1. Global Forecast System (GFS) Model
Previous called the Aviation (AVN) and Medium Range Forecast (MRF) models.
Spectral global model and 64 levels
Relatively primitive microphysics.
Sophisticated surface physics and radiation
Run four times a day to 384 hr (16 days!).
Major increase in skill during past decade derived from using direct satellite radiance in the 3DVAR analysis scheme.
T574 (~27 km) over the first 192 hours (8 days) of the model forecast and T190 (70 km) for 180 through 384 hours--major implications for resolution change!

2. GFS
Vertical coordinates are hybrid sigma/pressure… sigma at low levels to pressure aloft.

3. Vertical coordinate comparison across North America

4. GFS Data Assimilation (GDAS)
Has a later data cut-off time than the mesoscale models…and thus can get a higher percentage of data.
Uses much more satellite assets..thus improve global analysis and forecasts.
Major gains in southern hemisphere
Data assimilation based on 3DVAR (they call it GSI)
Every 6 hr.

6. Big Change: May 22, 2012
Effective on Tuesday, May 22, 2012 NCEP upgraded the GFS model and its associated data assimilation system (GDAS).
The major component of the analysis change was the incorporation of a hybrid variational/ensemble assimilation system. 
In this system, the background error used to project the information in the observations into the analysis is created by a combination of a static background error (as in the prior system) and a new background error produced from a lower resolution (T254) Ensemble Kalman Filter system.
This produced a significant improvement in GFS forecast skill.

8. Improved Verification