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).
