Altostratus and a falling barometer

Why would you do your own weather forecasting?

Among the subjects our navigator has had to master for licensing and examination purposes is meteorology.  This hasn’t been as a science or an academic subject, but as something with an immediate practical application.  When on a ship near a typhoon, for instance, there are rules for how to work out where the storm might be, from clues in the sky and from instruments; and this bit of information is vital for avoiding the worst of its effects.  He has also learned the sequence of clouds and wind patterns one expects with (say) the passage of a cold front, and in general what his own observations can tell about the weather in his immediate future.

He admits he hasn’t actually used this knowledge very much.  At sea, he received weather forecasts based on enormous quantities of data, crunched by very powerful computers, that far surpassed the effectiveness of his own guesses.  On his smart phone nowadays he gets an hourly forecast for temperature, wind and precipitation, along with predictions over a week into the future.  Even though the weather is a prototype scientific hard problem, enough progress has been made that the rules of thumb from former times have been pretty much superseded.

But there are aspects of do-it-yourself meteorology that, we think, make it a useful exercise.  The first is that it necessarily combines a variety of data.  The reading of the barometer, the direction and strength of the wind, the type of clouds in the sky, are not informative individually; together, they can tell you something.  Second, as a rule it is the change that is important, so you must keep track.  Altostratus thickening and lowering with a falling barometer: storm coming.  Being aware of all these things and knowing their meaning, as opposed to checking the smartphone forecast, is like having a map instead of relying on turn-by-turn directions.

And there’s another aspect.  Each location is unique; it has its own microclimate.  The weather services are concerned with large pieces of real estate; your side of the hill will have differences from other other side.  With time, you can notice these, and add them to your own private sky.  Our navigator remembers the Navy weather officer on Okinawa (responsible for that island) arguing with his Pacific Ocean counterparts on Guam about where a threatening typhoon would go, and being right.

Nowadays the wind is the hardest to observe.  In a rectangular grid of buildings, what meets you at the corner may have very little to do with what’s happening up above, where the clouds are moving.  Our navigator is willing to take what his smartphone tells him, consoled by the thought that the observation comes from an actual weather station and not a rumor on social media.

This afternoon, the barometer is falling slightly, and the fog of early morning has burned off to show some cirrus and scattered cumulus.  No storms are in the offing, but we can’t offer our astronomer photometric conditions.