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 Post subject: Best way to predict rain from current conditions?
PostPosted: Sun Mar 11, 2012 8:41 pm 
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Joined: Tue Feb 01, 2011 8:22 am
Posts: 344
Location: Wokingham, Berkshire, UK
Weather Station: WH1081
Operating System: Win 7, XP, Xubuntu, Linux Mint
Just wondered if anyone has an ideas on the best way to predict if it could rain
based on current conditions reported by a PWS.
As I am currently using the following way to predict in my "Cumulus RealTime Data Grabber"
program. It seems to be fairly accurate, but just wondering if anyone else has a more
accurate way of predicting.

Currently I have my code looking at the CurrentTemperature, DewPoint and Humidity,
in the following (Pseudo code).

If DewPoint is within +- 1 degree of Current Temperature, And Humidity is at 90% or greater Then
Chance of Rain is High.

Else Chance of Rain is Low

I did wonder about adding in a condition for Pressure but I am a bit unsure what would be the best
pressure reading to use a a switch between more or less chance of rain. Also, from looking at other
PWS readings when it had been raining, the pressure can vary from say 988 - 1035 and rain is still
produced. So am a bit unsure whether it would be more or less accurate to include the a pressure
condition into my code.

Any ideas would be appreciated.

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Cumulus Real Time Data Grabber
http://bit.ly/WjBh5z

Wokingham Berkshire - weather station
http://www.wokinghamweather.co.uk

MRD Photography
http://www.mrdphotography.co.uk

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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Sun Mar 11, 2012 11:18 pm 
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Joined: Wed May 06, 2009 6:29 pm
Posts: 1734
Location: Cheadle Hulme, Cheshire, England
Weather Station: Davis VP2 with Daytime FARS
Operating System: Windows XP SP3
Wind backing from west round to south with a drop in pressure is common in the UK when Atlantic depressions and their associated fronts approach the country. Humidity will also increase but I'd go with the change of wind and pressure drop and see how you get on.

That wouldn't apply to showers of course. Those are harder to predict.

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Cheers,
Ray, Cheshire.

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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Mon Mar 12, 2012 7:41 am 
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Joined: Tue Feb 01, 2011 8:22 am
Posts: 344
Location: Wokingham, Berkshire, UK
Weather Station: WH1081
Operating System: Win 7, XP, Xubuntu, Linux Mint
Hi Ray,

Thanks for your input, I will have a look into recoding and see how I get on.

Thanks

Mark

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Cumulus Real Time Data Grabber
http://bit.ly/WjBh5z

Wokingham Berkshire - weather station
http://www.wokinghamweather.co.uk

MRD Photography
http://www.mrdphotography.co.uk

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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Tue Mar 13, 2012 12:57 am 
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Joined: Tue Sep 09, 2008 3:37 am
Posts: 704
Location: Auckland, New Zealand
Weather Station: wh-1081
Operating System: Weather Laptop - Windows 7 Pro
Don't forget Auckland, with 4 seasons in a day :-)

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Terry Wiltshire
http://www.janter.co.nz/weather/index.htm
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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Tue Mar 13, 2012 8:15 am 
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Joined: Mon Jun 02, 2008 6:49 pm
Posts: 17835
Location: Sanday, Orkney
Weather Station: Davis VP2
Operating System: Windows Home Server 2011
There's a section on forecasting (with some 'rules of thumb') on the weather faqs site that I maintain - http://weatherfaqs.org.uk/ - but I don't know how much use it will be for your particular purpose.

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Steve
Sanday Weather
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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Tue Mar 13, 2012 8:24 am 
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Joined: Tue Feb 01, 2011 8:22 am
Posts: 344
Location: Wokingham, Berkshire, UK
Weather Station: WH1081
Operating System: Win 7, XP, Xubuntu, Linux Mint
Thanks Steve,

I will have a look.

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Cumulus Real Time Data Grabber
http://bit.ly/WjBh5z

Wokingham Berkshire - weather station
http://www.wokinghamweather.co.uk

MRD Photography
http://www.mrdphotography.co.uk

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 Post subject: Re: Best way to predict rain from current conditions?
PostPosted: Tue Mar 13, 2012 12:58 pm 
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Joined: Thu Jan 07, 2010 9:44 pm
Posts: 2596
Location: Wilmslow, Cheshire, UK
Weather Station: Davis VP2
Operating System: XP SP3, Win 7
Hmm, up here in the northwest...

Code:
var rainState = "It's going to rain soon";

do {
    if (rainRate > 0) {
        rainState = "It's raining";
    } else {
        rainState = "It's going to rain soon";
} while (true);

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Mark
Wilmslow Astro Weather


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