Developers

I have been looking at the cloud coverage predictions used in Windy. I commonly find cases where the (total) cloud coverage percentage is less than the Low, Medium, High cloud predictions.

For example, using ECMWF at a particular time I see

Low Clouds 0 %
Medium Clouds 64%
High Clouds 70%
Clouds 54%

I just can't wrap my head around what that means. How can the total coverage be less than both the Medium and High cloud coverage?

In the description of the Clouds layer it says: "Clouds and rain/snow accumulation in the last 3 hours". All I can think of is that this is an average of the clouds in the past 3 hours, whereas the high, medium, low is hourly. Is that what is going on? The sentence is ambiguous at best.

First let me say (again) that I really like the Windy user interface and the types of data it provides. However, I'm trying to reconcile some of the weather data with what I see on other sites.

The other site I have used for a long time is weather.us. I also provides access to the ECMWF forecast with a modest subscription fee. The problem with weather.us is that it has a very klunky user interface. I would love to switch over to Windy as my go-to source of weather.

However, I've noticed that the ECMWF predictions between the two sites can be significantly different and it is not clear why that would be.

1. I have made sure that both are using the same run of the ECMWF model
2. I have made sure the locations are the same (to within a couple hundred meters)

Despite that I will sometimes get temperature predictions for the same hour that vary by 5ºF. As an amateur astronomer, I'm very interested in cloud predictions. I find significant differences between those as well

As an example, I was looking at the weather in a nearby city I'm going to tonight

At 9 PM here are what the two sites say:

(Temp, high clouds, middle clouds, low clouds)

Windy:       51º, 09%, 06%, 0%
Weather.us:  56º, 21%, 01%, 0%

At 12 PM we have:

Windy:      47º, 24%, 34%, 0%
Weather.us: 53º, 28%, 28%, 0%

These are just two examples, but the discrepancies are rampant. They are not huge, but they are worrisome.

I have asked weather.us if they have any ideas why these significant discrepancies would exist. Of course, they didn't really know but did say they apply an elevation correction to some of the data. I wouldn't think that would be done for cloud predictions. It also seems unlikely that an elevation correction would yield a 5ºF temperature difference.

So I'm asking the Windy team if they have any thoughts on this. Unfortunately, I don't know of a third site I could check to see who they agree with.

To be honest, I probably trust weather.us more. It is run by a team of meteorologists and you would think they would know what they are doing. As far as I can tell the Windy site is run by weather enthusiasts.

I would appreciate any ideas about why this difference might exist.

@btschumy Hi, the whole composite is created from multiple images from multiple satellites. This is boundary of two satellite images (from Goes West and Goes East). Infra composite is almost perfect, but visible composite suffers many problems especially due to reflections and refractions of the light. We will focus on this in future, but unfortunately some of these visual artifacts can not be completely removed.

Use weather.com

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Create your own animation at https://www.windy.com/animate

To download this video just click with right mouse button on this link and select "Save link as..."

This video is licenced under Creative Commons licence (CC-BY 3) and can be used/modified freely in any possible way. Just mention Windy.com

Create your own animation at https://www.windy.com/animate

To download this video just click with right mouse button on this link and select "Save link as..."

This video is licenced under Creative Commons licence (CC-BY 3) and can be used/modified freely in any possible way. Just mention Windy.com

Create your own animation at https://www.windy.com/animate

That surprises me a bit. I’m an iOS developer and that kind of change should be extremely simple. It is a change to the app code rather than the web code.

Anyway, I would appreciate it if you could add it to a TODO list to be addressed at some point.