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Gary McManus, state climatologist, regarding El Nino

By Gary McManus, state climatologist, Oklahoma Climatological Survey:


El Nino is not a tropical storm, of course, but it is of tropical origin. This warming of the waters off the west coast of South America tends to bring the southern tier of the U.S. (including Oklahoma) wetter and cooler weather, mainly during the cool season (as seen in this very simplified map).


With drought holding strong over western Oklahoma (for 3.5 years, unfortunately) and continuing to creep east over the rest of the state (only a bit of moisture here and there held it back this week … check out this morning’s Drough Monitor map and the moisture tally from our latest couple of storms)


a good dose of El Nino and its wetter and cooler (although the cool signal is stronger for folks south of here) weather would be a welcome change. Provided that the El Nino produces impacts like it “normally” does. They aren’t foolproof, of course. I’ll show you some maps in a minute on how they impact our area, on average.


So here’s some good news! The National Weather service’s Climate Prediction Center (CPC) has issued an “El Nino Watch” signifying at least a 50% chance of seeing an El Nino develop down in the equatorial pacific. Here is the pertinent information from CPC’s monthly ENSO (El Nino/Southern Oscillation) discussion, fresh off the presses:


“While all models predict warming in the tropical Pacific, there is

considerable uncertainty as to whether El Niño will develop during

the summer or fall. If westerly winds continue to emerge in the western

equatorial Pacific, the development of El Niño would become more likely.

However, the lower forecast skill during the spring and overall

propensity for cooler conditions over the last decade still justify

significant probabilities for ENSO-neutral. The consensus forecast is

for ENSO-neutral to continue through the Northern Hemisphere spring

2014, with about a 50% chance of El Niño developing during the summer

or fall.”


You can view the entire document for yourself righ’chere!


And here you can see the spread of the model predictions and also the odds via a bar graph. For the modeled output, you’re looking for those anomalies to reach into the +0.5C area, which signifies El Nino (-0.5C is La Nina territory … everything in between would be considered ENSO Neutral conditions, which we’ve been in for the last two winters).


If you’re thoroughly confused, this table might be the easiest way to show you.

You can see that by the JAS (July-September) time frame, the probability for El Nino finally overtakes the odds for Neutral conditions and even pulls away through the OND (October-December) season. The best news is that the odds of La Nina are nearly non-existent.


OK, that’s the good news. The bad news is that *normally* (there’s that word again!), our area won’t feel the impacts until we get into late fall, through the winter, and with a little momentum … into early spring. And all of this is also dependent upon how strong the El Nino becomes. There’s some hint that a weak El Nino can actually bring drier conditions to the state. But, check out these maps that show the impact of El Nino on the different seasons.

Officially, they show the risk of extreme wet or dry years. “Extreme” in this case is defined as being in the highest 20% of the 100 year record. To make it simple, because I’m confusing myself, just look for the green colors in your area.


Clearly you can see the odds of having one of those extreme wet seasons is dominated by the winter months (again, with some bleed-over into late fall and early spring). I’m showing you those maps because El Nino are famous for ending droughts, or at least they have been shown to be great helpers in drought eradication. Given what we’ve seen across Oklahoma over the last 3.5 years, especially in western Oklahoma, a little help from a strong El Nino could be just the miracle we need.


The bad news, of course, is that we have to wait until winter for the best odds, and we also have to actually get this El Nino to develop! The skill for predicting the odds of El Nino (or La Nina or Neutral Conditions) is lowest in the spring, but that skill is not zero. So the issuance of an El Nino Watch is still significant.


Until then, we’ll continue to just look at the week-to-week forecasts, knowing that our rainy season of spring is right around the corner. The 7-day rainfall forecast looks promising (but not drought-ending).


The medium-range CPC outlooks still show us to be in between the trough in the eastern U.S. and the ridge across the western U.S., so expect us to continue our see-saw temperature battle, with a bit of whatever moisture we can coax up from the Gulf before the next front comes through. These cover March 13-19.


Farther out, the Canadian model still gives us pretty low odds of seeing at least 0.4 inches or so of moisture accumulate in the state through March 20, at least.


So it does look like we’ll tend to be on the dry side for a bit with occasional bouts of moisture here and there. That can change in a hurry as we warm up and get back to spring. The next big deluge might be sitting right off the end of the 7-day forecast as we speak!



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Bryan Painter

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