THE NWP “BREAKTHROUGH” FOR CLIMATE THE NWP “BREAKTHROUGH” FOR CLIMATE ANALYSIS CENTER MONTHLY PREDICTIONS ANALYSIS CENTER MONTHLY PREDICTIONS

IN 1981IN 1981

Bob LivezeyBob Livezey

Climate Services Division/OCWWS/NWSClimate Services Division/OCWWS/NWS

Symposium on the 50Symposium on the 50thth Anniversary of Operational Anniversary of Operational NWPNWP

College Park, MD, June 17, 2004College Park, MD, June 17, 2004

OUTLINEOUTLINE

• IntroductionIntroduction– 1981 Implementation1981 Implementation– Somerville’s (1980) ExperimentSomerville’s (1980) Experiment

• Verification EvidenceVerification Evidence– Description of Study for Monthly Mean Temperature ProgsDescription of Study for Monthly Mean Temperature Progs– ResultsResults– Monthly Mean 700-hPa Forecast ResultsMonthly Mean 700-hPa Forecast Results

• DiscussionDiscussion– Monthly Forecast ProcessMonthly Forecast Process– Impact on the ProcessImpact on the Process– Possible Corroborative StudyPossible Corroborative Study

INTRODUCTIONINTRODUCTION

• Aug. 12, 1980 NMC operational NWP suite changeAug. 12, 1980 NMC operational NWP suite change– Replacement of 7LPE (Shuman and Hovermale, 1968, Replacement of 7LPE (Shuman and Hovermale, 1968, JAMJAM) )

with the Spectral Model (Sela, 1980, with the Spectral Model (Sela, 1980, MWRMWR). For 00 GMT). For 00 GMT• 0-48, global, 30 waves, 12 layers0-48, global, 30 waves, 12 layers• 48-144, hemispheric, 24 waves, 12 layers48-144, hemispheric, 24 waves, 12 layers

• Mar. 18, 1981 NMC operational NWP suite changeMar. 18, 1981 NMC operational NWP suite change– Extension of the 00 GMT global Spectral Model Extension of the 00 GMT global Spectral Model

• 48-84, 24 waves, 12 layers48-84, 24 waves, 12 layers• 84-144, 24 waves, 6 layers84-144, 24 waves, 6 layers

• NMC Forecast Div. (now HPC) found that the new NMC Forecast Div. (now HPC) found that the new system increased “the number of cases with usefull system increased “the number of cases with usefull skill” (Cooley’s Feb. 23, 1981 memo)skill” (Cooley’s Feb. 23, 1981 memo)

INTRODUCTIONINTRODUCTION

• Somerville’s results Somerville’s results (1980, (1980, JASJAS) ) anticipated the anticipated the improvements. improvements.

• 500-hPa errors 500-hPa errors (30m contours) for (30m contours) for 11 January 1973 11 January 1973 case.case.

VERIFICATION EVIDENCEVERIFICATION EVIDENCEForecast and Control Forecast Definitions and TimingForecast and Control Forecast Definitions and Timing

VERIFICATION EVIDENCEVERIFICATION EVIDENCE

• Verification of monthly mean U.S. surface Verification of monthly mean U.S. surface temperature forecaststemperature forecasts– Issued twice-monthly for three categories at “zero” lead (3-5 Issued twice-monthly for three categories at “zero” lead (3-5

days) from 1973 through 1994days) from 1973 through 1994– Verified with a modified Heidke skill score for 102 mega-Verified with a modified Heidke skill score for 102 mega-

divisionsdivisions– Verification repeated for “operational persistence”Verification repeated for “operational persistence”– Differences computed to normalize for “predictability”Differences computed to normalize for “predictability”– Smoothed with a 25-forecast running meanSmoothed with a 25-forecast running mean

VERIFICATION EVIDENCEVERIFICATION EVIDENCE

OFFOFF OPROPR ΔΔ

pre-pre-GNWPGNWP

10.310.3 12.112.1 -1.8-1.8

post-post-GNWPGNWP

13.813.8 8.58.5 5.35.3

ΔΔ 3.53.5 -3.6-3.6 7.17.1

VERIFICATION EVIDENCEVERIFICATION EVIDENCE

• Verification of monthly mean extratropical N.H. 700-Verification of monthly mean extratropical N.H. 700-hPa heightshPa heights– Issued twice-monthly at “zero” lead (3-5 days) from 1973 Issued twice-monthly at “zero” lead (3-5 days) from 1973

through 1994through 1994– Verified with the spatial anomaly correlation over the Verified with the spatial anomaly correlation over the

Pacific/North American region (Livezey Pacific/North American region (Livezey et al.et al., 1995), 1995)– Not normalized for “predictability” with “operational Not normalized for “predictability” with “operational

persistence”persistence”– Smoothed with a 25-forecast running meanSmoothed with a 25-forecast running mean

VERIFICATION EVIDENCEVERIFICATION EVIDENCE

NH pre-GNWP

NH post-GNWP

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

• Step 1 of 3-step process, “Step 1 of 3-step process, “prognosisprognosis of the 700 mb of the 700 mb height anomalies”height anomalies”

• For step 1, subjective blend of “three available For step 1, subjective blend of “three available indicators”indicators”– ““kinematic/synoptic extrapolation of recent anomaly fields”; kinematic/synoptic extrapolation of recent anomaly fields”;

the five-day mean centered at the five-day mean centered at D-3D-3– ““statistical forecasts derived from lagged correlation fields”; statistical forecasts derived from lagged correlation fields”;

effectively effectively damped operational persistencedamped operational persistence– ““a five-day averaged NMC forecast centered at the 1a five-day averaged NMC forecast centered at the 1stst day of day of

the month”; the month”; D+3D+3

MONTHLY FORECAST STRATEGYMONTHLY FORECAST STRATEGY

D-3 D+3

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

• ““Of these, experience indicates that the dynamical Of these, experience indicates that the dynamical forecast [forecast [D+3D+3] is the most skillful. Although the ] is the most skillful. Although the forecast extends only two or three days into the forecast extends only two or three days into the verification period, the five-day averaging process is verification period, the five-day averaging process is an effective filter that seems to accurately reveal the an effective filter that seems to accurately reveal the low-frequency trend.”low-frequency trend.”

• A corroborating test: Comparison of the scores for 6-A corroborating test: Comparison of the scores for 6-10 day forecasts (10 day forecasts (D+8D+8)with persistence of D-3.)with persistence of D-3.

MONTHLY FORECAST STRATEGYMONTHLY FORECAST STRATEGY

D-3 D+3 D+8