Is anyone able to provide a reasonable explanation as to why the LL GPWT data format uses:

- 2 digits for wind direction, and

- 3 digits for wind speed?

All wind directions can be intuitively described with 3 digits, even if the leading digit is zero. I can generally grasp where a forecast wind of 030 or 090 is coming from.

But how often is a forecast low level wind in excess of 99 knots? The occasional cyclone involves low level winds in excess of 99 knots, but I generally don’t fly if the low level winds are forecast to be in excess of .... hmmmm.... I’ll pluck 75 knots. Makes things unpleasant, I guess.

Smart enough to remember that 9999 means in excess of 10KMs visibility. I reckon I have enough brain cells left to remember that a forecast wind of ‘99’ means in excess of 99 knots.

I note that all current LL GPWTs at the time of this post have a ‘0’ in the front of every forecast wind direction.

What awful and dangerous risks to aviation safety would arise if the LL GPWT format was:

- 3 digits for wind direction

- 2 digits for wind speed (with the rule that ‘99’ means in excess of 100 knots).

I realise my question assumes that someone’s reading LL GPWTs, and that that’s an heroic assumption. But humour me.

It might be the ICAO compliant format. I wonder where low level winds are routinely in excess of 99 knots...

Have to agree. I’ve seen a few students transpose wind speed and direction with the new format. Clearly whoever designed this was not a pilot, nor did they consult a pilot.

That solves at least one mystery for me, Cloudee: Student pilots (at least some of them) are being required to interpret LL GPWT charts. I feel for them.

How on Earth do they work out the grids to be used for a flight? My EFB now (mercifully) plots the plan on the electronic copy of the GPWT and does some ‘automatic’ calculations, but .... jeeez ... I’d hate to be doing it the ‘old fashioned way’ on these ‘new’ charts.

2 digits, 3 digits...

Probably commonality with the the upper level charts.


Heres a question, a tangent from the topic but on a similar path. Why not name runways with 3 digits? Runway 26 is 260 degrees....

I asked about the safety risk...

Runway numbers? What do they do in the USA?

Aviation seems to be unique in the propensity to come up with counter-intuitive systems. 2 (or even 1) digit to describe the magnetic orientation of a runway (or wind direction), yet 3 digits to describe a wind speed that, at low level, is almost never above 99 knots.

What could possibly go wrong?

Thus demonstrating, once again, why using single or double digits to describe runway or wind direction, while using three digits to describe low level wind speed, is a patent and confusing nonsense.

But what could possibly go wrong.

Yep. I’m sure I would be severly disappointed on each occasion that a forecast had 150 kts rather than 99 kts. It would make a profound difference to my decision to remain on the ground...

We’re talking about low level forecasts.

That makes sense. “They” being bureaucrats and “need” being their convenience. It goes without saying that they don’t give two ****s about GA down low.

Here’s another stupid idea:

- 3 digit wind directions

- whatever number of digits the winds happen to be.

The wind is forecast to the nearest 10 degrees, so if you switched it around you’d have the same situation anyway.

Every 3 figure direction value would have a zero at the end, instead of every speed value having a zero at the beginning.

This is is a big fat waste of time.

A big fat waste of time, except for people like Cloudee’s students who transpose counter-intuitive numbers.

But we get it loud and clear: It’s not about reducing the risk of mistakes. It’s about the convenience of the ‘service’ provider.

I personally only use the GPWT for an overview. The wind/temp profile function in NAIPS is handy when doing a manual flight plan for a long leg. Gives you an expected head or tailwind component with no maths required.