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Status of Spring
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.
How does this spring compare to "normal"?
May 30, 2023
Spring has arrived in all but the highest elevation parts of the country. Spring arrived several days to weeks earlier than average (the period of 1991-2020) in much of the Southeast, lower Midwest, mid-Atlantic, Northeast, and parts of the upper Midwest. Spring was several days to weeks later thank average across much of the West, lower Midwest, and northern Great Plains.
Spring bloom was days to weeks early in the Southeast and mid-Atlantic, and days to over a week late in much of the West.
How often do we see a spring this early or late?
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.
Parts of the Southeast, lower Midwest, mid-Atlantic, and New York City area saw either the earliest spring leaf on record or a spring that only occurs once every 40 years (dark green). Parts of the West saw a spring that only occurs this late once every 40 years (purple).
Spring bloom is latest on record across parts of the Southwest including California and Arizona, and earliest on record in parts of the upper Southeast including Tennessee, Georgia, South Carolina, and North Carolina.
When did spring arrive at locations across the country?
The First Leaf Index map at right shows locations that have reached the requirements for the Spring Leaf Index model so far this year.
The First Bloom Index map at right shows locations that have reached the requirements for the First Bloom Index model.
Learn more about the Extended Spring Indices and the data products available.
USA-NPN also produces a suite of Accumulated Growing Degree Day map products.
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 (1991-2020) day of year it was met. Long-term averages were calculated using PRISM Climate Data daily minimum/maximum temperature data (Oregon State University).
In 2022, we updated the period of comparison for our spring leaf out and bloom anomaly maps to the new climate normal of 1991-2020, following standards set by NOAA and the World Meteorological Organization. Climate Central offers more detail about how seasonal average temperatures have shifted from the prior to the current climate normal period.
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 the previous decades. We determine how often a spring was at least this early (or late) by taking the number of years in the record divided by the count of years that were earlier (or later) than the current year.
Learn more about these spring maps in our AGDD and Spring Indices info sheet.
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