Archive for the Meteorology Category

Meteorology Exam : Passed

Monday, February 18th, 2013 | Permalink

Meteorology - PPL3

Meteorology – PPL3

After months of putting it off and finally just putting a date in the aero clubs books a few weeks back – which makes it a heck of a lot easier to revise for once you have a deadline you can’t ignore.   I finally sat my Meteorology exam.

With a final revision blitz over the weekend and not stopping until my head was about to explode with information about weather fronts and Form 215 interpretation.   It was time to see how I did for real.

Passed :  100%

I was quite amazed by the score, there was a question on icing I was 50/50 on and the last question I spent a good 5 minutes hmmm’ing and ahhh’ing about if the flight was safe or should be delayed.  Still, after a weekend of revising this much and all the previous months of opening the book and reading it over and over again.  I’m not sure I could have faced having to re-sit it, so I’m very glad it’s a done deal 🙂

…… on to the next one.

Lesson 24: Circuits (Cancelled – High Wind)

Monday, June 25th, 2012 | Permalink

The day before the lesson, the wind was forecast to be 24 mph (20 knots) and gusting even higher.

So, I was well prepared when the phone rang for this lesson to be cancelled.

It wasn’t a total loss, I guess as my instructor was just going to be sitting around anyway she said to come in and we could get some other ground work bits and pieces signed off in my training record.

You don’t pay if the propeller ain’t spinning (money makes the propeller go round), so this was a bit of a freebie, we like free stuff 🙂


Metars are actual observations of the weather, they attempt to give you a picture of what it’s like right now.

TAF’s (Terminal Aerodrome Forecast) are, as the name suggests, forecasts of the weather and give you a ‘best guess’ at what it might be like in the near future and for how long it might be like that.

Both come in an encoded text format, standardised by the ICAO if you can read them in one location, you should be able to read them anywhere in the world.

Met Office : Aviation Services

If you want accurate and up to date METAR’s & TAF’s, one of/the best source at least in the UK is The Met Office and thankfully they offer an “Aviation” service, for free.  You just need to register (free) and then login and you can get at all the information.

In addition to METAR’s & TAF’s, The Met Office provides Form F214 & 215, which provide wind speeds and graphical displays of the weather updated regularly during the day.

Really good service, if you haven’t found it/aren’t fully using it to its full potential yet, check it out.   As with all big websites there’s a lot of information and it’s sometimes hard to find where the good stuff on there is, but just those handful of bits are useful.

Aerodrome Information

Having gone through that lot and decoded a few METAR’s & TAF’s (more stuff signed off in the training sheet), I was shown possibly the only book I’ve yet to buy, the UK VFR Guide.

Maybe I shouldn’t have jumped in with “Ahhh yes, I need one of those….”  Because the excitement was shot down pretty promptly by a reminder that actually, it can go out of date and the publisher is under no requirement to inform you.

The official source of information for aerodromes, should be the CAA’s AIP, specifically the Aerodrome section.   If something changes, they will re-issue the page(s) affected.   So another useful bookmark to have is where you can find all of this information.

In addition on there you can quickly search NOTAM’s (NOtice To Air Men) and find out things like why an area is currently marked as a danger area etc.

The Out of Date Chart

When you start to fly, there’s a lot of stuff you need and you’ll either buy it all in one big spending spree of ‘super preparation’ (there’s not masses of point to this), or you’ll add loads of it to wish-lists etc. and get friends & family to buy it you….. After years of “What do you want for….???”   I finally had a huuuge list I could point people at 🙂

So of course when asked “Do you have a chart?”

The answer was an excited “Yes”, finally the beginnings of using it in anger for something!

Nicely folded, we began to unfold it and discovered it was Issue 37……bought just around the new year marker (guess), we had sailed past April and well, now it was out of date!    Issue 38 is now out 🙁

If you ever wanted proof that buying stuff before you really need it  isn’t useful, this is it – but hey, I got to practice my map folding with it so it wasn’t a total loss.

