It had this to say of 24 February: “This is one of the feast days of St. Matthias, the apostle who was chosen to replace Judas Iscariot after the death of Christ. (In 1969, his feast day was moved to 14 May in the Roman Catholic Church.) According to various weather proverbs, a frost on St. Matthias’s Day will last for anything from a week to two months.”
I can find two versions of the weather which can be forecast according to what it does on St. Matthias Day - and we are, hopefully, referring to the traditional February celebration of this saint’s life and not the revised May date. The first is: “If it freezes on St. Matthias'
Day, it will freeze for a month together;” and the second says: “St. Matthias breaks the ice; if he finds none, he will make it.” And, while I believe that every reader will know what is meant by frost, no harm will come of quoting the first entry in the Oxford English Dictionary (OED) under the heading ‘frost’: “A deposit of small white ice crystals formed on the ground or other surfaces when the temperature falls below freezing:.” The OED then gives a number of examples of the noun ‘frost’ as it is used in sentences. The first two are: ‘The lanes were glistening with frost;’ and ‘it is not unusual for buds to be nipped by frost.’
Now two possibly different circumstances are illustrated in these two examples, for the first …‘the lanes were glistening with frost’ … requires the temperature on the ground to be below freezing while the second … ‘it is not unusual for buds to be nipped by frost’ … can occur when the air … but not the ground … temperature falls to less than 0ºC or 32ºF; and it is not uncommon for the ground and air temperatures to be different. This is how the Meteorological Office describes the differing circumstances: “A ground frost refers to the formation of ice on the ground, objects or trees, whose surface have a temperature below the freezing point of water. During situations when the ground cools quicker than the air, a ground frost can occur without an air frost. A grass frost, an unofficial type of ground frost, can occur when other surfaces - such as concrete or road surfaces - don't experience a frost, due to their better ability at holding onto any warmth. It is possible for a grass frost to occur in late spring or even early summer when the risk of more wide-spread frosts has disappeared and is something that gardeners in particular need to be aware of.”
As gardener know, many plants can be damaged or even killed by frost, especially by what we call a ‘hard frost’, which occurs when the temperature falls below -2 °C … 28 °F in old money. What happens is that sap in the stems and foliage of the plants freezes, expanding as it does so … for sap needs a bigger space when it is a solid than it needs when it is a liquid … and bursting the sides of the veins in which it is contained and moves through the plant.
This is exactly the same as happens when domestic water pipes are exposed to temperatures below freezing; the water freezes, expands and bursts the pipe. Neither burst veins nor burst pipes can fulfil their purpose, meaning Trouble with a capital T. Some species of plants can survive a so-called ‘light frost’; and all those plants which lie dormant during the winter months with their veins essentially free of sap are unaffected by most frosts.
Sometimes we get what is termed ‘black frost’ This occurs when the temperature falls so low that even dormant plant tissues may freeze and die, becoming black. And there is ‘black ice’ (not really a frost) which arises when freezing rain hits a surface to form a smooth,transparent ice coating that can be bad news for trees. Jack Frost? B***** frost, more like!