In Australia, a 15-degree day can be a little chilly, but have you ever wondered why it feels colder in winter compared to the same temperature in spring?
The simple answer comes down how long the day is. A longer day in spring allows more time for the air to heat up. But that doesn’t really explain things when the maximum temperature is the same.
Take these two days in Melbourne for example. Plotted below is the temperature on 15th July and 16th November, both from this year. The maximum and minimum temperatures were both very similar on these days, ranging from 7°C to 15°C.
Image: Temperature on 15th July (blue) and 16th November (orange). Note that the data has been shifted to account for daylight savings
Despite the July maximum being slightly warmer than the November top, the warmer day overall is the November day. Looking at the daily average temperature, 15th July averaged 11.1°C, while the 16th November averaged 11.8°C.
During the middle of the day between about 10am and 4pm, the temperatures were largely the same (excluding the two dips in the late morning in November, these were showers that passed over).
When looking at the morning and late afternoon temperatures, November is clearly warmer. This is when the benefit of an earlier sunrise and later sunset become apparent. On these days, the sun rose 2.5 hours earlier and set 1.5 hours later in November. Even on cloudy days, an extra 4 hours of daylight still help to raise the temperature from the minimum to the maximum much faster than in winter.
The final piece of the puzzle is how high the sun is in the sky. Anyone from southern Australia can attest to how much lower in the sky the sun is during winter when compared to the other seasons. The comparison between these two months is rather stark. At noon the July sun is about 31° from the horizon, while in November its closer to 71°, illustrated below.
Image: Diagram showing the sun angles in July vs November
That steep angle allows for more light to filter through the clouds during spring and summer, meaning faster warming even on completely overcast days.
So, it’s not just the longer days but also the suns angle why spring and summer days feel warmer than their winter counterparts, even if the maximum temperature is the same!
DTN APAC provides temperature forecasts all around Australia up to 14 days in advance through its Opticast forecasting system. To find out more, please email us at apac.sales@dtn.com.
