# using the barometer to predict weather...



## RoyR (May 5, 2011)

Since I acquired my ABC watch about a month ago, my interest in using a barometer to forecast weather has been renewed. I wanted to get your thoughts on rules of thumb you use when you use your barometer/watch to try to forecast the weather. I read a post from Queen6 back in February where he said that observation of barometric trends was VERY useful when he predicted the weather while on a somewhat hazardous trip he had to make, so his comments would be particularly welcomed.

I know that dropping pressure can signal bad weather approaching, and rising pressure can signal improving weather, but so far, my forecasts have not been particularly accurate.

My questions run like this: 
--How much of a drop constitutes a "large" drop in pressure? 
--What do you determine is a high and low pressure, particularly when you use that pressure to mark the start of a trend (up or down)? 
--How quickly would pressure need to rise (or drop) to indicate a weather change?

I'm looking for general rules of thumb you apply when you try to predict the weather using just your watch, when you have no other information available when you are out in the field. Perhaps you also have ways of factoring in cloud observations, temperature, and humidity? I realize there are no magic answers here, but personal experiences from others could be beneficial as I gather my own opinions about how pressure changes can be used to predict weather.

By the way...to provide some context, I live near sea level, just south of Washington, DC, about 125 miles west of the Atlantic coast. Pressure has varied between between 29.65 and 30.20 in Hg since I received the watch on May 2. We've had no big storms during this first month with the watch.

thanks! 
Roy


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## bezgeo85 (Apr 19, 2011)

RoyR said:


> Since I acquired my ABC watch about a month ago, my interest in using a barometer to forecast weather has been renewed. I wanted to get your thoughts on rules of thumb you use when you use your barometer/watch to try to forecast the weather. I read a post from Queen6 back in February where he said that observation of barometric trends was VERY useful when he predicted the weather while on a somewhat hazardous trip he had to make, so his comments would be particularly welcomed.
> 
> I know that dropping pressure can signal bad weather approaching, and rising pressure can signal improving weather, but so far, my forecasts have not been particularly accurate.
> 
> ...


My friend hello

My opinion is that only by baro meter you cant predect weather

In order to do this you have to know the temperature , baro pressure (as about watch)
and (as about field) take a look at the clouds and feel the humidity and the air velocity etc>

I may be wrong but this is what i do

Other more experienced members may know something more

Really hope i helped you


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## duke4c (Feb 12, 2006)

It's impossible to answer to this question because it depends on so many varables including where you live and the weather patterns that are typical to your area and time of year.

For me it boils down to 3 things: experience, experience and experience...

I observe the weather, check my ABC (C in this case used mostly to determine direction of the wind... wind speed is purely subjective but good enough...)
and make predictions based on experience.

It took me about a year or so to get it right but now I'm at a point where I can predict rain and rain duration with about 80% accuracy... that by itself was well worth it getting ABC watch. After all my iPhone often says it will rain... and I look at the sky, check the wind speed and direction (preferably at wide open area) and wery often I can tell that it will actually no rain, or if it does I can tell if it will last long or not...

Now I see this as nice hobby and daily distraction for me... fun and practical...

SIDENOTE:
After about a year of doing this I can tell you that baro reading by itself doesn't mean a squat... it's the baro graph over last 6 hours that counts (at least in my area). Hence the reason why never bother calibrating the baro according to my local weatherstation. Not only that but I can actually tell you that I can have my Core in "alti" mode and still be farily accurate for the weather (baro graph still gives me better prediction %). I simply stand at known location and check the altitude. If it's higher that it's suppose to be than baro is going up... if it's lower, baro is going down... heck I can even tell the baro reading just by observing + or - difference in altitude.

EDIT:
I actally studied clouds and cloud formations... this helps greatly to predict upcomming storm.. also, at the beggining at least I used satelite imaging a lot to get experience of where the bad weather usually comes from.. I combined this knowlege with ABC readings to get this level of accurate prediction (I consider 80% to be amazing to be honest with you...)

Cheers


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## ThomAsio (Feb 26, 2010)

I agree with duke4c - though I havent taken it to your level ;-)

Anyway, I find it usefull to not only observe the trend, but also look at the actual barometer value. Where I live, a value of ~1012 hPA seems to be important - values above, usually means better and stabil weather, and opposite for values below. When the barometer hovers around 1012, maybe +/- 3, it usually means changing weather. It can be both good, and not so good. In this range, it's tough to predict based on barometer. While the other two situations are more predictable.

As a sidenote, on the Tissot T-Touch, the user can select a climate zone, which reflect the location. So far, I've only been in the northern tempered zone, so I cant comment on the efficiency of this feature.

Sidenote 2: The T-Touch is permanently observing if the user changes altitide. This is most likely done by measuring how fast the air pressure changes - so fast changes are considered as altitude changes and slow ones as weather related changes. This works very well most of the time (at least where I live). However, if the weather detoriates very fast, like a millibar or two in less than 5-10 minutes, the barometer wont reflect that, but it'll be measured like a altitude change. That's very rarely a problem where I live, just a detail to consider. The good thing though, is that the barometer trend aint thrown off, just because one change altitude.


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## xevious (Feb 1, 2008)

If one could accurately predict weather just by barometric pressure changes alone, there would be a lot of meteorologists out of work! ;-)

Temperature, wind speed+direction, humidity, and geography/climate also contribute to weather effects. You will see cases of pressure dropping, but no precipitation due to the various other factors. You must get to know your climate well in order to have a better chance of predicting weather changes based mostly on barometric pressure trends.


