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July 2016 SW Climate Outlook - La Niña Tracker

Friday, July 22, 2016

All oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) have returned to neutral conditions (Figs. 1-2). The development of a La Niña event in 2016 remains a distinct possibility, even while the timing and intensity remain relatively uncertain. 

On July 14, the NOAA Climate Prediction Center (CPC) highlighted the persistent neutral conditions currently observed and identified some tension between statistical and dynamical models, the former predicting a later onset and weaker event than the latter. The CPC forecast took a middle ground between these models and forecast a 55–60 percent chance of a weak La Niña event starting sometime between August and October 2016. On July 19, the Australian Bureau of Meteorology maintained its La Niña watch but saw some recent declines in model projections that decreased the forecast probability to a 50 percent chance of a La Niña event developing. On July 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts highlighted that while most of the oceanic and atmospheric conditions were indicative of a La Niña event forming, the trade winds had not yet shifted towards La Niña, and there was a lack of coupling between ocean and atmosphere that is crucial to the formation of a La Niña event. The IRI-CPC forecast still sees the formation of a La Niña event in 2016 as more likely than not, but with the timing delayed and the intensity of the event not likely to exceed weak status (Fig. 3). The North American multi-model ensemble characterizes the current model spread and highlights the variability looking forward to 2017, but the ensemble mean hovers close to weak La Niña status for fall and winter of the coming year (Fig. 4).

La Niña typically brings drier-than-average conditions to the Southwest, and it will be important to track both the timing and intensity of this event in relation to precipitation, temperature, snowpack, and water supply over the coming year. CLIMAS researchers are contributing to a La Niña information hub that will mirror the El Niño hub, with the goal of providing a curated set of news and forecast models regarding La Niña, as well as expert commentary and analysis on the possible impacts to the Southwest. 

Visit for more information.

July 2016 SW Climate Outlook - Monsoon Tracker

Friday, July 22, 2016

The southwestern monsoon officially starts June 15 and ends September 30 – the dates the National Weather Service began using in 2008 to identify the window of typical activity for the region. The historical start date of monsoon activity (increased dew point, onset of precipitation events) varies across the region and is reflected in a generally westward migration over the season (Fig. 1). The monsoon ridge also shifts throughout the season, and the location of this ridge helps determine where storms and precipitation events will occur. 

The Southwest saw a strong start to the monsoon in the second half of June, with a number of heavy rainfall events, particularly across southern Arizona. Most of July has been characterized by a monsoon “break” for the Southwest, with very few precipitation events other than in the southeastern corner of Arizona. Since the start of the monsoon, most of Arizona and New Mexico have recorded below-average precipitation (Figs. 2a-b), but this is early in the season and a wide range of precipitation totals and considerable spatial variability is to be expected at this point (Figs. 3a-b). The percent of days with rain highlights the irregular coverage of monsoon precipitation thus far, with much of the heavy precipitation activity clustered in southeastern Arizona and across much of New Mexico (Figs. 4a-b).

July 2016 Southwest Climate Outlook - Climate Summary

Thursday, July 21, 2016

Precipitation & Temperature: June precipitation totals generally were average to above average in Arizona and New Mexico, with the exception of southern Arizona (much above average) and the Four Corners region of New Mexico (below average) (Fig. 1a). Temperatures were above average to record warm across most of the Southwest (Fig. 1b), with two periods of extreme heat (June 3–5 and June 18–20), the latter of which resulted in multiple fatalities in southern Arizona. As of July 20, temperatures this month have remained mostly above average across the Southwest (Fig. 2). 

Monsoon: Following a strong start to the monsoon in late June, there was a considerable decline during much of July, aside from sporadic storms that pushed into the southeastern corner of Arizona (Fig. 3). This decline, or “break,” is associated with a shift in the monsoon circulation patterns, in which a high pressure ridge diverts moisture and storm activity away from southern Arizona (see Monsoon Tracker for more information).

Drought & Water Supply: Long-term drought persists across the Southwest (Fig. 4), reflecting multiple years of drought and accumulating precipitation deficits. The southern half of Arizona and the western edge of New Mexico are experiencing moderate drought, while most of the rest of these two states are designated as abnormally dry. Water year precipitation to date in Southern California, most of southern Arizona, and western New Mexico is below average (Fig. 5).  Lakes Mead and Powell in Arizona and Elephant Butte Reservoir in New Mexico are at 36, 57, and 14 percent of capacity, respectively (see reservoir storage diagrams). Lake Mead is of particular interest, given water restrictions that would be triggered were levels to drop below critical thresholds (see CLIMAS 1075 podcast series).

La Niña: Sea surface temperature anomalies and atmospheric patterns all indicate ENSO-neutral conditions. Most models point towards the formation of a weak La Niña event sometime in late summer or early fall that is likely to last through winter 2017. Some uncertainty remains regarding the strength and timing of the event (see La Niña Tracker).

Wildfire: Given the abundant fine fuels that grew following a strong monsoon and tropical storm season in fall 2015 and given the warmer- and drier-than-expected conditions in winter and early spring 2016, there was concern over the possible severity of wildfire in 2016. Relatively cooler and wetter-than-average conditions (linked to the lingering effect of El Niño) tamped down early-season fire activity in April and May. Fire activity increased in June, but numerous precipitation events, a strong start to the monsoon, and increased relative humidity across the region helped limit the risk of severe wildfire. As of July 20, wildland fires had burned approximately 177,000 acres in Arizona and approximately 135,000 acres in New Mexico. Much of the fire activity this year has been managed for beneficial use. With the onset of the monsoon and the associated increase in precipitation activity and relative humidity, the window for severe fire is nearly closed.

Precipitation & Temperature Forecasts:  The July 21 NOAA-Climate Prediction Center’s one-month seasonal outlook calls for increased chances of above-average precipitation for most of Arizona and western New Mexico (Fig. 6, top), and increased chances of above-average temperatures across the entire western United States (Fig. 6, bottom).

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