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Texas Emergency Management ONLINE 2016 Vol. 63 No. 11


Meteorologist Aaron Treadway, National Weather Service Austin/San Antonio

La Niña Update

What is La Niña?
La Niña occurs when there are unusually cold ocean temperatures in the Equatorial Pacific and off of the South American west coast. This usually occurs during the fall and winter months and has impacts across the Northern Hemisphere.

What does La Niña mean for Texas?
La Niña for Texas usually translates into both warmer and drier than normal conditions. When La Niña (part of El Niño-Southern Oscillation, or ENSO) is coupled with two other global Oscillations, the Atlantic Multi-decadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO), there is an even clearer picture of what to expect across Texas. For most of Texas when there is a negative PDO and positive AMO (the current conditions), this is associated with drier than normal and drought conditions about 45% of the time. There are obvious exceptions to this; for example, parts of Central Texas saw massive amounts of rainfall from October to December in 1998, although we were in La Niña during that time.

For more information on the Pacific Decadal Oscillation visit the Climate Data Guide/PDO.
For more information on the Atlantic Multi-decadal Oscillation visit the Climate Data Guide/AMO.

What does the Climate Prediction Center (CPC) say about the current La Niña?
While the Northern Hemisphere is currently in ENSO-Neutral conditions, as of September there are negative sea surface temperature anomalies expanding across the Equatorial Pacific. This has prompted the CPC to issue a La Niña watch with a 70% chance of La Niña developing over the Northern Hemisphere during the fall of 2016. In addition, there is about a 55% chance that it will persist into the winter of 2016-2017. Most of the climate models show that the sea surface temperatures will continue to cool through December and possibly into January before beginning to warm again. This is the reason for the issuance of the La Niña Watch by the CPC.

To read the Weekly ENSO Updates or the full ENSO Diagnostic Discussion visit the Climate Prediction Center.

Winter Outlook
Based on the current ENSO and other global conditions, the forecast from the CPC for the Meteorological Winter months of December through February are greater chances of above normal temperatures and greater chances of below normal precipitation. The graphical forecasts are below. These predictions are in line with the warmer and drier trends associated with La Niña.

While below normal rainfall and above normal temperatures would normally lead to drought conditions and possibly an active fall fire season, the offsetting conditions this year may be the wet spring and the summer rains that much of the state has received. According to the current drought monitor, most of the state is either drought free or abnormally dry, with only the northeast corner of the state in drought conditions. The monthly and seasonal drought outlooks from the CPC also do not show high chances of drought developing, thanks to the rains earlier this year and any rain received this fall going into winter, despite the La Niña forecast.

For more information on the drought monitor and drought outlook visit the National Weather Service.
For updated seasonal forecasts throughout the fall and winter visit the CPC homepage.

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