Barometric Pressure?

[Winderlust]

This is probably a stupid question, and here it goes:

Will a barometer, calibrated to altitude on land and synchronized to a local airport’s reading, give the same indication of weather change as one, correctly setup, but operating on a large body of water i.e. wind strength, etc? Or does the large water body impart other properties to the air mass and cause different indications?

I have recently purchased a barometer and I’m trying to sensitize my awareness of its daily changes and predictions. I’m about 60 statute miles inland from the southern coast of California. We have lately received more El Nino activity than usual.

It seems that some fronts bring lots of rain with little change on the glass. Other times the needle moves 5-8 millibars and nothing happens, weather wise. I did however, detect a low system with wind and rain from a 24 hour, 8 millibar drop, last week. Of coarse the local news and NOAA spotted it for me, earlier than my $130 Weems & Plath.

How should I use this seemingly antiquated and beautiful instrument? Is it something that you salt dogs use or am I playing too much at nostalgia?

I have no boat. So I’m waiting for my equities to heal or my bailout to come and I play sea captain with my little toy.

[celenoglu]

A barometer is one of the instruments used for indications of the atmosphere. Even if it is not properly calibrated a drop means a low and a rise means a high. But making good estimate of weather needs more instruments and a good eye. The best instrument to be used with a barometer is a thermometer. These two devices will give better estimates for the weather. You should also watch the cloud shapes and their changes as well as colour of the sky specially at sunset and sunrise.

The best estimates are the ones receivedfrom the wether stations. They have more devices than we have, and they know how to interpret the valıues better than us.

But be aware that although they have enough resources and knowledge the information is always "estimate". Non of them can predict the coming weather precisely.

[sailingdog]

Originally Posted by Winderlust

This is probably a stupid question, and here it goes:

Will a barometer, calibrated to altitude on land and synchronized to a local airport’s reading, give the same indication of weather change as one, correctly setup, but operating on a large body of water i.e. wind strength, etc? Or does the large water body impart other properties to the air mass and cause different indications?

Yes, a barometer will work on land or water.

I have recently purchased a barometer and I’m trying to sensitize my awareness of its daily changes and predictions. I’m about 60 statute miles inland from the southern coast of California. We have lately received more El Nino activity than usual.

It seems that some fronts bring lots of rain with little change on the glass. Other times the needle moves 5-8 millibars and nothing happens, weather wise. I did however, detect a low system with wind and rain from a 24 hour, 8 millibar drop, last week. Of coarse the local news and NOAA spotted it for me, earlier than my $130 Weems & Plath.

It depends, some storms, like the regularly occurring summer afternoon thunderstorms won't cause a shift in pressure—since they're fairly localized phenomena and due to thermal differences—not caused by a low pressure system. A better use of a barometer is to look at the rate of air pressure change, rather than the actual change. If the pressure drops quickly, you're more likely in for a bad storm than if it drops gradually. Of course, this generally only warns of frontal systems, rather than localized phenomena.

Of course, the variety of weather you're going to see in southern California is a bit more limited than it would be say in New England or the Midwest, where you get cold air masses coming down from Canada hitting warm air masses coming up from the Gulf of Mexico.

How should I use this seemingly antiquated and beautiful instrument? Is it something that you salt dogs use or am I playing too much at nostalgia?

I have no boat. So I’m waiting for my equities to heal or my bailout to come and I play sea captain with my little toy.

[Tea-Rex]

i think the important part is that you're inland. a pressure drop might result in weather that is deflected by geographic features. depending on wind, there might be pressure changes because of bernouli effects that don't result in weather changes at your place and so on.
short version, atmospheric pressure alone will only give you one piece of a puzzle that is far more complex.

[soulesailor]

A pilot friend of mine told me to tap the glass with my finger to un-stick the needle prior to each reading. Sure enough, it always moves just a little bit.

