/ Modified mar 30, 2023 4:02 p.m.

Did spring come late this year?

The Southwest has experienced cooler and wetter conditions.

Locals may have noticed cooler temperatures in recent weeks as Tucson tip toes into the official threshold of spring. This past winter season, there’s been a weather pattern that has been dominated by cooler and wetter conditions across the western United States, and drier and warmer conditions across the east. “That’s been pretty persistent for December into early March,” said Michael Crimmins, climate science professor at the University of Arizona’s department of environmental science.

The persistent pattern has led to cooler than average conditions and the accumulation of temperature that climate scientists observe, to see when spring will spring. This year it was later than average.

“The thing we look at in weather and climate is the position of the jet stream,” Crimmins said. The jet stream is a fast and narrow current of air that flows from the west to east and encircles the world. North of the jet stream is cooler air and south of it has warmer air. It also dictates where storms go.

“There’s been a dip in the jet stream, what we call a trough across the western US, so the jet stream has been further south and that has pushed up further north than usual in the eastern US,” Crimmins said.

This phenomenon links up with the rainfall in California and the epic snowfall through the Colorado Rockies, down to the Southwest.

Theresa Crimmins, director of the USA National Phenology Network (USA-NPN) and professor of the UA’s school of Natural Resources and Environment says that wetter conditions that began in October may have contributed to the ongoing super bloom. “We don’t have much of a biological rest here in the winter,” she said. “Things keep photosynthesizing.” Photosynthesis is the process in which plants capture sunlight, water and carbon dioxide and convert it into chemical energy. “What we really need to see good wildflowers in the spring is a decent triggering rainfall in October, and then ideally sustained moisture throughout the rest of the fall, winter and into spring,” Theresa Crimmins said.

The USA-NPN is national in scope but based at the University of Arizona. “What our aims are to do is to keep track of when seasonal events occur in plants and animals,” Theresa Crimmins said. When species of plants put on their leaves, when birds migrate or flower, which locals may have witnessed in recent weeks. The reason why we care about these events, Crimmins said, is because those events are responsive to local, environmental conditions such as temperature and moisture. “They are a really good indicator of how conditions are playing out in a particular season,” she said.

One of the main ways the USA-NPN collects this information is through their program, Nature’s Notebook which invites volunteer and professional observers across the country to regularly report what they are seeing happening in plants and animals in their yards. The information is managed in a database that is then used by scientists to better understand what the conditions are that seem to trigger particular events to occur and how those things are changing as our climate is changing. The information is also used for immediate decision making, Theresa Crimmins said. “Better understanding when to undertake management action to control invasive species or to anticipate wildfire risk or to understand weather tourism events,” she said. Such as the statewide super bloom or national cherry blossom festivals.

“We look at how climate has changed and consequently how the timing of things like leaf out or flowering is being impacted in various locations,” Theresa Crimmins said about her husband and colleague, Michael Crimmins, who is loosely affiliated with the organization.

As the days grow longer and the sun gets higher, warmer temperatures will quickly follow. “We should see pretty typical conditions over the next month or two,” Michael Crimmins said.

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