The back is broken in terms of summer heat from Denver to St Louis in a big way with cool shot no. 2 coming acalling late this week. Just when many thought this seemingly never ending summer would continue, the flip has begun but like I said in the previous article, this doesn’t mean summer is over, but it means the change and downward trend has begun. Warmth which does return, won’t be nearly as severe.

So, why is there cool now getting into the very areas which has been hottest this summer? Well, the el nino warm waters are now shifting WEST and so instead of the warmest waters compared to normal sitting right on the South America coast, their now pushing out into the central Pacific, following what the long range models have been suggesting and this is likely a key reason for the shift in the US heat core.

What’s interesting is that more often than not when waters are warm right in close to SA, the Plains is warmer than normal and now that the warm pool is shifting west, so the heat shifts into California, exactly where this summer has been running a good 1-2 below normal, especially along the CA coast.

This shift in warm water west is crucial for winter. Many think an el nino brings an automatic warm winter. If waters were to stay warm nearest the coast, i.e a strong el nino, then the warm pool would have setup over the US and so a warm winter would have been on tap but thanks to the cold PDO, the el ninos which do develop, are often less strong (so positioned more centrally in the Pacific) and are shorter lived. This tends to make for a colder US winter.

Anyway, I shall look at the upcoming fall and winter in coming days. Stay tuned.

Tags: el nino 2012, el nino and us weather, winter 2012-2013, winter forecast 2012-13