- For example, the mean wind speed increases from 11–12 m s21 on average around 1000 m to around 17 m s21 above 3000 m, while the MAE decreases slightly, so the error decreases in the free atmosphere from 13% to around 9%. In January, the WRF PXACM has consistently less wind error (speed and direction) than the MM5 PXACM. Figure 6 indicates that the WRF PXACM has almost identical diurnal error to the WRF Noah YSU at 1300 and 2000 m. However, the WRF PXACM has noticeably lower error around the 700-m level relative to the WRF Noah YSU at night (0100–1000 UTC), but similar error during the day.