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Amnon Dalcher, Eugenia Kalnay, and Ross N. Hoffman

9 dayforecasts of the 500 mb fieight field. The results show.the statistically filtered LAF is a marked improvementupon the operational forecast after 5 days. We find that on a global scale forecast skill is weakly correlated withthe dispersion of the ensemble, as measured by the rms difference between the operational forecast and thestatistically filtered LAF.1. Introduction The problem of numerical weather prediction(NWP) is stochastic, in the sense that the initial conditions may be

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LCDR. W. E. HUBERT, CDR. P. M. WOLFF, and C. L. CAVE

FEBBUABY $058 MONTHLY WEATHER REVIEW 53A COMPARISON OF JNWPTRAJECTORYFORECASTS WITH TRANSOSONDEFLIGHTSLCDR. W. E. HUBERT, U. S. Navy,' CDR. P. M. WOW, U. S. Navy,' and C. L. CAVE, U. S. Weather BureauJoint Numerical Weather Prediction Unit, Suitland. Md.Manuscript received January 28, 1958; revised March 3, 19581ABSTRACTTrajectories at 300 mb. numerically computed from the JointNumerical Weather Prediction Unit's operational forecasts arecompared with transosonde balloon tracks. The method

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Xiong-Shan Chen

, 300, 250, 200, 150, 100, 70, 50, 30, 20, and 10 hPa. The 1985 version of the operational spectral model at the European Centre for Medium-Range Weather Forecasts (ECMWF) is adopted as the dealiased reference model. The corresponding aliased model is developed by modifying the ECMWF spectral model. The horizontal diffusion of divergence, vorticity, temperature, and specific humidity used in both models is represented by a simple linear fourth-order diffusion. Operationally, the diffusion

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HARRY R. GLAHN and DONALD L. JORGENSEN

1 36MONTHLY WEATHER REVIEW Vol. 98, No. 2UDC 551.509.314:551.677.38(73)CLIMATOLOGICAL ASPECTS OF THE BRIER P-SCORE HARRY R. GLAHN and DONALD L. JORGENSENTechniques Development Laboratory, Weather Bureau, ESSA, Silver Spring, Md.ABSTRACT The P-score has come into widespread usage for the evaluation of probability forecasts of weather events.Verification data for operational Weather Bureau forecasts of probability of precipitation are used to study thetendency for the P-score to be a function

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R. G. Tapp, F. Woodcock, and G. A. Mills

forecam throughout the forecast ranges. The skill with which large rainfalltotals were predicted was particularly enhanced in this manner, the MOS forecasts showed much greater skillin the prediction of large totals than was achieved by either the operational or persistence forecasts, whilepredictins small totals with comparable proficiency. The MOS.probability forecasts were better able to predict rainfall occurrence than were the quantitative MOSforecasts, and additionally were superior in this

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BANNER I. MILLER and PETER P. CHASE

upto 48 hr. The forecast equations have been tested on an operational basis during the 1964 and 1965 hurricaneseasons. The accuracy of these forecasts compares favorably wit,h that of ot,her standard hurricane forecasttechniques.1. INTRODUCTIONDuring the past ten years a number of object,ive met,hodsfor forecasting hurricane movement has been developed11, 2, 5, 7, 8, 9, 101. Several of these methods have beenevaluated at the National Hurricane Center [6]. Themethods tested demonstrated varying

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G. A. Mills and R. S. Seaman

initialization phase of the assimilation cycle, and that these vertical motion fields correlatewell with the areas of cloud seen in satellite imagery. Prognoses from this trial period show a much more rapid spinup of forecast rainfall rate than did a series ofcontrol forecasts based on operational analyses, and both mean rainfall for the 17-day period and individualcases are presented to demonstrate improved skill of forecasts from the assimilated analyses. Objective verificationof mass-field forecasts

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J. D. Jarrell, C. J. Mauck, and R. J. Renard

a Monte Carlo simulation of initial position inaccuracies, as well as for forecastsgenerated from 1973 operational cyclone positions. The latter are intercompared with a homogeneous setof objective persistence and MOHATT forecasts as well as subjective OFFICIAL forecasts for the 24, 48,and 72 h intervals. The 1973 EPANALOG accuracy is shown to generally excel that of the existent techniques for all forecast intervals tested.- Introduction Tropical cyclone forecasting (development, movement

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Graham A. Mills and Sixiong Zhao

. Forecasts are compared from a static cold start analysis (the operational system at the time), alimited-area data assimilation system with operational (2.5 h) data cutoffs, and the same assimilation systemwith an infinite data cutoff. It is shown that the operational forecasts of the cyclone's position, intensity, andprecipitation were clearly inferior to both assimilation forecasts. The assimilation forecasts of rainfall subjectivelyshowed a greater margin of improved skill over the operational

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André Tremblay, Anna Glazer, and Louis Garand

, precise forecasts of the three-dimensional distribution of clouds and their phase (liquid, ice, supercooled, or mixed) are required for aircraft operations. Unfortunately, the treatment of cloud microphysics is oversimplified in many operational NWP modeling systems, and it is often difficult to fulfill specific forecast needs. At the Canadian Meteorological Centre (CMC), mixed-phase clouds are not predicted and precipitation is not advected. This imposes constraints on the forecasting capability of

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