Notes on NWP and the History of Long Range Forecasting Don Gilman ret and Huug van den Dool, NOAANCE

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Notes on NWP and the History of Long Range
Forecasting Don Gilman (ret) and Huug van den
Dool, NOAA/NCEP/CPC
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Legend written by Namias.
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• Very little NWP-influence on operational seasonal
  forecasts (at NMC/NCEP) prior to 1995.
• Beginning in 1995 the coupled ocean/atmosphere
  model routinely became a tool for the seasonal
  forecast. NWP? NCP

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The precursors of NWP (? NCP) are1.
Pioneering integrations by Miyakoda, Gilchrist,
Shukla and others. 1970s, 1980s2. (linear,
steady state) Global models describing Rossby
wave dispersion from long-lived tropical sources
of heat and vorticity. Explained
Teleconnections?? 1980 onward3. AMIP runs from
1989 onward (Gates, PCMDI)4. An ocean data
assimilation system (Leetmaa et al) for initial
conditions of the coupled system..Missing a
proper land initial condition
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Defensive approaches with a profound impact

• The two-tiered approach to Coupled Modeling
  (still widespread)
• Invented to deal with (very) large biases
• Can the anomaly be salvaged when the mean is
  that far off?? (history of bias correction)
• Summer 2004 NCEP is going 1-tiered

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Coupled Models at NCEP

• Ji, Leetmaa and Kumar (CMP12/14 1995 ?
• Kanamitsu et al (SFM 2001 ?
• Saha et al (CFS 2004 ?
• CMP and SFM had only Pacific Tropical ocean and
  were 2-tiered. CFS is global, 1-tiered, and at
  T62L64 (atmosphere), 1/3rd degreeL40 (ocean)
  resolution. CFS has 2500 years worth of hindcasts.

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Issues of skill and consolidation

• What is the skill of NCP?
• What is the skill of NCP vis-à-vis other methods
  (like CCA)
• How to combine Methods A, B and C?
• The pioneering role of seasonal prediction in
  hindcasts and a-priori skill requirements
• Will the shorter range NWP follow with hindcasts?

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Skill assessment of CFS.
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OFFicial Forecast(element, lead, location,
initial month) a A b B c C
Honest hindcast required 1950-present.
Covariance (A,B), (A,C), (B,C), (A, obs), (B,
obs), (C, obs) allows solution for a, b, c
(element, lead, location, initial month)
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Conclusions

• NWP techniques have entered the arena of seasonal
  forecasts, from 1995 onward, and are expanding.
• Skill remains modest (predictability?)
• Empirical techniques have not yet been retired
• Reanalysis (as such NWP related) has boosted
  empirical work thru availability of global data
  sets (1948-present). (Reanalysis was a revolution
  for empirical work).