Re: Significant upgrade to GEFS
Posted by Chris in Tampa on 9/23/2020, 4:36 pm
When viewing Tropical Tidbits model data, it is under GEFS (Ensemble > GFS) on that site:

https://www.tropicaltidbits.com/analysis/models/?model=gfs-ens&region=atl&pkg=mslp_uv850

I never look at that particular page. I assume that is the mean in that imagery but I don't know.

I look at the individual ensemble member lows on the imagery here:

https://www.tropicaltidbits.com/analysis/models/?model=gfs-ens&region=atl&pkg=lowlocs

When they come into the HurricaneCity model system for a current storm, it comes under:

AC00: GFS Ensemble Control Member
AP01 - AP20: GFS Ensemble Members, 1 to 20
AEMN: GFS Ensemble Mean



I don't really follow model upgrades, but I do hope they improve. It has seemed in the past few years that maybe the GFS hasn't done as well at times. Then again, we've had some complex setups I guess, particularly this year. Maybe I am just wrong. I haven't compared the models from year to year.

Hurricane Michael if I remember correctly was not forecast to develop a week out. After that the NHC was really good on the forecast so I assume the GFS was probably good after that on track, I can't remember. I usually see the GFS as being pretty good for determining what has a chance of developing in the shorter term.

But that is the GFS and this in particular is about the GFS ensemble system. I usually look at the GFS ensemble members to determine if they are close together or far apart. The closer they are together, maybe the more confidence you can have in the track. If they are all over the place, less confidence.

I never can explain that well. They do it here:
https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-ensemble-forecast-system-gefs

"The Global Ensemble Forecast System (GEFS), previously known as the GFS Global ENSemble (GENS), is a weather forecast model made up of 21 separate forecasts, or ensemble members. The National Centers for Environmental Prediction (NCEP) started the GEFS to address the nature of uncertainty in weather observations, which is used to initialize weather forecast models. The proverbial butterfly flapping her wings can have a cascading effect leading to wind gusts thousands of miles away. This extreme example illustrates that tiny, unnoticeable differences between reality and what is actually measured can, over time, lead to noticeable differences between what a weather model forecast predicts and reality itself. The GEFS attempts to quantify the amount of uncertainty in a forecast by generating an ensemble of multiple forecasts, each minutely different, or perturbed, from the original observations."

Basically if all those slight perturbations have the tracks of the members close together for a tropical cyclone for example, then you can have more confidence that slight changes in conditions from what you might expect will have less impact on the path. If they go all over the place, then not knowing something about the forecast conditions as well could mean that it could have more impact on the track.

Of course a lot of people look at much more than that, but that's the only thing I sort of understand.
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Significant upgrade to GEFS - AlligatorPointer, 9/23/2020, 3:07 pm
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