From the USA Phenology Network:
HOW DOES THIS SPRING COMPARE TO “NORMAL”?
How do you know when spring has begun? Is it the appearance of the first tiny leaves on the trees, or the first crocus plants peeping through the snow? The First Leaf and First Bloom Indices are synthetic measures of these early season events in plants, based on recent temperature conditions. These models allow us to track the progression of spring onset across the country.
February 10, 2020
Spring leaf out has arrived in the Southeast, over three weeks earlier than a long-term average (1981-2010) in some locations. Charlottesville, VA is 24 days early, Knoxville, TN is 20 days early, and Nashville, TN is 18 days early.
Comparison of 2020 spring bloom to average from 1981-2010
Spring leaf out has also arrived in parts of the West. Spring leaf out is on time to 2 days late in San Diego, LA, and San Francisco, CA and 10 days early in Portland, OR and Seattle, WA.
Spring bloom has also arrived in several Southeast states as well as parts of southern CA, NV, and TX. Spring bloom is between 1 day and 2 weeks early.
Check back on this page throughout the spring for updates on when spring arrived and whether spring was early or late for your location.
HOW OFTEN DO WE SEE A SPRING THIS EARLY OR LATE?
In places where spring has sprung, how typical is this year’s spring? Darker colors represent springs that are unusually early or late in the long-term record. Gray indicates an average spring.
In parts of the Southeast, this year’s spring is the earliest in the 39-year record (dark green).
WHEN DID SPRING ARRIVE AT LOCATIONS ACROSS THE COUNTRY?
WHAT IS BEHIND THESE MAPS?
The Extended Spring Indices are mathematical models that predict the “start of spring” (timing of leaf out or bloom for species active in early spring) at a particular location (Schwartz 1997, Schwartz et al. 2006, Schwartz et al. 2013). These models were constructed using historical ground-baesd observations of the timing of first leaf and first bloom in a cloned lilac cultivar (S. x chinensis ‘Red Rothomagensis’) and two cloned honeysuckle cultivars (Lonicera tatarica ‘Arnold Red’ and L. korolkowii ‘Zabelii’). These species were selected because they are among the first woody plants to leaf out and bloom in the springtime and are common across much of the country.
Primary inputs to the model are temperature and weather events, beginning January 1 of each year (Ault et al. 2015). Maps for the current year are generated using temperature products from NOAA National Centers for Environmental Prediction Real-Time Mesoscale Analysis. More information is provided in our Gridded Product Documentation.
To determine how the current spring compares to “normal”, we difference the day of year the leaf out or bloom was reached this year from the long-term average (1981-2010) day of year it was met. Long-term averages were calculated using PRISM Climate Data daily minimum/maximum temperature data (Oregon State University).
To calculate how often we see a spring as early or late as the current spring, we compare the current year’s Spring Index Anomaly value to the anomaly values from 1981-2019. We determine how often a spring was at least this early (or late) by taking the 39 years in the record divided by the count of years that were earlier (or later) than the current year.
From The Washington Post (Jason Samenow):
Thanks to an abnormally warm winter, green leaves are sprouting and flower buds are bursting weeks early across the Southeast this year. Spring has sprung prematurely, and depending on the weather during the next two months, this could have detrimental effects on this vegetation.
In several other recent abnormally mild winters, vegetation has emerged early only to be heavily damaged by brutal invasions of cold in early spring, which has come at a large cost to agriculture.
A similar scenario is setting up for another devastating frost, on the heels of what is known as a “false spring.” The warmth across much of the Lower 48 states has been exceptional, with most locations in the southern and eastern third of the United States seeing one of their top 10 warmest winters on record to date, as if skipping ahead a season.
Theresa Crimmins, director of the network and a research scientist at the University of Arizona, said spring has arrived up to four weeks early in some locations based on several indexes.
“One of the biggest [concerns] is that we’re absolutely not past the risk of frost in a lot of these locations,” she said in an interview. “I’m seeing a lot of reports [of] leaf buds breaking and flowers blooming in a lot of those early-blooming plants. That’s definitely a problem.”
Crimmins explained that trees can bounce back from a frost. “But if flower buds get hit by frost, typically they do not regenerate those buds and then you won’t see fruit,” she said.
In 2017, abnormally warm conditions in February resulted in many species flowering prematurely in the Southeast and Mid-Atlantic. Then a severe frost hit in mid-March. South Carolina lost 85 to 90 percent of its peach crop. In parts of Georgia and North Carolina the blueberry crop was “devastated.” In Washington, about half of the cherry blossoms were damaged.
In 2012 and 2007, there were also so-called false springs. A study published by the American Geophysical Union in 2013 determined the false spring of 2012 was the earliest on record in North America…
Rising winter temperatures from human-caused climate change would seem to increase the likelihood of false springs in the future. However, the rising temperatures would also potentially decrease the intensity or even eliminate the occurrence of killer frosts that might follow.