Which data is most essential to determine the thermal index at all soaring levels?

• A. The upper soundings
• B. Ground temperature readings at the surface
• C. Radar reflectivity from the nearest radar
• D. Surface wind observations

Answer: (A)

To determine the thermal index at all soaring levels, you need the vertical thermodynamic profile of the atmosphere—that is, how temperature and humidity change with height. Upper air soundings provide a direct measurement of temperature and dew point as a function of altitude, giving you the environmental lapse rate and moisture content throughout the vertical column. This information lets you assess buoyancy and stability at every level, which is essential for predicting where and how strong thermals will be.

Ground temperature at the surface only tells you conditions at the bottom of the atmosphere and can miss inversions or changes in lapse rate aloft. Radar reflectivity indicates precipitation structure, not the vertical thermodynamic profile needed for the index. Surface wind observations describe near-surface motion but don’t reveal how air behaves higher up.