Phenology is the timing of natural events. For example the timing of when flowers bloom in the spring, when certain birds appear, or when trees change color in the fall. These events are dependent on temperature, so they can potentially be predicted in advance using weather forecasts. Read more about how this is done here.
The phenophase is the specific event being forecast. Such as flowers, leaves, fruit, fall colors, etc. Currently fruit forecasts are only available for four Pacific Northwest plants (black huckleberry, salal, Oregon grape, and hazelnut).
The issue date is the day a forecast was made. The farther away in time a forecast is made the less accurate it will be. For example predicting when flowers will bloom for dogwood is much harder in December than it is in March.
There are tens of thousands of plant species in the U.S. but here we only have some of the most abudant. Listed in the dropdown and on the maps is the common name (ie. Aspen) and the scientific name (ie. Populus tremuloides).
The Predicted date maps show the expected date of when something will happen. The Anomaly map shows how early or late a plant will be compared to the long term average. The Uncertainty maps show the variation around the predicted date and can be read as "plus or minus this many days". Uncertainty will be relatively high for things that are far into the future.