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Back in mid December I posted about how the MJO (Madden Julian Oscillation) was projected to enter and travel through the holy grail of cold phases 7, 8, 1, just before Christmas into early Janaury. Here's a segment of my blog written December 20th alluding to the MJO and the cold that was coming. Did it ever!

The Madden Julian Oscillation (MJO) has now reached phase 7. That's a key benchmark as it means the Midwest is entering a prolonged period where the MJO will remain in cold phases that correlate strongly to below normal temperatures. In fact, this is likely to last much of the next 15 to perhaps 20 days once the cold kicks in this weekend.

If you follow the dotted green lines you can see the MJO's path through 7, 8, and 1 between now and January 1st. To the right you can see the corresponding temperature anomalies for each phase.

I looked at the CFSv2 mean temperature departures the next 15 days and it agrees much of the nation and Canada will be consumed by the chill. The Midwest is right in the thick of it.

All the models agree some of the most intense and widespread cold will be in the period December 25th-30th. Look at these departures. T. Swails.....

On to the present. The reason I bring this up is because before the MJO really made its push to deliver the cold, the stratosphere was already giving us an even earlier hint that Arctic air was coming by signaling what's called a strat-warming.

In the layer of our atmosphere known as the stratosphere (roughly 30 miles up, or 30mb), temperatures instead of remaining cold, were actually getting warmer. The warming was projected to reach its peak in late December. Here's what the GEFS was forecasting December 12th for anomalies December 28th. Dramatic stratospheric warmth in the western and central Arctic.