Nov 2017 SW Climate Outlook - La Niña Tracker
Assistant Research Professor, Arizona Institutes for Resilience
Assistant Professor of Anthropology, School of Anthropology
Ben McMahan joined CLIMAS after completing a PhD in Sociocultural Anthropology at the University of Arizona. His dissertation research was on hurricanes and disaster on the U.S. Gulf Coast, where he focused on
- Human interactions in dynamic social and environmental contexts,
- Risk perception and landscape changes during and after disaster, and
- Social network and policy responses to governance issues related to the acute threats of disaster; as they layer onto long term environmental issues and landscape scale changes.
He was also a key contributor to UA Bureau of Applied Research in Anthropology (BARA) collaborative/trans-disciplinary research on the social, economic, and environmental impacts of the US Oil and Gas industry (2007-2011), and the aftermath of the Deepwater Horizon oil spill (2010-2013).
At CLIMAS, his research activities included tracing how climate information is incorporated into regional decision maker networks, leading CLIMAS team research on the risks and effects of climate extremes, and collaborative research on the effects of climate variability on phenology and temporality of native plants in the region. He was also responsible for working to develop collaborative research opportunities and outreach efforts at CLIMAS, and as part of ongoing assessment and science/strategic planning, he contributed to strategic planning used to prioritize future research and outreach directions. He also coordinated publication of the monthly Southwest Climate Outlook, produced the Southwest Climate Podcasts, and was the online editor for CLIMAS’ blog - Southwestern Oscillations.
Most models now suggest that a weak La Niña event has emerged (Figs. 1-2) and is likely to last through this winter. On Nov. 8, the Australian Bureau of Meteorology called for a 50-percent chance of La Niña forming in 2017, noting that while sea-surface temperatures had cooled, the cooling had stalled, whereas atmospheric indicators had shifted slightly toward weak La Niña. On Nov. 9, the NOAA Climate Prediction Center (CPC) took a stronger stance, identifying the emergence of La Niña conditions in October and calling for a 65- to 75-percent chance of the event lasting through the winter. The CPC forecast consensus took into account below-average sea-surface and sub-surface temperatures as well as atmospheric indicators of La Niña conditions. On Nov. 10, the Japanese Meteorological Agency (JMA) also determined that La Niña conditions had emerged, and called for a 60-percent chance of these conditions lasting long enough to meet the JMA criteria for a La Niña event. The North American Multi-Model Ensemble (NMME) nudged back toward borderline ENSO-neutral conditions in October 2017 (Fig. 4), but a majority of the models predict a swing into weak La Niña this winter while some even veer into moderate La Niña. Notably, very few of the models in the ensemble predict an ENSO-neutral event this winter.
Summary: The seasonal outlooks have mostly converged on a weak La Niña event having formed, and most predict these conditions will persist through February 2018. As noted in last month’s Tracker, the signal is usually clearer by mid-October, but this year there was quite a bit of movement around the boundary between ENSO-neutral and weak La Niña well into the fall. Given the warmer- and drier-than-average winter conditions associated with La Niña in the Southwest, its likely presence may heighten ongoing concerns regarding winter precipitation and persistent drought. Southwestern winters are already relatively dry, however, so the emergence of a weak La Niña doesn’t necessarily ensure an exceptionally dry winter, it just takes wetter-than-average winters off the table, based on past La Niña events (see following page for a few examples).