Global Forecast System (GFS) Model • Previous called the Aviation (AVN) and Medium Range Forecast (MRF) models. • Global model and 64 levels • Relatively primitive microphysics. • Sophisticated surface physics and radiation • Run four times a day to 384 hr. • Major increase in skill during past five years derived from using direct satellite radiance in the 3DVAR analysis scheme. • T382 (~35 km) over the first 180 hours (7.5 days) of the model forecast and T190 (70 km) for 180 through 384 hours--major implications for resolution change!
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Global Forecast System (GFS) Model Previous called the Aviation (AVN) and Medium Range Forecast (MRF) models. Global model and 64 levels Relatively primitive.
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Global Forecast System (GFS) Model
• Previous called the Aviation (AVN) and Medium Range Forecast (MRF) models.
• Global model and 64 levels• Relatively primitive microphysics.• Sophisticated surface physics and radiation• Run four times a day to 384 hr.• Major increase in skill during past five years derived
from using direct satellite radiance in the 3DVAR analysis scheme.
• T382 (~35 km) over the first 180 hours (7.5 days) of the model forecast and T190 (70 km) for 180 through 384 hours--major implications for resolution change!
GFS
• Just changed vertical coordinates from sigma to 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
• Based on 3DVAR
CDAS/Reanl vs GFSNH/SH 500Hpa day 5
Anomaly Correlation (20-80 N/S)
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1960 1970 1980 1990 2000
YEAR
Anomaly Correlation
NH GFS
SH GFS
NH CDAS/Reanl
SH CDAS/Reanl
Skill Improvements (ECMWF)
Useful skill until:
1980 - day 5
2000 - day 7
2003 - day 8
Rapid Update Cycle-RUC
RUC• A major issue is how to assimilate and use the
rapidly increasing array of offtime or continuous observations (not a 00 and 12 UTC world anymore!
• Want very good analyses and very good short-term forecasts (1-3-6 hr)
• The RUC ingests and assimilates data hourly, and then makes short-term forecasts
• Uses the MAPS mesoscale model…which uses a hybrid sigma/isentropic vertical coordinate