The great quandary…

We know we should be purely metric, but both the culture of Meteorology and the public we serve require that we be bi-unital (is that a word?)

Example: The Fahrenheit is a metric system of human experience – it will not go away anytime soon.◦ 0 to 100 F is the rough scale of “normal” weather for

most Americans. Anything either side is considered way outside of the ordinary.

What’s so wrong with millibars? If it was good enough for the Bjerknes, shouldn’t it be good enough today?

A meteorologist really has to have a feel for both. Anything scientific you read will be in Celsius, most forecasts will be in F.

The dreaded formulae:◦ To convert degrees Fahrenheit to degrees Celsius:

Subtract 32 degrees from Fahrenheit, then divide by 1.8 (aka 9/5)

◦ To convert degrees Celsius to degrees Fahrenheit: Multiply Celsius by 1.8, then add 32 degrees

◦ To convert degrees Celsius to Kelvins (K): Add 273 to Celsius temperature, as K = Degrees Celsius + 273

My suggestion – learn a few equivalents so you can have a rough idea of Celsius temps:◦ Besides the obvious (32F = 0 C)◦ Necessary condition for tropical cyclone

development (79F = 26C or 80F =26.5)◦ Comfort Ranges:Celsius Fahrenheit Comfort10 50 Chilly15 59 (nearly 60) Cool20 68 Cool side of Nice25 77 Perfect30 86 Warm35 95 Hot38 100+ New Normal for

BCS

We drive in mph, and the public likes wind in mph.

Operationally, Meteorologists talk knots because of mariners and pilots.

We read science in m/s . Hints:

◦ Knots are nautical miles per hour. A nautical mile is 2000 yards, while a statute mile is 1680 yards. So a knot is a little bigger than an mph. Add 15 percent or multiply knot by 1.15 to get mph. Multiply mph by .87 to get knots.

◦ A m/s is about twice as big as a knot: 10 m/s is about 20 knots (more precisely, 19.44)

Rarely see kph for wind, thankfully

Even the metrics have a problem here – in any field the metric units which give the item of interest a 1 or 2 digit character tend to dominate.

Hints:◦ Get a feel for a cm. Takes about two and half of

them for an inch. ◦ A meter is a little bigger than a yard or 3 feet.

1m is 39.4 inches◦ A kilometer is quite a bit smaller than a mile,

takes 1.6 of them.

Inches of Mercury – What’s that all about?◦ Very physical and first principles

“Standard” pressure:◦ 29.92 inches◦ 1013.2 mb◦ Commit both to memory

A hecto-Pascal (hPa) is a mb. Also is 100 Pa. I hate hPa. Don’t you? BTHOhPa Blaise was a good friend of mine… Not Really