alperton - use barometer-

Barometer pressure readings

Product Disclaimer

The verdict associated with the speed of pressure variation graph is the result of applying simple empirical rules. It is only meant to be an alternative method of weather forecast given specific L-H weather systems are present. It comes without any warranty of any kind regarding the precision of the foreacast, rather aimed at giving possible interpretations to the changes in atmospheric pressure in the context of weather forecast.

If you need more information on the subject, search on the following


- weather pressure

- weather fronts

- high and low weather systems

Sample data

Presure falling only 1.4 hPa in 3 hours (0.57 hPa per hour), at less than 1006 hPa, can indicate conditions for rain and periods with rain:

Fig 1. Barometer 'verdict' in red.

Barometer verdicts

A classic barometer's speed of change can be utilised as alternative for grand weather change forecasts. It has been emulated with today's modern data acquision.

It is like having a barometer at your disposal, the setting hand ("golden") goes to the time = 0 (now), marking whatever the pressure reading is there; and the measuring hand will be observed at t = 5 hours (in the future). In the end, you will not only see the total hPa difference, but the hourly variation. If you used a barometer before, this will be easy with the caveat that the verdit applies 5 hours into the future.

The thresholds of 1010 hPa and 1022 hPa separate the pressure into zones where speed of pressure rise or fall give distinct weather change verdicts, see table below. We split the pressure thresholds as per first column, the first interval being from -0.3 (small fall) to + 4 hPa( really large rise) and beyound. The other intervals are all falling levels, see table.

Speed hPa/hour LOW PRESSURE under 1010 hPa CHANGE 1010 - 1022 hPa/mb HIGH PRESSURE over 1022 hPa

-0.3 .. +4.0

Clearing and cooler

Current conditions continue

Steady fair weather

-2.0 .. -0.3


Little/No immediate change

Fair weather

-4 .. -2.0



Cloudy and warmer

Analysis span of 5 hours is utilised. We are forecasting weather based on forecast pressure data indeed, but we believe it still adds value to the 'will it rain?'' decision and offers another approach and insight. It is about L - H weather systems, about colision of cold and warm weather fronts, these will be captured by the 'sofware barometer'.

Therefore, this is one interpretation - not all implementation details were described accurately here - but you can choose your own model, see: 'Tutorial' in this task;

You can change the analysis span to 3 or 7 hours, use different pressure range thresholds (+1.0 .. -0.3 .. - 2.0 .. -4.0 hPa/h), change the description of the verdict.

More captured data, sample images from the app:


Fig 1. (above) 12.9 inch 4th generation iPad image shown;

Weather clears @ 1004 hPa, but data, not included yet in 5 hour analysis, show rain may return. However, the user can see it coming:

Fig 2. (above) 12.9 inch 4th generation iPad image shown;

How precipitation chances coordinate to the change of pressure on an instance when the rain seems to be stopping. Also, how relatively slow variation of 0.4 hPa / hour is compatible with rain:

Fig 3. (above) 12.9 inch 4th generation iPad image shown;

Summer showers can be observed even if barometer conditions not concurring, that is because it is not a weather system with HIGH and LOW PRESSURE hitting your location that caused it. Rain data is coming through from sensors & precipitation radars:

Fig 4. Screen captured on iPhone 11 Max Pro;

pls note: Some empirical rule of thumb.

One can have a rain/storm that is part of the weather system coming to your place. Usually you watch for pressure falling below 1010 hPa, how fast it does it, the main event -rain or storm- is when you reach the LOW pressure eye. The barometer does its job with this, predicting both going into and coming out of it.

But one can also have rain at higher than 1010 hPa, notably with no weather system, air pressure flat-ish, rain showers driven by local weaker winds, the situation can persist for days. Forecasting this is only possible with precipitation radars. A barometer cannot see such a situation. However the barometer can still help with this heralding the end of it. When it does read rapid & steady rise of pressure to 2020 hPa and beyond it signifies fair weather. (rather than the: 'Current conditions continue' see table cell (row 1, col 3)).

In conclusion, if the precipitation forecast shows rain and, at the same time, the pressure is above 1012 hPa, the verdict would be: "would take the 'rain showers' advice";

We can also have the barometer forecast more fair weather on top of already fair weather:

Fig 5. Screen captured on iPhone 11 Max Pro;

pls note: If we value real data cases, gathered in time, then we have to show screens captured with various older app versions, in use at the given time.

Therefore, one will observe slight wording differences when compared to the downloaded final version app. Also the weather icons from the bottom of the pressure change graph, visible in older versions, now have been removed.