Web maps can warn of frosts on the way
From the August 2011 edition of Agriculture Today.
Has this winter taken some of us back to the sounds of childhood as the frost crunches underfoot?
During childhood winters I was often woken by mum’s animated commentary on the lack of water flow to the kitchen, thanks to frozen exposed pipe work hampering her morning breakfast and school lunch preparations.
Typical active frost mitigation – usually at some ungodly hour of the night – requires human or mechanical intervention, whether it’s inside the house or out in the paddock.
Now you can get advanced notice that frost could be coming, so you can at least schedule some sleep and plan a tactical response.
The Bureau of Meteorology’s Water Land web portal now offers free “Frost Potential” maps for NSW, updated each day at 10am, showing a forecast for the next 48 hours.
Coloured dots on the maps indicate the lowest expected temperature at the standard Stephenson screen height of 1.2 metres; typically ground temperatures may be up to 2.2°C lower.
Strategies to protect plants from frost damage can be either passive or active.
Passive protection strategies involve appropriate site and varietal selection, sowing or planting at an appropriate time and soil surface preparation.
Active protection replaces radiant energy lost to the atmosphere by methods such as irrigation, heaters and wind machines.
Apart from impeding farm water supplies, frost can also damage plant tissues during critical stages of development, typically germination and flowering.
Green plants contain mostly water.
On freezing the water expands and, if severe enough, can rupture the cell walls of the plant tissue.
Once melted, the frozen water drains away, giving a burnt appearance on affected leaf surfaces.
Radiation or white frost forms when a surface cools to zero degrees Celsius through loss of infrared radiation to the atmosphere, and the adjacent air gets below dew point.
This most commonly occurs under clear night skies with little or no wind.
Black frosts occur when surface temperatures reach below freezing point, the cooler air temperature limits the water holding capacity of surrounding air, consequently frost coatings are often thinner and less visible.
To access free frost potential maps follow the link to www.bom.gov.au/jsp/watl/weather/frost.jsp - and you can find additional information on chill duration by clicking a site location on the map.