Goodbye La Nina

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 Weekend Forecast and Discussion of Heat Islands on KPLU

Finally, La Nina's days are numbered, and its expression in the ocean and atmosphere are beginning to fade.   In two months, it should be history, which is fortunately for us in the NW, where it brings cool, wet weather.

Here is the proof--something to savor.  Lets start with the key index that meteorologists look at, the sea surface temperature anomaly (difference from average) in the central Pacific (the 3.4 area, see map

 Here it is.  The cold anomaly (a sign of La Nina is rapidly fading)

Now lets check under the sea surface to see what is happening, since surface temperatures can be deceiving.  Here is an east-west cross section under the central Pacific, showing you the water temperature anomalies down to 300 meters (red and orange warmer than normal, blue is colder). The panels start in February, with the latest one April 3.  Notice how the blue colors with depth in the central and eastern Pacific have faded, with warmer than normal temperatures taking hold.   Very bad for La Nina.

A number of organizations run statistical and dynamical (simulating the temperatures of the Pacific) models of La Nina/El Nino and here are the latest results:

Virtually all the models are taking us to neutral conditions (temperature anomaly near zero) during the next few months, with some even heading towards El Nino by next winter (large warm anomalies).  Plus it would be extremely unusual to have three La Nina years in a row.   So we can rest easy about the end of La Nina.

Since it will take months for La Nina to fade and the atmosphere to reconfigure itself, don't expect a sudden transition to warm and dry conditions.  Besides, the correlation between La Nina/El Nino and our weather fades as we move into the warm season.  But the implications for next year are substantial, particularly after the New Year.  Years in which the sea surface temperature anomalies are near zero (neutral or La Nada years) are climatologically normal except for one thing:  the biggest of the big weather events (floods, windstorms, etc.) like neutral years.

The long range forecast models, both U.S. and European Center (ECMWF), suggest a good weekend, particularly on Sunday.  Here is the ECMWF upper level flow (500hPa) forecast for Saturday and Sunday mornings.   A ridge is moving in on Saturday and will be over us on Sunday, with a trough messing up weather over the southwest U.S..  I would worry about some serious thunderstorm activity on Monday from Texas, OK, and eastward, as the uplift from the trough reaches the SE U.S.
PS:  Some good news for those who like Seattle's roads clear of ice during the winter.  The city of Seattle is now putting several road temperature sensors on bridges and other locations around the city.  This will greatly assist SDOT in knowing that is going on during the winter-- a major advance.    Imagine what the TV snow/ice hypsters will do with this data! And we have some major improvements in mind for SNOWWATCH.
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