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FV3-GFS is now operational: cold bias is obvious

GaWx

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#1
Attached is a screenshot from True Wx that clearly show that the FV3 has a strong cold bias. Note how much lower are the day by day CDDs on today's 12Z run (purple line), the first operational GFS using the FV3 vs the prior 3 runs (old GFS). Every single day of the 12Z has lower CDDs vs both the 18Z and 0Z, and all but 2 days are lower vs the 6Z. Also, note the whopping 6 fewer CDD on the 12Z just for days 1-5 vs the 6Z. I’ve been following the DD on the True Wx site for quite a while and have never seen anything close to that much change that early in the run vs the prior run. To me, this is clearly indicative of the FV3 strong cold bias remaining.

I thought it was important to document this today because this is the only opportunity to see the direct comparison of old vs new operational:
FV3cddGraphTransitionRun12Z061219.jpeg
 
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#3
Here are some screenshots with a bit better res.

For those who do not know:


Cooling degree day: temps<65

example: A day with a temp of 75 degrees would be a CDD of 10. 75-65=10

The lower the number the Cooler the day. Obviously the 12z fv3 has more cool days than the 06z gfs had. Is this a cold bias in the fv3 or a warm bias in the gfs? or a combo of both? Didn't the old GFS way overshoot some of these hot days recently? I don't remember any 110 degree days in Georgia like it had shown....


GFS Screenshot (4).png


GEFS

No noticeable changes
Screenshot (8).png

They have EURO graphs as well but paid subscription. Maybe the old gfs had a warm bias o_O
 

GaWx

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#4
ok so tell me how many of a degrees are we talking in difference
CONUS weighted CDDs for 6/13-26 by run:

18Z (old GFS): 197
0Z (old GFS): 195
6Z (old GFS): 188
12Z (FV3): 163

Now granted, there was normally much run to run volatility from run to run of the old GFS as well as FV3. So, SOME of the relative coolness of the 12Z could easily be related to that, mainly late in the run. In other words, this may have been a relatively cool FV3 run and the next few runs may end up warmer. However, what makes me quite confident that the FV3 cold bias is a big factor is the CDD total for early days of the run, which hardly ever vary significantly from run to run. So, I'll now break it our for only week one (days 1-7):

CONUS weighted CDDs for 6/13-19 by run:
18Z (old GFS): 85
0Z (old GFS): 83
6Z (old GFS): 80
12Z (FV3): 67

So, for just days 1-7, the 12Z (FV3) had 13-18 fewer CDDs than the prior 3 runs (all old GFS). That's a lot for week 1. No let's see if the next few FV3 runs are similarly "cool" to the 12Z FV3 for days 1-7.
 
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Myfrotho704_

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#5
This might be a little bit different, and I know the cold bias majorly correlated to this, but the FV3 sucks with WAA, often not showing much WAA causing suppression (since you need some WAA for ascent allowing precipitation) , also super CADs that would never scour, big high pressures that never really verify, and based off winter it was off badly with z500 patterns, again that contributed to often badly suppressed looks, only for it to become a pattern supporting miller Bs or cutters at short range
 

GaWx

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#7
Obviously the 12z fv3 has more cool days than the 06z gfs had. Is this a cold bias in the fv3 or a warm bias in the gfs? or a combo of both? Didn't the old GFS way overshoot some of these hot days recently? I don't remember any 110 degree days in Georgia like it had shown....

They have EURO graphs as well but paid subscription. Maybe the old gfs had a warm bias o_O
Excellent points! I think it is a combo of both. The GFS seems to have a warm bias overall but per Radiant/Maxar any warm bias has been small since last winter compared to overall large cold biases for the GEFS, Euro and EPS. I'm waiting for them to confirm that to me. The FV3 cold bias is well-known and has been admitted by NOAA. But interestingly even that cold bias appears to be much smaller than the very strong GEFS/EPS/Euro cold biases based on today's 12Z CDDs for days 1-5:

6Z GFS (old): 52
12Z GFS (FV3): 46
12Z GEFS: 39
12Z Euro: 38
12Z EPS: 37

So, let's suppose the true unbiased were near 50. IF that were true, the old GFS was slightly too warm, the FV3 was too cold, and the GEFS/Euro/EPS were much too cold. I kind of think this is what's happening.
 
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#8
Excellent points! I think it is a combo of both. The GFS seems to have a warm bias overall but per Radiant/Maxar any warm bias has been small since last winter compared to overall large cold biases for the GEFS, Euro and EPS. I'm waiting for them to confirm that to me. The FV3 cold bias is well-known and has been admitted by NOAA. But interestingly even that cold bias appears to be much smaller than the very strong GEFS/EPS/Euro cold biases based on today's 12Z CDDs for days 1-5:

6Z GFS (old): 52
12Z GFS (FV3): 46
12Z GEFS: 39
12Z Euro: 38
12Z EPS: 37

So, let's suppose the true unbiased were near 50. IF that were true, the old GFS was slightly too warm, the FV3 was too cold, and the GEFS/Euro/EPS were much too cold. I kind of think this is what's happening.

So it’s possible the other models are too cool? I wish we knew what the true unbiased number was.

The point still remains that something in the fv3 translates to too much snow and too long of a CAD. Of course they have had 6 months to work on t since then.

I guess the real test will come this winter. And this hurricane season. Supposedly the fv3 should no longer erroneously bomb out cyclones.
 
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#12
It'll be interesting to see what it says on other days outside of this day since it has the caveat of it being cloudy all day, but my high was 71 (or 73 officially) in the morning and if the upgrade was put out for 12z, at 18z it had 77 on that run. So it actually was wrong in the other direction this go around.

21z on meteostar had 72 at the peak as well. I think with the factors in today, if there was a cold bias it'd probably have been 65 and now that I'm looking at the run, it doesn't seem way out of the ordinary. Maybe there are factors there that suggest the temps should be a few degrees higher (and I'll look on that), but it has the peak in the mid 90s for me multiple times. That's normal summer weather now, unfortunately.
 

Jon

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#15
It'll be interesting to see what it says on other days outside of this day since it has the caveat of it being cloudy all day, but my high was 71 (or 73 officially) in the morning and if the upgrade was put out for 12z, at 18z it had 77 on that run. So it actually was wrong in the other direction this go around.

21z on meteostar had 72 at the peak as well. I think with the factors in today, if there was a cold bias it'd probably have been 65 and now that I'm looking at the run, it doesn't seem way out of the ordinary. Maybe there are factors there that suggest the temps should be a few degrees higher (and I'll look on that), but it has the peak in the mid 90s for me multiple times. That's normal summer weather now, unfortunately.

This site appears still functional and will allow you to compare past OBS and the two models

https://www.emc.ncep.noaa.gov/gc_wmb/tdorian/fv3plumes/EMCGFSXplumes.html


Sent from my iPhone using Tapatalk
 

GaWx

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#16
Here are the CDDs for the 1st 3 operational FV3 runs vs the last old op. GFS (6Z of 6/12/19 in light blue). You can clearly see the old GFS run's much higher CDD count:





FV3cdd1st3vsLastOldGFSgraph061319.png
 
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