Is This El Nino?

Currently, the equatorial sea surface temperature within Niño Region 3.4 is +0.9°C -- holding at a borderline El Niño event. Could El Niño be a factor behind the recent widespread heavy rain that resulted in severe flooding along the Missouri and Mississippi River Basins? During active El Niños, a southern branch of the jet stream, originating within the Pacific, is unusually strong. This jet stream transports atmospheric energy and Pacific moisture across the southern tier of the U.S. While this can result in heavy rain over the southern tier of the U.S., further north, the Ohio and Upper Mississippi Rivers trend drier.

During past 2-month March and April El Niño years, areas shaded in blue were usually wet and areas in yellow unusually dry.

Compare past El Niño year rainfall patterns (above) with the actual over the past 60 days (below). While there does seem to be a correlation with usually heavy rain over the South Central U.S., elsewhere correlations much are less certain.

More recently, over the past 30 days, the enhanced South Central U.S. rainfall El Niño pattern shows up more clearly. However, California does not fit the pattern, with unusually-dry conditions.

Currently, the southern branch of the jet stream is active, originating within the tropical Pacific and transporting energy and moisture northwest.

Here is a satellite image showing atmospheric moisture (water vapor). BWO has discussed the importance of a connection between the ocean and atmosphere during El Niño events. Take a look at the connection (via green arrows) between equatorial convection and the current middle U.S. weather system.

Here is the rainfall outlook for the next week.

And the next 10-day outlook does seem to indicate an El Niño-like enhancement of rainfall over Southern California and the southern tier of the U.S.

Take Away

Classic El Niño impacts might not be expected with a weak to borderline moderate event. 

However, based on recent-past rainfall patterns and an analysis of the alignment of the jet stream there does seem to be a connection with the current El Niño and the excessive rainfall over the South Central U.S. 

As El Niño is expected to persist for several more months, the South Central U.S. and other sections of the southern tier of the nation, could be vulnerable for additional heavy rainfall and flooding. 

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