Precipitation and Temperature: Sept precipitation was between below average and above average in Arizona and New Mexico with much of the above-average precipitation found in central and southern Arizona and far western New Mexico (Fig. 1a). Sept temperatures were average to record warm in Arizona and New Mexico (Fig. 1b). Jul-Sept precipitation ranks were average to record wet in Arizona and between much below and much above average in New Mexico (Fig. 2a). Jul-Sept temperature ranks were above average to much above average across the Southwest (Fig. 2b). Annual precipitation totals skew wet in areas with increased monsoon totals (i.e. central and southern Arizona and parts of southern New Mexico), while most of the rest of the southwest was average to much below average for precipitation, and above-average to much above average for temperature (Fig 3a-3b).
Drought: Total water year precipitation (Oct 1 – Sept 30) is between much below normal and above normal across most of Arizona and New Mexico, with much below normal and record driest more prevalent in much of the rest of the Southwest (Fig. 4). Extending a trend from last month, the U.S. Drought Monitor (USDM) scaled back drought categorizations in New Mexico and Arizona, albeit to a lesser degree than last month (Fig. 5). This was in response to the wetter than average monsoon in parts of the Southwest. These summer storms brought some short-term relief, but long-term and cumulative precipitation deficits remain a concern. Additionally, the USDM expanded drought characterizations in much of Colorado. This is something to watch given possible implications for water storage in reservoirs, snowpack, and soil moisture.
Water Supply: Most of the reservoirs are at or below the values recorded at this time last year. Most are also below their long-term average (see Arizona and New Mexico reservoir storage).
Monsoon Recap: Monsoon activity was widespread and persistent from July through mid/late August, but tapered in September, save for a last-minute transition event that rolled through on Sept 30. The timing and progression of this season’s monsoon activity were relatively typical, but the seasonal totals were much higher than average especially in southern/central Arizona and parts of southern New Mexico (Fig. 6 and SW monsoon tracker, for maps and more information). 2021 did not quite break any monsoon records, but it came close in a few places. Regardless of the records, the sustained and widespread rainfall was an especially welcome pivot from 2020's failed monsoon.
ENSO Tracker: ENSO has shifted to La Niña according to some outlooks (NOAA CPC, in particular), owing to observed and forecast SSTs, and emergent atmospheric conditions. Others forecast an onset of La Nina soon and lasting through winter 2021-2022 (see ENSO-tracker for details).