A model question?

[Potent Gust]

I love this site and I have enjoyed my first three months on here. However why is it that when models show cold weather it seems to always get downgraded but mild weather does not get downgraded as much?

Why do models show such great cold weather in F1?

Andy

[chionomaniac]

Hi PG

Having watched the models for over 3 years I don't think this is the case. It seems to me me that the models fluctuate between mild and cold and meet somewhere in the middle by T=0Z . The thing is the majority of people on here (myself included) are always on the lookout for the colder scenarios and these are the one we pay more attention too. By the time forecasting comes into a more reliable timeframe the models error is less, and the cold or mild scenarios are less pronounced (not always!). Therefore it seems that cold scenarios are downgraded ( but mild ones are as well, but the majority of us don't notice). Having said that because of other factors such as warmer sea surface temps etc I reckon that lot of model forecasting may be programmed on synoptics of (even recent) yesteryear that may not come into fruition today.

c

[Roger J Smith]

Well, over three years of intense observation, I have noticed that the GFS has a tendency to advect too much cold air over large expanses of open ocean. Clearly there is something in the programming of the GFS that is in need of a tune-up because it has happened more times than not, the -10 C isotherm at 850 mbs which is a good indicator of snowfall potential, is almost always 100-300 kms too far west or south depending on the direction the cold air is flowing, at times beyond 72 hours, and this is probably due to the fact that ocean temperatures are nowadays 1-2 C warmer than perhaps when the GFS was first developed, not sure if that's the only reason ... mild air masses on the other hand are coming at the UK from a direction where ocean temperatures are more similar to the past, so whatever the programming is there, still works reasonably well.

Other models have had similar issues, but each model seems to have one flaw that continues to show up and needs some urgent attention. The GEM is quite good for N America actually, but has the reputation of being too progressive with systems east of the central Atlantic, say 20 W. Not sure what you would say the ECM has as a regular flaw, being wrong I suppose.

[Paul Sherman]

Moving this to learners area!

Paul S