Originally published in the Feb 2016 CLIMAS Southwest Climate Outlook
El Niño conditions continued for a 12th straight month, but we have passed the peak intensity of one of the strongest El Niño events on record. This does not mean that El Niño is over, though. Despite the recent warm and dry conditions in the Southwest, we are likely to see more weather events associated with El Niño conditions through spring 2016. In monitoring and forecast discussions, we continue to see persistent sea surface temperature (SST) anomalies (Figs. 1–2) and enhanced convective activity in the central and eastern Pacific, and most models forecast that this El Niño event will continue through spring or early summer. Precipitation and temperature outlooks mirror this forecast, calling for increased probabilities of precipitation across most of the southern U.S.
On Feb. 10, the Japan Meteorological Agency identified ongoing El Niño conditions as having passed their “mature” stage in the equatorial Pacific and predicted that this remarkably strong event would gradually weaken to neutral conditions by summer. On Feb. 11, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory and identified the current atmospheric and oceanic anomalies as reflecting a strong El Niño that will persist through most of the spring before transitioning to ENSO-neutral conditions in late spring or early summer, with increasing chances of La Niña conditions by early fall. On Feb. 16, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, but noted that deceasing temperature anomalies and building trade winds are indicators of this event’s gradual decline. On Feb. 18, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated a gradual weakening of El Niño from late spring into summer (Fig. 3), and reiterated that this El Niño would likely gradually decline, with lingering effects and impacts through spring 2016. The North American multi-model ensemble currently shows a strong event extending into early spring with gradual weakening to neutral conditions by late spring or early summer (Fig. 4).
In the Southwest, seasonal forecasts and past events suggested we should see well above-average cumulative precipitation totals throughout our cool season (Oct–Mar). However, the past 30–40 days of mostly warm and dry conditions, including numerous record-setting high temperatures combined with the melting of our previously abundant mountain snowpack, makes it hard not to feel like this El Niño is a “bust.” Is this a fair assessment, or does this simply reflect the difficulty of interpreting climate events (e.g., El Niño conditions) on a weather timeline? In previous discussions, we’ve highlighted the fact that we should expect periods of inactivity between storms, but we were hopeful those inactive periods would be on the order of days to a week, not weeks to a month. Even so, the default state for the desert Southwest is dry, so even a strong El Niño event can only alter that system so much, and past events do show periods of extended inactivity. Precipitation during the 1997–1998 El Niño event (strongest on record) was well below average in January 1998 (Fig. 5), with an extended run of dry days before it roared back to life from February through April 1998 (Fig. 6). If we look at cumulative cool-season precipitation during our current El Niño event (October 2015 – January 2016), our precipitation totals are at or above average (Fig. 7), and January 2016 was less dry than it may have seemed thanks to an active first week of the month (Fig. 8).
Even though the 2015–2016 El Niño event peaked in December 2015, the impacts in the Southwest lag behind this spike in intensity, which means we look to late winter and early spring as the most likely times for increased storm activity associated with the El Niño signal. We won’t be able to fully evaluate the 2015–2016 El Niño event until we know how much rain and snow fell over the entire cool season, and given past events, our best bets for seeing above-average precipitation will be in February and March. In the short term, we are left waiting for the jet stream to shift to a favorable pattern that funnels moisture into the Southwest, rather than directing it around us.