About the Freeze Date Tool:

Description:

The Freeze Date Tool is a product created by the Midwestern Regional Climate Center (MRCC) in collaboration with the USDA Midwest Climate Hub to provide information about the climatology of freezing temperature dates across the north-central and northeastern United States. This tool can be used to answer questions such as:

  • On average, what day of the year does this county experience its first fall 32 °F freeze?
  • What would be considered an early last spring 28 °F freeze for this county?
  • When did the record latest first fall 32 °F freeze occur for this county?
  • How have the dates of the last spring 30 °F freeze changed over time across the region?
  • Has the growing season for this county gotten statistically significantly longer over time?

Definitions:

  • Freeze Date: A freeze date is defined as any date in which the observed minimum temperature reached a specified freezing temperature threshold.
    • Earliest: The earliest date on record where the freezing temperature threshold was reached.
    • Early: Statistically, "early" is defined as the 10th percentile of all freeze dates on record for that location. Stated more simply, only 10% of all freeze dates occurred earlier than the "early" freeze date.
    • Average: The statistical mean of all freeze dates on record for this location.
    • Late: Statistically, "late" is defined as the 90th percentile of all freeze dates on record for that location. Stated more simply, only 10% of all freeze dates occurred later than the "late" freeze date.
    • Latest: The latest date on record where the freezing temperature threshold was reached.
  • First Fall Freeze: The first date during the fall when a given freeze threshold was met. This date does not have to occur during the fall season. Rather, it describes the first time after a prolonged period of non-freezing temperatures that the minimum temperature reached the specified freeze temperature threshold.
  • Last Spring Freeze: The last date during the spring when a given freeze threshold was met. This date does not have to occur during the spring season. Rather, it describes the last time before a prolonged period of non-freezing temperatures that the minimum temperature reached the specified freeze temperature threshold.
  • Growing Season: The consecutive period of time (number of days) between the last spring freeze and the first fall freeze in a given year.
    • Shortest: The shortest length of a growing season on record.
    • Short: Statistically, "short" is defined as the 10th percentile of all growing season lengths on record for that location. Stated more simply, only 10% of all growing seasons had shorter growing season lengths than the "short" growing season.
    • Average: The statistical mean of all growing season lengths on record for this location.
    • Long: Statistically, "long" is defined as the 90th percentile of all growing season lengths on record for that location. Stated more simply, only 10% of all growing seasons had longer growing season lengths than the "long" growing season.
    • Longest: The longest length of a growing season on record.

All trends in the Freeze Date Tool use a simple linear regression to define the trend in the data over time. The magnitude of the trend is the slope of the linear regression function. The statistical significance of the trend is based on whether the slope of the linear regression is statistically-significantly non-zero (based on a 95% confidence interval). Because trends in climatological data are not necessarily linear, these trends should be interpreted with caution.

Data:

The Freeze Date Tool uses the Northeast Regional Climate Center's interpolated dataset from the Applied Climate Information System (ACIS) to obtain spatially continuous daily surface minimum temperature observations. These observations were spatially aggregated by taking the average of all daily surface minimum temperature observations within each county to obtain a single minimum temperature observation for each county. Please be aware that local freeze conditions may differ from the county averages used in this tool due to influences from topography and data availability.

The growing season is defined by the longest period of continuous above-freezing temperatures in a given year. Similarly, the last spring freeze and first fall freeze are the freezes that occur immediately preceding or following that same period of continuous above-freezing temperatures respectively.