Transcript GFS2013.ppt

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 (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.
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
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.
Improved Verification