Friday, December 02, 2011

Ocean Temperature Changes & Our Early Winter Pattern

One basic element of long term weather trends lies in the changing ocean surface temperatures.  The effects of these ocean temperature changes are very apparent here in North America where we are surrounded by the Atlantic, Pacific and the Arctic to the north.

My last post looked at how different the last 3 Decembers have been when comparing the different indices located over the oceans. What about the changes in the oceans comparing, say last December to the current levels?

Let's break down last December in two parts. The colors show the warmer and colder locations compared to the average. I indicated these "cool and warm" pools with a "C" and a "W". Notice how they changed from the beginning of the month to the end of the month.
Now look at this year. The Atlantic cold pool shifted more north toward Greenland. The temps off of the SE coast are a bit warmer. The warm pool from last year in the western Atlantic (driven by the strong arctic levels) shifted west into the Caribbean, Gulf of Mexico and New England waters. The cool pool in the Pacific is cooler near Alaska while the classic La Nina "cool" signature between Hawaii and Mexico is now more extensive and cooler.
How did the storm tracks differ over the US last December to the current setup?  The ripples in the flow over the US and Ohio brought small snows and repeat cold air shots throughout the month last December.

This year, the Bermuda High in the Atlantic is now situated near the Southeast Coast. The Pacific Ocean high northeast of Hawaii is also more north this year. Both of these Highs have shifted the trough out west. So any strong front (the "L" over the middle of the US) that tries to make it into Ohio gets squashed. 
The temps in Cleveland last December were very cold.  The "blue/purple" bulls-eye over the central US highlights much below temperatures. We had three separate stretches of 20 degree high temperatures. The first was 4 days, the second was 8 followed by a 5 day stretch at the end of the month. Snowdays at Progressive Field were cold and snowy. I cut down my Christmas tree in a blinding snowstorm!

The temperatures finishing out November this year were slightly above normal in Cleveland. Absent were the strong fronts necessary in driving cold air south 

All of these maps are just more illustrations of how the tiny changes in the oceans can alter the weather patterns across Ohio. Given this current pattern that features no significant drivers of arctic cold, I highly doubt we will see a long stretch of cold temperatures like last December. More details on the prospects of short-lived lake effect snow next Monday.

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