Oscillations between warm and cool weather continue to define the early summer pattern over North America. While the west warmed last week, a renewed push of cold this week has sent temperatures reeling across the Rockies, where small accumulations of snow fell in the highest terrain.
We are hung up on this to-and-fro weather pattern. What’s causing it, and will we be able to rely on some seasonal stability – a hallmark of the benign summer pattern – at all in the coming weeks or months?
Right out of the gate, the projections for spring and summer supported an evolving El Nino in the Pacific. As time went on and the models settled down, it became clear that El Nino had flatlined and water temperatures were drifting toward a La Nada (ENSO Neutral) setup.
So if that’s the case, what is driving the forecast this month and will it last?
We’ve mentioned the strong presence of the Aleutian Low in previous weekly discussions, in addition to the often robust Madden Julian Oscillation (MJO). While neither seems to be driving the weather pattern over North America completely, it appears that when superimposed on a background of neutral – or even slightly negative – sea surface temperatures in the equatorial Pacific, the MJO in particular sets off a somewhat predictable temperature oscillation.
We are expecting this to continue for the foreseeable future as we cross into early July. Expectations are for the East to warm once again in the lead up to Independence Day and the West to cool down.
Of course, if it were that easy, everyone would just read my blog and make 20+ day forecasts. But it’s not, and our “good friend” the North Atlantic Oscillation could make life difficult if it were to flex once again.
That’s right. The East could cool down sharply in that time frame, and foil the plans of the MJO.
If there was any time to sit on the sidelines for us, this is it. Summer volatility can be crushing, so as we round the corner into early July, we’ll just have to wait to see how things shake out.