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Monthly Archive

El Niño Tracker - March 2016 - Time Winding Down for El Niño in the Southwest

Friday, March 18, 2016

Originally published in the Mar 2016 CLIMAS Southwest Climate Outlook

El Niño conditions continued for a 13th straight month, but the peak of this event has passed. Monitoring and forecast discussions emphasize strong positive sea surface temperature (SST) anomalies (Figs. 1–2) and enhanced convective activity in the central and eastern Pacific. These positive temperature anomalies are waning, and trade wind activity is increasing, indications that this El Niño event is on the decline. Most forecasts emphasize this event will continue through spring or early summer before returning to ENSO-neutral status. There is also the possibility of swinging to La Niña conditions later in 2016, although there is considerable model and forecast uncertainty regarding the chances of La Niña vs. ENSO-neutral conditions.

On Mar. 10, the Japan Meteorological Agency identified ongoing El Niño conditions that had peaked and were actively decaying and expected to weaken to neutral conditions by summer.  On the same day, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory, identifying current atmospheric and oceanic anomalies as reflecting a strong El Niño that will likely persist through most of the spring before transitioning to ENSO-neutral conditions in late spring or early summer. On Mar. 15, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, but noted a slow and steady decline, with decreasing positive temperature anomalies and near-normal trade winds as two key indicators of this event’s ongoing deterioration. On Mar. 17, the International Research Institute for Climate and Society (IRI) and CPC forecasts described mixed signals regarding El Niño, with zonal winds and SSTs in decline, while convective activity and the Southern Oscillation Index (SOI) remained strong. The IRI/CPC forecast still identifies a return to ENSO-neutral conditions by summer, with a 50 percent chance of transition to La Niña conditions later in 2016 (Fig. 3), but also points out that the spring predictability barrier will affect our certainty regarding ENSO-neutral vs. La Niña outlooks. The North American multi-model ensemble currently shows a strong event extending into early spring with gradual weakening to neutral conditions by early summer (Fig. 4).

This El Niño is not over; atmospheric and oceanic conditions are still indicative of a strong El Niño event. The CPC/IRI forecast noted this fact, stating that “El Niño is not done yet,” and that at a global scale, strong signals are still associated with El Niño, particularly in Brazil and southeast Asia (Fig. 5). In the southwestern U.S., we are nearing our dry season, meaning limited time remains for additional El Niño-influenced precipitation events of significance.

The IRI/CPC forecast also made note of the lack of “typical teleconnections” in this El Niño event. In the Southwest, for example, winter precipitation has been sparse following the storms of early January. These storms were exactly the sort of events expected in an El NIño year, but they were followed by a persistent ridge of high pressure that set up and limited the influx of additional moisture into the Southwest. This diverted moisture resulted in well above-average precipitation in the coastal northwestern U.S. and northern California, even while the Southwest was drier than normal (Fig. 6), a pattern which more closely aligns with La Niña. This occurred at an especially inopportune time in terms of southwestern climate patterns, as it effectively limited the opportunity for El Niño-associated storms during much of the the winter season. Sub-seasonal variability limited El Niño’s potential, and with the Southwest already characterized by dry conditions in a normal year, conditions that limit opportunities for precipitation can cut into seasonal totals significantly.

Next month’s issue will include a seasonal recap of El Niño and comparisons to seasonal averages as well as other El Niño events, but this high pressure ridge is likely one of the major reasons why the Southwest (and Arizona in particular) have not seen as frequent or as intense precipitation events as were forecast in seasonal outlooks. These forecasts and projections were dependent on the influence of a strong El Niño signal at a climate timescale (i.e., how these events cluster over years or decades), without the benefit of foresight of how a persistent high pressure ridge operating at a weather timescale (i.e., days or weeks) would knock the precipitation signal out of alignment for weeks on end.

Southwest Climate Outlook March 2016 - Last Gasp for El NIño?

Thursday, March 17, 2016

Precipitation & Temperature: Over the past 30 days, precipitation totals were well below average for most of the southwestern U.S. (Fig. 1). Despite anticipation for above-average precipitation this winter due to the strong El Niño event, a ridge of high pressure diverted moisture around the Southwest for much of the last 60 days. The resulting precipitation patterns look more like La Niña than El Niño, as the coastal Northwest and northern California have recorded well above-average precipitation and the Southwest has been very warm and dry (see El Niño Tracker). Temperatures in February were well above average for most of the Southwest, setting numerous high-temperature records, especially in southern Arizona and coastal Southern California (Fig. 2).

Image Source - Advanced Hydrologic Prediction Service

Image Source - NOAA National Centers for Environmental Information

Drought: Long-term drought persists across much of the Southwest, and recent warm and dry conditions have done little to improve regional outlooks on short-term drought (Fig. 3). There was hope that a strong El Niño might reduce precipitation deficits, but multi-year droughts, such as those experienced during much of this century so far, will require more sustained above-average precipitation over multi-year periods to fully recover. 

Image Source - U.S. Drought Monitor

Snowpack & Water Supply: This winter, below-average precipitation and above-average temperatures have dropped snow water equivalent (SWE) percent of normal to well below average in Arizona and southern New Mexico, with values ranging between 0 and 25 percent of normal. Northern New Mexico and much of the Upper Colorado River Basin are faring somewhat better, with SWE values between 75 and 110 percent of normal (Fig. 4). It remains to be seen how the rest of winter and spring will play out in high elevation areas, and how this will affect reservoir storage in the region (See reservoir storage information).

Image Source - Western Regional Climate Center

El Niño Tracker: With winter winding down and little on the horizon to indicate a shift towards a wetter signal, this El Niño event is shaping up to be a bit of a disappointment compared to forecasts and media characterizations that dominated the run up to the actual event. Expectations for a strong El Niño had been high, beginning with the false start of this El Niño event in 2014–2015, and continuing with a general sense of the potential a strong El Niño event could have to mitigate ongoing drought conditions (see expanded El Niño Tracker).

Environmental Health & Safety: The Southwest has been awash in color as flowering plants exploded to life, fed by the increased precipitation during fall 2015 and kickstarted by above-average temperatures of the past month or so. As a result, pollen counts are up, and as dry conditions persist, we can expect increased dust and particulate matter as well.  Wildfire also looms on the horizon, as growth spurts in fine fuels last fall and dry conditions this winter and spring have combined to increase fire danger classifications across the Southwest (Fig. 5). 

Image Source - Wildland Fire Assessment System

Precipitation & Temperature Forecast: The March 17 NOAA-Climate Prediction Center three-month seasonal outlook calls for increased chances of above-average precipitation for most of the Southwest (Fig. 6, top), and increased chances of above-average temperatures across most of the western United States (Fig. 6, bottom).

Image Source - NOAA/NWS - Climate Prediction Center