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More Winter Indicators: Siberian Snow & El Nino

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The questions continue to roll in about winter these days, and I'm happy to report that we're taping our official WBZ Winter Outlook today (Wednesday) on the coolest and wettest day of the month so far. Seems appropriate! This will air shortly, but I wanted to continue our little series here on the blog about seasonal indicators and what we've been monitoring. I wrote a blog post on the presence of a strong El Nino and what that means for us back in early July, and there's also a blog post on very warm Novembers and what they tend to indicate in the Boston area. For this post, let's take a new look at El Nino and another variable that gets a lot of press - Siberian snow cover.

Let's start with the current state of El Nino. It is now contending with the strongest ever recorded, reaching levels (and surpassing them in some areas of the ocean) seen in 1997-98 and 1982-83. NOAA is expected to update its monthly El Nino forecast this Thursday, and we'll gain some more insight into their thinking. But the trend has certainly been for a strong and potentially record breaking El Nino to start winter, with gradual weakening heading toward the spring. It's also interesting to note that the largest sea-surface temperature anomalies have been a little farther west than in classic cases. That being said, a couple of strong westerly wind bursts, pushing that warm water toward South America, could keep us on pace for a record event.

multivariateindex

As for this November, we're still WAY above average as we approach the midpoint when it comes to temperature. The trend is for mainly above average temperatures with a couple of chilly days over the next 7-10 days, so we'll be keeping a large (+) departure from average. The blog post linked above shows the relationship between warm Novembers and our winter snow - the more warmer than average it gets, the less snow we see. The more below average November gets, the more snow we see. The relationship is a strong one.

strongelninos

These numbers are for the city of Boston

So when you look at this November, and you look at El Nino, the inclination would be to forecast a torch of a winter with limited snow. There has never been a recorded winter with even average snowfall in Boston when ENSO is in an El Nino phase and November has been a Top 10 warmest. The only year we were even close to average snow in that top 10 (in fact a couple inches above it) was during a La Nina winter, which is typically colder and snowier than average here. These signs are hard to ignore and offer an important signal.

warmnov

BUT...there are still some other variables out there. There's nothing easy about a seasonal forecast, as the whole picture has a whole lot of players involved. One that has received a lot of attention is Siberian snowfall in autumn. Evidence has been found to show that a quick build-up of ice and snow in Siberia can lead to harsher winters in the eastern U.S.. That's because all that snowpack is linked to the AO, the Arctic Oscillation. The more snow you have building up early in the season, the higher the odds of a negative phase of the AO in winter. In simpler terms, a -AO leads to a weaker jet stream and more cold air outbreaks for us.

snowanom

Source: Rutgers University Global Snow Lab

So how does this year stack up? While not as impressive as the last two autumns, there was yet again a hefty increase in snow cover this past October (and it's holding strong). This is one variable which is at odds with the others, and is worthy of consideration.

marchsstelninonov10

On the top, March 2015. On the bottom, November 2015. Easy to spot the changes! Source: Weatherbell

We also still have a warm pool of water in the North Pacific, but it's much different than last year's. Last year the 'warm blob' was focused mainly in the northeast Pacific, possibly aiding in the persistent jet stream ridge over western North America. This year, that warm pool has spread out and weakened, while El Nino is a glaring dominant feature in the equatorial Pacific. The theory is that the warm pool in the North Pacific will be eroded by autumn/early winter storms, and that the main climate driver will become El Nino.

So where that takes us is to a place where it's certainly possible we get very low snow totals this winter, but there are enough wild cards to keep us away from placing all our money on that bet. An outlook closer to an 'average' Boston winter is the more likely outcome, and we'll have the full details coming up on WBZ soon!

 

 

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