What better time than the first day of summer to put thoughts of winter chill and snow in your mind? Moving forward, days shorten and, in about a month, average temperatures start to fall.
Although making projections about the winter are difficult even in the fall, there are important indicators developing in the summer that point to possible snow excitement in the winter.
Let’s examine each of them.
El Niño is probably coming
The National Weather Service has officially declared an El Niño watch, and most computer models forecast a weak to moderate event by the winter.
El Niño increases the odds of snow for Washington in the winter. Since 2000, we have experienced a snowier-than-normal winter in two-thirds of El Niño cases, compared with just over a 10 percent rate for La Niña, its opposite phase:
The average entire winter’s snow in the El Niño cases is a robust 26.5 inches, while La Niña is about 10.5 inches (normal is 15.4 inches). That’s a big difference.
El Niño does not guarantee a snowy winter, but the odds are considerably higher, as it sends more moisture through the southern branch of the jet stream toward the East Coast.
But if you’re a snow lover, two additional factors may boost our odds of cashing in on it.
The northeast Pacific Ocean is warming
Cold air is, of course, critical for snow in Washington, and the evolving configuration of ocean temperatures in the northeast Pacific Ocean may help support a pattern that will foster its delivery into the eastern United States.
Most long-range forecast models are favoring a broad area of above-normal water temperatures in the Gulf of Alaska area in winter. These warm waters are usually associated with more zones of high pressure in winter in this region, a condition known as the negative Eastern Pacific Oscillation (-EPO).
When this pattern is in place, the jet stream tends to dip in the eastern United States, allowing frigid air to surge south. We saw this pattern assert itself in the latter part of the 2014-15 El Niño winter, which turned out quite snowy around Washington.
The sun is quieting
Research has suggested that very quiet solar periods with reduced sunspot activity are connected to zones of high pressure in the high latitudes, which favor colder than normal air in the eastern United States and Western Europe.
The last solar minimum in Solar Cycle 23 was the quietest of our lifetimes. When the inactive sun coincided with a moderate El Niño event in the winter of 2009-2010, the Mid-Atlantic was colder than normal, and many areas experienced their snowiest winter, including Washington.
The Solar Cycle 24 is fading in intensity, and the signal bears similarity to the previous one in the 2008 to 2009 time frame.
In fact, it looks as if the cycle’s descent is faster and stronger than the 2007-2009 decline. Records for high pressure over Greenland were set in 2009-2010, which facilitated the delivery of cold air into the Mid-Atlantic. When strong high pressure is positioned over Greenland, it also tends to push the storm track south over the Lower 48 states placing the Mid-Atlantic on the colder, snowier side of storms that develop. And, when El Niño is present, it can intensify the moisture feed into these storms.
So, if you want winter to be snowy, the ingredients are a weak to moderate El Niño, a warm northeast Pacific Ocean and a quiet sun. All of them are on the table but need to remain and then gel.