Does the late arrival of winter bug you out? Here's why

Wednesday was the coldest day in New York City since March 14th of last winter; with a high temperature in the upper 30s, it certainly feels like December is right around the corner. This past Saturday, on November 25th, we reached a low temperature of 30°, officially recording the first freeze of the season. The average is on November 14th, and it has happened much later; the latest first frost on record in NYC was on December 22nd, 1998! But overall, the first freeze in the Tri-State is trending later and later. The ten latest first frosts in Central Park have primarily happened in the 21st Century, and only two happened before 1950: 

Data from the National Weather Service office in Upton, NY

For those of us who don't love winter's chill, this is not necessarily a bad thing! And it certainly helps with the heating bills as well. But there are negative consequences to a late freeze. 

For example, bugs LOVE it. Deer ticks, which are vectors of Lyme Disease, do not die off until temperatures dip to the teens or single digits. Many deer ticks survive the winter by burrowing underground or finding other protection from harsh temperatures, like piles of leaves. A deep freeze is more likely to kill the eggs of these disease vectors, so a milder winter could increase your chances of encountering ticks carrying Lyme Disease when the weather turns warmer. 

Graphic courtesy of Climate Central

Deer ticks can be active if the temperature is above 34°, so it's important to check for ticks after any outdoor adventure, especially in the woods or tall grass. 

Another warm weather pest, mosquitoes, thrive in hot and humid weather; they're most comfortable with temperatures in the 80s. However, some mosquito eggs (especially Northern species) can survive in areas that later end up under ice or in frozen mud, and adults can hibernate during the colder months. 

Graphic courtesy of Climate Central

The later start to winter allows mosquitoes to stay active longer, and it can contribute to larger populations as well. It takes a prolonged deep freeze to kill hibernating adult mosquitoes and their eggs, assuming that they found a safe spot. And that's just not happening as often in the Tri-State as it used to. The table below shows the number of days below 10° in Central Park since records started in 1869: 

Data from the National Weather Service office in Upton, NY

The most recent year on the list was during the Great Depression. Of course, we are no stranger to very cold winter days, but when it happens, the cold snap is brief and anomalous. This trend is reflected in more recent decades by the rise in average temperatures in New York: 

Winter is the fastest-warming season in NYC. The average temperature is computed for

December, January, and February in this graphic from Climate Central. 

4 degrees may not sound like much, but in the winter, it can be enough to turn a pond into a skating rink. According to an article in Olmsted Now, "Central Park welcomed its first official visitors, the ice skaters" on December 11th, 1858! The idea of ice skating on a natural pond in Central Park is kind of unthinkable today, but it was a popular winter activity for 19th Century New Yorkers.

Image courtesy of New York Public Library

So as we try to shake off winter's first chill in the Tri-State this week, just remember: it used to be a lot colder, for a lot longer, during a typical New York winter. 
This article references reports and materials from Climate Central. Thank you! 

Will the return of El Niño mean the return of snow?

Last winter was a disappointment for snow-lovers in the Tri-State area. Though it snowed several times, including a bunch of trace amounts, we ended up with a grand total of 2.3"of snow in Central Park. Last year at this time, we were in La Niña, or the cold phase of ENSO. Now that the pattern has flipped to El Niño, or the warm phase, the outlook for our upcoming winter is quite different. Whether it results in a larger snow total remains to be seen. 

If you use the Farmer's Almanac to help plan your winter, I have bad news for you: It's already wrong about this year. The Almanac's winter forecast says, "snow will arrive beginning in November" in the Tri-State area. You're probably aware that we have yet to see a single flake of snow. This is true not only in NYC, but throughout the entire region. Whoops! 

Only time will tell if the Farmer's Almanac forecast for "oodles of powder" pans out 

for the Northeast and Mid-Atlantic. 

As Yogi Berra famously said, "It's hard to make predictions, especially about the future". Boy is this true when it comes to seasonal snowfall forecasting. Keep in mind that the snow-to-rain ratio is usually about 12:1; that means foot of snow melts down to about an inch of rain. Add up an entire season of snowstorms, and the margin for error is as wide as the Hudson. But, there are insights we can gain from our current pattern- insights that could be more valuable than a prediction for the number of inches of snow we'll see this year. 

In the Northeast, La Niña winters tend to be drier, whereas El Niño usually brings more precipitation. But that doesn't mean all El Niño winters are snowy in the Tri-State area!

Above is a list of the snowiest seasons ever recorded in NYC on the left, with the least snowy on the right. The snowiest winter of 75.6" occurred during El Niño. The third-snowiest, at 61.9", was during a strong La Niña. And #6 on the least snowy list was also a Super El Niño year! While knowing the ENSO phase doesn't help us figure out how many inches of snow we'll get, it can offer valuable insight to the winter ahead. 

La Niña winter conditions are more favorable for two types of snowmakers: Alberta Clippers and Four Corner Low pressure systems (often called "Colorado Lows"). Even if you're not familiar with the term Alberta Clipper, you probably know what they feel like: a little bit of powdery snow followed by an Arctic blast. Clippers usually bring 3" of snow or less to the Tri-State. 

Source: NOAA's Weather-Ready Nation Infographics Page

A Four Corners Low is so named because it originates in the Rockies, near the "Four Corners" region where Colorado, New Mexico, Arizona, and Utah meet. After exiting the Rockies, their trajectory often leaves the snowy side of the storm to our north, leaving us with slush or rain- but not always. 

Source: NOAA's Weather-Ready Nation Infographics Page

In an El Niño winter, coastal systems like Nor'Easters are more common and more frequent than the Clippers and Colorado Lows described above. These coastal storms draw more water from the Atlantic Ocean than their continental cousins, bringing heavier precipitation to the Northeast and Mid-Atlantic. And if it's cold enough when the Nor'Easter arrives, we could have a major snowstorm on our hands. 

Source: NOAA's Weather-Ready Nation Infographics Page

Such was the case during the record-breaking snowstorm of January 2016. We were in a "Super El Niño", with temperatures way above average in the equatorial Pacific. After a record-shattering warm December, it finally got cold in the Tri-State by the second half of January. The environment was primed and ready to turn a disturbance in the Gulf Coast into a raging blizzard. 

Graphic (above) and map (below from NWS Upton, NY)

When making a forecast for an entire winter season, meteorologists look for analogs, or similar atmospheric setups. ENSO is one factor, but other patterns such as the North Atlantic Oscillation play a role. So does the supply of cold air upstream from the Tri-State, even as far away as Siberia. 

So here's what I'm thinking: 

• In a year with a strong El Niño like this one, it's more likely that the entire season's snow will fall in a couple of big storms, rather than us having to deal with several "nuisance" snowfalls. 
• In most NYC winters, we don't need to break out the shovel until after the New Year. But this winter, a plowable snowfall is likely before Christmas- maybe even before the final night of Hanukkah!
• This winter's pattern is NOT conducive to a big, damaging ice storm. Hooray!
• This pattern is also NOT favorable for a nasty March (remember in 2017 when we dealt with four consecutive snowstorms?) Double Hooray! 

Here are some of the resources I used to put this outlook together. 

Climate Prediction Center's ENSO Page & North Atlantic Oscillation Page 

Rutgers Global Snow Lab Monthly Snow Cover Maps

Dr. Judah Cohen's Arctic Oscillation discussion

National Weather Service in Upton, NY's Climatology/Historical Data Page