The cold start to spring, explained

Lately, it feels like the winter that won't let go. Only two of the first nine days of April were above average - the rest below.

This consecutive stretch is the seventh coldest in Boston in the last 50 years, fifth coldest in the last 40.

>> Boston 25 StormTracker Weather Forecast

So, why is it so cold? It's easy to blame Mother Nature, but we can also look to what we call the Madden Julian Oscillation - or MJO - one of the reasons for the chilly March and April so far.

It's an index that measures tropical activity or thunderstorms in the Pacific and Indian oceans. Depending on the position, our weather can be warmer or colder than average.

It also drives the jet stream, which is a fast-moving river of air high above us - helps steers storms, but also is the dividing line between mild air to the south, and colder air to the north.

Unfortunately for us, the jet stream has been far enough south to keep that cold air locked in across New England recently.

Good news for later this week.... the jet stream will build to our north allowing for mild air to move in.

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