Is the NAM “too good”?

[bombogenesis]

Remember, my whole "pro-gem" argument was regarding the regional, NOT the global. Yes, the gem global had some very bad runs leading up but its not easy to compare the gem global to the NAM in this case. The global's worst runs (which were worse than the NAM 84 hours out) were in the 96 or so hr time frame leading up to the storm at which time the NAM was out of range. By the time the NAM came into range the global was starting to catch on. Also, remember the GFS had some bad runs too. In fact around Tuesday / Wednesday or so of last week the gem global brought the storm close to the coast and the GFS was out to sea. They did the ole's switcheroo around about Thursday at which time, yes, the gem global was out to lunch.

Speaking of this recent storm, the GEM REG was showing Moncton NB where I am now getting 60cm of snow 24 hours out, while the NAM and GFS had us getting 20, guess which models were right.

[stormguy80]

the NAM and GFS were probably right. the gem regional has a wet bias that I am indeed aware of. I never said this model was perfect and that it was always going to beat the other models. My point was simply that quite often when it comes to getting lows, fronts, etc..in the right places with the right track and the correct timing of systems it does remarkably well and more often than not beats the other models when there are differences. In cases where its a 24 hour forecast and all models have come into good agreement regarding the timing and track I don't doubt that the gem will sometimes be less accurate with QPF. the gem seems to have a wet bias with moisture laden systems and a dry bias in scenarios where the PW values are low, like in the plain states and Prairies.

Speaking of this recent storm, the GEM REG was showing Moncton NB where I am now getting 60cm of snow 24 hours out, while the NAM and GFS had us getting 20, guess which models were right.

[stormguy80]

Yes, obviously this is true and something that I learned fairly early on in my career. I've been doing this for a number of years now. Hence the reason for this thread. I think some people put too much faith in the NAM. No model is perfect and even while I've been talking about how good I think the gem reg is for a lot of scenarios I know it has its weaknesses and is far from perfect.

Well, it seems you might be slowly realizing that computer models are to be used as Guidance, not forecasts to hang your hat on.

[Dark Energy]

My old boss where I worked as an operational met in a private firm, was always high on the GEM. It was his fav model, always. He knew it by heart and knew how to adjust for it. I would always see him looking at the black and white CMC maps and estimating the qpf from there! Now, I know it recently had an upgrade that made it better, but it still struggles at times (tropical anyone??, lol) . This past storm it cont to be SE with the blizzard (but it did have some hits like the GFS at times, but it flip flopped like most of the guidance). But if you know how to use a combo of guidance (ensemble), you can be a great forecaster and eventually get it right. To me, the GFS had the late return W with the blizzard, which was discounted by HPC. The EC had the blizzard first, even with a 75kt CCB, which verified nicely (see the 77kt h85 wind on the KOKX RAOB during the storm!!). The GGEM lost the storm, as some models did, but it brot it back but later than the GFS. The GFS had a recent upgrade that did well with tropical forecasting FIRST. It is still early in the winter season to see how it does in this season. So far, at 180 hrs out, it had the storm, lost it, but brot it back sooner than any other guidance, which proves to me it may be getting a bit better with the ever so troublesome la nina forecasting package that most guidance have trouble with. The NAM, which I was waiting for a late trend to be right, was still off. my 2 cents.

[stormguy80]

yeah. the gem is great, you just have to know how to adjust for its weaknesses like you said. The NAM has some strengths too but the whole reason for my post was that no one seems to ever talk about its weaknesses of getting synoptic weather right beyond about 18-24 hours.

My old boss where I worked as an operational met in a private firm, was always high on the GEM. It was his fav model, always. He knew it by heart and knew how to adjust for it. I would always see him looking at the black and white CMC maps and estimating the qpf from there! Now, I know it recently had an upgrade that made it better, but it still struggles at times (tropical anyone??, lol) . This past storm it cont to be SE with the blizzard (but it did have some hits like the GFS at times, but it flip flopped like most of the guidance). But if you know how to use a combo of guidance (ensemble), you can be a great forecaster and eventually get it right. To me, the GFS had the late return W with the blizzard, which was discounted by HPC. The EC had the blizzard first, even with a 75kt CCB, which verified nicely (see the 77kt h85 wind on the KOKX RAOB during the storm!!). The GGEM lost the storm, as some models did, but it brot it back but later than the GFS. The GFS had a recent upgrade that did well with tropical forecasting FIRST. It is still early in the winter season to see how it does in this season. So far, at 180 hrs out, it had the storm, lost it, but brot it back sooner than any other guidance, which proves to me it may be getting a bit better with the ever so troublesome la nina forecasting package that most guidance have trouble with. The NAM, which I was waiting for a late trend to be right, was still off. my 2 cents.

[stormguy80]

Lots of stats here http://www.hpc.ncep.noaa.gov/html/hpcverif.shtml that show that the GFS has generally be superior to the NAM in QPF verification.