What is Synthetic Sky?

Synthetic Sky gives you a peek at tomorrow’s sky. By merging together timelapse videos of the sky collected from times in the past that are similar to tomorrow’s hourly weather forecasts, it creates a synthetic view of what tomorrow may look like.

The current version only supports major cities in Japan, but other countries will be supported (eventually.)

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Why did I make this?

Various ways of telling the weather exist already, mostly involving numbers and figures:



Numbers and figures, unfortunately, are terribly uninformative. They tell you very little about what you really need to know:

Just how cloudy is “Partly Cloudy”?

Am I going to need an umbrella for tomorrow’s “Light Showers”?

Does an easterly wind of 20km/h mean I should postpone tomorrow’s BBQ?

These are questions that could be answered on the day, simply by looking outside the window (which is usually too late). The aim of creating Synthetic Sky is to provide a way for people to look outside tomorrow’s window.

How does it work?

Synthetic Sky is based on two sources of data:

(1) Global Spectral Model data (GSM-GPV)

This is an hourly grid-point prediction of weather conditions (temperature, barometric pressure, wind speed, humidity, etc.) of every surface point on the planet, provided by the Japanese Meteorological Agency.

Using this data, we can find out what the weather conditions were like at any point in the past, as well as up to 3 days into the future.

The following video is an example of the kind of data GSM gives:

(2) My balcony timelapse repository

I have been collecting a continuous timelapse video of the view from my balcony since April 2011. As an example, the video below shows snapshots taken from noon of every day for the past 2 years:

With these two sources of data, we now have associations between what the sky looked like (2), for a certain weather condition (1).

Assuming that the sky looks similar when the weather conditions are similar, we predict what tomorrow’s sky will look like by finding the time in the past that had the nearest weather conditions as the forecast for each hour of tomorrow, and then merge together timelapse images from those times, to synthesize a view of tomorrow’s sky.

Does it work?

These things are difficult to evaluate quantitively. Here are some comparisons of synthetic sky images and actual recorded images to help you decide for yourself.

22 Dec 2012

• Synthetized
• Actual

13 Aug 2012

• Synthetized
• Actual

6 Feb 2013

• Synthetized
• Actual

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