Tuesday, April 28, 2009

If it's Tuesday, It Must Be...


Tuesday night is IFR ground school night. This will be the fourth session.

I put a lot of emphasis on weather. Each student picked a route, and is supposed to get a weather briefing for that route every week. This was impossible the first week, when the class was interrupted by the loud bangs of the hail to the left on the metal hangar roof.

The next week, we mostly worked on getting good weather briefings.

The next week we had mountain obscuration in light rain (RASH-) and mist (BR). We looked at the winds aloft and the circulation around highs and lows. A low near Washington, DC was bringing warm moist air, and weather in New York and New England was predictably messy.

I teach students to judge the forecast, not just read it. "What's wrong with this forecast?" I ask. "Why are they forecasting mountain obscuration? Where is the freezing level?"

I personally find undecoded METARs and TAFs easier to read, because in many cases passing your eye down a formatted column tells you what you need to know. With the decoded forecasts, you have to read the whole paragraph, which is kind of purple. The phrase "automated station with precipitation discriminator, sea level pressure 29.79" Hg (1008.8 hPa), 0.04 inch (water equivalent) of precipitation in the previous hour" takes much longer to process than "A02 SLP088 P0004." And remember that for a long flight you will read "0.04 inch (water equivalent) of precipitation in the previous hour" many times.

This week it is raining, and I'm afraid that my students are going to come to a conclusion about forecasts: it doesn't matter what they predict for Tuesday, it will be wet.

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