This monsoonal flow in turn causes a significant increase in atmospheric moisture levels across the typically parched desert region as tropical air moves northward. This causes a reversal in the weather pattern across the region, with storms moving from generally the west-to-east in the spring months to east-to-west in the summer. An unusually high amount of activity was noted across far southwest Arizona into southeast California and the Gulf of California.ĭuring the summer months, high pressure in the mid-levels of the atmosphere over northern Mexico (often referred to as the “monsoon high”) strengthens, expands, and drifts northward. However, it was more than double the record low 1.1 million observed in 2020. Despite the increase in rainfall across the area, this was 30% under the historical average of 3 million. Over 2.3 million cloud-to-ground (CG) lightning strikes occurred June 2021 through September 2021. (Right) Regional map of the relative CG frequency for June 2021 through September 2021, with red (blue) areas observing less (more) lightning activity than usual. (Left) Total cloud-to-ground (CG) lightning strikes across the broader region during Jun-Sep by year. Average temperature by year across the Southwest for June through September.
Average temperature anomaly (compared to 1991-2020 normals) across the region for June 2021 through September 2021. The average temperature across the Southwest for June 2021 through September 2021 was 76.7☏, which was the coolest since 2017 but 6th warmest on record (since 1895).įig 4. Only areas that saw some of the most abnormally heavy rain observed subtly below average temperatures, a clear indication of how strong the climate change signal has become within the temperature records (Figure 5). Data source: NCEI NClimGrid.ĭespite the wetter than usual monsoon, temperatures were above normal for much of the region (Figure 4).
(Right) Standardized rainfall anomalies for June 2021 through September 2021 based on a normal period of 1991-2020. Black contours indicate areas of record rainfall (records since 1895). (Left) Total rainfall for June 2021 through September 2021. Notably, much of northern New Mexico observed drier than usual conditions.įig 3. Correspondingly, these record-setting areas were within broader regions of above average rainfall, though above average rainfall was not observed across the entire Southwest (Figure 3-Right). Areas that saw record rainfall include (outlined in black, Figure 3-Left): northeast of Phoenix, AZ, east of Payson, AZ, and west of Show Low, AZ northwest and south of Tucson, AZ near Ajo, AZ near the Guadalupe mountains (NM/TX). Data source: NCEI NClimGrid.Īs is usually the case, the absolute heaviest rainfall amounts fell near and over the mountains across the region. Average monsoon rainfall across the Southwest by year. Average rainfall during the core monsoon months of Jun-Sep across the region was 7.93", which was the 20th wettest on record (since 1895), wettest since 2014, and well above the 1991-2020 average of 6.39” (Figure 2).įig 2. In a stark turn of events, following the driest monsoon on record ( 2020 ), the 2021 monsoon was one of the wetter on record across the Southwest US (here defined as Arizona, New Mexico, and far west Texas Figure 1). Areal extent of the “Southwest” commonly referenced in this analysis. Note: click on images for full-resolution versions.įig 1. Review of the 2021 Monsoon Across the Southwest U.S.Ĭompiled by NOAA/NWS Phoenix, AZ.
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