What is the likely cloud base when the surface temperature is high and dewpoint is relatively low, such as 82°F and 38°F?

• A. About 10,000 feet AGL
• B. About 6,000 feet AGL
• C. About 2,000 feet AGL
• D. About 14,000 feet AGL

Answer: (A)

A high cloud base comes from a large difference between the surface temperature and the dew point. When the air is warm and dry (large T minus Td), it must rise much higher before it cools to the dew point and condensation begins, so the base of the cloud sits higher.

Convert to Celsius: 82°F is about 27.8°C, and 38°F is about 3.3°C. The spread is about 24.5°C. A common rule of thumb for the lifting condensation level is roughly 125 meters for each degree Celsius of spread, so the LCL height is about 125 × 24.5 ≈ 3,060 meters. That’s roughly 3,060 × 3.281 ≈ 10,000 feet above ground level.

So the likely cloud base is around 10,000 feet AGL. The other options would require much smaller or much larger temperature-dew point spreads than what’s given.