12z VS 0z runs

[Adam Lucio]

I've often noticed that 12z runs appear "colder" than the 0z runs.

Is this because of their respective samplings of the balloon network? As I continue to get more in depth with my own self taught forecasting skills this is one of the things I am beginning to wonder.

I don't put much weight on 6 or 18z runs after 3 days because they don't get those samples, so I am talking about 0 and 12Z

Anyone know anything to either prove or disprove my thoughts? I'd be interested to know.

 

[Scott Olson]

At what level are you refering to? Can you post some examples?

 

[rdale]

HPC has some model verification pages, you can find more info there.

http://www.hpc.ncep.noaa.gov/html/model2.shtml

Saying 12Z is "colder" than 00Z (or vice versa) is probably too much of a simplification.

 

[Adam Lucio]

Going off looking at surface data, I would assume all other layers would be similar. Yea, colder is a general term which is why I put it in quotes because I'm not sure how else to describe it. In particular when digging for chaseable setups I noticed the 12Z shows an overall cooler, less favorable chase pattern whereas 0Z tends to heat things up a bit.

Sorry for being vague, Ill try and dig up some examples with the recent runs.

 

[Patrick Marsh]

Unfortunately the atmosphere, and the models that attempt to simulate the atmosphere, is (are) much more complex than that. Just because one level in a model is colder than observed, doesn't necessarily mean the others levels exhibit the same bias. Typically, immediate behind a cold front, you still have warming ongoing in numerous levels of the atmosphere above the cold front.
It all depends on what physical processes are ongoing at that layer of the model...and which processes have the model bias.

For example, is the bias in temperature advection? Is it a diabatic process error? Is it an adiabatic process bias? All of these would end up affecting the model output differently. Also, at what time lengths are you examining?

And just so we all use the same terminology...

level = single level
layer = region between two different levels (and in this case, you are in effect referring to thickness/mean temperatures and not actual temperatures)

 

[Scott Olson]

Based on the verification At 500 MB, at day 5 for example, the Northern Hemisphere temperature Bias for the last 30 days was +0.147 and at 12Z it was +0.157. At day 10 the scores do go negative, but both 00Z & 12Z are approximately the same.

So I suppose it might just be that you've seen a couple runs that may make it look that way but in the scheme of things the 12z/0z models appear to have no significant tempature biases. Notice the 12z is actually slightly warmer not colder.

 

[Adam Lucio]

Yea that was a very useful link and I'm glad it was posted, that was the kind of info I was looking for.