How to use barometer readings

[JinksyFerry]

Hi Guys,

I am an electronics enthusiast and I am making an electronic barometer using an Arduino board, a couple of sensors and a display.

OK, the board will read the atmospheric pressure once per minute and store the readings for a couple of house so that it can also look at change over the last 15, 30, 60 and 120 minutes all of which it can display.

Now, if the pressure is dropping, it can also print up a warning and possible sound a buzzer but what levels of pressure and whet changes should I set as an alarm limit?

The board will also display time, humidity and temperature and again, these (apart from time) could be trended - all three readings temp, humidity and pressure may give a greater accuracy of impending bad weather - any suggestions?

I'm also looking to interface a GPS device so I can display other info too but that's for future development, I'll stick with keeping an eye on the weather for now.

Thanks for any advice, Steve.

 

[Vegable]

I read somewhere that a pressure change of 3 millibars in an hour signifies a gale is likely, and that 6 mb/hr a gale is a statistical certainty. Where I got it from I've no idea, and if it's true I've no idea either, but it might be worth checking and creating an alarm indication?
Mike

 

[GHA]

Your time scales seem a bit out, displaying hourly readings over 24 or even 48 hours would be more useful on a boat.

 

[VicS]

Hi Guys,

I am an electronics enthusiast ......................................................................

Thanks for any advice, Steve.

I read somewhere that a pressure change of 3 millibars in an hour signifies a gale is likely, ..................................................it might be worth checking and creating an alarm indication?
Mike

Your time scales seem a bit out, displaying hourly readings over 24 or even 48 hours would be more useful on a boat.

I agree with GHA the timescale should be extended. There is no need to record the pressure more frequently than hourly, even 3 hourly perhaps, but one would want to see the trend over a much longer period than 2 hours.

According to my YM notes gales are almost certain to occur if the pressure falls by more than 8mb in 3 hours . I believe this leads to an gale "imminent" ( ie within 6 hours) warning being issued.

 

[Halo]

If you are planning trans ocean sailing then your project could be useful. I would have thought that for virtually everyone else these days navtex or radio or internet would be better options.

 

[macd]

I read somewhere that a pressure change of 3 millibars in an hour signifies a gale is likely, and that 6 mb/hr a gale is a statistical certainty. Where I got it from I've no idea, and if it's true I've no idea either, but it might be worth checking and creating an alarm indication?
Mike

RYA Weather Handbook, page 33: "As a rule of thumb, a 6mb drop in three hours indicates a Force 6, whilst 8mb indicates Force 8. Any faster sustained fall would indicate an even stronger blow."

Or as Vic's YM notes indicated.

It should be borne in mind, however, that it's perfectly possible (if somewhat unusual) for a gale to arrive with only a small and steadier drop in pressure if you happen to be located where the same isobar tracks across you.

 

[laika]

I agree with GHA the timescale should be extended. There is no need to record the pressure more frequently than hourly, even 3 hourly perhaps, but one would want to see the trend over a much longer period than 2 hours.

+1. Might be an idea to give an alert if in the "falling quickly" category (i.e. >3.6hPa in 3 hours). My own planned version of this project would inevitably have included a Toots and the Maytals sample for the alert....

 

[nigelmercier]

See this thread where I asked the same question, for the same reason.

 

[cpedw]

A while ago I made a 5 day barograph using a picaxe micro http://www.picaxeforum.co.uk/showthread.php?9545-Boat-project-2-Barograph

I have been pondering turning it to 2.5 days with a trend display alongside, like the NASA Meteoman shown in Nigel's previous thread.

Derek

 

[GHA]

With a bit of programming you could attach a bmp180 to an esp8266 and have it broadcast it's own Web page with pretty graphics

 

[JinksyFerry]

If you are planning trans ocean sailing then your project could be useful. I would have thought that for virtually everyone else these days navtex or radio or internet would be better options.

Yeah but where's the fun in that. I like to tinker.

