Perhaps you like to shop around for your weather, checking out Environment Canada (EC) and The Weather Network (TWN) or you hear talk from others that it will be cold next week, but that’s not what you heard.

Today forecast’s from the two weather sources is a prime example of how they can be so different.
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As you can see the difference from Saturday onward, including Monday which is a whole 6 degree difference in the daytime high.  How can that be? Aren’t they looking at the same data? Well the answer is, yes and no.

There are a variety of different weather models out there, but for arguments sake, there is really the big 3…The Euro (ECMWF), The American (GFS) and The Canadian (CMC or GEM).  There are others widely used like the NAM and the UKMET, but let’s go with the big 3.  If you asked TWN or EC, they would probably say they don’t favour any model, but its a combination of looking at all of them and using their skills, which is probably true.  But if you look at the models, there is clearly some favourites.

The picture I posted yesterday of the height anomalies from the big 3 shows you their favourites:

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If you notice above the first North American frame to the left is from the Euro, which shows the High pressure cold trough larger and stronger and sitting right in Quebec.  This would favour colder conditions in Ontario, and would be how TWN would get their forecast.  The last frame is from the CMC, which shows the trough a little weaker and sitting more towards eastern Canada, and would favour conditions to be a little warmer in Ontario, which would be EC’s forecast.  EC almost always seems to favour the CMC, while TWN favours the Euro or the GFS, which is the one model in the middle frame in the above picture, which is also stronger and closer to Ontario.  This is also why often with a winter storm the 2 weather sources can have very different snow forecasts.  When they are the same, it often means there is good model agreement from all of them.

So who is right?  Well, the Euro has become the favourite of many forecasters.  It handles the long range very well, but its not perfect and has made mistakes before.  The GFS also performs fairly well, but has its bad moments.  The CMC is mixed results, and I would say certainly not a favourite.  My preference in order is; the Euro, GFS, CMC and then the NAM.

When we see a spread like this, I typically take the middle road and say that Monday will be a high around 9c.  Let’s see which model was right, either way it will certainly be colder next week.

 

If you are looking for sustained warmth, its certainly in the west coast. BC and Alberta have been having an amazing winter and spring so far.  It’s quite summer like out there!

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