Usually, when a weather forecast has a fifty percent chance of some particular feature developing, the forecast is met with a collective "Is that it?" type reaction from the public. But when NOAA posted an El Nino watch Thursday March 6, it was big news all over. That included the ag community--I had a couple e-mails from farmers asking about the effect of El Nino for their areas. All this attention came from--once again--a forecast that said the following:
"...models show a better than 50 percent chance of El Nino conditions developing this summer or fall in the equatorial Pacific Ocean..."
Will this feature actually develop? We'll see. As the attached graphic shows, El Nino chances do not rise to more than 52 percent by fall 2014. And, both the U.S. and Australia forecast models indicate that Pacific equator temperatures are on track to reach values of around one degree Celsius above normal by the August-September-October period. Such a trend is a weak El Nino.
Why are El Nino chances getting so much attention? Let's start with moisture for dry areas. Subtropical jet streams due to El Nino circulation can bring heavy precipitation to the Far West and the southern Plains. As we all know, those regions could definitely use the precipitation. Another benefit from those El Nino-related wind patterns is that they interfere with hurricane formation, which would reduce the threat of damage from tropical weather systems in late summer and fall. In the Midwest, El Nino summers are usually milder on the temperature scale, which is beneficial for crops. There is also some thought that El Nino during winter would keep the bitter-cold temperatures from repeating in 2014-15. And, in South America, El Nino has a high correlation to rain in southern Brazil and Argentina.
But, El Nino is not a universal benefactor. Eastern Australia is almost guaranteed to have moderate to severe drought when El Nino is going on. Some of Australia's smallest wheat crops have been in years when El Nino is in effect. Southeast Asia--particularly Indonesia--can also be in jeopardy from drier conditions if El Nino is around.
There are a couple reminders with those details mentioned previously. One such reminder is that the El Nino watch issued is for El Nino to possibly form by later this summer or early fall. In other words, El Nino development may be too late to improve the drought problems in California and the southwestern Plains this season. We could see a number of months yet of frustrating and damaging dryness in these areas. Another reminder is that Pacific forecasts in spring do not have a real solid track record. NOAA itself pointed that out in the El Nino watch bulletin:
"While all models predict warming in the tropical Pacific, there is considerable uncertainty as to whether El Nino will develop during the summer or fall. If westerly winds continue to emerge in the western equatorial Pacific, the development of El Nino 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."
One final note--NOAA also issued an El Nino watch a couple years ago in 2012, also in the spring, and with similar Pacific temperature trends expected. That watch expired with no El Nino development. So, this watch is an identification of developments, but it is not the same as a forecast.
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