Advance warning of cold conditions
Parts of New Zealand have experienced near record low air temperatures in the past month. For example, Tara Hills, near Omarama, recorded a minimum temperature of -14 °C on 14 June, the lowest overnight temperature since records began in 1950. The cold conditions disrupted electricity and water supplies, and caused more problems than usual for winter feeding programmes for livestock.
An example of the extreme conditions is shown in the figure below, which gives the maximum snow depths at Ashburton. The snowfall of 12 June was measured at 38 cm, the deepest on record.
The adjacent figures illustrate the likelihood of low temperatures during July. The data are derived from international models downscaled to New Zealand locations, and weather observations at each location during the past 30 years. These forecasts, accessible on Climate Explorer, are updated on a daily basis for over 100 climate measuring sites around New Zealand.
The forecasts show both the expected minimum temperature and the probability each day of temperatures dropping below 0 °C. In each case, the red line shows the climatological (or historical average) values. The dark line gives the mean model output, while the shaded band is a measure of the agreement between models – when the band is narrow, the models agree reasonably well, and higher confidence can be placed on the output.
The forecasts shown in these figures indicate that overnight temperatures at Tara Hills are likely to be lower than average on most nights during the two weeks. One exception, on 9 July, predicts the minimum temperature at almost +2 °C, but there is still a 20% chance that it will be below zero.
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