Saturday, February 27, 2021
Home Weather Here comes the rain again…

Here comes the rain again…

By: Natalie Harvey

British persons are nicely famend for his or her obsession for speaking about the climate. This is partly as a result of it’s a “safe” subject for dialog and partly as a result of it’s actually fascinating! This is very true in the UK the place our climate is so diversified.

Since my son began faculty in 2017, I’ve discovered myself having quite a few conversations about the climate and the accuracy of climate forecasts at drop off and pick-up occasions. These conversations are sometimes essential of the forecasts, which I do my greatest to dispel in the brief time I’ve. The UK Met Office four-day forecasts at the moment are as correct as our one-day forecast was 30 years in the past, with over 90% of forecasts of subsequent day temperature correct to inside 2 °C [1]. Bauer et al. (2015) [2] give an in depth description of the revolution in numerical climate prediction over the final 40 years.

Another query I hear loads is “why does it always rain at pick up time?” Now, I reside a good method from my son’s faculty, so my stroll is longer than most and I don’t actually really feel prefer it rains that a lot. However, final Wednesday, at 3pm, it did! I obtained very soggy. It made me take into consideration the query once more as it’s one thing that we will check utilizing rainfall knowledge from the Atmospheric Observatory based mostly on the University’s Whiteknights campus [3] which is a brief stroll from my son’s faculty.

Figure 1 – Screenshot from the Met Office climate forecasting app displaying rain forecast at 3pm.

In Figure 2a the bars present the fraction of time it rains for rain aggregated over two-hour home windows from the final 5 years (2015-2019). Each two-hour window is cut up into five-minute chunks and every five-minute chunk is counted if at the least 0.2mm of rain is recorded. The black bars point out all days, teal bars point out summer time days (June, July, August) and light-weight blue bars point out winter days (December, January, February).

Overall, as I believed, it doesn’t rain a lot per 2-hour window, with every 5-minute chunk being categorized as raining simply as soon as a month on common. In common, the fraction of time it rains does enhance all through the day, with the sign strongest in the summer time months. This is most probably associated to the diurnal cycle of convection over land in the summer time which brings heavy rain showers. The impact will not be very giant although, with rainfall throughout the afternoon round 20% extra widespread than between 8 and 10am, faculty drop off time.

Figure 2 – (a) Fraction of time rain happens all through the day for 2015-2019 in two-hour home windows. Black bars point out all days, teal bars point out summer time days and light-weight blue bars point out winter days. (b) Mean rainfall per 5-minute window all through the day when rain is recorded.

Figure 2b exhibits the imply rainfall (bars) for the occasions that it’s raining in the identical 2-hour home windows. The gray bars point out the 5th and 95th percentile of the noticed rain at these occasions. These are included to offer a sign of the variability of rainfall and present the extremely skewed distribution of rainfall charges. The imply rainfall within reason uniform all through the day with a better worth between 2 and 4pm in the summer time months, once more that is prone to be associated to convective occasions. During that point window there are some giant rainfall occasions, so it’s potential that my fellow dad and mom at the faculty gate reminiscences are skewed by a number of occasions after they (and their kids) obtained very soggy or perhaps it’s the rain affecting their temper [4]. This is barely a really small-scale examine utilizing a small quantity of rainfall observations, but it surely appears to me that it doesn’t all the time rain at college decide up time however perhaps it’s best to have your umbrella prepared simply in case, particularly in the summer time.

[1] Met Office, 2020 Global accuracy at an area degree. Accessed 4 December 2020,

[2] Bauer, P., Thorpe, A. & Brunet, G., 2015: The quiet revolution of numerical climate prediction. Nature 525, 47–55.

[3]Reading University Atmospheric Observatory, 2018: Atmospheric Observatory. Accessed 4 December 2020,

[4] Flook,J 2019: Can’t stand the rain? How moist climate impacts human behaviour. Accessed 4 December 2020,

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