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Southwest Climate Outlook November 2018 - Climate Summary

Thursday, November 15, 2018

Precipitation and Temperature: October was relatively wet and cool across the Southwest. Precipitation ranged from average to much-above average in New Mexico and from above average to much-above average in Arizona (Fig. 1a). Temperatures were much cooler than normal, ranging from below average to average in Arizona and from below to above average in New Mexico (Fig. 1b). Year-to-date precipitation is highly variable across the region, ranging from record driest in the drought-stricken Four Corners region to much-above average in parts of southern Arizona impacted by heavy tropical storm precipitation (Fig. 2a). Year-to-date temperatures show much less variability, generally much-above average to record warmest throughout the region (Fig. 2b).

Drought: The Nov. 13 U.S. Drought Monitor (USDM) highlights the presence of drought across the entire Southwest, with persistent and severe drought conditions in the Four Corners region (Fig. 3). The USDM reveals the challenge of mapping different timescales and intensities of drought in the Southwest on a weekly basis. In a region already characterized by dry conditions, where accumulated precipitation deficits may build over seasons and years, and where the timing and intensity of precipitation may have a bigger effect than short-term or seasonal totals, these drought characterizations can struggle to capture all of these inputs. The 18-month and 36-month standardized precipitation indices (SPI) for the Southwest (Figs. 4-5, respectively) demonstrate how these different timescales reveal differential patterns of drought and precipitation deficit.

Snowpack & Water Supply: Snow water equivalent across the Southwest is generally below average, although there has been some early-season activity of note in the Upper Colorado River Basin and portions of northern New Mexico (Fig. 6). Reservoir storage remains a persistent concern in terms of long-term drought and accumulated precipitation deficit, with most of the reservoirs at or below their long-term averages, including a few of the Rio Grande reservoirs that are at especially low levels (see Arizona and New Mexico reservoir storage).

Tropical Storms: The Pacific hurricane season has been very active, with 23 named storms at the time of this writing, including ten major hurricanes (category 4 or above) (see Tropical Storm Recap). This far surpassed the NOAA forecast of 14-20 named storms and seven major hurricanes. This year also marked the most intense Pacific hurricane season on record, with an Accumulated Cyclonic Energy of 317, breaking the previous record of 295 set in 1992. In addition to the overall intensity, a few notable aspects of this season were the multiple incursions of moisture into the Southwest (Bud, TD 19-E, Rosa, Sergio) and the damaging storms that hit the coast of Mexico (TD 19-E, Vicente, Willa).

El Niño Tracker: This has been an odd year for El Niño. Oceanic indicators are now well into El Niño territory, with warming sea-surface temperatures in the equatorial Pacific, but atmospheric indicators have lagged behind. Most forecasts noted a lack of coupling between ocean and atmosphere but remain confident of an El Niño event during winter 2018-2019, with forecast probabilities hovering around an 80-percent likelihood in most outlooks (see El Niño Tracker).

Precipitation and Temperature Forecast: The three-month outlook for December through February calls for increased chances of above-normal precipitation in Arizona and New Mexico (Fig. 7, top), and increased chances of above-average temperatures for the entire western United States (Fig. 7, bottom).


Online Resources

  • Figures 1-2 - National Centers for Environmental Information - ncei.noaa.gov
  • Figure 3 - U.S. Drought Monitor - droughtmonitor.unl.edu
  • Figures 4-6 - Western Regional Climate Center - wrcc.dri.edu
  • Figure 7 - NOAA - Climate Prediction Center - cpc.ncep.noaa.gov

Southwest Climate Outlook El Niño Tracker - November 2018

Thursday, November 15, 2018

Not quite El Niño? Widespread areas of above-average sea-surface temperatures (SSTs) now exist in the equatorial Pacific (Figs. 1-2), but atmospheric conditions have lagged behind. Most forecasts and outlooks, while still bullish on the emergence of an El Niño in 2018, identified current conditions as ENSO-neutral, but see an imminent shift in atmospheric circulations more characteristic of an an El Niño event. On Nov. 7, the Australian Bureau of Meteorology noted persistent above-average oceanic temperatures, but saw the continued presence of atmospheric conditions much closer to normal. The agency noted that coupling between oceanic and atmospheric conditions “is critical in any El Niño developing and becoming self-sustaining.” It maintained its ENSO Outlook at an “El Niño Alert,” with a 70-percent chance of its formation in 2018. On Nov. 8, the NOAA Climate Prediction Center (CPC) continued its El Niño watch, identifying neutral conditions at present and an 80-percent chance of an El Niño event developing this winter, and a 55- to 60-percent chance of it lasting through spring. CPC also noted the lack of oceanic/atmospheric coupling as hindering the progression of an El Niño event in an otherwise much-warmer-than-average ocean. On Nov. 8, the International Research Institute (IRI) issued an ENSO Quick Look that also reflected the warmer-than-average oceanic temperatures and the lagging atmospheric conditions, and maintained a greater-than-80-percent chance of an El Niño event by the end of 2018 (Fig. 3). Breaking from the other agencies, on Nov. 9, the Japanese Meteorological Agency (JMA) did identify the presence of El Niño conditions in the equatorial Pacific, with a 70-percent chance of these conditions lasting through spring 2019. JMA declared the El Niño despite the absence of atmospheric conditions consistent with such an event, stating that the lagging onset and resulting conditions are “common features of past El Niño events.” The North American Multi-Model Ensemble (NMME) points toward a weak-to-moderate El Niño by the end of the year (Fig. 4).

Summary: Equatorial SSTs have been rising and would appear to indicate the onset of an El Niño event except that the atmospheric patterns remain ENSO-neutral. Most outlooks are not particularly concerned about the current lack of oceanic/atmospheric coupling and expect that to occur by year’s end—in fact JMA considers the El Niño to have already begun. Further, most forecasts call for this El Niño event to last through spring. Cool-season precipitation totals (Oct – March) in the Southwest during previous El Niño events reveal considerable variability under weak events, including some drier-than-average seasonal totals. However, under moderate-intensity events, drier-than-average cool seasons have been rare, and it is not difficult to understand why there is eager anticipation for anything that might increase our chances of more winter rain.


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