What’s Graupel? It was reported today in parts of central Ohio

Cbus Weather Nerd

COLUMBUS (WCMH) – It has been a chilly, windy, and at times wet day across parts of Central and Southern Ohio.  Some of you may have even experienced Graupel, even though you thought it was sleet or hail.  You now might be asking yourself, what is Graupel?

First, the atmosphere today was cold:

Not only on the ground, but above the ground as well.  While many of us started in the upper 40s this morning on the ground, only about 4500 feet above us, the temperatures were freezing or below freezing.

(below is the morning sounding from the balloon launch in Wilmington, which is the closest sounding to Central/Southern Ohio)

Yes, did allow for shallow rain showers this morning to stay above freezing from the cloud to the ground, but as the morning progressed, we had clouds dropping precipitation that were well above the freezing level throughout the cloud.  This would allow for snow showers up in the sky to form, but typically cause we have a warm enough layer of air near the ground, these melt and we get cold rain showers.

This was the case for most of the area, however some spots had some super-cooled air trap in those tiny flakes, and that precipitation was able to overcome the warm layer and hit the ground as a squishy looking pellet.  This is actually not uncommon for us this time of the year, or in the spring, typically April to early May.The temperature of the clouds and near the ground can tell us what to expect. 

Let us discuss briefly rain:

Rain falls when the temperature is above freezing in the layer of air at and above the ground level.   If the depth and warmth of that level is enough to melt the snow aloft, it turns to rain.  Sometimes you can also have shallow rain showers that form this time of the year, that the precipitation stays in a “warm enough” layer to remain a cold rain shower.

What makes snow?

Snow falls when water droplets in the clouds freeze and form ice crystals, they stick together and get big enough to fall as snow.   The warmer the temperatures are in the clouds, the bigger and wetter snowflakes could be as they melt on the edges and stick together.

Also, snow can fall when surface temperatures are a bit above freezing.  The snowfall will generally melt as it is falling, but the bigger flakes will still be visible before melting completely.

What makes freezing rain?

Freezing rain occurs when rain droplets fall through a warmer than air mass, freezing keeping the droplet as rain.   The air near the ground is cooled and below freezing, and that droplet freezes on contact, forming a coating of ice.  On the ground and other surfaces freezing rain looks like a shiny, slippery, rather smooth coating.

What makes sleet?

Sleet forms when melted snowflakes from the clouds, (known as rain) falls out of the clouds falls through a thicker, and higher sub-freezing layer.   It causes the rain, or melted snow to refreeze again as an ice pellet.

Typically these little tiny balls of ice hurt a little when they hit you, and because they are small, they will bounce too.   When you look at sleet, it will appear to take on a bit more of a clear appearance, like an ice cube, but round like a tiny ball.

How can I tell sleet and hail apart?

An easy way is the time of year.   Sleet will fall in late Autumn, Winter, and early Spring.   Hail will fall in Spring, Summer, and Autumn.

This isn’t 100% perfect though, so the next thing you can do is see the process that caused the item to fall.   If it is associated with a thunderstorm, it is hail.   Hail forms when rain droplets are pulled upwards by strong updrafts associated with thunderstorms.   The updrafts are strong enough to pull the droplet past the freezing level in the cloud and turn it into an ice pellet.

As hail gets heavy, it will fall, the stronger updrafts will lift the hail back up, colliding with cold rain drops which will make it bigger.  It will then refreeze as it gets higher in the clouds and get bigger and fall.   If the updrafts are strong enough, hail will repeat this process several times, even connecting with other hail to make bigger, odd shaped hail.

Eventually, the hail will be too heavy and fall to the ground.   This is why when hail is huge, we know the storm is massive and strong, because the updrafts are strong enough to push this heavy object up high enough into the clouds repeated times.

What is Graupel then?

Graupel is a snowflake that falls through the cloud and gets covered by a supercooled rain droplets in a lower layer of the atmosphere on the way down to the ground.  They freeze and cause a coating of water around the snowflakes.   When they hit the ground they sometimes will bounce a bit too, but are much softer than hail, but harder than a snowflake.

They also have a white appearance to them, vs the clear look of sleet.   Graupel is generally pretty smooshy if you push on it with your hand as its basically a snowflake that has a thin layer of ice over it.

The easiest way I can describe what Graupel looks and feels like is, Dippin’ Dots.   I can’t vouch for the taste, but I am guessing Dippin Dots taste a lot better, and less atmospherey 🙂

(thank you to www.dippindots.com for the image above)

If you happen to get good pictures of this stuff, or have any questions about it, you can always email them to me dmazza@wcmh.com

-Dave

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