David Epstein: April’s off to a chilly start. Here’s what’s ahead.

Not to totally bum you out, but the European model forecast through about Memorial Day is forecasting colder-than-average readings for a large swath of the country.

Elle Marrone walked in Pope John Paul II Park last week as April got off to a cold start.

With about a third of the month of April now in the record books, we can say it certainly hasn’t been very spring-like.

It’s actually been colder to start the month than it was at the end of February. When the temperature reached near 80 then, I said we might not be that warm again until nearly June; that could still be the case if this pattern continues.

This has been the seventh-coldest stretch for the first nine days of April over the past 50 years (and the coldest since 2007), so this is a significantly chilly April for most people. Two of the first nine days of the month had above-average temperatures, the other seven were below average.

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It’s worth noting April itself isn’t becoming colder. The month is trending warmer over time, but that doesn’t mean there can’t still be cold years.

April’s average temperature has increased over the past 100 years.

You might wonder why it’s been so chilly, and the quick answer is that the jet stream has been positioned far enough south to allow cold air to continue to infiltrate the Northeast.

Blame the Madden Julian Oscillation (MJO)

One the primary drivers for the jet stream is the Madden Julian Oscillation. I wrote about this back in February as one of the reasons for that month’s warmth, and it’s once again the culprit for the chilly March and April so far. To review, the MJO is an index that measures the position of clusters of thunderstorms and their movement across the Pacific and Indian oceans. Depending on the position of these storms, our weather can be warmer or colder than average.

This chart shows the position of thunderstorms propagating around the equatorial region of the Pacific and Indian oceans.

In February, the MJO was stuck in a warm phase 7, and then it went into phase 3, which puts a lot of pressure on the east to be cold. In the coming week to 10 days, the MJO is forecast to stay in phases 1 and 2. After that, the picture isn’t as clear.

Phases 1 and 2 are also cold phases, meaning while there will be warm days between now and mid-May, the likelihood of additional periods of colder-than-average weather is quite high. You can see the different phases below and which are cold for us and which are warm.

Note that in February, March, and April, phases 2 and 3 tend to be cold. Phases 4 and 7 are warm.

A quick taste of spring

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Some milder air will briefly make itself felt on Friday into Saturday, and then be gone by Sunday. Friday’s highs should make it into the 60s for most of us. If the cold air holds off until later in the day Saturday, we could reach well into the 60s to near 70. The best chance of seeing warm weather Saturday will be west of Interstate 495 and south of the Mass. Pike. By sunset, Boston will be back to the lower 40s.

via GIPHY

No end in sight yet

Not to totally bum you out, but the European model forecast through about Memorial Day is forecasting colder-than-average readings for a large swath of the country. While this doesn’t mean there won’t be warm days for the next seven weeks, it does mean it’s likely we may be keeping the heat on a bit longer than usual this spring.

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