Check of calculations

:cry:

I have just set up my WS2300 and such a simple thing like pressure is causing me to lose more of my hair as I read this forum. I would be grateful if someone could check my calculations for applying the MSL pressure to my weather station?

My weather station height is 192 Mtrs ASL (from OS map my weather station sits just above a contour line) and roughly confirmed from a GPS reading

My ABS pressure reading at the time was 992.5 hpa
I have therefore applied 19.2 mb to this to give the real pressure reading of1011.8mb.

Is this correct?

My nearest airport is London Gatwick which at the time showed an updated 1016 hpa and its height is shown as 62 Mtrs. If the same rule is applied this would mean my reading should show 1003mb

I also have another weather close by which is 17 Mtrs lower than me at
175 Mtrs that reading showed at the time 1015.8 Hpa. That would mean my reading should show 1014.1 hpa

Who is right or am I completely wrong?

One other question if I may,

I have added my MSL correction to my WS2300 and Weather Display, displays this reading. My Weather Display other settings has been set to show 629ft above sea level. The WD Cloud base is not correct it shows 250 Mtrs but I can see the stars!!!

What am I doing wrong apart from owning a weather station?

Many thanks

Steve
:oops: :?: :x

Try this link, http://oww.sourceforge.net/bp_scale.php
the person wrote a script to do the calculation (there is an actual equation used). Remember that barometer readings are slightly affected by temp too, so a difference of a few tenths is possible when comparing with “official” sites.

WD, I believe, just uses a equation to determine cloud height using the humidity. So high humidity, low cloud deck. The only way to deterimine cloud height actually, is to “guess” with your naked eye, or to use some sort of “doppler” like device to measure time to travel to cloud deck and back, and find a distance.

Hopes this helps.

Chris

Chris,

Many thanks for the reply,
The calculation gives me a figure of 1.02308 but how do I apply this to my real pressure readings. I have assumed this to be a correction you add.

Therefore given that my real pressure at present is showing just the height correction added which is 1009.8mb @ 9.8 C this would make the reading jump to 1010.82mb :smiley:

London Gatwick showed at this time 1013hpa @ 11C

I am now assuming this is not an exact science is the above correct so far? Is a 2mb error as close as I would be able to get given the temperature differences? :?

As for the cloud base answer many thanks I will get my assistant to stick their head out of the window as it is raining at the moment! :twisted:

I appreciate any help with above you can offer, sorry for the density of my thought.

Many Thanks

Steve

That number from the website is actually a factor. You need to multiply your barometer reading by it to get the corrected reading.

I am now assuming this is not an exact science is the above correct so far? Is a 2mb error as close as I would be able to get given the temperature differences?
Actually, personal weather stations use aneroid barometer (a metal "box" expanding due to pressure changes) which should not be affected by temp much at all. However, the official sites will have a mercury barometer. Those are affected by temperatures. If London barometer is outside and the temp is 11C, while your is indoors at 22C, the difference would be near 7.79 mb!

sorry for the density of my answers :lol:

~Chris~

Chris,

You have saved the day, :smiley: :smiley: Your help has saved my last tiny patch of hair. Thank you very much for your help. My readings are now perfect!!

Many Thanks

Steve

Your very welcome. :smiley: :smiley:

~Chris~