Weather Wednesday — The Week That Was

It’s been an eventful week on the weather front, so let’s highlight a few points.

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-Damage near Van, TX — KSFY

What started out as a very quiet first quarter of the year as regards the number of tornadoes has become much more active since mid-April. There have been several widespread, damaging and deadly outbreaks, especially over the last ten days or so.

The organization U.S. Tornadoes has begun to compile a rolling list of the highest incidence of tornadoes in 2015. One can see that May is headed toward reversing the early year trend of below normal activity.

storm-thumb-051015In addition, the storms over the past weekend (May 9 and 10) included extremely high rainfall rates in some areas which led to flash flooding and necessitated swift water rescues. Some of the rescues were broadcast live by television stations in Dallas and retransmitted to the entire country via The Weather Channel.

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— NWS

And if that wasn’t enough, a late season snowstorm on the same weekend buried parts of the Rocky Mountains into the Dakotas. The heavy, wet snow damaged buildings and had to be shoveled out of Coors Field before the Colorado Rockies could host their Sunday afternoon game against the Los Angeles Dodgers.

tropical-storm-anaAnd to top it all off, Tropical Storm Ana, brought gusty winds and copious amounts of rain to the Southeast.

Weather Wednesday – First Tornado Captured by Radar

62 years ago this month, April 9, 1953, about 3 miles from where I am sitting, a tornado was caught by radar for the first time. Scientists and electrical engineers at the Illinois State Water Survey at the University of Illinois at Urbana-Champaign had modified a former WWII airborne radar for use in estimating amounts of precipitation falling from storms.

Don Staggs, an electrical engineer, was preparing the radar for later field tests. He started to notice what we now call “hook echo” returns in the scans of the storm. As afternoon turned to evening, a strong thunderstorm developed just north of Champaign, about ten miles from the radar site at the university-owned Willard Airport. The storm image included a pronounced hook on the bottom rear flank much as we see hook echoes on modern Doppler radar.

first radar image of a tornado
Illinois State Water Survey via The News Gazette

Still photos and a 16mm film of the images on the scope captured that moment. A team of meteorologists and technicians were able to study the image capture. Later, Dr. Ted Fujita the creator of the tornado strength measurement scale that bears his name, sketched over 200 of the frames of the film in his own hand. All of this can be seen in a terrific article from Colorado State University.  Note especially the photos of the tornado and the well-developed wall cloud.

We now know that the radar captured the early stages of an F3 tornado that eventually traveled about 160 miles and dissipated near Albany, IN. There were two fatalities and about $4-million in property damage in Illinois. The path of the storm took it across mostly rural areas.

Next week, we’ll discuss current use of radar and what may be the next generation of this important forecast tool.

Weather Wednesday –New Definitions from the Storm Prediction Center

There’s been much talk in recent weeks of a more detailed method of describing the potential for severe weather now being employed by the Storm Prediction Center in its Convective Outlooks. The SPC worked with National Weather Service offices, communications experts and consumers of its products to expand its long time use of the “Slight, Moderate and High” risk categories to “Marginal, Slight, Enhanced, Moderate and High.”

In addition, the chart below describes what the storms might look like under each newly-defined category and what the main threats would be.

Understanding Categories
The Storm Prediction Center has many products that can be used by broadcast meteorologists, emergency managers and the general public to look as far as 8 days ahead. These tools are especially valuable for planning purposes and should never supplant your detailed local forecast.

The Mesoscale Discussions are particularly helpful on days when severe weather is expected. The discussions are issued on an “as needed” basis as storm threats develop. Other tools are updated as often as four times a day. If you’ve never visited the site at spc.noaa.gov, now would be a good time to familiarize yourself with the offerings.