NOAA's National Weather Service Storm Prediction Center publishes tornado, wind, and hail reports on a daily basis, as well as offers an historical archive of past events. Under reports you can find the current storm reports, and also search back in time to retrieve previous reports. The reports are delivered as .CSV files, one of the formats that can be imported directly in ArcGIS Explorer.

Here's yesterday's hail reports shown in Explorer. By clicking on the report location we can view additional information, and can see there was golf ball size hail reported near El Paso, Texas, mostly pea-sized hailstones in Rosita, Colorado, and quarter-sized hail covering the ground near Elizabeth, Colorado.

And here's what the hail report looked like a year ago yesterday. There were many more hail events reported, and the hailstorms stretched from the Oklahoma panhandle through eastern Kansas, across the southeast corner of Nebraska, and on into Iowa and parts of South Dakota and Minnesota.

To make the maps, we downloaded the .csv file with the events that we wanted from the NOAA Web site. Once we saved the .csv file locally, we used File > Import and opened the file.

Using the Import Text File Wizard, most of the defaults worked perfectly. On the first panel we just accepted all of them (after looking at Data Preview to make sure things looked ok), and clicked Next...

On the second panel most of the defaults were exactly what we wanted, but we made two additions. First, we chose the Location field from the .csv file as our Title Field. This is what we wanted to be displayed as the hover text, and is also the title of the popup window. We also chose Comments as the field from the .csv file to use in the Description. This is what we wanted shown in the popup window contents.

And here's the final result:

See the File Import Wizard Help topic for more information on importing files.