Dark Sky map view.
Dark Sky map view.
We British are known for being preoccupied with the weather but, in our defence, we have rather a lot of it. We don’t have a hot season, a rainy season or a snowy season as such, rather there’s a lot of intermingling of seasonal weather.

This summer (2018) was pretty good for a while. We had reliable 23C+ temperature and sunny days from about mid-June until the end of July, but that’s unusual. It has now (late-August) returned to more typical British summer weather: some warm days, some rainy days and some days when it’s even outright chilly, all interspersed in a random fashion.

Such weather makes it tricky to plan anything — like a barbecue, for example — because it could just as easily be a cold day of constant rain as a day hot enough to need sunscreen.

I am led to believe that weather prediction is horrendously difficult and that a butterfly flapping its wings in Hong Kong could spark a tornado in Wigan. As far as I’m aware they can make fairly safe predictions for the next 24 hours and make a reasonable fist of predicting the next three days, but after that it all gets a little fuzzy and they become reliant on long-term probabilities, historical cues and crystal balls.

All this means I have to be reasonable in any assessment I make of a weather app.

The app in question is Dark Sky Weather, which I chose because it is purportedly one of the more accurate weather apps. I’ve read it’s particularly accurate for American weather but I thought I’d see how it fares with the swirling mess that is British weather.

Dark Sky day view.
Dark Sky day view.

What I did is I used it for a week and each morning at 8AM I looked at the weather it predicted for six hours ahead, 24 hours ahead, three days ahead and seven days ahead. I noted down what the app said about temperature, cloud cover and the percentage chance of rain and then compared that with what the weather actually did.

You can see the data and results I recorded at the end of this post where I’ll talk about accuracy a bit more.

The app itself consists of two main displays: a forecast, which gives you predictions for today and the next seven days, and a weather map, which shows temperature and precipitation in the form of a globe centred on your location. This map can be ‘played’ and it’ll show you how things are likely to develop over the next few days.

You can also set up notifications to remind you take an umbrella or plaster yourself in suncream, depending on what the weather’s going to do on a particular day.

The Interface

Disappointingly, I had some interface problems on my 2016 iPhone 6 and my 2018 iPad Pro. The weather map struggled to display the temperature overlay from time-to-time and occasionally the forecast for a given day would be blank, only clearing itself by shutting down and restarting the app.

Sometimes, going into the app it wouldn’t give me the forecast screen. I had to switch to map and then back to forecast to make it refresh and present some data.

So there are some glitches and Dark Sky need to polish the app a bit more.

To be honest, the forecast screen was all I was really interested in and this attempts to display all you need to know for the next seven days on one page. It works fairly well and I’d rather tab the various displays on one screen, as Dark Sky does, than page off to another screen.

The forecast screen shows predictions for temperature, feels-like temperature, precipitation, wind, wind gust, humidity, dew point, UV index and cloud cover. The daily views for the next seven days provide an at-a-glance symbol to indicate the weather and minimum and maximum temperatures expected.

Dark Sky 7 day forecast.
Dark Sky 7 day forecast.

Accuracy

As you’ll see from the data table below, Dark Sky made a fairly good go of predicting the weather over seven days. One has to be reasonable when it comes to weather predictions and there are always going to be inaccuracies, particularly with the variable UK weather.

As we’d expect, the longer-term predictions (3 days+) are the ones that suffer the most but the predictions for the next 24 hours are pretty good. I’d suggest Dark Sky predicts the weather as well as any other weather app and better than most of them.

I compared this alongside the BBC’s weather predictions and Dark Sky is certainly the more accurate of the two.

Data Table

In the table below, I've record what Dark Sky has predicted for temperature, cloud cover and the chance of rain for various time periods. Then, over the course of the week, I've gone back and filled in the results (last column). I've used my own subjective opinion on whether I thought the prediction was "correct" (green), "partly correct" (orange) or "wrong" (red). I've allowed leeway for a few degrees difference in temperature and a few percentage points difference in the chance of rain.

PeriodTempCloudPrecipComments
Saturday 25 August
Now12CPartly Cloudy0%Correct
+6H18CPartly Cloudy0%Correct
+24H13CMostly Cloudy31%Correct, it rained
+3D8CPartly Cloudy0%Mostly correct, although it was warmer than predicted
+7D16CMostly Cloudy8%Good long-term prediction as it happens
Sunday 26 August
Now13CRain and Breezy56%Correct, it's raining
+6H19CRain83%Correct, it was pissing down
+24H15CMostly Cloudy7%Correct
+3D11CPartly Cloudy0%It was actually spitting with rain and a bit warmer than 11C
Monday 27 August
Now15CMostly Cloudy8%Correct, it's cloudy but not raining
+6H20CPartly Cloudy2%Correct
+24H11CPartly Cloudy0%Correct
+3D9CClear0%Not clear and a bit warmer than predicted
Tuesday 28 August
Now13CPartly Cloudy0%Correct
+6H20CMostly Cloudy0%Correct
+24H15CMostly Cloudy3%Partly correct, but raining - chance of rain underestimated
+3D12CClear6%Correct, although chance of rain overestimated
Wednesday 29 August
Now14CMostly Cloudy11%Spitting rain
+6H21CPartly Cloudy9%Correct
+24H10CMostly Cloudy0%Correct
+3D13CPartly Cloudy4%More or less
Thursday 30 August
Now11CMostly Cloudy0%Correct
+6H20CMostly Cloudy0%Correct
+24H10CClear0%Correct
Friday 31 August
Now10CPartly Cloudy0%Nearly. It was actually clear, not a cloud in the sky
+6H23CClear0%Correct
+24H13CMostly Cloudy0%Correct
Saturday 1 September
Now15CMostly Cloudy0%Correct

Conclusion

I like this app and I’m sure Dark Sky will fix the interface problems I encountered. I’ll be making regular use of this app, anyway, and it will be interesting to see how it copes with the UK winter.