Joint wmo technical progress report on the global data processing and forecasting system and numerical weather prediction research activities for 2013
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| Fig.1) Mean daily cycle of observed (dotted) and forecasted (solid, 00:00 UTC forecast runs) wind speed at Lindenberg for July and August in 2012. Forecasted u and v values were carefully interpolated to measurement height. After sunrise, a strong decrease of wind speed aloft is observed, whereas the model fails to represent such sharp transition from stable to mixed conditions and vice versa.
Fig.2) Risø, 18. August. 2012; Top: forecasted (solid) and observed (dotted) wind speed at 125 m. Note that the model simulates the Low Level Jet too weak and too late. Bottom: forecasted and observed wind speed converted to power. Within the critical range of the power curve, errors amplify significantly. 
Fig.3) Cabauw, 18. August. 2012; Observed (blue) and fore-casted (red) wind speed profiles for lead times +18 up to +21 hours, corresponding to 06:00 UTC up to 09:00 UTC. Note the persistence of a decoupled layer in the forecasted profiles after sunrise (04:30 UTC). Similar profiles can be found for Lindenberg and Risø for the same date. Fig.4) Lindenberg, 18. August. 2012; Observed (dotted) and operationally forecasted (solid) wind speed in 20 and 98 m. Note that the LLJ is too weak and too long-living in the model. A test run (dash dotted lines; momentum flux at the ground was slightly reduced, stability during night as well as mixing after sunrise were increased) shows better results. 
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