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Global Forecast System (GFS) Model

Global Forecast System (GFS) Model

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Global Forecast System (GFS) Model

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  1. 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!

  2. GFS • Just changed vertical coordinates from sigma to hybrid sigma/pressure… sigma at low levels to pressure aloft.

  3. Vertical coordinate comparison across North America

  4. 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

  5. Skill Improvements (ECMWF) • Useful skill until: • - day 5 • 2000 - day 7 • 2003 - day 8

  6. Rapid Update Cycle-RUC

  7. 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 • Resolution: 13 km and 50 levels

  8. 13km RUC Terrain elevation - 100 m interval • Improvements expected from 13km RUC • Improved near-surface forecasts • Improved precipitation forecasts • Better cloud/icing depiction • Improved frontal/turbulence forecasts NCEP computer upgrade allows RUC13 to run in same time as current RUC20

  9. Observations used in RUC Data Type ~Number Freq. -------------------------------------------------- Rawinsonde 80 /12h NOAA profilers 30 / 1h VAD winds 110-130 / 1h Aircraft (V,temp) 1400-4500 / 1h Surface/METAR 1500-1700 / 1h Buoy/ship 100-150 / 1h GOES precip water 1500-3000 / 1h GOES cloud winds 1000-2500 / 1h GOES cloud-top pres 10 km res / 1h SSM/I precip water 1000-4000 / 6h -------------------------------------------------- GPS precip water ~300 / 1h Mesonet ~5000 / 1h METAR-cloud-vis-wx ~1500 / 1h -------------------------------------------------- Cloud analysis variables NCEP RUC20 operational RUC13 (at NCEP June 2005)

  10. RUC History – NCEP (NMC) implementations • - First operational implementation of RUC • - 60km resolution, 3-h cycle • 1998 – 40km resolution, 1-h cycle, • - cloud physics, land-sfc model • 2002 – 20km resolution • - addition of GOES cloud data in assimilation • 2003 – Change to 3dVAR analysis from previous OI • (April) • 2004 – Vertical advection, land use (April) • PBL-depth for surface assimilation (September) • 2005 – 13km resolution, new obs, new model physics • (June) • 2007 – WRF-based Rapid Refresh w/ GSI to replace RUC

  11. 20km RUC 13km RUC Soil moisture – 22z - 21 Feb 2005 Dark blue = water More detailed coastline with 13km resolution

  12. WRF RUC • A new version of RUC has been developed, but not yet operational that uses the WRF model instead of the MAPS model.