Last Freeze Frost Probability Date
Late Spring and Early Fall Freezes Determine Plant Growing Seasons
Determine the growing season for a specific area, using the Climate Atlas of the U.S. Understand the importance of freeze probability to agriculture and planting times.
Determine Planting Times
Use charts and tables to determine the approximate times for planting seeds. Seed catalogs and seed packet information usually provide planting dates and length of days needed for harvest. Charts provided by National Climatic Data Center provide the average last spring frost and average first fall frost. The USDA Plant Hardiness Zone Map helps farmers and gardeners determine which climates are best for plants. Local extension services and nurseries can provide this information in local areas.
Using the Climate Atlas of the U.S.
The Climate Atlas of the United States is available online for internet users. Consumers can interact with the map, selecting search data for a specific area. Begin by selecting a Geographic Area, either Lower 48 States, Hawaii or Alaska. Then choose an Element Type, such as Temperature, Precipitation, Snow, etc. Finally, choose an Element based on Element Type.
If Temperature is chosen as the Element Type, choose an Element from the list, such as “Date of Last 32 degree F temperature in Spring” or “Length of Freeze-Free Period”.
By viewing these maps, consumers can determine the median growing season for the geographic area identified or the last spring freeze date.
Climate Data in Agriculture
The National Climatic Data Center (NCDC) maintains information and comparisons on all weather and climate data. The commercial agriculture producers in the United States can use historical data and comparisons in determining length of growing seasons.
Cumulative Growing Degree Units are used to predict temperatures required for crops, determining planting times. This table can also be used to calculate the approximate date for harvesting.
Freeze Probability Date
Freeze/frost probability tables are available for nearly 2,000 locations and over 3,000 observation sites in the United States. These tables predict the probability for first and last frost occurrence, using data from August 1 through July 31st.
The freeze and frost tables display the probability of experiencing a certain temperature on each date throughout the year. These tables are calculated by using climate normals for a 30-year period for a given location. Freeze frost probability maps are available from the NCDC.
Freeze Classifications
In the agriculture sector, freezing temperatures have a large impact on plant production with late spring freezes or early fall freezes. Timely freeze and frost warnings by the National Weather Service are important. The freeze classifications for agriculture are as follows:
- Light freeze, between 29 and 32 degrees Fahrenheit, a light freeze has little destructive effects on plants. Only small, young, tender plants will be killed during a light freeze.
- Moderate freeze, between 25 and 28 degrees Fahrenheit, a moderate freeze produces widespread destruction of crops, with damage to blossoms of fruit, and semi-hardy plants
- Severe freeze, below 24 degrees F, a severe freeze will produce heavy damage to most plants, especially if the ground freezes solid, depending on the moisture in soil.
