Rochester’s last frost date typically comes in May
As days are getting warmer and flowers are beginning to bloom, one question on the mind of gardeners around the area has been: When will the last frost happen in Rochester?
The answer varies year-to-year with the weather, though May is a not uncommon time of year to see the final frost of the preceding winter.
Frost is the formation of thin ice crystals on the ground and over surfaces, according to the National Weather Service. It’s tied closely to radiational cooling, which is the cooling of the earth’s surface at night. As a result, it frequently occurs when thermometer level temperatures – typically three to four feet off the ground – are in the mid-30s, not even below freezing.
This typically occurs when cold air sinks to ground level on clear, calm nights.
How does frost form?
Frost can be formed by either deposition or freezing. Depositional frost, which arranges itself in branching patterns, occurs when the dewpoint is below freezing. Frozen frost, or frozen dew, occurs when dew forms at above freezing temperatures, but dropping temperatures overnight cause those dew droplets to freeze.
When is last frost in Rochester?
The National Weather Service in Buffalo doesn’t track the first or last frost of the year, so it can be hard to ensure exactly when it occurs. The Weather Service does track air temperature data, however, which can be useful for determining when it may have been cold enough for frost.
For Rochester, the mean date of the last temperature of 32 degrees is April 29, based on data from 1872 to present. The earliest date for the last day at 32 degrees or below in Rochester history was April 8 in 2017 and the latest final freeze was May 29 in 1889.
Last year, the final day of below freezing temperatures was on May 18.
As previously mentioned, however, frost doesn’t just occur at freezing temperatures as recorded via official weather measurements, which is taken in an instrument shelter four to five feet above the ground.
As a result, temperatures as warm as 36 degrees at thermometer level can produce ground-level frost. So what is the date range for temperatures as low as 36 degrees?
For Rochester, the mean date of the last temperature of 36 degrees is May 12, based on data from 1872 to present. The earliest date for the last day of 36 degrees is April 9 in 1955 and the latest final day with temperatures below 36 degrees was June 11 in 1972.