Which Pressure Is Sent To Wunderground?

[RayProudfoot]

RCE Wrote:
On wunderground the MADIS stations "should" be the best ones to use for reference.

In my area the MADIS station is always waay lower than the others, including the airport.

Paul

The OP (PDC) lives about 8 miles from Manchester Airport and its pressure is updated hourly and available on WU. About the most reliable source you could wish for. If it's good enough for aircraft safety it should suffice for wx enthusiasts. MADIS stations are no more reliable than any other PWS.

[RCE]

The OP (PDC) lives about 8 miles from Manchester Airport and its pressure is updated hourly and available on WU. About the most reliable source you could wish for. If it's good enough for aircraft safety it should suffice for wx enthusiasts. MADIS stations are no more reliable than any other PWS.

If I lived near an airport then that would be my preferred point of reference

I did say "should" about the MADIS stations, all the MADIS ones reporting around me seem to have very similar pressure readings (I assumed wrongly or rightly) that they would have better quality instruments than the average joe, even if some of the temperature/wind readings can seem off (due to compromised locations ?!?). I know when we had the recent high pressure my record value exactly matched that reported on the local tv weather news, my station is set about the average for our area and generally reads the same as the MADIS stations.

[RayProudfoot]

Alan,

I don't know anything about the criteria required for a MADIS station but most anomalies in PWS readings compared to 'official' ones is accurate placement of the equipment rather than the quality of the hardware. So a poorly placed Davis station would be worse than a ideally placed cheaper one.

So what's special about MADIS stations?

[RCE]

Alan,

I don't know anything about the criteria required for a MADIS station but most anomalies in PWS readings compared to 'official' ones is accurate placement of the equipment rather than the quality of the hardware. So a poorly placed Davis station would be worse than a ideally placed cheaper one.

Though pressure shouldn't be affected by location (but could be by incorrect calibration).

MADIS seems to be a gov thing, my nearest official anything is about 40 miles away which is pretty useless for setting up. The MADIS stations around here all seem to have pretty consistent pressure readings between stations.

I guess for normal folks you need to analyse the data available and come up with a value that suits, and wait for the high pressure to try and get the best tuned value.

[RayProudfoot]

Double post.

[RayProudfoot]

Though pressure shouldn't be affected by location (but could be by incorrect calibration).

Indeed. I was thinking more about temperature than pressure. Pressure is one of the simplest things to get right (within the limitations of the kit). My 10 year-old OS weather station only has 10 metre settings for station altitude but nevertheless matches the Davis VP2 console pretty well.

Thanks for the info about MADIS. Seems to be a US Govt. thing. Weird acronym!

[steve]

Aren't some of the MADIS stations just people like us submitting data to CWOP? But with quality checking of the data?

[EvilV]

Setting for altitude is pretty easy, even if you don't have a nearby Met Office station. I believe that the correction factor is to add 3.7158 millibars for every hundred feet you are above sea level. Since I am at 227 feet ASL, I just add 8.4mb in the correction box of Easy Weather (2.27 x 3.7158) To be honest I think I added about 9mb, but I was a gnat's whisker off the local airport about 8 miles away.

I'd be surprised if many personal weather stations were ideally sited. There are one or two around the North East which show laughable temperatures when the sun comes out, and a lot of the wind apparatus is mounted too low and in among large wind blocking houses. People in the UK rarely have a lot of open space unless they live out of the cities, so most stations are a compromise. My wind direction indications can be off when it blows from certain quarters, but I think my temps and pressure are pretty accurate. Rainfall, I don't know. I'd need to check it with an old fashioned gauge.

[Gina]

I agree. I'm in a rural area but there are trees around and I think the turbulence produced spreads out far more than would be expected. Although I have raised my wind sensors by 5ft I believe they really need to go higher. I think this would be much more likely to result in stabilising the wind vane than any amount of modifications. The higher location has already resulted in much reduced "waggling" of the wind vane, particularly for certain wind directions.

[Areco747]

Hi Steve I need your help, that conversion factor uses Cumulus to raise the relativa pressure on Wunderground? Many Thanks!

[steve]

Hi Steve I need your help, that conversion factor uses Cumulus to raise the relativa pressure on Wunderground?

For Wunderground, the pressure that is sent is the same as the pressure displayed by Cumulus. For Fine Offset stations, it gets this by first reading the current absolute and relative pressures when it starts up, so it can work out the difference between the two (a fixed value). Then, every time it reads the data from the station, it reads the absolute pressure and adds the fixed offset to get the relative pressure.