Cumulus Support

The above web tags are outputting a strange forecast of "Rain at times, very unsettled". I know the forecasts calculated by the weather stations and Cumulus aren't brilliant, but this one is well wide of the mark (pun unintended) and have made me curious.

I have checked the usual suspect of pressure extremes defined in my MX configuration.

I initially suspected something I had done - so I checked what MX was actually outputting with the shiny new MX endpoint for webtags - http://localhost:8998/api/tags/process. ... usforecast

Both display the forecast text from the first paragraph. I have MX configured to generate the forecast, rather than use that supplied by my VP2 - so there is no surprise that they are identical.

Am I missing something?

"Rain at times, very unsettled" is from the Zambretti forecast scale

viewtopic.php?t=9318

Thanks Simon. Yes, MX uses Zambretti, and I have MX configured to supply the forecast.

It's giving me "Rain, very unsettled" - so v. similar.
I wonder what the Sager algorithm is giving across the UK at the moment? I don't run it anywhere at present.

The answer for Sager appears to be... "Increasing cloudiness or overcast followed by rain or showers and warmer. South or Southwest winds, Probably increasing."

mine says "its raining" - typical weather for NI

Sager sounds about what I would've expected. Strange that you've got a similar forecast to mine. I wouldn't have anticipated that forecast as there's nothing in the data that would trigger it. Not 100% sure how it works, but I would've thought you would need either low pressure values or rapidly falling pressure. I've got neither - and I don't suppose you have too.

I used the @beteljuice JS implementation of the Zambretti algorithm to confirm the text I was seeing. Indeed it is as expected (by Zambretti).

In that case, I will go back to ignoring it again

From memory, I have not looked up what MX does, Negretti and Zambra's wartime forecast worked on
-actual s-l pressure and whether steady, rising, or falling
-wind direction, plus veering or backing
-that min & max pressure range you mention

freddie wrote: ↑Thu 30 Jul 2020 3:52 pm I used the @beteljuice JS implementation of the Zambretti algorithm

I believe beteljuice advised Steve Loft, so they use same basis, but I might be wrong on that too.

Here I have had a mix of fair weather cloud types all day, but the blue sky is increasing now it is evening so I don't expect rain. I think I trust the sky more than an algorithm - MX is telling me "Stormy, much precipitation". Given how little rain I have had in June and July, the local fields and gardens might be wishing the algorithm was true, but I have been outside painting a rusty complex antique object the last few days and I don't want rain.

Mine was/is saying rain, and so is the Davis forecast.

My Davis wasn't earlier, but is now. My point was that the pressure didn't seem an overly low value (and was only falling very slowly) so I thought that a forecast of "rain, very unsettled" seemed at odds with the measurements. Now I have read up on the Zambretti algorithm I can see that it was reporting the correct (if unrealistic) value. So I am going to go back to ignoring this type of forecast - and probably will remove it from my website as it has the potential to be so far off the mark.

I use the met office forecast on my site, it's a bit more accurate, but not always!