Best way to predict rain from current conditions?

Solorize · **Posted:** Sun Mar 11, 2012 8:41 pm

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.

RayProudfoot · **Posted:** Sun Mar 11, 2012 11:18 pm

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.

Solorize · **Posted:** Mon Mar 12, 2012 7:41 am

Hi Ray,

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

Thanks

Mark

Super-T · **Posted:** Tue Mar 13, 2012 12:57 am

Don't forget Auckland, with 4 seasons in a day :-)

steve · **Posted:** Tue Mar 13, 2012 8:15 am

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.

Solorize · **Posted:** Tue Mar 13, 2012 8:24 am

Thanks Steve,

I will have a look.

mcrossley · **Posted:** Tue Mar 13, 2012 12:58 pm

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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Best way to predict rain from current conditions?

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