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The latest NOAA forecast model data regarding ENSO continues to predict La Nina
conditions by April and a continuation of such conditions through the balance of 2007. Nearly all of
the forecast model runs in the CFS ensemble are still in agreement about La Nina. This fact and
consistent model runs coming to the same conclusion over the past few weeks have removed most
doubt about the evolution of La Nina. It is important to note that La Nina will be very weak early this
spring and probably will not strengthen significantly until late summer. That may allow some timely
Midwest rainfall to occur early in the summer with late summer and autumn being driest – not
because of La Nina alone, but because of its interaction with other weather signals suggesting a dry
finish to the growing season.
There has not been any reinforcing cold water development in the subsurface equatorial
Pacific Ocean thus far. That suggests we will reach La Nina’s threshold and stay there until summer
when reinforcing cold water is more likely to resume the cooling trend.
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Sea surface temperature data is reflecting the changes in ENSO very well. The charts above clearly show the
demise of warmer than usual ocean water in the eastern Pacific Ocean with developing colder than usual ocean water in eastern portions of the region. Subsurface ocean water is still quite cold and it will be
reinforcing the cooling trend for another few weeks. However, there is some warmer water that will
move into the region thereafter inducing a temporary lull in the cooling trend and producing very
weak La Nina conditions for a while during the second half of spring.
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