First Frost - late but not a record

The chances of first frosts occurring before a particular date can be summarised in a graph as shown above.

04th Jun 2024

The first frost of the year was late this year, coming well into the middle of May. Was this a record? Unfortunately, the BoM weather stations don’t record frosts – but they do record the daily minimum temperature. We have 43 years of daily minimum temperatures from the Guyra Hospital weather station. Put this together with the commonly used frost threshold of 3degC and we can estimate the date of the first frost each year since records began in 1981.
The earliest date in the year for the first frost was 2nd March, both in 1993 and in 2003. The latest date for the first frost was 22nd May in 1989, which tells us that this year’s first frost date did not set any records.
What about the local wisdom that we usually get a frost by Anzac Day each year? The daily minimum temperature data with the 3degC frost threshold says that for just under 70% of years since 1981, the first frost occurred before Anzac Day. That suggests the local wisdom is pretty close to the mark.
The chances of first frosts occurring before a particular date can be summarised in a graph as shown above.
The graph shows, for example, that there is a 51% chance of the first frost occurring before 15-April. By 15-May, it’s a 98% chance – almost a certainty – that the first frost has occurred sometime previous to this date.
Of course, this is all based on historical averages for one weather station. There will be local exceptions around the district. There are sure to be readers who have seen a patch of frost on the car roof in January or February.
Ian Reeve
Black Mountain

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First Frost - late but not a record

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