News

From the October issue of the CLIMAS Southwest Climate Outlook

In the last month, oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) have pushed forecasts back towards an increased likelihood of a La Niña event this winter (Figs. 1-2). Models are indicating an increased possibility of these conditions sustaining through winter 2017, leading to greater certainty regarding the formation of a weak La Niña event in late 2016 or early 2017. However, the chance of an ENSO-neutral winter cannot be entirely ruled out. Fluctuations in forecasts and models are likely due to the limited coordination between oceanic and atmospheric conditions described in previous outlooks, as well as generally borderline conditions between weak La Niña and ENSO-neutral.

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From the October issue of the CLIMAS Southwest Climate Outlook

Precipitation and Temperature: September precipitation totals were near average across most of the climate divisions in Arizona and New Mexico (Fig. 1a), with one notable departure being the swath of above-average precipitation in the borderlands region linked to Tropical Storm Newton. September temperatures were average to below average in Arizona and average to above average in New Mexico (Fig. 1b). October precipitation to date has been below average across most of the region (Fig. 2), although October is one of the drier months in the Southwest, so dry conditions are not unexpected, and a single tropical storm or fall storm can skew the percent of normal. October temperatures have been 2 to 6 degrees above average for most of New Mexico and 0 to 4 degrees above average for most of Arizona (Fig. 3). This is in part connected to global trends that are likely to see 2016 as the warmest year on record (breaking the record set in 2015).

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Climate Summary from the September issue of the CLIMAS Southwest Climate Outlook

The southwestern monsoon is characterized by spatial and temporal variability. Storm events are interspersed with breaks of limited activity as migrating high pressure systems and available moisture dictates where in the Southwest rain might fall. This results in highly variable precipitation totals on a daily or weekly timescale. Regional climatology gives some indication as to the expected cumulative total precipitation any location might expect but says less about how those precipitation totals will be achieved. Any given year of monsoon activity is difficult to categorize on a week-to-week basis, and simple score-carding using seasonal precipitation to date will be skewed by recent runs of heavy rain or extended breaks in the monsoon. Totals should even out over the course of the season and vary around the long-term average, but outliers and extremes are always possible. 

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Climate Summary from the September issue of the CLIMAS Southwest Climate Outlook

Oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) remain in the range of neutral conditions (Figs. 1-2). In the last month, seasonal forecasts and models further reduced their certainty of a weak La Niña event forming in late 2016 or early 2017. The current projections find ENSO-neutral conditions to be the most likely outcome for this fall and winter, although the chance of a weak La Niña event cannot be ruled out. As past outlooks have noted, there was ongoing uncertainty regarding the prospects for La Niña, especially as it appeared to be having difficulty organizing, with limited coordination between ocean and atmosphere.

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The Southwest saw the first strong burst of widespread monsoon activity near the end of June.  Most of the first half of July was characterized by a distinct break in monsoon activity, as atmospheric circulation patterns and lack of available moisture limited opportunities for widespread storms to develop, especially at lower elevations.  As July progressed, there were increasingly favorable conditions for storms to develop and spread, culminating in an extended period of widespread activity during late July and early August. Tropical Storm Javier helped jumpstart activity in mid-August, just as the previously mentioned extended run was winding down, and provided a brief extension to storm activity via a surge of moisture from the Gulf of California. The remainder of the monsoon window will be a waiting game to see if favorable moisture and atmospheric circulation patterns develop, as well as the potential influence of eastern Pacific tropical storm activity that could supplement storm activity and provide additional moisture to fuel storm activity. (read more)

Oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) remain in the range of neutral conditions (Figs. 1-2). Seasonal forecasts and models identify the most likely scenario being a weak La Niña event forming sometime in late summer or fall 2016 and lasting through winter 2017. Some uncertainty exists regarding the specific timing of this event, as the equatorial sea surface temperature (SST) anomalies have not yet dropped into La Niña range and there is a lack of coordination between ocean and atmosphere (and in particular the lack of enhanced trade winds). (read more)

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. (read more)

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. (read more)