KXAN Weather Q&A: How does size factor into how fast hail falls?

AUSTIN (KXAN) — Questions pour in constantly for the First Warning Weather Team, as viewers ask about different things happening with the weather in Central Texas and elsewhere. There’s now a new, interactive way to find out answers.

Every Monday morning, Meteorologist Rich Segal will comb through his inbox and join anchor Will DuPree for “KXAN Weather: What’s on Your Mind?” to talk through some of the questions submitted that week.

Here’s a list of the questions that will get addressed:

• From Robert Tycast: Didn't Galileo show that all objects fall at the same rate? So why do larger hail fall faster than smaller ones?

Rich answer: The fall speed of hail takes into account the friction between the hail and the air, called the drag effect. It also factors the wind and how much melting occurs. Researchers show, for hail stones less than an inch in diameter, the speed is between 9 and 25 seconds, but for hail stones in a severe storm, 1" or larger, that fall speed can be between 25 and 40 mph. It goes up to greater than 45 mph for stones that are measured 2" to 4".

• From James Machin: The dew point varies widely between morning and afternoon. Why is that? I know that when a new air mass comes in, like with a front, it will change, but why does it change during the day?

Rich answer: The air with the highest dew point in this region comes in at surface-level on southeast winds from the Gulf of Mexico. The air higher in the atmosphere is always a bit less moist (lower dew point temperature). During the heat of the day, the sun heats the ground and causes vertical mixing in the atmosphere (aka, hot air rises). This mixes some drier mid-level air down to the surface, thus lowering dew points.

• From Dave Easterwood: Why is it when the radar shows rain over your area yet there is no rain falling?

Rich answer: This could be a situation where this could be ground clutter from the radar sites that make it look as if it is raining. It also depends on what mode the radar is in. NOWRAD shows a single elevation of the radar, while NEXRAD shows the rain and wind return at all elevation layers. There are also cases where the rain evaporates before it reaches the ground because the air is too dry. It's call VIRGA.