[paulk]

Part of the puzzle is to realize that the barometer is measuring BIG things - air masses - in tiny increments. It is also more useful for reflecting trends, rather than the weather at any specific moment. Seeing it trend down over a period tells you something may be coming. This allows you to prepare for bad weather, even if bad weather never actually arrives. For cautious sailors, especially before NOAA, this was a good thing. With satellites now able to tell us about actual weather conditions all over the planet, a barometer on board is still useful to help gauge possible severity of local conditions. You need to be pro-active in using it, however. By the time the low point of a passing front shows on the barometer, it will be too late to do much preparing for it! It takes practice, and it helps to record the readings over extended periods to get the hang of things.

[Boasun]

A recording barometer is expensive but you will have a graph of the changes in air pressure to help you correlate the weather changes as they go by.
Note: I have seen the Barometer drop rapidly as a fast moving front flowed by. On the Graph it looked like a 'V' That brought a strong wind with it. When the air pressure rose the wind died away and the weather returned to normal for that area.
But you do have to track the barometer readings as you sail far far off shore in order to predict on coming weather.

[Insails]

The tendency is the most important aspect of an aneroid barometer. I have this one

What the tendency tells you is wheather or not you have wind..and wind is what it is about to us sailors...A sharp rising tendency means High Pressure is ridging in and the winds will be howling If the tendency is to drop then a storm or low pressure is headed your way and the winds will increase followed by storms...When the pressure is steady you will notice calm conditions...
As far as their accuracy right now my digital reading on my Davis weather station is 30.37 inches or 1028mbs the analog reads 30.32 inches so you can see they are pretty accurate just a little slower to respond..My barometers are calibrated at sea level but if I went to a lake over 4000ft in altitude the readings would be way off where they should be BUT the tendency would be the same...Hope this helps..

[Valiente]

The tendency and speed are the important bit, but the effects in your local are typically not favourable for a fast learning curve. I suggest a weather class so you can incorporate more points of data, such as wind shifts, barometer tendency, cloud type and level and humidity changes. Two of these you sense with your skin, sometimes three, but they will give you an idea if the wind will come with rain or the rain will fall with wind or both.

Nothing is 100%. The remnants of Hurricane Isabel came over Toronto a few years back and I noticed a wild pressure drop from 992 mb down to 979 mb in about six hours...you bet I went down and double-lashed the boat and the boom cover! But we got maybe 20 knots of warm, moist wind and really sporadic rain...if it wasn't for the astounding cloud deck, it could have been just a p*ssy summer day.

[jackdale]

Originally Posted by Winderlust

This is probably a stupid question, and here it goes:

Will a barometer, calibrated to altitude on land and synchronized to a local airport’s reading, give the same indication of weather change as one, correctly setup, but operating on a large body of water i.e. wind strength, etc? Or does the large water body impart other properties to the air mass and cause different indications?

I have recently purchased a barometer and I’m trying to sensitize my awareness of its daily changes and predictions. I’m about 60 statute miles inland from the southern coast of California. We have lately received more El Nino activity than usual.

It seems that some fronts bring lots of rain with little change on the glass. Other times the needle moves 5-8 millibars and nothing happens, weather wise. I did however, detect a low system with wind and rain from a 24 hour, 8 millibar drop, last week. Of coarse the local news and NOAA spotted it for me, earlier than my $130 Weems & Plath.

How should I use this seemingly antiquated and beautiful instrument? Is it something that you salt dogs use or am I playing too much at nostalgia?

The barometric pressure on land is adjusted for sea level. I live 3500 feet. My barometer at home reads 1024.3 while the one in my sailing watch reads 888. The watch is calibrated for sea level, the home weather station was calibrated using local observations.

Get a barometer that has the capability to retain a history. La Crosse weather stations (and most others) do so. My watch also has a graph of the past 24 hours.

The analog aneroid barometers look really "shippy" but the modern ones are more useful. And you do not need to tap them.

The barometer should also be used in conjunction with cloud cover and wind speed and direction observations. Relative humidity can also be helpful.

Jack