Now for the bad news, I couldn’t get the box for “Current / Valid Chart” ticked off, I might have had a very recent chart, but it wasn’t the current one  🙁

A good hour on the ground

All in all, a very enjoyable hour on the ground learning some new things, getting better at others and being shown around a few sites I probably should have been playing with a long time ago but have been far to busy with flying 🙂



Wind, Pressure and Coriolis Force

Sunday, September 11th, 2011 | Permalink

Lesson cancelled today due to a high cross wind, almost at a right angle to the run way.   Rather than dwell on the fact that I now seem to have complete control of the wind and rain (but cannot tame the sun!!).   Time to look back at the cause of today’s cancellation…… The Wind.

Air Pressure

First thing to remember when looking at a map plotted with measurements of pressure (e.g. 1010mb),  is that you’re actually  looking at a plot of ‘elevation corrected‘ pressures – not the actual measured pressures.   This is because if you didn’t correct all the measurements taken across a large chunk of land, all you’d have a is a map of pressure with respect to elevation.    This will tell you nothing about wind, it would just be telling you that the high point had low pressure and the lower point had a higher pressure…..  Which is obvious because pressure decreases with altitude.

The correction is roughly 1mb per 27ft above mean sea level of the location, though is often rounded to 1mb = 30ft.

If lots of points are taken at the same time across a large area (i.e. a country), and the measurements are elevation corrected to put them all at mean sea level.   Then you’ve effectively got a map of pressures which you can then use to see how steep the pressure gradients are, which will tell you about the wind.


With all the pressure measurements elevation corrected and plotted on a map.  Lines can be drawn to connect points of equal sea level pressure.   These lines are isobars.

Lines close together indicate:  A steep gradient in pressure over a short distance.

Lines far apart indicate: A slack pressure gradient.

Pressure Gradients

Air flows down a pressure gradient, from high pressure to low pressure.

The steeper the pressure gradient, the faster the air flows….  The greater the wind!

As the proximity of the isobars dictate the steepness of the pressure gradients:   The closer the isobars are together, the greater the wind will be.

Coriolis Force

Coriolis force is caused by the earths rotation, instead of traveling in a straight line along the pressure gradient line – Coriolis force causes the wind to be deflected and flow in an arc.

The force is strongest at the poles (north/south) and acts at 90 degrees to the Right of the moving air particle in the Northern hemisphere.   While it acts at 90 degrees to the Left in the Southern hemisphere.

Because air will flow from high pressure to low pressure and the Coriolis force can act at a different angle to that flow.   It is feasible for the air flow caused by the pressure gradient and the Coriolis force to cancel each other out.

Wind Measurements

Finally wind is always measured as a Velocity.

This means it must always be expressed as having two components:

  1. Direction
  2. Speed

There’s lots more to wind:   Local Winds, Wind Velocity with altitude, ground obstacles & turbulence etc. etc.   All for another post….

Buys Ballot Law

Friday, August 5th, 2011 | Permalink

In a previous post I talked about Buys Ballot Law (Finding Low Pressure)the danger of flying on a constant indicated altitude (caused by not updating the altimeters pressure setting).

Buys Ballot Law is a means by which you can work out if you’re flying into high or low pressure, from effects that will be felt on the airplane performance & direction.   Hopefully setting off the mental spark of “I’m not updating my altimeter!!”

In the Northern hemisphere, if you stand with your back to the wind, the low pressure is on your left.

This is because in the northern hemisphere air flows clockwise around high pressure areas and anti-clockwise around low pressure areas.  Thus no matter which area you’re in, if you have your back to the flow of air (wind), to the left will be low pressure.

In the southern hemisphere the inverse is true.

Practical Use

So if an aircraft is getting blown/drifting to the right (the wind is coming from the left of the aircraft).   If you were to turn your back to the wind, your left would be in the direction the plane was flying……thus the plane is flying into low pressure (and the altimeter, if not updated, will begin to over-read).

The reverse is also true, if the wind is coming from the right and pushing the plane left.  Then the plane is flying into High Pressure and the altimeter will begin to under read if not corrected.