The environmental lapse rate is the rate at which the ambient air temperature changes with height in the real atmosphere. It describes the actual temperature profile you’d observe with increasing altitude at a particular place and time, which can vary from day to day and location to location. Typical values are around 6.5°C per kilometer in the standard atmosphere, but the rate can be steeper or shallower, and inversions occur when temperature increases with height. This concept helps explain atmospheric stability: if the environmental lapse rate is steeper than the dry adiabatic lapse rate, the atmosphere tends to be unstable; if it’s shallower, it tends to be stable. Humidity, wind, and pressure change with height are described by other profiles, not the temperature profile.

Friction near the surface slows the air, which weakens the Coriolis effect and allows the wind to cross the isobars toward lower pressure. In the upper atmosphere, the Coriolis force more effectively deflects the wind so it tends to flow more parallel to the isobars (geostrophic balance). When you bring friction into the picture at low levels, the balance shifts, and the wind veers across the pressure gradient toward lower pressure. That cross-isobar flow changes the direction from aloft to the surface, producing the surface wind that is more southerly while the higher wind is southwest. Temperature lapse rate and the mere pressure gradient aren’t the primary drivers of this directional change; friction is.

Understanding where the tropopause sits helps you picture how high weather can grow. At mid-latitudes, the tropopause is typically around 36,000 feet (about 11 km). It marks the boundary between the weather-active troposphere and the more stable stratosphere, so most cloud development and storm tops stay below or near this level. This is why it’s relevant for VFR/IFR planning: knowing the approximate height of the tropopause lets you estimate how high thunderstorm tops can reach and how tall cloud layers might be. If storm tops approach or exceed this altitude, you’ll need to factor in potential IFR conditions, plan alternative routes or altitudes, and consider flight levels that keep you clear of the weather. The other options don’t fit because ground level or very low takeoff elevations don’t describe the typical tropopause height, and 60,000 ft is far above where casual VFR/IFR planning usually applies and relates more to high-altitude operation and oxygen.

Visibility comes in different forms because pilots need both a general sense of what the weather looks like and a precise measure along the path you’ll actually use for landing. Prevailing visibility is the broad distance you can see in most directions at ground level. It’s a general measure used for planning and airspace decisions, and it’s what you’d rely on when you’re not focused on a specific runway path. Runway Visual Range is a runway-focused measurement. It’s measured along the runway centerline with dedicated instruments and tells you how far you can see down that particular runway. Because landing and rollout depend on the exact visibility along the landing path, RVR is what’s used to gauge whether a safe approach and landing are possible. There are usually separate RVR readings for the touchdown zone, the middle of the runway, and the rollout. So, the correct understanding is: prevailing visibility is the greatest distance you can see in all directions, while RVR is the distance you can see along the runway and is specifically important for landing operations. RVR is not used for en route segments.