Flying weather = whether we go flying

Having now completed just a little over 8hrs as PUT (Pilot Under Tuition), I’m starting to take more notice of the weather than even your average Englishman. I recently started flying circuits, and it was apparent that some further study was required on my understanding of the weather. Meteorology is a huge topic, so today I’m just looking at one of the tools we can use to determine the winds we are likely to encounter en-route.

The Met office has a fantastic little booklet “Get Met”. It has a lot of useful information for pilots – you can download it here

One of the things not explained in there is how to read the Form214 spot wind charts.

Met Office Spot Winds Form 214

Met Office Spot Winds Form 214

Here is a sample chart from today. I have particular interest in today as I’m supposed to be going up in a couple of hours, and it looks like I’m going to be dealing with some decent cross winds. Looking at the big box over the midlands we can see that at 1000ft the winds will be roughly 200 degrees at 15 knotts, with a dry bulb temperature of +11 degrees C.

So, the first column is flight level (in thousands of feet AMSL – Above Mean Sea Level). Bear in mind this isn’t the same as height AGL (Above Ground Level). AMSL is what your altimeter would read if it were set at standard 1013Mb (ok, strictly 1013.25Mb but who’s got eyes that good?). So, as my airfield is at about 300ft above sea level, then I will be flying circuits at around 1300ft AMSL. As long as the QNH is within 20Mb of 1013Mb, then I’m not going to be more than about 1900ft AMSL or below 700ft AMSL – either way, the chart gives the same wind forcast.

The second column gives the wind direction – or rather the direction the wind is blowing FROM.

The third column is the average wind speed in knotts.

The fourth column is the dry bulb temperature in degrees C. This is the temperature of the dry component of the air, without any windchill factor. If you were to wrap a wet bit of cloth around the thermometer and stick it out of the window you get the wet bulb temperature, which would be  much cooler. By using these two temperatures, you can determine the relative humidity. The dew point point is almost exactly (for practical purposes) the same as the wet bulb temperature.

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