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"?

June 8, 2020

Spring leaf out has arrived across much of the country, 3-4 weeks earlier than a long-term average (1981-2010) in parts of the West, Southeast, and Northeast and up to 3 weeks late in parts of the northern Great Plains, upper Midwest, and upper Northeast.

Spring bloom has also arrived across much of the country and follows a similar pattern of earlier spring bloom across the Southeast and later spring bloom in the northern Great Plains, Midwest, as well as parts of the Northeast.

Download static maps of Spring Leaf Out and Spring Bloom.

Download the maps in KML/KMZ and other formats via our Geoserver Request Builder Tool.

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 and Northwest, this year's spring leaf out is the earliest in the 39-year record (dark green). In parts of Nevada, Wyoming, and Montana, this year's spring is the latest on record.

In parts of the Midwest and Northeast, this year's spring bloom is the latest on record.

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.







Access Phenology Maps

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 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.

Re-use of Maps and Data



Content, maps, and data accessible via usanpn.org are openly and universally available to all users. USA-NPN is not responsible for the content or the use of the data. Content may be re-used and modified with appropriate attribution (e.g., "source: USA National Phenology Network, www.usanpn.org"). See our complete Content Policy and Data Use Policy.