Climate Viticulture Newsletter - 2021 October

Southern Arizona and extreme southwestern New Mexico were the primary areas that measured monthly average temperatures within 2 °F of the 1991-2020 normal (light green and yellow areas on map). Apart from this part of the region, temperatures were 2 to 6 °F warmer than normal (orange and dark orange areas on map). For reference, monthly temperatures in September last year were 2 to 4 °F warmer than the 1981-2010 normal for the western two-thirds of Arizona and within 2 °F of normal for the rest of the region.

Generally speaking, precipitation totals for the past month were near (yellow and light green areas on map) to above (dark green, blue, and purple areas on map) the 1991-2020 normal for much of Arizona and extreme western New Mexico. Amounts were below 75 % of normal for the rest of the region (orange and red areas on map). Precipitation during September 2020 was below 50 % of the 1981-2010 normal for almost all of Arizona and much of New Mexico.

With the North American monsoon now in the rear-view mirror and harvest wrapped up for many, comparison of the ripening periods in 2021 and 2020 probably couldn’t offer more contrast. Record hot and dry conditions last year brought questions of water stress and heat damage to vines and fruit to mind. This year, relatively cooler and wetter conditions more likely led to concerns of increased pest and disease pressures along with additional pauses in vineyard access. Field notes from these two vintages will be valuable for future ones as a more variable and extreme summer climate is anticipated for the Southwest in the coming years.

View more NOAA ACIS climate maps

View more-detailed regional maps and station summaries of monsoon rainfall

Temperatures for the coming month for almost all of the region have equal chances for being below, near, or above the 1991-2020 normal (white area on map). Only extreme northeastern New Mexico is showing that such conditions are leaning in any particular direction, with a slight increase in chances for above-normal temperatures (light orange area on map). As a comparison, monthly temperatures in October last year were 2 to 6 °F warmer than the 1981-2010 normal for much of Arizona and many areas in the western two-thirds of New Mexico.

A lack of conditions leaning in any particular direction also is the case for precipitation across Arizona and the western third of New Mexico, with equal chances for below-, near-, or above-normal totals for this month (white area on map). There is a slight increase in chances for totals to be above the 1991-2020 normal for the eastern two-thirds of New Mexico (light aqua area on map). Precipitation during October 2020 was below 75 % of the 1981-2010 normal for almost all of the region.

For the previous two growing seasons, October brought about the first fall freeze. Depending on vine phenology and vineyard location, the timing could have been prior to plants reaching cold-hardiness levels – through, for example, tissue dehydration – needed to withstand such temperatures. Resulting damages to vascular tissue look to have been the likely reason why vines showed no or slow growth during the following springs. Some of the surprise from these events may stem from the fact that it had been about 10 years since such a relatively early first fall freeze had last occurred in some locations.

Read more about the October 2021 temperature and precipitation outlook

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.

October also brings about our last look at the amount of time spent below 65 °F and above 95 °F during the ripening period. September didn’t yield any surprises in this context this year, at least at the AZMet Willcox Bench station in the south-central Willcox AVA, as an increase in hours below 65 °F appears during the month (blue and purple bars in top graph). Although temperatures above 95 °F have occurred occasionally in September over the previous five growing seasons (yellow bars in bottom five graphs), they were absent in 2021. For the overall ripening period, temperature conditions in 2021 look most similar to those in 2017 and suggest that fruit quality and composition variables like Brix, titratable acidity, and pH from these two vintages may be similar, as well.

It may be worth mentioning again that comparison of the ripening periods in 2021 and 2020 probably couldn’t offer more contrast (top two graphs). The switch from record hot and dry conditions last year to relatively cooler and wetter ones this year suggests more notable changes in fruit quality and composition with less heat-tolerant varieties than with more tolerant ones. Notes from these two vintages also will be valuable for future ones when it comes to evaluating variety viability for a more variable and extreme summer climate.