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The role of the human forecaster in improving upon the accuracy of numerical weather prediction is explored using multiyear verification of human-generated short-range precipitation forecasts and mediumrange maximum temperature forecasts from the Weather Prediction Center (WPC). Results show that human-generated forecasts improve over raw deterministic model guidance. Over the past two decades, WPC human forecasters achieved a 20%-40% improvement over the North American Mesoscale (NAM) model and the Global Forecast System (GFS) for the 1 in. (25.4 mm) (24 h) 21 threshold for day 1 precipitation forecasts, with a smaller, but statistically significant, 5%-15% improvement over the deterministic ECMWF model. Medium-range maximum temperature forecasts also exhibit statistically significant improvement over GFS model output statistics (MOS), and the improvement has been increasing over the past 5 yr. The quality added by humans for forecasts of high-impact events varies by element and forecast projection, with generally large improvements when the forecaster makes changes $88F (4.48C) to MOS temperatures. Human improvement over guidance for extreme rainfall events [3 in. (76.2 mm) (24 h) 21 ] is largest in the short-range forecast. However, human-generated forecasts failed to outperform the most skillful downscaled, biascorrected ensemble guidance for precipitation and maximum temperature available near the same time as the human-modified forecasts. Thus, as additional downscaled and bias-corrected sensible weather element guidance becomes operationally available, and with the support of near-real-time verification, forecaster training, and tools to guide forecaster interventions, a key test is whether forecasters can learn to make statistically significant improvements over the most skillful of this guidance. Such a test can inform to what degree, and just how quickly, the role of the forecaster changes.

The diurnal variation of wind in the atmospheric boundary layer over the Kanto plain is studied in order to find the contribution of each of the land-sea breeze and the diurnal variation of turbulence as a function of the magnitude of the larger-scale pressure gradient. The land-sea breeze is found to be the main source of the diurnal variation of wind when the pressure gradient is less than 5ms-1 in geostrophic wind speed. As the pressure gradient intensifies the land-sea breeze weakens and is replaced by a turbulence-induced diurnal variation, which dominates over the land when the pressure gradient exceeds 10ms-1.