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Southwest Climate Outlook - El Niño Tracker - February 2019

Sunday, February 17, 2019

 

After months of El Niño on the horizon (but each month not appearingto get any closer), forecasters have identi ed the convergence ofatmospheric and oceanic conditions that indicate the presence of a weak El Niño event. This is expected to last through spring, although there is not complete agreement across the international agencies. On Feb. 12, the Japanese Meteorological Agency (JMA) maintained their assertion of the presence of El Niño conditions inthe equatorial Pacific and called for a 70-percent chance of these conditions lasting until summer 2019. On Feb. 14, the NOAA Climate Prediction Center (CPC) switched to an El Niño advisory, given the convergence of oceanic and atmospheric conditions, as well as warm subsurface waters on the way, but their outlook dropped to a 55-percent chance of an El Niño lasting through spring. On Feb.19, the Australian Bureau of Meteorology remained in an El Nino watch, reflecting the increased chance of an El Niño developing over spring and summer. On Feb. 19, the International Research Institute (IRI) issued an ENSO Quick Look, highlighting above-average sea surface temperatures (SSTs), warm subsurface waters, and the development of atmospheric conditions over the past few months. They maintained a 65-percent chance of an El Niño Feb-Apr, and a 50-percent chance Apr-Jun (Fig. 3). The North American Multi-Model Ensemble (NMME) points toward a weak El Niño at present lasting through spring 2018 (Fig. 4).

 

Summary:  Sea surface temperatures (SSTs) are still above-average across the equatorial Pacific (Figs. 1-2), and atmospheric conditions finally caught up – the question is: will it be too late for the Southwest, or have we already been observing borderline weak El Niño impacts? The delayed convergence of oceanic and atmospheric conditions was the main factor holding back a more confident outlook, but 2018-2019 looks like it will be classified as a weak El Niño event. In the Southwest, El Niño is associated with increased chances for above-normal winter precipitation, but weak events demonstrate limited correlation with increased precipitation, and some of the wettest winters in the Southwest have been under ENSO-neutral conditions. Winter thus far in parts of Arizona and New Mexico line up with the narrative of winters under El Niño, but direct attribution is challenging given small sample size, aforementioned weak correlations, and the challenges in tracking precipitation anomalies in a region that already sees relatively infrequent rain events in a “wet” year. Additionally, it remains to be seen whether this will turn out to simply be a normal southwestern winter, which only feels wetter and cooler after multiple warm and dry winters altered expectations.


Online Resources

  • Figure 1 - Australian Bureau of Meteorology - bom.gov.au/climate/enso
  • Figure 2 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov
  • Figure 3 - International Research Institute for Climate and Society - iri.columbia.edu
  • Figure 4 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov
  • Equatorial Niño Regions - For more information: ncdc.noaa.gov/teleconnections/enso/indicators/sst/
  • Madden Julian Oscilation - For more information: cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml

Southwest Climate Outlook February 2019 - Climate Summary

Wednesday, February 6, 2019

January Precipitation and Temperature: January was wetter-than-normal across much of northern Arizona and New Mexico, near-normal in southern Arizona, and below-normal across most of southern New Mexico (Fig. 1). January temperatures were normal to above-normal (Fig. 2). Winter storms brought wet and cool conditions to the region in February – including some heavy snow forecast later in the week of Feb 18. These storms feel like a departure, but may simply be closer to normal winter conditions in the Southwest, with expectations having shifted after persistent warm and dry winter conditions over the past few years or decades.

Seasonal & Annual Precipitation and Temperature: Nov-Jan precipitation was mostly normal to below-normal across Arizona and most of New Mexico (Fig. 3), while the temperature rankings were normal to above-normal in Arizona, and below-normal to above-normal in New Mexico. Water year precipitation includes a particularly wet October, and most of the Southwest recorded above-normal precipitation since Oct. 1, while 12-month totals highlight above-normal precipitation in southern Arizona and New Mexico, and persistent precipitation deficits in the four corners region (Fig. 4).

Drought: The Feb. 14 U.S. Drought Monitor (USDM) shows modest but widespread improvements in regional drought conditions, with much of Arizona and the four corners region seeing up to two levels of improvement in their drought designation (Fig. 5). Persistent drought conditions remain in the Four Corners region, although characterizations of drought extent and intensity are reduced on this map. Accumulated precipitation de cits built up over seasons and years, and weekly snapshots may struggle to capture the nuance of drought conditions that work across multiple timescales. This also applies to drought recovery, where above-normal precipitation in the short term is likely insuficient to make up for years of drought, but above-normal cool season precipitation should help in both short and long-term timescales.

Snowpack & Water Supply: Snow water equivalent (SWE) increased since last month. SWE values (as of Feb. 20) in northern Arizona and New Mexico are near normal, ranging from 90-110 percent of average, while southern stations are lower, ranging from less than 25-percent to 75-percent of average (Fig. 6). Heavy snowfall forecast for Feb 21-22 would increase these values considerably, but it remains to be seen how widespread this event will be in the Southwest. Reservoir storage remains a persistent concern, as water levels have been impacted by long-term drought and accumulated precipitation deficit. Most of the reservoirs are at or below their long-term averages, and a few of the

El Niño Tracker: In the on-again, off-again saga, we are back “on” for a weak El Niño in 2018-2019, with a possible second year of El Niño in 2019-2020 (reminiscent of the sequence in 2014-2015 and 2015-2016). The atmospheric conditions are nally catching up with the ocean, and while the equatorial waters had cooled, they remain borderline weak El Niño, and a pulse of warm sub-surface water is poised to help. What this means for the Southwest, especially in the cool season that remains, is up in the air (see El Niño Tracker on p. 3 for details). Given a choice, and considering the accumulated drought conditions over the past months and years, anything that hints at wetter and cooler than average conditions – or even to simply have a ‘normal’ southwestern winter – is welcome. Precipitation and Temperature Forecast: The three-month outlook for March through May calls for increased chances of above-normal precipitation in most of Arizona, New Mexico, west Texas, and northern Sonora (Fig. 7, top). The three- month temperature outlook calls for slightly increased chances of above-normal temperatures in pockets of Arizona and Sonora, but otherwise would suggest equal chances of above, below, and near normal temperatures (Fig. 7, bottom).


Online Resources

  • Figures 1-4,6 - Western Regional Climate Center - wrcc.dri.edu
  • Figure 5 - U.S. Drought Monitor - droughtmonitor.unl.edu
  • Figure 7 - International Research Institute for Climate and Society - iri.columbia.edu