The variability of the middle atmosphere is driven by a variety of atmospheric waves covering various spatial and temporal scales. In particular, the northern winter mesosphere/ lower thermosphere at mid- and polar-latitudes shows a huge variability related to planetary waves, which can disturb the polar vortex leading to large scale coupling effects like sudden stratospheric warmings (SSWs) altering the vertical propagation conditions of tides and gravity waves. Here we are going to investigate and diagnose the short time variability of tides (several days) at the MLT using ground-based observations at mid and polar latitudes and data from NAVGEM-HA for selected periods. NAVGEM-HA provides information about the global structure of the zonal mean zonal and meridional wind and the zonal mean temperature as well as the tides. At mid- and high-latitudes the semi-diurnal tide (SW1 and SW2) is the dominating tidal wave during the winter season, which is also seen in meteor radar and lidar climatologies. Further, we analyze local meteor radar and lidar observations at Andenes (polar-latitude) and Juliusruh (mid-latitude) to diagnose the local amplitude and phase variability due to changes in the background mean winds caused by planetary waves and SSWs. We will show that the tidal phase (in UT) can drift significantly within several days and weeks. These local measurements are also compared to NAVGEM-HA applying the same diagnostic as to the observations. In addition to the winter time observations, we will also show results for the phase propagation of tides from summer periods.