Thanks for your informative replies guys. I think that I'm going to set a refresh rate of 1 minute still and store data every 15 minutes so that I have 48 hours worth. I appreciate what you say about recording the pressure on a 2-3 hour basis but I really don't want to wait an hour (or more) to find the pressure has fallen 8 millibars when I could have found it had fallen 2 millibars 45 minutes (or more) earlier and lets face it, you may have more things to do on your boat than check the pressure every minute, the device doesn't and if its capable of storing 200 readings, why only store 10?

I'll certainly refer to the RYA weather book to set my alarms.

Steve.

 

[franksingleton]

As usual, a late input. Why do I miss important questions.

Before computers were as good as they are now, Met Office forecasters had a rule of thumb, 6 hPa rise or fall in 3 hours for a gale 8 . 10 hPa in 3 hours for a storm 10, these are fairly short term warnings. Note a RISE or FALL. Strongest winds often occur behind a cold front when pressure is rising.

These days, I pay more attention to the GFS GRIBs. Obviously allowing for some under-forecasting. If I see winds above 25 kt's on the GRIB, my immediate thought is F 7-8. The point about GRIBs is that I get several days warning of strong wind not just several hours. By all means watch your barometer but pay more attention to the big picture. Maybe a little sweeping, somebody will probably instance major thunderstorms and other such nasties. Got these the mark 1 eyeball is your best tool - informed of course by GMDS texts which should mention their possibility.

 

[prr]

''Long foretold, long last;
short warning.... soon past''

 

[Gwylan]

Hi Guys,

I am an electronics enthusiast and I am making an electronic barometer using an Arduino board, a couple of sensors and a display.

OK, the board will read the atmospheric pressure once per minute and store the readings for a couple of house so that it can also look at change over the last 15, 30, 60 and 120 minutes all of which it can display.

Now, if the pressure is dropping, it can also print up a warning and possible sound a buzzer but what levels of pressure and whet changes should I set as an alarm limit?

The board will also display time, humidity and temperature and again, these (apart from time) could be trended - all three readings temp, humidity and pressure may give a greater accuracy of impending bad weather - any suggestions?

I'm also looking to interface a GPS device so I can display other info too but that's for future development, I'll stick with keeping an eye on the weather for now.

Thanks for any advice, Steve.

All of the above about the time scale and the rate of change to trigger alarms.
Also that a lot of kit has this facility built in, or it exists as an app

I have one of these which do an excellent job, providing time and an alarm clock too.

http://www.sunroadtech.com/en/products_view.php?id=69

 

[franksingleton]

Remember that a barometer, like any other single weather observation only tells you what is happening at a single point at a single time. It is a truism that to "Know the weather somewhere, you have to know the weather everywhere,"

 

[OceanSprint]

My samsung galaxy s5 has a built in barometric sensor, but i often wonder why as no function on the phone uses it, and no Apps i can see except MadMutt electronic log App.

 

[Roberto]

I have one of these which do an excellent job, providing time and an alarm clock too.

http://www.sunroadtech.com/en/products_view.php?id=69

I have the same (apart from half a dozen other barometers ), it is remarkably accurate indeed, I frequently check against the Metar report from a very near airport and it is spot on, even after several ups and downs of winter storms I found at most a couple of hPa drift.

BTW, have you figured out how the display works the pressure maximum and minimum to build the graph ? Sometimes the end of the graph bar simply disappears, like plunging below the lower limit.

regards

 

[duncan99210]

I have two barographs on board. One is a traditional one, sitting on a custom made oak bracket, recording pressures using a pen and paper chart. It is a thing of beauty I inherited from my father. But it's not much use...... The other is a combined clock, temperature, humidity and pressure instrument that also captures outside data. It's barograph display is excellent, looking back up to ten hours if required. No alarms, but then I'm not sure if I'd want one to add to the cacophony of beeps going on in the boat. It cost €15 from Lidl about four years ago.

 

[KellysEye]

That's making it complex all we did is look at the barometer reading when were updating the log and add the reading to it, we also logged wind speed, wind direction, boat speed, any traffic seen and engine hours if used, we did that every 2 hours on passage. If the pressure is changing downward by more than 2 mb/2 hour expect a gale.

 

[macd]

If the pressure is changing downward by more than 2 mb/2 hour expect a gale.

Alternatively, expect KellysEye to be wrong by a factor of two.