Frost tonight in the SE

Naah, the guys I talked to were ex-aircrew and were definite about not taking any notice about outside forecasts of air pressures and would only take local readings from the Station Met Boys.
I can remember a certain Lightning pilot, in the 60's, doing a low level run supposedly at just below the speed of sound past the Air Traffic Control Tower and Wing Commander Flyings Hut. He broke the sound barrier, broke the windows of the ATC Tower, lifted the roof of the Hut, broke light bulbs and knocked out the Commcen. He only got off a severe reprimand because the Station Met admitted that the local air pressure was in fact different to the general Met Office one handed out to the Squadrons. He was our Squadron Aerobatic Officer, a genius with the Lightning, had flown the prototype of the Lightning, and was a serious pro. From there on in there was always a double check of the air pressures.........and not for the altimeter.

 

Not a lot different to the aircrew though, Pete, theory is great but actually reality and practice is a totally different thing. Despite using Super Computers we still aren't able to accurately forecast air pressures, the Jet Stream's position, when the High or Lows will arrive, or how far they will extend..........and in this important point cannot give micro climate and local predictions of any accuracy whatsoever.

 

I don't know anything about air pressure etc. but I do know that in Shineyland our weather rarely follows the local forecast.

 

They've got my number if they need help

 

For Pete,
Mean sea level pressure



The mean sea level pressure (MSLP) is the atmospheric pressure at sea level or (when measured at a given elevation on land) the station pressure reduced to sea level assuming that the temperature falls at a lapse rate of 6.5 K per km in the fictive layer of air between the station and sea level.

This is the atmospheric pressure normally given in weather reports on radio, television, and newspapers or on the Internet. When barometers in the home are set to match the local weather reports, they measure pressure reduced to sea level, not the actual local atmospheric pressure. See Altimeter (barometer vs. absolute).

The reduction to sea level means that the normal range of fluctuations in atmospheric pressure is the same for everyone. The pressures that are considered high pressure or low pressure do not depend on geographical location. This makes isobars on a weather map meaningful and useful tools.

The altimeter setting in aviation, set either QNH or QFE, is another atmospheric pressure reduced to sea level, but the method of making this reduction differs slightly.

QNH
The barometric altimeter setting that will cause the altimeter to read airfield elevation when on the airfield. In ISA temperature conditions the altimeter will read altitude above mean sea level in the vicinity of the airfield
QFE
The barometric altimeter setting that will cause an altimeter to read zero when at the reference datum of a particular airfield (in general, a runway threshold). In ISA temperature conditions the altimeter will read height above the datum in the vicinity of the airfield.

The above extract points to the fact that there can and is a difference in local air pressures and those issued by the Met Office, the main causes of those differences can be physical geographical features of the areas, height, and the temperature and the fact that the Met Office is issuing general figures to cover a large area rather than exact figures referring to local areas. It also means that to agree with the Met Office figures you have to set your barometer at their calibration which is sea level. Those wishing to have true air pressure readings of their local area let their digital wireless barometers calibrate themselves while allowing their aneroid barometers to do the same.