A long winter is coming to an emphatic end with a series of dramatic spring storms. This hailstorm from April 3rd was one of the most remarkable I’ve experienced.
Hailstone with a glove for scale.
There was a bit of discussion about just how big the hailstones were. After all, could we say that the hail was the size of golf balls if only the largest were? Or would it be more honest to go with some sort of median or modal size.
Mr. Schmidt and Dr. Hurwitz discuss the semantics and logic behind the qualitative reporting of hailstone size.
Mrs. F. brought out the calipers and a rule for a few of the larger stones.
Measuring hailstone diameter.
And I will report that the hail was large enough to put small dents in the roof of my car.
Hailstones banging off the roof of the schoolhouse, and off the cars in the parking lot.
The infra-red satellite image below shows the frontal system that dumped the hail on St. Louis.
Infra-red satellite image showing the clouds of the frontal system that affected St. Louis on April 3rd, 2014. Image from NOAA.Weather map for April 3rd showing the mid-latitude cyclone that produced the hailstorm. Image from NOAA HPC.
Over 30 cm of rainfall in just two days resulted in extensive flooding in Nashville, TN, last week. The precipitation was produced by one of those typical mid-latitude cyclones that sweep across the United States, from west to east, every spring and fall. The Boston Globe has some amazing picture of the flooding.
The news media tends to have the most dramatic photographs of disasters, but the Federal Emergency Management Agency (FEMA) also tends to have good images from their aerial surveys (like the image at the top of this post). And images produced by the government are in the public domain so you don’t have to worry about using them.
May 2-6 fronts. Animation generated using images from the HPC.
For discussing warm fronts, cold fronts and mid-latitude cyclones, NOAA‘s Hydrometeorological Prediction Center (HPC) is a great resource. You can find an archive of daily weather maps for the U.S. that you can click through to see the fronts move.
Infra-red satellite image of the continental U.S.. Note the alignment of the clouds and precipitation with the fronts in the first (static) weather map above. (Image from GOES).
Satellite imagery usually complements to the frontal weather maps very well. Most satellites orbit around the Earth pretty quickly, at just the right orbital speed that the centrifugal force just balances the Earth’s gravity so the satellite does not crash into the atmosphere or escape into space. Some satellites are set into orbit a bit further out so that they can rotate with the Earth, effectively staying above the same place all the time. NOAA has a few of these geostationary satellites monitoring the weather around the world, and you can get real-time images from the Geostationary Satellite Server. There used to be archived satellite images but I can’t seem to find them at the moment.
