The upslope flow is called a parcel of air that has a specific rate of cloud forming potential. That potential will lapse as the moisture in the air rises. The lapse term describes that the parcel of air will cool as it rises and lose its invisible moisture in the form of vapor and form a visible cloud That moisture that the upslope flow loses condenses out at different levels and appears to us on the ground as a cloud. The cloud appears at the level in the atmosphere where the rate of ascent of the moisture lapses and a visible cloud is formed. If a low pressure area is to the west of our position and contains upslope warm moist air we will often see high ice clouds overhead 500 to 600 miles in advance of the front. This is a natural phenomenon of a storm front approaching. If however the warm and moist upslope flow is crossing over a large stagnant, dry air mass near the ground that has no moisture in the lower layers, the ascending flow can’t form clouds at lower levels. If that is the case the ascending air forms clouds at the very high altitude that the airlines use approaching and leaving airports.
The contrails form visible clouds at a high altitude since there is not enough moisture in the very low layers to form clouds. When that happens the upper air becomes filled with contrails that are putting abundant ice nuclei in the moisture laden upslope flow from the storm approaching from the west . In reality this is happening all of the time during frontal passages but it is only when the rising warm air has the proper dry adiabatic lapse rate that we see only the highest areas of the atmosphere fill with clouds. This is when people take photos of the many contrails and say that they are chem trails made of aluminum particles or other metals.