David Epstein: What does the rest of winter have in store?

The past two weeks have featured warmer than average conditions along the East Coast. This seems likely to continue for the foreseeable future.

Boston, MA., 02/12/18,  Warmer temperatures in Boston brought out skaters on the Frog Pond on the Boston Common as snow continued to melt. 

Suzanne Kreiter/Globe staff
Skaters at Frog Pond on Monday. –Suzanne Kreiter / The Boston Globe

Meteorological winter runs from Dec. 1 through the end of February. This month of that season can show some signs of spring or remain deeply in winter mode. A cold and snowy February can often continue into the first couple weeks of March, when cold and snow can still plague much of the country.   

At this point in winter many of our thoughts are turning to spring. This year winter started early but hasn’t been so terrible since. Already the increase in daylight is noticeable, and we are several weeks beyond the coldest average days of the season. The rain of the past weekend has melted much of the snow across Southern New England, and, with temperatures well above freezing, you may be asking if winter is over.

More February cold and snow?

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A few years ago we got to this point and I started thinking we were mostly done with winter, then we got another 10 to 15 inches of snow. Predicting the final snowfall in mid-February isn’t prudent, but there are signs at least the rest of February will bring very little in the way of winter weather our way. The eight to 14 day outlook (below) now has a strong probability of warmer than average weather along the East Coast. As I write this, I don’t see any significant snow in sight. If we do get through the rest of February with little cold and snow, there could still be some winter left in the tank for March — and even April.

What about March?

There are many factors that determine whether or not we’ll see the recent lack of cold and snow last into March. One of the more important influencers this year is the Madden Julian Oscillation (MJO) and its phase. A phase is simply the position of clusters of thunderstorms from the Indian Ocean to the eastern Pacific. The image below shows where thunderstorms have been occurring across that part of the world over the past few weeks. That purple line relates to the storms progression around the equator thus far. The green is the average of many European model forecasts and predicts which phase these storms will enter in the coming weeks. Remember phases as different spots around the middle of the planet near the equator. The storms add tremendous energy to the atmosphere in a particular spot and that leads to particular jet stream patterns affecting weather around the globe, including North America.

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One example of correlation

As February began, it appeared the MJO might move into a strong phase 8. If phase 8 does materialize in February, the East is more likely to turn cold. However, the latest computer model trends are less sure, and that’s part of the reason Arctic cold isn’t in our forecast. The map below shows what typically happens with the MJO in phase 8. These maps exist for all the phases, and some have stronger correlations than others.

Thus far the warmer days are outnumbering the colder ones. Notice on the map below that the East has been milder than average recently. Remember, milder than average this time of year is still cold, but not intolerable.

The past two weeks have featured warmer than average conditions along the East Coast. This seems likely to continue for the foreseeable future.

More cold, but where does it go?

There is cold around the globe. If you have been watching the Winter Olympics, you know how chilly it’s been in South Korea. That Arctic air means business, but we aren’t seeing it here.

One forecast (above) that averages out all of February shows colder weather over the northern Rocky Mountain states east to the Great Lakes, but notice how warm it is compared to average from the Gulf Coast up to New England.

Many variables at play

Using the MJO solely won’t work because these things are not a one-to-one correlation. The MJO forecast does raise the odds of a colder late winter and early spring, provided that the forecast for where the thunderstorms form around the equator materializes. I am stating the obvious, and this is one of the more difficult aspects of medium-range predictions, there are all these different factors at play. We actually have a pretty good idea how they relate. The problem is that if you forecast a certain factor to be in a certain phase and it doesn’t materialize, your prediction for the overall temperature and precipitation regime fails to validate.  

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via GIPHY

The current pattern favors milder air in the East through the end of the month.  Credit: Tropical Tidbits

Spring storms

As daylight continues to increase, the temperature contrast over North America grows. This is because the cold areas stay chilly well into March, and the warmer airs get quite hot rather fast this time of year. It’s this difference between the warm and cold air that becomes a breeding ground for storm systems. Moisture has been rather scarce in much of the country this winter as compared to normal, with about two-thirds of the U.S. anywhere from drier than average to major drought. This isn’t a good place to be at this time of the year when winter storm systems should have dropped enough precipitation.

Notice the southern tier of the U.S. is driest, and the forecast favors this pattern to continue with adequate moisture over the northern third of the country the rest of the month.

Meteorological winter ends in two weeks, and astronomical winter ends a few weeks later. The pattern we are presently in isn’t conducive to cold and snow here in Southern New England, and, if this continues, we are going to be looking at an early spring. Don’t be totally lulled into a false sense of comfort yet and put away the snowblower. The odds may favor an early spring, but we all know those are only odds and here almost anything is possible when it comes to weather. The European Ensemble forecast would still bring another foot or more of snow through the end of March to Boston. Were that to happen, it would still be pretty much an average snow season for the area, and that is what most forecasters had in mind when all of this began back in the fall.

This chart shows the ensemble mean snowfall forecast based on the Euro model. —WeatherBell