All the weather reports I encounter, print - tv - web, state the current pressure. I can appreciate the usefulness of the trending. Dropping that a low is coming or Rising that a high is approaching. I also remember from piolt training that the current air pressure at ground level being used to correct my altitude calculation.
At the time of this posting, here in Toronto the air pressure is 101.8 kPa
Who uses this information that it is consistently reported in all weather reports?
Yes, I agree that the trend is more useful than the absolute value… but if you know that the average is around 100 kPa, then you can see whethe it’s more likely to rise or fall.
Surveyors need it to adjust the distance calibration on EDM (electronic distance measurement) devices, like the cyan or yellow optical instruments you often see them looking through (I mean the more powerful ones with boxy looking sides and a little telescope in the middle).
I was looking for barometric pressures briefly last week to test an idea about beta radiation pentrating an air gap.
I think pilots use, or used to use, barometric pressure to adjust altimeters - but I’m not sure, maybe they only compensate for it by adjusting the altimeter at known altitudes.
Pilots do indeed use barometric pressure to calibrate their altimeters. Below certain altitudes, they use a figure supplied by ATC. Above these altitudes, they use a standardised setting.
It’s also useful in numerous technical and scientific studies. Boiler efficiency studies sometimes use barometric pressure, for instance.
It doesn’t matter what altitude you’re at when you adjust the altimeter. If you couldn’t do it at altitude there would be no way of knowing what your altitude is as you fly through different pressure areas. Nothing worse than seeing mountain goats outside your window.
Sure, but the people who really need barometic pressure don’t get it from the morning news, they have good and accurate instruments.
I have no use at all for that information.
To amplify, the “altimeter setting” is the local sea-level pressure at the reporting location (what the pressure would be if you dug a hole from there down to sea level). Diligence at adjusting their altimeters keeps everyone actually at the altitude they think they’re at, which is helpful for preventing unpleasantnesses from occurring. It also lets everyone know how high above the ground they are, since the ground may be rough but its elevation is known.
Above 18,000 feet (in the US, anyway), everyone sets their altimeters to the same standard setting (29.92 inches of mercury, btw), to avoid the bother of constantly adjusting it, and because there’s hardly any land up there to run into anyway. Up there, pilots speak of “flight levels” instead of altitude. A flight level is the indicated altitude with the setting at 29.92, divided by 100. FL330 may be higher or lower than 33,000 actual feet, for instance, but everyone at that flight level will be at the same altitude anyway.
In some large wilderness areas, like northern Canada, there are too few reporting stations on the ground to get a useful setting anyway, so everyone uses 29.92 at all altitudes and keeps track of height above the ground visually.
Generally, high pressure = clear weather, low pressure = bad weather, and not everyone has a window handy.
This is how I use the barometric pressure as reported. I know what normal barometric pressure is, and the reported figure, as well as the trend in pressure (“the barometer is falling,” “the barometer is rising”) gives me an idea whether I should expect fair weather or stormy weather.
I use it to decide how long I must boil my eggs.
I have an electronic weather station and one function it has is collating changes in air pressure, temperature and humidity to give a fairly accurate weather forecast for the next couple of days.
As a recreational fisherman is something I keep an eye on, certainly a high pressure system will bring many species of freshwater fish on the bite, I’m sure it’s a factor pro fisherman consider.
Maybe you can answer a long-time question: when authorities report barometric pressure, do they mean the true pressure as measured at whatever altitude they happen to be? Or do they measure it and then apply a correction for their own altitude so it is an estimate of the pressure if you dug a hole, et c, as you describe? By “authorities” I guess I typically mean weather forecasters and reporters, and web sites that include it with other weather data, but I don’t really know who else reports barometric pressure and am curious about them too.
In other words, does the reported barometric pressure work like the “altimeter setting” you describe? Or does the weather station in Denver always report really low barometric pressure?
Official weather stations report actual barometric pressure, not an adjusted one.
The airports I tend to fly out of don’t have ATC, so I usually use whatever the equipment at the airfield is reporting, though on occasion I have used what is reported on the TV or regular radio. For what I do in the air, it’s sufficient. The only time I worry about getting official ATC altimeter settings is when I’m flying into a busy airport with ATC towers where there is definitely a real reason to use the same setting as everyone else.
Interesting thing about small airplane altimeters - if you know the exact altitude of the runway you’re sitting on you can adjust it to read that altitude and thereby get the current barometric pressure.
Yes. That’s why the altitude-corrected pressure is called an “altimeter setting”, not a pressure.
Thanks for that. Here in the UK transition altitude is only 6000 feet. Presumably that’s because the highest land-based obstruction is less than 4000 feet elevation.
At what altitude does one have to start to take ambient pressure into consideration for cooking? I live around 85 metres above sea level. Do I need to adjust boiling time? I don’t think so. What about 1000 metres (around 3900 feet)? 2,000 metres?
seconded, I have just started up a new gas pipeline in Northern Italy, To do this we had to buy gas from the local grid. We bought it in Standard Cubic Metres ( over one million) So it is imporatnt that I know the absolute pressure and temperature when calculating absolute volumes.
But I dont depend on weather.com We have our own instruments installed at the metering station