I found a web site that can be valuable for genealogists. You probably won't need it very often, but when you do have a call for it, it could be valuable. I'm recording this one in my notes because I'll never know when I might need it.
If you find a reference in family papers or any historical document that refers to the weather on a certain date, you can now find the details. For instance, a family Bible might say, "George was born at home on January 11, 1912. The doctor was unable to get there because of a blizzard." You may wonder just how significant this blizzard was.
Today in Weather History can supply significant weather for any date in American history. It won't have the weather for every location for every day, but it lists most of the major storms, heat waves, tornadoes, hurricanes and the like. If the weather was bad enough to be recorded in some ancestral documentation, it may well be detailed on Today in Weather History at http://www.weatherforyou.com/history/.
The main page always shows weather on today's date in past years. However, you can search for most any date of any year by using the search boxes near the top of the screen. Not all dates in all years have weather information - only the dates on which something unusual happened and was recorded. For instance, there is no weather listed for my birthdate. I guess it was a quiet day, other than for my parents.
One caveat: the site seems to carry only U.S. information. If your interest lies outside of North America, you probably should skip this site. In fact, if anyone knows of any similar sites for other countries, please post a comment at the end of this article so that others may learn of it.