Topic: Low reading of barometric pressure

[JamesB]

Hi all, hope you're well. I stumbled across this forum and hope someone can help answer a question for me.

I'm interested in weather and forecasting - although a long way from being anything more than an amateur - and recently decided to buy my first weather station. After a fair bit of research, I chose an Explore Scientific 7-in-1, which arrived last week.

I've been really happy with it so far and the data it pulls through to Wunderground. However, the barometric pressure seems to be a lot lower than other stations in my immediate vacinity. Also the BBC weather site which carries Met Office stats. My station is set to relative pressure and hPa but for some reason the readings are low. For example, today it's showing 1006 while others stations nearby are much closer to the current 1015 on the BBC site.

I'm presuming this will likely affect its ability to forecast weather over the next few hours. Is this normal? If not, is there a way to correct it? The station is sited on top of a fence post in an urban garden - around 6.5 feet above the ground which is grass and soil. Thanks.

EDIT: meant to add that I live in the UK

[JohnAweather]

Hey James, I'm a new member myself... long time lurker haha

I may or may not have THE right answer for you, as I'm unfamiliar with your weather station. But, in my experience with Davis and Kestrel weather stations, you have the ability to set elevation. Because barometric pressure is factor of elevation, changing the value of the elevation at your site will result in a completely different pressure reading. Does your weather system ask for elevation by chance?  If so, this would probably fix the problem. A few feet won't make a significant difference however so a close approximation should work just fine. But if not, if there's no prompt for elevation, then I really have no idea what would be causing the low pressure reading.

Things like exact station placement, sun vs shade, on fence/on ground, etc., should not have an impact on your barometer reading like it would with a temperatures/wind/rain/RH sensor.

What I DO know is that barometric pressure typically changes very gradually over distance; short of, say, a cold front - or some sort of weather system with a steep pressure gradient in your vicinity - your barometric pressure should be virtually the same as your local weather ob.

John

 

[OldAlaskaGuy]

Here is an excellent tool to calibrate your barometer. The elevation is the height where your BARO sensor is located. If it has a console, it may be located inside and not in the array.
 
BARO calibration tool:  https://caboose700.github.io/ws-barometer-offset-calculator/
 
Elevation tool:   https://www.freemaptools.com/elevation-finder.htm



EDIT: add map tool link

[JamesB]

Here is an excellent tool to calibrate your barometer. The elevation is the height where your BARO sensor is located. If it has a console, it may be located inside and not in the array.
 
BARO calibration tool:  https://caboose700.github.io/ws-barometer-offset-calculator/
 
Elevation tool:   https://www.freemaptools.com/elevation-finder.htm



EDIT: add map tool link

Thanks very much for this advice. Seems to have worked. Console is now reading 1014hPa rather than 1006hPa, which is almost completely in line with the Met Office detail of 1015hPa for the local airport (about 15 miles away and similar elevation). Much appreciated.

[galfert]

...about 15 miles away and similar elevation.

The airport's elevation is irrelevant. The 1015 hPa is the METAR's adjusted for sea level reading at the time. That 1015 hPa essentially says that if they were at sea level then the pressure at that location would be 1015 hPa. We don't know and we don't care what their absolute station pressure is. The purpose of you adjusting for your elevation is so that you can then match the METAR barometer reading at sea level. The fact that the METAR was 1015 hPa and you were at 1014 hPa means that there is still some tweaking that is possible, provided that you got the METAR data at an optimal time when pressure was steady and timely.

[Jim_S]

Seems to have worked. Console is now reading 1014hPa rather than 1006hPa, which is almost completely in line with the Met Office detail of 1015hPa for the local airport (about 15 miles away and similar elevation).

I'd suggest not making any more adjustments for the time being based on one comparison. Watch things over a week or two and see what happens. If your station is consistently low then maybe make a small tweek. I have 3 airport metars near me within about 15 miles of each other and it's quite common for all of them to be slightly different.

[JamesB]

Many thanks both. I'd followed Roger's advice and weblinks above which appears to have helped. I understand that readings fluctuate but mine were a significant way out compared with local weather forecasts and other weather stations in the immediate vicinity. I'll keep an eye on it, but much appreciate the guidance.

[OldAlaskaGuy]

Just a quick Baro calibration question, when making small adjustments to calibration offsets is this done only to the absolute setting? QC shows it at
Average barometer error: -0.4 milliBars  Error standard deviation:0.7 milliBars.

[galfert]

Just a quick Baro calibration question, when making small adjustments to calibration offsets is this done only to the absolute setting? QC shows it at
Average barometer error: -0.4 milliBars  Error standard deviation:0.7 milliBars.

The answer to your question depends on the brand/model of your station. On some stations like Davis you enter your given elevation and then you directly adjust the Relative Pressure. On FO clone stations you have to deal with the complexity of enacting your elevation by way of the static differential of the Relative vs Absolute pressure, and then you do the final calibration via adjustments to the Absolute Pressure. This thread lives in the subtopic that is not pertaining to any particular brand. But the OP is using a Bresser type station that is yet a different thing and I have no experience with its calibration particulars.