Fall Climatology Without La Niña Back »

The latest news from NOAA’s Climate Prediction Center is that the likelihood of La Niña developing this fall or winter has reduced, and now ENSO neutral conditions are slightly favored by the computers models and forecasters.

El Niño-Southern Oscillation (ENSO)

ENSO? That is the El Niño-Southern Oscillation, the more accurate and scientific description of the phenomenon that warms or cools the Pacific Ocean near the equator, and the atmospheric connections to those ocean temperatures.

The Climate Prediction Center uses sea surface temperature in some specific regions of the equatorial Pacific to define what phase of ENSO we are in, be it El Niño, La Niña, or neutral. El Niño criteria is +0.5 degree C or warmer than average in a specific region of the ocean for at least a three month period. La Niña criteria are an average of -0.5 degree C or cooler than average in that same region for at least a three month period. ENSO neutral conditions are when the sea surface temperatures are between +0.5C and -0.5C from normal, in other words, near the long-term average.

ENSO Neutral Conditions

We have been in ENSO neutral conditions for most of this growing season—essentially since El Niño said “Adios!” earlier this spring. The forecasters have projected a weak La Niña to develop this fall and winter, but now the likelihood of neutral conditions are more favored, with 55-60% likelihood through the winter season. The probability of La Niña is gradually decreasing from now through the winter and spring.

Historically, ENSO neutral conditions have brought drier than average climate in October to East Central and Southeastern South Dakota (Figure 1). In the last few decades, ENSO neutral conditions have not affected temperature very much in October, with near average temperatures historically in South Dakota during ENSO neutral years. The Climate Prediction Center will release their official outlook for October this week, so this is not necessarily the current forecast, but a historical look at ENSO neutral conditions in October.

If history is any indicator of the future this year, we may see some favorable dry conditions for soybean and corn harvest in the East Central and Southeast regions, and air temperatures may end up near the long term average across the state.

Figure 1. (Left) Historical October precipitation departure from average in ENSO neutral conditions. Brown colors are drier than average. (Right) Historical October temperature departure from average in ENSO neutral conditions. Gray shading indicates near average temperatures during ENSO neutral years. Source: Useful 2 Usable Climate Patterns Viewer.

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