precipitation – including rain – will be below normal.”
AccuWeather’s snow forecast for Philadelphia is 14 to 20 inches compared to the average of 23.1 inches. In Washington, D.C., the prediction is 6 to 10 inches of snow, compared to the 13.7-inch average.
How do forecasters know?
To make AccuWeather’s predictions, a team of veteran long-range forecasters analyze computer models, look at results from previous winters and use their personal experience.
One of the factors they check is the temperature of the central and east-central Pacific Ocean near the equator which influences the jet stream and the overall weather patterns in North America.
This year, the temperature is cooler than normal, known as La Niña. Usually, La Niña cooling happens once every three to five years, but Pastelok said this is the third winter in a row for the condition, a “triple dipper.”
“Typically it’s a strong signal during the winter season. La Niña…usually means moist and cold air come together in the west, and so most of the snow and cold are west of the Appalachians,” Pastelok said.
That’s one reason for a prediction of above-normal temperatures and below-normal snowfall in the Mid-Atlantic.
However, after three straight winters, La Niña is weakening, so it might not be as strong of an influence this year, he said.
“Since 1950, we’ve only had two events like this,” with a third La Niña in a row, “so the evidence we have to examine is a small sample size,” Pastelok said.
One of those winters was mild with less snow in the Mid-Atlantic while the other was cold and snowy.
“They are on opposite sides of the spectrum so that brings our confidence down,” Pastelok said.
Another “wild card,” was the January eruption of an underwater volcano in the south Pacific near the equator.
“That released a tremendous amount of water vapor that reached all way up to the stratosphere,” Pastelok said. “That could cause all sorts of issues, because that water vapor is going to stick around for probably two years. Our top researchers are looking at that, but we don’t know the answers yet. We don’t know how far north that water vapor is going to get.”
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Delaware’s forecast by month
While October has started colder than normal and November could have “a couple periods of chilly air,” temperatures should be back to normal in December and early January, Pastelok said.
“Then we should see milder conditions in late January and February,” he said. “Now that doesn’t mean warm, but above normal, maybe by a couple degrees. It could be more, but the mild surges will outweigh the cold surges.”
What’s normal? According to National Oceanic & Atmospheric Administration, for Dover, the mean high temperature in December is 48.6° with a low of 32.1°; in January, a high of 44.4° with a low of 27.6°; in February 47.4° and 29.0°.
The forecast for less snow than normal in the Mid-Atlantic “may mean more rain or even dry weather,” Pastelok said.
The big four winter weather forces
Along with La Niña, Pastelok said three other main factors will influence winter weather in Delaware:
- First, the “Alberta Clippers,” fast-moving, low-pressure systems from western Canada which bring cold air but usually not a lot of precipitation to the Mid-Atlantic.
- Second, when an Alberta Clipper from the northwest combines with a storm system from the Gulf Coast that heads north toward the Appalachian Mountains. “That usually brings more rain than snow or sometimes nothing on the East Coast, while precipitation is heavier to the west,” he said.
- Third, the temperature of the Atlantic Ocean. Right now the waters off the coast of New England are warmer than normal. If that persists this winter, the storms coming up along the Appalachians might not reach their full potential until they get to New England, causing snowfall to be heavier in New England and lighter in the Mid-Atlantic.
“When we look at those scenarios, they’re not good for producing a lot of snowfall in Delaware this winter,” Pastelok said.
Almanacs’ forecasts lean the other way
While AccuWeather is calling for above normal temperatures and below normal precipitation in the Mid-Atlantic, two almanacs are giving more hope to the snow lovers.
Published every year since 1792, The Old Farmer’s Almanac is predicting winter temperatures below normal and precipitation and snowfall above normal for the Atlantic corridor which includes Delaware.
“The coldest periods will be in early December, early and late January, and most of February. The snowiest periods will be in early to mid-January, late January and late February,” according to The Old Farmer’s Almanac press release.
More details from the almanacs:Are we destined for a mild or harsh winter in Delaware?
Meanwhile, the Farmers’ Almanac, providing a long-range weather forecast since 1818, is warning readers this winter “will be filled plenty of shaking, shivering and shoveling.”The forecast “might send people in the Great Lakes areas, Northeast, and North Central regions hibernating,” with the worst weather in the North Central area.
The almanac predicts a stormy winter, “especially for the eastern half of the country. For some areas this may mean snow, but for others it will result in more slush and mush.”
Reach reporter Ben Mace at rmace@gannett.com.
