GFS and Global Models

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 decades derived

from using direct satellite radiance in the 3DVAR analysis scheme and other satellite assets.

• 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• Hybrid Data assimilation based on 3DVAR (they call

it GSI) and GFE ensemble (next slide)• Every 6 hr.

GFS Hybrid Data Assimilation

GFS is not the only global model and is not even the best

Next Generation Global Models Under Development!

• Will use different geometries

MPAS: Hexagonal Shapes

NOAA FIM Model