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Falling Barometer Forecast Trainer

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About This MicroSim

Students reliably learn "low pressure means bad weather" and stop there. It produces wrong calls, and it is wrong in both directions.

The forecasting signal is the rate of change, not the value. The only way to teach that is to present traces where the two disagree and let the learner get it wrong somewhere it costs nothing.

You see 24 hours of trace. The next twelve are covered up until you commit. The panel gives you the current pressure, the reading three hours ago, the tendency in hPa per 3 hours, the rate in hPa per hour, and a plain-language category - the same set a synoptic observer reports.

The dial has two needles. The black one is live; the brass one you drag and leave. The gap between them is the tendency. That is what the second needle on your grandmother's barometer was for, and it is the only reason a pressure dial was ever useful to a non-specialist.

Six traces, two of which are traps:

  • High and falling fast reads 1025 hPa, comfortably inside the normal band, and is dropping 4 hPa every three hours. Predict "fair" from the value and you will be wrong in four hours.
  • Low and rising reads 990 hPa, which looks alarming, and is climbing steadily. The storm has already gone past.

Plus rapid deep fall, more than 6 hPa in three hours, which is the rate Robert FitzRoy built the first storm warnings on in the 1860s; steady low, where a frightening-looking value does nothing at all for a day; and the diurnal wobble, a twice-daily atmospheric tide of a couple of hectopascals that is not weather and must be learned and then ignored.

How to Use

  • Pick a Trace, or press Random trace.
  • Scrub the Hour slider back through the last 24 hours. Watch the tendency change.
  • Drag the brass needle to the current reading, then scrub forward and watch the gap open up.
  • Commit to one of the five forecast buttons. The next twelve hours appear and the panel tells you which cue mattered.
  • The score keeps count. Work through all six.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://iowerx.github.io/pi-env-monitor/sims/falling-barometer-forecast/main.html"
        height="654px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

6-12

Duration

25-30 minutes

Bloom's Taxonomy Level

Evaluate (L5)

Prerequisites

  • Reading a line chart
  • Chapter 7 sections on highs, lows and why air rises

Activities

  1. Establish the wrong rule (5 min): Run Steady low and Steady high without looking at the tendency, predicting from the value alone. Note your score.
  2. Break it (10 min): Run High and falling fast and Low and rising. For each, write down what the value suggested and what the trend suggested, and which turned out right.
  3. The whole set (10 min): Work through all six traces. For each, write the rate in hPa per hour and your forecast before pressing a button. Aim for six out of six on a second pass.

Assessment

  • Predicts from the tendency rather than the absolute value.
  • Recognises the diurnal oscillation as non-weather.
  • Justifies a forecast by reference to a rate, in hPa per hour, and a physical mechanism.

References

  1. Wikipedia: Robert FitzRoy - the first storm warning service, and the barometers he had installed in fishing ports.
  2. Met Office: how pressure affects our weather - highs, lows and tendency.
  3. Wikipedia: Atmospheric tide - the diurnal wobble scenario.
  4. WMO-No. 8, Guide to Instruments and Methods of Observation - the three-hour pressure tendency as a reported quantity.