Predicting Frosts At Home
Hello friends,
This week I thought I'd share with you how I predict frosts at home using weather resources for New Zealand which are available on the internet.
More often that not, thanks to us being in an inland valley, the weather forecast for Dunedin doesn't apply to Mosgiel, and yet the Mosgiel regional forecast is meant for areas further inland than us. Over the years I've used a bunch of different weather forecasts and also my gut feeling to know when to put frost cloths on my citrus and other frost sensitive plants.
The usual frost set up for us goes something like this: In autumn, winter, and spring, a southerly front/storm comes in from the south west from out over the southern Pacific Ocean. It brings with it either rain/snow, wind, and cold temperatures. After the southerly blows through, the wind dies down, and the sky clears, usually mid afternoon/early evening, then it cools overnight and then we get a frost (or a number of frosts) in the days following. Our frosts can get down to around -6˚C in the middle of winter, but in autumn and spring they can hover just around 0˚C.
Because this set up is pretty predictable, I've come to get a gut feeling about frosts in our local inland valley. So in the late afternoon after a southerly storm when I tend to get a feeling that it'll freeze, that's when I turn to my top three weather forecasting methods.
First up I go to Metservice's website:
On the today forecast in the Dunedin Regional Forecast the -4˚C predicted isn't for "today" but rather than the next morning, on Monday. It's all a bit confusing but it's the best way that it works for me, and the temperature is approximately right. I then look at the "Monday" forecast to see if it says calm winds and frost. In autumn and spring, this forecast tends to be incorrect in predicting frosts.
The second forecast I check is Weather Watch's frost risk forecast. The blue and purple sections on the map show the medium and high risks areas for frosts for the coming days. You can also look at their minimum temperature map to see the temperature bands.
From my observations, Weather Watch's frost predictions are the most accurate. Basically if frost risk map shows blue (or just on the edge of blue), we will get a frost. I trust this frost predictor rather then the other two that I use.
And finally the last frost predictor I use is Rural Weather's forecasts. Just go to rural weather, enter which area of the country you are in, and it'll show you rain, wind, temperatures, fog/cloud, and frost predictions for the coming days.
Their frost trend graph is still in beta, but it is good for predicting frosts. The dark red sections means most likely to have a frost, and the pink is a slight risk of frost. It also shows you what times the frosts might occur. This is my second favorite frost forecast.
With all three of these forecasts in mind, and with my gut feeling telling me there will be a frost, it's time to pull out my frost cloth. My citrus plants and my wasabi plant are sprayed with liquid frost cloth, which protects them down to around -3˚C (depending on how much rain there has been recently). And I also put frost cloth on top of them as double protection, because sometimes, if the plant is still actively growing, the tips of the leaves and flowers may not have been sprayed by the liquid frost cloth. This method works down to around -6˚C, which is usually the coldest frosts we get. If the frost is predicted to be lower than -5˚C, then I just chuck more and more frost cloth on the plants until they are cocooned.
In this case, we did indeed get a frost, which got down to -2.4˚C, which is warmer than the predicted -4˚C by Metservice, but colder than the predicted temperature for Dunedin. It was well and truly worth spending the time putting the frost cloth on my beloved citrus and wasabi plants overnight.
And so, as you can see that my frost prediction method for home is a good setup, and it works for me most of the time. It's much more tricky to predict frosts in late spring though, and we are now getting frosts up until the first week of November, which is a huge risk for my newly emerged dahlia plants. And considering that I have over 50 dahlia plants in my garden, I do not have enough frost cloth and buckets to protect all my plants that late in spring. And that's when I raid the linen cupboard, and use all my spare sheets and blankets as frost protection. As climate change continues to evolve in the coming years, I think our late spring frosts will only get worse.
Have a wonderful day
Julie-Ann
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