Friday, July 27, 2012

Atmosphere May Be Showing El Nino Signs in Precipitation Placement

The latest GEM 144 hour accumulated precipitation forecasts displays a very El Nino-like pattern, with little precipitation in the Midwest and a lot of wet weather on the East Coast.

As is typical in El Ninos, precipitation is favored over the East Coast into the Gulf of Mexico coast, with little precipitation over the Ohio Valley and Midwest. The image above very well shows the pattern described, with a wet pattern holding out over the East Coast. But is the atmosphere showing an El Nino in other indices?

The Southern Oscillation Index, or SOI, is rapidly dropping, characterizing an El Nino pattern. El Ninos are detected when the SOI is below -8, and as shown above, the SOI is below -10.
A look at the 30 day average of the SOI, used in the graph above, shows that the 30 day average has shot up to a value of positive 2. Positive values above 8 indicate a La Nina. This is fairly confusing for the atmosphere, because sea surface temperatures are positive, while the SOI is in fairly neutral territory. This will become interesting to monitor as we progress into the fall months to see if the atmosphere can sort itself out.

So while the precipitation appears to support an El Nino pattern, the SOI is in disagreement, and it will likely take a good month to see the SOI sort itself out.