That is caused by XPs weather system that generates the weather per tile (1 degree longitude x 1 degree latitude). A plugin can only tell XP the weather within that tile and XP the decides where the clouds are, where stormcells are and so on. If you enter the next tile, you will get the "next weather". This is not changeable by a plugin. The XPGFS plugin has rather precise data so times where you fly in CAVOK conditions and find yourself in a fat thunderstorm in the next minute are over. XPGFS also enhances your cloud layers by removing the lowest and adding one on top after passing, thus giving you more clouds in upper flightlevels. It also adds turbulence what I personally find pretty neat. It still does but maxes XPs options out. From what I know, the weather system does not allow more. Sure No Thats what the transition does. NOAA data is not very good in lower flightlevels, here METAR data that comes straight from the airports is more precise. I chose FL110. At FL100 you usually reduce speed to 250kts and thus stay there for a while. The plugin will then switch between both "weathers" many times because you are flying 9550 ft and then 10500 again. With FL110 setting, your deceleration can take place with XP or VATSIM weather.