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## RoyR (May 5, 2011)

I was mainly looking for your anecdotal experiences using a barometer to try to predict weather. You know, something like, "the pressure dropped .2 inches of mercury in an hour yesterday from 1 to 2pm, and all h*ll broke loose at 3pm..." That kind of thing.

I realize a barometer alone is insufficient to make a scientific, highly accurate, and detailed prediction. 

Roy


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## got6ponies (Jan 31, 2011)

*today @ 12:00*








about 1:20 now....







the _needle_ is stationary. the pressure on the _graph_ has dropped, in the last hour, and im hearing thunder from my desk(i should be working)......... today its being pretty accurate!


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## domino (Feb 26, 2008)

My experience is that I can pretty much tell when rain/storms are coming by looking just at the barometer trend over the last 8 to 12 hours if I have been stationary. This seems very accurate in eastern North America, Central America, and the Andes in South America. Now, in most cases where I've done this, temperature has been relatively stable, but not in eastern North America. Even without considering other parameters, just looking at the barometer, I've found it very reliable in predicting weather changes (from no rain to rain or reverse).


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## xevious (Feb 1, 2008)

RoyR said:


> I was mainly looking for your anecdotal experiences using a barometer to try to predict weather. You know, something like, "the pressure dropped .2 inches of mercury in an hour yesterday from 1 to 2pm, and all h*ll broke loose at 3pm..." That kind of thing.
> 
> I realize a barometer alone is insufficient to make a scientific, highly accurate, and detailed prediction.


Ah, I see what you're getting at. Sorry for my assumptions, you do seem to be more aware than I thought.  (I used to be a meteorologist in the USAF). Looks like *got6ponies* has a pretty good example of what you're requesting.



domino said:


> My experience is that I can pretty much tell when rain/storms are coming by looking just at the barometer trend over the last 8 to 12 hours if I have been stationary. This seems very accurate in eastern North America, Central America, and the Andes in South America. Now, in most cases where I've done this, temperature has been relatively stable, but not in eastern North America. Even without considering other parameters, just looking at the barometer, I've found it very reliable in predicting weather changes (from no rain to rain or reverse).


It sounds like this is also in regions you are familiar with, where there is enough stability in other factors to lend more weather influence to the changes in barometric pressure. Do you find your accuracy on predictions pretty consistent across the seasons?


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## domino (Feb 26, 2008)

xevious said:


> Ah, I see what you're getting at. Sorry for my assumptions, you do seem to be more aware than I thought.  (I used to be a meteorologist in the USAF). Looks like *got6ponies* has a pretty good example of what you're requesting.
> 
> It sounds like this is also in regions you are familiar with, where there is enough stability in other factors to lend more weather influence to the changes in barometric pressure. Do you find your accuracy on predictions pretty consistent across the seasons?


I only have data from Central and South America between April and August, and all year round in eastern US. I look for pretty obvious trends - not just dropping one block on the graph, for instance. I think that most of the situations in which I use these watches are in fact pretty stable, and most rain is in the form of storms which come with dropping pressure - I'll have one again this summer in Central America during the rainy season - I'll look to see if I can predict the daily rains that we often get there.


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## RoyR (May 5, 2011)

Hey Domino...incredible post about using your watch while mountain climbing...what a place to be when you need to try to predict the weather. But I guess you did ALOT of weather research before you attempted that long ascent! I would be interested if you could elaborate on your other weather-related experiences with the watch. If anyone relies on field weather observations and predictions, you certainly do!

Here in the eastern US, we are getting very similar weather, day after day after day: usually high in the upper 80's, mostly clear with some clouds, and a ~30% chance of showers or thunderstorms, which seem to usually miss me.

In some weeks, I have watched the barometer trend slowly upward by .2 inches over 12 to 18 hours or so, then go down by .2 inches over another 12 hours, with no obvious change in weather. In the past few weeks, the pressure has gone up and down between about 30.10 and is now at 29.75. Pretty big change for summertime here, but no observed change in the weather.

About the only thing I've observed that seems to reliably predict bad weather, real soon, is a very quick drop of maybe .15 inches over 6-8 hours or so. It looks like a little "wave" on the barograph. Maybe the wave on the graph reflects what meteorologists sometimes say that there is "a wave in the atmosphere" when bad weather is coming? After this little wave, I get a quick shower and heavy clouds for awhile. Then back to the same weather I wrote about above. 

I've only been watching pressure closely since early May, when I got the watch. I guess I'll need a year or more of observations--through all the seasons--to learn any reliable (or semi-reliable) tricks about forecasting around here. 

Keep the comments coming...

Roy


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## domino (Feb 26, 2008)

Hi RoyR,

I think I'm seeing the same thing as you noted - when I see a noticeable drop in the graph, quickly, bad weather follows within a few hours. I haven't noted what that amount is - I just use the graph (not very sophisticated, I realize!). While mountain climbing, I do the same thing. In my relatively limited experience, it seems that a stable barometer would indicate similar weather to what we had seen the last day or two, and a rapidly falling barometer indicates a change for the worse. A rising barometer seemed similar to a stable barometer in terms of what I observed. I realize this is very basic and anyone with a real meteorological background will cringe at this kind of thing, but I'm just reporting what seems to have worked for me.



RoyR said:


> Hey Domino...incredible post about using your watch while mountain climbing...what a place to be when you need to try to predict the weather. But I guess you did ALOT of weather research before you attempted that long ascent! I would be interested if you could elaborate on your experiences with the watches in your other experiences. If anyone relies on field weather observations and predictions, you certainly do!
> 
> Here in the eastern US, we are getting very similar weather, day after day after day: usually high in the upper 80's, mostly clear with some clouds, and a ~30% chance of showers or thunderstorms, which seem to usually miss me.
> 
> ...


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