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!
GFS
• Vertical coordinates are hybrid
sigma/pressure… sigma at low levels to
pressure aloft.
Vertical coordinate comparison across North America
GFS Data Assimilation
• 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)
CDAS/Reanl vs GFS
NH/SH 500Hpa day 5
Anomaly Correlation (20-80 N/S)
NH GFS
SH GFS
NH CDAS/Reanl
SH CDAS/Reanl
90
85
Anomaly Correlation
80
75
70
65
60
55
50
45
40
1960
1970
1980
1990
YEAR
2000
Skill Improvements (ECMWF)
Useful skill until:
1980 - day 5
2000 - day 7
2003 - day 8
GFS