# How to guess weather conditions?

Hi,

I have a DHT22 humidity and heat sensor and I have sucessfully made a project with it, receiving information and printing the values of the screen.

But now I'd like to get a pressure sensor and combine all these 3 key values (atmospheric pressure, heat and humidity) to guess weather conditions (whether it will rain, snow or whether it'll be foggy, sunny, windy etc...)

I know the guesses won't be %100 correct and there are other elements to consider in order to predict the weather condition but I want to do it as best as I can with these 3 values.

The reason I'm asking here is that I don't know what do with the combination of these values mean. For instance
high humidity + low pressure = rain?
low humidity + high pressure = windy and dry? etc...
high humidity + low pressure + extra low heat = snow?

You better look at the trend line of a sensors (over several days), is it going up /down or equal.

my father once told me the easiest weather prediction is that it will be the same as yesterday.
That is 70% right in the NL.

If the summer is coming you can say the weather is better or equal to today and get up to 75%
If the winter is coming ...

Nothing is sure in life except it is raining in Tavistock

robtillaart:
You better look at the trend line of a sensors (over several days), is it going up /down or equal.

my father once told me the easiest weather prediction is that it will be the same as yesterday.
That is 70% right in the NL.

If the summer is coming you can say the weather is better or equal to today and get up to 75%
If the winter is coming ...

Nothing is sure in life except it is raining in Tavistock

First things first, do I need an external EEPROM to store the values or internal EEPROM of Arduino will be sufficient ?

Will I need a RTC ?

I'm already using several delay commands to display stuff on the LCD. So i believe recording the data periodically is out of question like this.

It's not the conditions in your own location that determine what weather is coming your way. It's the conditions in the air mass heading your way. Since this can come from any direction, it's not possible to make much meaningful prediction from just your own readings.

Generally Higher pressure leads to clearer skys. In temperate regions in this will lead to higher temperatures during the day, although it can lead to cooler nights.

The rate of change of the pressure is also important though. A rapidly falling pressure will tend to indicate that you have some high winds and possibly storms on their way.

But this is all just general stuff. It would be interesting to network with others that also have data. If they are scattered around a large area then you could probably get some more meaningful data out of the exercise.

I’ve had various computers giving me various graphs of sundry weather parameters for years… looking at the details of local conditions day after day has been fascinating. If you want to do this exclusively with an Arduino, and without spending a lot of money, the little module from Hobbytronics (SerialToVGA. A great little interface board for microprocessors- SerialToVGA) would let you do a “graph” with characters on an old VGA display (50 lines of 100 characters). Or, you could use the Arduino for data capture, pass the sensor readings to a PC over a serial line, do the displays there. More on the non-Arduino possibilities at… Software for monitoring Dallas MicroLan / 1-Wire sensors, weather- ssds025

You might also want to do Google searches on various specific weather phenomenon… wind speed, rainfall. There are many general discussions out there of sensors for them, sensors which can be connected to anything, including an Arduino.

The FAA and AOPA have some good “how to predict the weather” pages, because private pilots need to be good at weather forcasting, if they aren’t licensed to fly in bad weather.