Water Droplets and Ice Crystals Weight

A. You’re absolutely right! The time a water droplet or ice crystal can stay suspended in a cloud can vary significantly, from hours to days, and in some cases, even longer.

It all depends on the interplay of those factors we discussed:

Strength of updrafts: Strong, persistent updrafts in a storm cloud can keep even relatively large and heavy particles suspended for a long time. This is why thunderstorms can sometimes rage for hours.
Cloud type: Different types of clouds have different characteristics. For example, high-altitude cirrus clouds, made of ice crystals, can persist for days or even weeks as the ice crystals are small and the air is very stable.
Moisture content: A cloud with high moisture content will have more water vapor condensing or depositing onto the particles, making them grow faster and potentially fall sooner.
Temperature: Temperature affects the rate of evaporation and condensation, influencing the size and lifespan of the droplets or crystals.

Think of it like this:

Hours: This is typical for many clouds, especially those associated with showers or shorter-lived storms.
Days: This is common for larger storm systems or stable cloud formations like those high cirrus clouds.
Week or more: This is less common but possible for certain types of clouds in specific atmospheric conditions. For example, some high-altitude ice clouds in the polar regions can persist for very long periods.

It’s a fascinating and complex process, and meteorologists use sophisticated tools and models to study and predict how clouds and precipitation behave.

The actual weight that causes water droplets or ice crystals to fall from clouds as precipitation depends on several factors, including their size, shape, and the surrounding air currents.

Size Threshold:
- Water Droplets: Cloud droplets are typically very small, around 10 micrometers in diameter. These are so light that they can remain suspended in the air due to weak updrafts. When droplets grow to about 200 micrometers or larger, their weight overcomes the air resistance and they begin to fall as drizzle or rain.
- Ice Crystals: For ice crystals or snowflakes, the size and density vary more widely. Larger, fluffier snowflakes fall at a lower weight threshold than compact ice particles like hailstones.
Weight Estimate:
A single raindrop (1-2 mm in diameter) weighs approximately 2-6 milligrams. The critical factor is not just the absolute weight but how much surface area the droplet or particle presents to air resistance.
Suspension Dynamics:
Clouds are supported by updrafts of air, which can counteract gravity for small particles. As droplets or crystals grow larger through processes like condensation, deposition, or collision-coalescence, they reach a point where their terminal velocity exceeds the upward motion of the air. This triggers their fall.
Terminal Velocity:
- Tiny droplets (10 micrometers) fall at about 0.01 m/s but are easily kept aloft by even weak updrafts.
- Larger raindrops (2 mm) fall at around 6-7 m/s, which is why they overcome atmospheric resistance.

Thus, the “breaking weight” is not fixed but varies based on droplet size, air conditions, and updraft strength.

P. Can it remain suspended for hours, days, or even a week, depending on the environmental conditions?

A. Yes, water droplets or ice crystals can remain suspended in clouds for extended periods—hours, days, or even weeks—depending on the environmental conditions. Factors that influence this include:

Updraft Strength: Strong upward air currents in the atmosphere can keep small particles aloft indefinitely, as long as the upward force counteracts gravity.
Particle Size: Tiny water droplets or ice crystals, being very light and small, experience minimal gravitational pull and can stay suspended longer.
Humidity and Temperature: Stable atmospheric conditions with consistent temperature and humidity can prevent the droplets or crystals from growing large enough to fall as precipitation.
Cloud Type: In high-altitude clouds like cirrus clouds, ice crystals can remain suspended for days or longer due to the thin air and weak gravitational effects on very light particles.
Environmental Disturbances: Turbulence, shifting air currents, or changes in temperature can either help sustain suspension or cause the particles to coalesce into larger droplets and eventually precipitate.

Under stable atmospheric conditions, some particles in clouds, especially in thin or high-altitude formations, can persist for a surprisingly long time before falling or evaporating.