Climate Viticulture Newsletter - 2024 September

Monthly average temperatures were 1 to 4 °F above the 1991-2020 normal for almost all of Arizona (light orange, orange, and dark orange areas on map), including almost all of the three Arizona AVAs. A few areas along the western border as well as northern and southern tiers were near normal (white areas on map). For reference, monthly average temperatures in August last year were 1 to 4 °F above normal for much of southern, central, and eastern Arizona. Much of the rest of the state recorded near-normal temperatures except for extreme northwestern Arizona, where temperatures were 1 to 3 °F below normal for several locations.

Area-average maximum and minimum temperatures during August 2024 were 88.7 and 63.2 °F for the Sonoita AVA, 97.2 and 67.8 °F for the Verde Valley AVA, and 92.8 and 64.9 °F for the Willcox AVA. Respective August normals are 86.3 and 61.7 °F, 95.7 and 65.2 °F, and 91.2 and 63.8 °F.

Temperature last month ranged between 99.3 and 57.7 °F at the AZMet Bonita station and between 101.5 and 57.6 °F at the AZMet Willcox Bench station.

Monthly precipitation totals were less than 75 % of normal for most of the southern, central, and western parts of the state (light yellow, yellow, and dark yellow areas on map), including most of the three Arizona AVAs. Parts of southeastern and much of north-central and northeastern Arizona recorded near-normal amounts (white areas on map). A few locations in extreme north-central and northeastern Arizona measured totals above 125 % of normal (various aqua and blue areas on map). Precipitation during August 2023 was less than 75 % of normal for many parts of southern and central Arizona. Much of the rest of the state measured a mix of near-normal and between 125 and 200 % above-normal amounts.

Area-average total precipitation in August 2024 was 2.60 inches for the Sonoita AVA, 1.79 inches for the Verde Valley AVA, and 2.14 inches for the Willcox AVA. Respective August normals are 3.95, 2.40, and 2.80 inches.

Total precipitation last month was 0.82 and 0.78 inches at the AZMet Bonita and Willcox Bench stations, respectively.

Dig further into daily weather summaries for the AZMet Bonita and Willcox Bench stations in the Willcox AVA

View seasonal summaries of monsoon rainfall through regional maps and weather station statistics

Learn more about PRISM climate data

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Temperatures over the course of this month have a moderate increase in chances for being above the 1991-2020 normal across all but the extreme southwestern corner of the state (dark orange and red areas on map). For the extreme southwestern corner, there is slight increase in chances for above-normal temperatures (orange area on map). Monthly average temperatures in September last year were 1 to 3 °F below normal in northwestern Arizona, near normal for much of north-central and southwestern Arizona, and 1 to 4 °F above normal for many locations in central, east-central, and southeastern Arizona.

Area-average maximum and minimum temperatures during September 2023 were 89.1 and 59.4 °F for the Sonoita AVA, 90.9 and 58.0 °F for the Verde Valley AVA, and 91.0 and 57.9 °F for the Willcox AVA. Respective September normals are 83.9 and 57.0 °F, 90.4 and 58.4 °F, and 87.8 and 58.3 °F.

Temperature in September last year ranged between 99.7 and 50.2 °F at the AZMet Bonita station and between 102.0 and 49.5 °F at the AZMet Willcox Bench station.

Precipitation totals for this month have a slight increase in chances for being below normal across the eastern two-thirds of the state (light tan area on map). For the western one-third, there are equal chances for below-, near-, or above-normal totals (white area on map). Precipitation during September 2023 was more than 150 % of normal for extreme western Arizona, and a mix of near-normal totals and totals between 25 and 75 % of normal for areas elsewhere in the state.

Area-average precipitation totals in September 2023 were 0.60 inches for the Sonoita AVA, 1.18 inches for the Verde Valley AVA, and 0.76 inches for the Willcox AVA. Respective September normals are 1.95, 1.53, and 1.40 inches.

Total precipitation in September last year was 0.17 and 0.61 inches at the AZMet Bonita and Willcox Bench stations, respectively.

To stay informed of long-range temperature and precipitation possibilities beyond the coverage of a standard weather forecast, check in, too, with the six-to-ten-day outlook and eight-to-fourteen-day outlook issued daily by NOAA’s Climate Prediction Center.

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Based on data from the AZMet Willcox Bench station in the Willcox AVA, conditions in August led to one day with average hourly temperatures over 100 °F (dark red bars on top graph), for a total of two hours. The highest average hourly temperature was 101.5 °F on August 16. Temperatures between 95 and 100 °F occurred on 12 days (light red bars on top graph), for a total of 37 hours. This is less heat exposure than in August 2023, when there were three days and 13 hours with average hourly temperatures above 100 °F, and 13 days and 45 hours between 95 and 100 °F (dark and light red bars in second-from-top graph).

There were 12 days last month with average hourly temperatures between 60 and 65 °F (light blue bars on top graph), for a total of 29 hours. Temperatures less than 60 °F (dark blue bars on top graph) occurred on two days, for a total of four hours. The lowest average hourly temperature was 57.6 °F on August 29. This is less exposure to temperatures below 65 °F than in August 2023, when there were 11 days and 38 hours with average hourly temperatures between 60 and 65 °F, and two days and two hours less than 60 °F (light and dark blue bars in second-from-top graph).

Much like during July, the increase in humidity due to the monsoon during August is a typical feature that keeps daily minimum temperatures higher, as less heat radiates away from the surface and into the upper levels of the atmosphere during the night. Now that we’re into September, monsoon moisture moves out of the region and days become shorter and nights longer. Based on data from the previous four growing seasons, one might expect little to no exposure to temperatures over 95 °F and an increase of exposure to temperatures below 65 °F for varieties still ripening, at least near this location.

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