Topic: Rel and Absolute Baro readings.

[Stevebarker12]

My Absolute Baro readings seem to only tie in with true Relative Baro readings reported by Met Office.
My weather station is currently recording
Relative Baro pressure = 1015
Absolute Baro pressure = 1029
The Baro pressure being uploaded from my Youshiko YC9471 to Weather Underground and Weathercloud = 1015
The Baro pressures currently being reported by UK Met Office and other weather stations
in my area = 1030 ie agrees with Met Office/ other Wunderground sites
It is my understanding these official readings are Relative readings and not Absolute. ie they are corrected to sea level.
(I have an older YC 9386 which is reporting same Absolute and Std Baros as YC9471 - constent with each other)
Im a newbie - am I misunderstanding the readings and data being reported?
Any help appreciated.

[Vasco]

If Google Earth is correct, Walton-le-Dale is about 10 metres above sea level so I cannot understand the -14 hPa correction your station suggests: correction to your absolute reading should be about +1.2 hPa to correct to sea level. So your 1029 would become 1030, a pretty good match to the Met Office reading.

[Stevebarker12]

Thanks for replying.
Yes my elevation is actually 12 metres so yes its not very significant baro difference.
I dont understand why there is such a difference on my weather station unless 'Relative' being recorded by my weather station means something else.
Ive asked Youshiko for their comments.
Strangely I have an older version of  my Youshiko weather station and the readings also show the same values as new station.
And the Relative - lower value - is being uploaded to Weather Underground.
I assume the weather underground values being displayed from all other stations are relative - and not absolute?

[gszlag]

If Google Earth is correct, Walton-le-Dale is about 10 metres above sea level so I cannot understand the -14 hPa correction your station suggests: correction to your absolute reading should be about +1.2 hPa to correct to sea level. So your 1029 would become 1030, a pretty good match to the Met Office reading.

Good catch!
I am aware that in the UK, QNH is used extensively. and I suspect the REL readings mentioned by the OP is QNH I am however,searching for Met MSLP readings. Other than crude fax surface analysis maps, I haven't found a Met source for detailed MSLP readings.
Do you know where I might find them?

[Vasco]

Do you know where I might find them?

Sorry, I have great difficulty finding my way around the UK Met Office website. But I did find WOW MSLP readings from the OP's area: search here for Preston. There's quite a range. . .

[Stevebarker12]

The Met office readings from their weather surface pressure map match my Absolute measure reading ie 1030ish .Nowhere near my 1015 Rel reading.The majority of the weather underground readings are nearer 1030 as well.Yes,some odd lower ones.
Youshiko have just replied and said i should adjust both rel and absolute using Offset correction factors to agree with what they should be.
I'll do this to match professional values.

[Vasco]

I'll do this to match professional values.

Doesn't seem to be a Met Office station nearer than Crosby. . . Blackpool airport (EGNO) probably issues a regular METAR, don't know about Warton (EGNH).

[Stevebarker12]

Yes thats correct.
So as I sit here now
Met Office Crosby 1032
My Rel Baro 1015
My Absolute Baro 1029
My Rel reading doesnt make sense to me.

[gszlag]

Do you know where I might find them?

Sorry, I have great difficulty finding my way around the UK Met Office website. But I did find WOW MSLP readings from the OP's area: search here for Preston. There's quite a range. . .

Perfect! now bookmarked...
Thanks!

[Vasco]

Crosby (23.4 miles) is a wee bit far away for direct comparison but, if needs must. . .

On the basis of what you have told us, IMHO you should leave your absolute reading alone, set your relative reading to (abs+1), and see how you go 

[Stevebarker12]

I agree.

[gszlag]

@Vasco

At 12 m so close to MSL,  - no practical difference between QFE, QNH and QFF. According to the Weather Observer's manual, a simple additive constant is all that's required < 50 meter.

UK METAR usually reports QNH only.

As you might be already aware, when the new SLP algorithm arrives, all of our RELs will be reporting SLP which would make a difference at higher elevations.

[Stevebarker12]

Apologies but
dont know what SLP Algorithm means
REL - you mean Relative Baro pressure?
SLP? Whats this, Std Temp and Pressure?
Steve

[gszlag]

Apologies but
dont know what SLP Algorithm means
REL - you mean Relative Baro pressure?
SLP? Whats this, Std Temp and Pressure?
Steve

Yes, REL = relative pressure meaning relative to sea level
SLP is Sea level Pressure which is the pressure you would get if you moved your station down to sea level. You get the sea level pressure by adding a pressure adjustment called a "correction" to your station level pressure (ABS).

Basically,

ABS = Absolute pressure = station level pressure (live current pressure reading)
REL = Relative pressure = sea level pressure (SLP) In the UK it is referred to as mean sea level pressure (MSLP).

[Stevebarker12]

Brilliant.Thankyou.
So the summary of this post is:
On my new Youshiko YC9471 weather station  I am adjusted the displayed Relative Value, using an inbuilt Offset value, to show the Absolute value corrected by 1mb for my elevation (12m).
This will ensure the data exported to Weather Underground and Weathercloud will tie in ( as near as can be expected) with local UK Met Office station data.
Thankyou all for clarifying the information
Kind regards
Steve

[gszlag]

Brilliant.Thankyou.
So the summary of this post is:
On my new Youshiko YC9471 weather station  I am adjusted the displayed Relative Value, using an inbuilt Offset value, to show the Absolute value corrected by 1mb for my elevation (12m).
This will ensure the data exported to Weather Underground and Weathercloud will tie in ( as near as can be expected) with local UK Met Office station data.
Thankyou all for clarifying the information

Kind regards
Steve

Fantastic! You've got it!