Qnh!

[dynamite dean]

I experienced the highest QNH yesterday...a wopping 1038mb!!!! 830am wedensday morning beautiful day... a slight breeze, does this mean as high flows to a low , out there somewhere it was even higher QNH.

Surely not ?
I fly in George RSA where regularly QNH are around 1015mb just a boring query but anyone else experienced anything this high and my qestions is what does this really tell me about the atmosphere and does this happen often? and why would it happen ? It was a cloudless day , beautiful day , but is it nothing more than me marvelling at insignificant things?!!!!

[JEP]

I remember once on a bright winter day i february it was 1043

[oxford blue]

QNHs vary between about 930 and 1050, although both are exceptional.

[m&v]

Dynamite,sorry about the late response-I had to dig it up in the Canada AIP.the AIP refers to 'high alt settings(so we must have them occasionally)..It refers to pressures above 1050mb-31.00inches....Most Altimeters can't adjust 'higher' than 31#,so the 'procedure' is to revert to a datum of 31inches ,below the Trans level,thence ,if adjustable reset to the 'actual'
on the approach.If unable to reset datum higher that 31inches,'bug up'the minima 1/4 miles+100' the the charted limits for each0.1 reading above 31*(this of course doesn't apply to Cat2/3 ops(rad alt))
It doesn't happen very often,once in 37 years of airline flying!!!
cheers

[tomcs]

I was training last summer and i think we got a 1043/44 the air was so still....not very good for landings and the thing floats and floats but it is sorted for navigation

Tom

[Max Angle]

Out of interest the highest recorded pressure was 1083mb in Siberia during the 1960,s. Check out:

http://www.weatherwise.org/qr/qry.99.pressure.html

for a brief explanation.