Brian Bledsoe

We've been locked into El Niño conditions since last spring. Sea surface
temperature anomalies have been much above average in the equatorial Pacific
Ocean, but have recently really started to cool off. 

The El Niño peaked in late December and early January, and continues to weaken.
Here is the equatorial sea surface temperature anomaly animation, during the
past 90 days. This graphic represents the depth (0-450 meters) and east (120
degrees E) to west ( 80 degrees west) across the equatorial Pacific Ocean.
Basically, from Indonesia to off the west coast of South America.

You can clearly see the warmer than average water being eroded from bottom to
top. So, while still warm at the surface the upwelling of that cooler than
average water will continue to eat away at the El Niño and eventually end it. 

The two animations below are from the EURO seasonal model and the NMME model.
They show their respective sea surfact temperature anomly forecasts for the next
several months.

You can clearly see what both models are doing... The EURO seasonal model (1st
animation) is a less aggressive with the El Niño to La Niña transition. The NMME
model (2nd animation) is very aggressive with the El Niño to La Niña transition.

The way things are going right now, I think the NMME might be a little
aggressive, but might not be far off. The latest Climate Prediction Center ENSO
forecast shows the ENSO transition too, giving us a better than 50% chance that
we will be in La Niña conditions by June/July/August, and almost an 80% chance
by September/October/November.

Bottom line, the transition from El Niño to La Niña looks to be all but a
certainty.

So, what does that mean for the spring? I did some digging into years that
experienced El Niño to La Niña transition. The first map below shows the March -
May averaged out precipitation anomalies, during those years.

The blue/green represents above average precipitation, while the yellow/red
represents below average precipitation. You can see that areas along the Front
Range ended up wetter than average. Obviously, we will narrow down that list of
years, as we get deeper into 2024. However, a few of the years that particularly
stand out are 1973, 1983, 1995, 1998, 2010, and 2016. The graphic below shows
the prevailing upper level weather pattern for those years, during March through
May.

All that purple represents a large area of cold upper level low pressure. Simply
put, there was a large trough (storm generator) over most of the country, during
the spring of those years. On average, this made for a very stormy spring in
those years. What about the temperature anomaly during all of those years? Well,
it was largely colder than average...

We have largely had a pretty mild winter, so does it seem likely that we will
have a colder than average spring? I am less convinced about that... However, if
that large trough sets up across the western half of the country, we would
likely end up colder than average. I doubt late season Arctic air would be the
culprit though... I suspect the clouds and precipitation associated with an
active storm track would be the reason. 

What do the seasonal models say? Well, let's check 'em out...

EURO Seasonal Model Precipitation Anomaly Forecast March - May

EURO Seasonal Model Temperature Anomaly Forecast March - May

NMME Model Precipitation Anomaly Forecast March - May

NMME Model Temperature Anomaly Forecast March - May

Both models are pretty similar, but the EURO seasonal model is a bit wetter than
the NMME. Temperature anomalies are essentially the same, but I really don't
give a lot of credence to them. The seasonal models do not do very well with the
overall temperature forecast, as they are usually very warm biased. 

The good news is that we still have some time, before La Niña comes back. The
bad news is that La Niña is coming back. I think the next 90 days are crucial.
We need to boost the snowpack. East of the mountains, we need to shove as much
water in the ground as possible. Many times, La Niña is not kind to us on the
Plains. While there can always be exceptions, history is not on our
side...especially, for southern Colorado. 

I am still working on the summer forecast. However, there are signals that have
me concerned. Not just locally, but regionally, we will save that for a future
post.

Transitioning from El Niño to La Niña and what that could mean for spring