How amazing of a weather day did we have on Friday? Yes it was another damp and soggy day with a half inch of rain coming down. We also saw both sleet and hail recorded at the airport. It was a question I was pondering as a sleet shower rolled over and by my home in Fishers Friday morning. While technically things can get a little complicated on if it is or isn’t hail/sleet, it’s a good rule of thumb to lean with sleet if there is no thunder heard or lightning seen.
Hail can only develop if there is an updraft present. Updrafts occur in storms. Most storms with an updraft will create lightning due to the friction of the up and down particles in the storm and around the updraft. Rain caught in the updraft will begin to lift instead of falling to the ground. If the updraft is strong enough and the wet bulb zero temperature low enough, the rain drops will freeze making hail. Large hail is caused generally by moderate updrafts that can hold and suspend a rain droplet in the air for long amounts of time in an area conducive to hail formation and growth. If the updraft is too strong the storm will just eject the hail into another warmer part of the storm causing melting before hitting the ground. If the updraft is too weak the rain won’t make it to a level conducive to creating hail.
Sleet on the other hand is a winter weather phenomenon. In a technical sense, sleet will never move “up” in the atmosphere. It will only fall. Sleet starts off as snow, turns into rain as it hits a warm layer of air, and then refreezes as ice as it encounters another layer just above the surface of freezing temperatures.
Yesterday’s weather was interesting because I think you could argue that yesterday’s sleet shower may have been a rare hail shower. No updraft in the classic sense was
present but what we did have was waves in the atmosphere rotating around a powerful low. Each of these waves on their own can cause some “lift” for any rain caught in their path. So what we saw yesterday was not completely sleet. I’m pretty sure it rose in the atmosphere due to winds. Also a look at yesterday’s soundings did not show a warm layer and freezing at the surface. There was only one layer above freezing
yesterday and that was right at the surface. So it is possible that what the airport reported as sleet was in fact a rare hail shower. The automated system recorded it as sleet due to no thunder or lightning.
Today’s weather will be much easier to discern. We will remain cool for one more day with highs likely in the upper 50s. Places south of Indianapolis may hit the 60s. It is another cool start with frost advisories posted for those with tender plants outside. I hope you brought them inside if you could. There will be another chance for rain today and perhaps a snow flurry first thing this morning. I think qualifying shouldn’t be too impacted by the weather. If you’re going down to hang out at the track just remember to grab the rani jacket. It will be cool with a small chance for some drizzle and light rain.
Sunday’s Pole Day will be the best Indy 500 day yet with highs returning to the 60s. It may be a bit chilly to start off the day but things will improves. We should see plenty of sun along with low humidity. Monday to Friday looks mostly dry with the best chance for rain being overnight from Wednesday – Thursday. Temperatures from Monday through Friday will be in the 70s or 80s. Long range model data shows persistent rain around for 500 weekend next week. There’s still plenty of time for that to change.