In the last couple of weeks, Portland has experienced some hail or sleet storms. Usually brief in duration, these “storms” contain small hail stones in the shape of, well, they look like Hershey kisses to me. Which I find interesting, because being from the Midwest (Michigan to be exact, and also four years in Chicago), hail stones to me have always appeared to be more round, or spherical.

The odd shape of our Portland hail stones made me wonder why the shape is different from other parts of the USA.
So today, I will pass along the information that I have gleaned from my research into the shape and formation of hail stones in a new feature I will call Science Friday, but not to be confused with NPR’s Talk of the Nation’s Science Friday. Wait, maybe I should call it something else…I know that NPR is brutal when it comes to copyright infringement, as I had a syndicated radio show called “Car Talk“, and boy, that Click and Clack surprisingly do not have a sense of humor when it comes to someone stealing their idea. My knees hurt just thinking about it.
So here is “Science Class Friday.” Yeah, that’ll work.
Hail is normally associated with thunderstorms, but as we have relatively few thunderstorms on the Pacific coastline, we can read that as hail being associated with cumulus and cumulonimbus clouds. Cumulus clouds are formed when moisture is forced upward, and when that cloud is forced even higher upward, then it becomes a cumulonimbus cloud, or a “thunderhead”. This is fairly basic meteorology, from junior high science class, so you are most likely already aware of clouds and their names.
The difference between Pacific Northwest cumulus clouds and Midwestern cumulus clouds is that the PNW has mountainous terrain that forces the air upward, whereas in the MW, clouds form when a warm front meets a cold front. And that warm front/cold front thing also occurs here in Oregon, but add mountains to the equation and you get yourself Portland’s odd weather.
Now, hail is basically rain that happens to freeze. The liquid precipitation becomes hail when it is forced back up into the cloud, rather than falling to Earth. Hail is distinguished from “sleet” or “ice pellets” by size. Hail starts out as an ice pellet, and when that pellet grows larger than a quarter of an inch or about 5 millimeters, it then becomes hail.
Round or spherical hail is mostly associated with small-sized hail. Irregular shapes tend to occur when the hail “pellet” is kept up in the cloud for an extended period of time. This is due to a strong updraft within the cloud or cloud system. Serious updrafts are the result of a serious difference in pressure, with is associated with temperature for the most part.
According to the National Weather Service’s JetStream Glossary, our “hail” may be correctly labeled as “ice pellets”. I failed to measure the hail or sleet or ice pellet when they fell, so I cannot say for certain whether or not we had hail or sleet. But there are some other critera that may come play when defining our icy hershey kisses.
Ice pellets are defined as:
Precipitation of transparent and translucent pellets of ice, which are round or irregular, rarely conical, and which have a diameter of 0.2″ (5 mm), or less. Ice Pellets bounce when they make contact with the ground. It is sometimes called “Sleet”. There are two main types:
1. Hard grains of ice consisting of frozen raindrops, or largely melted and refrozen snowflakes.
2. Pellets of snow encased in a thin layer of ice which have formed from the freezing, either of droplets intercepted by the pellets, or of water resulting from the partial melting of the pellets.
Our ice pellets were more opaque to me, but I guess they could have been defined as translucent, kind of. And the above definition seems to relegate “conical” ice pellets to a rarity. But our ice pellets did indeed bounce and the definition for hail does not include that little tidbit.
Precipitation in the form of balls or lumps usually consisting of concentric layers of ice. A thunderstorm is classified as severe when it produces hail 3/4″ or larger in diameter.
Both definitions come from the National Weather Service, which is part of the NOAA or for all you laymen out there, the National Oceanic and Atmospheric Administration. Ah, our tax dollars at work.
I have found some other definitions for “sleet” that also mention the bounce, so I am now inclined to label our “hershey hail” as sleet.
But wait, I still haven’t figured out why our sleet is conical.
The American Meteorological Society clears all of this rather odd debate up.
graupel—Heavily rimed snow particles, often called snow pellets; often indistinguishable from very small soft hail except for the size convention that hail must have a diameter greater than 5 mm.
Sometimes distinguished by shape into conical, hexagonal, and lump (irregular) graupel.
I think we have a winner. Portland experienced not hail, nor sleet, but rather a graupel storm. When I crossreference the definition of graupel with the NWS, this is what they have to say about it.
Small pellets of ice created when supercooled water droplets coat, or rime, a snowflake. The pellets are cloudy or white, not clear like sleet, and often are mistaken for hail.
Yep, graupel it is. I grew up with hail, indeed, and now I get to experience graupel. Neat.

Portland, Oregon, ail, Sleset, precipitation, storms, clouds, rain, ice pellets, graupel