Frozen precipitation that fell on October 6th sure looked a lot like sleet. Temperatures were well below normal, and it felt like winter. Sleet seemed to be the logical description of the little balls of ice that fell from the sky. But there was also thunder and lightning in places. That usually means hail. So was it sleet or hail? Stay tuned.
Sleet and hail form through different processes. Hail is the result of rain forced aloft by updrafts into subfreezing air in cold cloud tops. Liquid becomes solid, and stones can become huge if updrafts suspend them for an extended period. Sleet usually happens when snow falls through a melting layer (above freezing temperatures) and then refreezes before reaching the ground. As far as size, sleet is small.
To put it simply, hail is created on way up, and sleet is manufactured on the way down.
Hail is most often associated with convective precipitation (such as scattered showers and thunderstorms). Sleet is more of a stratiform precipitation type (such as widespread rain or snow), but not always.
Early on the 6th, the sounding (temperature and dewpoint profile with height) at Springfield, MO showed moisture in the mid-levels of the atmosphere, with dry air farther down. This is a set-up for a stratiform event. It was just the opposite at Little Rock, AR. There was low-level moisture, and it was dry overhead. This is more of a convective situation.
Both soundings had something in common...it was dry somewhere. When moisture was introduced, this led to rapid cooling through evaporation. In the Little Rock, AR case, ascending moisture and falling temperatures upstairs yielded hail in central Arkansas. In the Springfield, MO example, descending moisture and a drop in mercury downstairs may have netted some sleet farther north.
The problem with the latter example is that surface readings were generally in the 40s as precipitation began. Sleet may have melted before reaching the ground. Rethinking the sleet process, maybe there was snow but it never melted entirely. Where low-level cooling occurred, supercooled water (liquid below freezing) existed. This would have created an icy shell around the flakes, which is graupel. It just so happens that graupel was reported toward the Missouri border.
Whether it was rain, sleet, hail or graupel, it was definitely an interesting day.