Periodically over the last fifteen years I've posted here updates about Tucson's Winter Rain totals. All of those posts can be viewed together under the heading Winter Rain on the right. Please see those earlier posts for additional discussion about the format and content of the scatterplot below. Here I'll just reiterate my contrarian definition of winter in Tucson as being the five months November through March, instead of the conventional meteorological three month winter of December through February. Either way this past winter in Tucson was very dry. The most significant precipitation events during the five-month winter came in early November and mid-March, and those brief "shoulder month" storms were very wintry, with cold rain in Tucson followed by panoramic views of mountain snow cover. The Tucson Airport recorded a total of only 0.86 inches of precipitation for the five months, with only a quarter inch of that from the middle three months.
The last time a five-month Tucson winter was this dry was fourteen years ago, during the moderately strong La Niña winter of 2010-2011 (unlabeled black square near the lower left corner of the plot). Over the last seven years we have had four La Niña winters (unlabeled 2020-2021 and 2021-2022, along with 2022-2023 and 2024-2025, labeled 23 and 25), one strong El Niño winter (2023-2024), one weak El Niño winter (2018-2019) and one winter that straddled the threshold between neutral and El Niño (2019-2020).
This time last year, as the strong El Niño was winding down, models were predicting continued rapid cooling in the critical 3.4 area of the equatorial Pacific, heading toward a moderate La Niña by winter, something like what happened in 2010. But that large swing did not happen in 2024. Instead, ocean surface temperature anomalies in the 3.4 area stalled in the neutral zone for months. Finally in December 2024 the La Niña threshold was barely crossed. (See the ONI section of the CPC's weekly ENSO update). Now in late March the 3.4 anomaly has already crossed back into the neutral zone. Nevertheless, total rainfall in Tucson for the 2024-2025 winter was near the bottom of the historical range for a weak La Niña (over a period of 76 years). For what it's worth, model predictions into the beginning of next winter are keeping the ONI in the neutral zone, drifting back toward the cold side of that zone.
The next post here will be about heat, and not just in Tucson. But that will wait until summer heat is closer, probably around mid-May.
