AAM GEFS explanation

The GEFS ensemble model has always had a negative AAM (Atmospheric Angular Momentum) bias. This means that the model slows down momentum, both tropically and extra tropically. This is why GEFS (and GFS) are known for wild cut-off low scenarios and other out-of-the-blue scenarios. The below image demonstrates the negative bias of the GEFS model, in accords to the topic of momentum.

Courtesy of Nicholas Schiraldi

Victor Gensini also runs a similar plot for the GEFS AAM predictions. However he runs his through a bias-correction model to improve the results. However the latest adaptation of FV3 has seemingly messed up this bias-correction. Standby for an improvement of it.

The below details provide access to a database of current AAM/GWO observations.

http://gsdmsolutions.com/~gsdm/clim/aam.rean.shtml

un = gsdm01

pw = gu3st#1

You require the login details to access the above links.

CFS GWO and AAM projections can also be found at the Victor Gensini site here.

An Andrea Winters run website shows the current GEFS forecast projection of the North Pacific jet stream