# Presentation: 297500

## THE NWP “BREAKTHROUGH” FOR CLIMATE ANALYSIS CENTER MONTHLY PREDICTIONS IN 1981

- Bob Livezey
- Climate Services Division/OCWWS/NWS
- Symposium on the 50th Anniversary of Operational NWP
- College Park, MD, June 17, 2004

## OUTLINE

- Introduction
*1981 Implementation*
*Somerville’s (1980) Experiment*
- Verification Evidence
*Description of Study for Monthly Mean Temperature Progs*
*Results*
*Monthly Mean 700-hPa Forecast Results*
- Discussion
*Monthly Forecast Process*
*Impact on the Process*
*Possible Corroborative Study*

## INTRODUCTION

- Aug. 12, 1980 NMC operational NWP suite change
*Replacement of 7LPE (Shuman and Hovermale, 1968, *JAM*) with the Spectral Model (Sela, 1980, *MWR*).  For 00 GMT*
- 0-48, global, 30 waves, 12 layers
- 48-144, hemispheric, 24 waves, 12 layers
- Mar. 18, 1981 NMC operational NWP suite change
*Extension of the 00 GMT global Spectral Model *
- 48-84, 24 waves, 12 layers
- 84-144, 24 waves, 6 layers
- NMC Forecast Div. (now HPC) found that the new system increased “the number of cases with usefull skill” (Cooley’s Feb. 23, 1981 memo)

## INTRODUCTION

- Somerville’s results (1980, *JAS*) anticipated the improvements.
- 500-hPa errors (30m contours) for 11 January 1973 case.

## VERIFICATION EVIDENCEForecast and Control Forecast Definitions and Timing

## VERIFICATION EVIDENCE

- Verification of monthly mean U.S. surface temperature forecasts
*Issued twice-monthly for three categories at “zero” lead (3-5 days) from 1973 through 1994*
*Verified with a modified Heidke skill score for 102 mega-divisions*
*Verification repeated for “operational persistence”*
*Differences computed to normalize for “predictability”*
*Smoothed with a 25-forecast running mean*

## VERIFICATION EVIDENCE

|  | OFF | OPR | Δ |
| --- | --- | --- | --- |
| pre-GNWP | 10.3 | 12.1 | -1.8 |
| post-GNWP | 13.8 | 8.5 | 5.3 |
| Δ | 3.5 | -3.6 | 7.1 |

## VERIFICATION EVIDENCE

- Verification of monthly mean extratropical N.H. 700-hPa heights
*Issued twice-monthly at “zero” lead (3-5 days) from 1973 through 1994*
*Verified with the spatial anomaly correlation over the Pacific/North American region (Livezey *et al.*, 1995)*
*Not normalized for “predictability” with  “operational persistence”*
*Smoothed with a 25-forecast running mean*

## VERIFICATION EVIDENCE

**NH pre-GNWP**

**NH post-GNWP**

## MONTHLY FORECAST STRATEGY(Kalnay and Livezey, 1985)

- Step 1 of 3-step process, “*prognosis* of the 700 mb height anomalies”
- For step 1, subjective blend of “three available indicators”
*“**kinematic/synoptic extrapolation of recent anomaly fields”; the five-day mean centered at **D-3*
*“**statistical forecasts derived from lagged correlation fields”; effectively **damped operational persistence*
*“**a five-day averaged NMC forecast centered at the 1**st** day of the month”; **D+3*

## MONTHLY FORECAST STRATEGY

***  ******D-3     ******D+3******    ***

## MONTHLY FORECAST STRATEGY(Kalnay and Livezey, 1985)

- “Of these, experience indicates that the dynamical forecast [D+3] is the most skillful.  Although the forecast extends only two or three days into the verification period, the five-day averaging process is an effective filter that seems to accurately reveal the low-frequency trend.”
- A corroborating test:  Comparison of the scores for 6-10 day forecasts (D+8)with persistence of D-3.

## MONTHLY FORECAST STRATEGY

***  ******D-3     ******D+3     ******D+8***