Nav Canada versus Environment Canada - what gives?

[PunkStarStudios]

When I am town - Tuesday nights is the night I go sailing with friends.
I've noticed something.
They always pull up wind from Environment Canada - I pull up the forecast for the Toronto Island airport. The forecast often doesn't match.
Today being a perfect example there's about a 15 knot or so discrepancy in the winds tonight (and I think even in the probability of thunder storms).

I thought I'd take a look at current conditions for Pearson for right now.

Environment Canada says it's 41 gusting to 55 km/h at Pearson right now.
Nav Canada (aviation) says it's 33 gusting to 44 km/h right now at Pearson.

(Converted Nav Canada from knots to km/h)

So for the above Nav Canada has the winds 10 km slower. For tonight for the island though - Nav Canada has the winds significantly higher than the Environment Canada forecast.

As a pilot - I relly only care about the METAR/TAF of course - but I've never had a satisfactory answer to the question on why the discrepancy when I am quizzed on it.

Anyone have any idea what's going on here?

[lilfssister]

A little confusing. You're talking reported winds and forecast winds AND discrepancies between NC and EC weather reports.

I just checked Pearson NC and EC weather.

NC: 13G22 knots= 24.076kmphG40.744

EC: 24kmphG41kmph

What are you using for a conversion multiplier?

[looproll]

I know it's pretty obvious, but make sure the times match. "Observed at: Date: " is on the EC site and often it is slow to update compared to the METAR. I usually check both. I have never noted any discrepancies between the two reports taken at the same place and time.

[PunkStarStudios]

I should have taken a screen capture of the two reports.... I will next time.

There was definitely a discrepancy. I did notice that at some point shortly after my post (I had been checking it very often) they equalized - it was almost like one was slower to get the updated numbers.

In all fairness - the winds were very bizarre yesterday. Island was forecast for gusts up to 45. Winds never made 20 and in fact settled around 13 for most of the evening - even though Hamilton and Pearson were both around 28 and 32 knots.

[W0XOF]

All of the Nav Canada forecasts, terminals (TAF) and graphics (GFA etc), are all provided by Environment Canada, aviation forecasters. The marine forecast (if that is the EC forecast you are referring to), is a totally different set of forecasters, and usually from a completely different office.

Also, the aviation forecasters usually are the least senior, followed by public forecasters and the most senior being the marine (at least that's how the Pacific Weather Centre has worked).

[Rudy]

So that's why the public forecast is often more accurate than the TAF.

[Gannet167]

I'd guess there are also a different set of parameters in publishing weather. When you look at tomorrow's forecast to see if you'll cut the lawn or not, there isn't as much on the line as if you're trying to figure out if an airport is a valid (or smart) alternate. I think there's more pessimism in the aviation weather to allow a better envelope of safety.

[jakey]

The Island forecast is NEVER accurate in my (limited) experience...