By Skip Rigney

The forecast is for perfect spring weather this weekend through Tuesday. However, by Wednesday a strong storm system will be moving out of the southern Great Plains into the Gulf South, and with it a threat of severe weather.

A tornado tracked through the eastern New Orleans metro area Tuesday night, providing a stark reminder that we are in the midst of the spring severe weather season. On Wednesday a team of National Weather Service (NWS) meteorologists surveyed the area affected by the storm in Jefferson, St. Bernard, and Orleans Parishes. They found a path 11.5 miles long varying in width from very narrow up to three football fields across.

The Enhanced Fujita (EF) Scale was developed in 2006 by meteorologists and wind engineers to relate tornado wind speeds to the damage left behind by a tornado. It is named in honor of meteorologist and engineer Dr. Ted Fujita who pioneered the first such scale in the 1970s.

Based on the damage observed by trained survey teams, tornadoes are rated as belonging to one of five classes from EF-1 with winds of 65-85 mph up to the rare and devastating EF-5 with winds over 200 mph. One key to determining an accurate rating is for surveyors to assess the type and quality of construction damaged. A good example is found in the survey team’s description of what they saw in the New Orleans suburb of Arabi:

“The highest EF3 rating was given to a house that was constructed in the last 6 months. While this house was raised on cinder blocks, every tower of blocks had strapping to the house. The house had additional strapping directly into the foundation, as well as strapping from the cinder blocks to the foundation.

The house itself held together but was shifted about 50 yards to the north and rotated about 90 degrees. The house next door was also swept off the foundation, moved and mostly destroyed. This also had some evidence of strapping to the slab foundation. This area is what will justify the 160 mph EF3 rating.”

The thunderstorm that spawned the New Orleans tornado was embedded in a squall line ahead of a cool front moving from west to east across the Gulf South.

The NWS in Slidell issued multiple tornado warnings Tuesday evening, including two for Pearl River County.

NWS meteorologists noted tornadic circulations on radar in two thunderstorm cells moving northeast out of St. Tammany Parish.  Fortunately, the tornadoes dissipated before reaching our county.

The warnings were preceded by a tornado watch, which the NWS issued last Tuesday morning for eastern Louisiana and most of Mississippi effective for Tuesday afternoon and early evening.

Remember the difference between watches and warnings. To use a baseball analogy, a watch is akin to saying that the team’s three best home run hitters are coming up to bat this inning. A warning is similar to saying that Babe Ruth has just hit a ball that’s on its way into the right field bleachers.

Keep that in mind Wednesday and Wednesday night as the next storm system heads our way.