The National Weather Service has a number of maps that break down a storm into everything from wind speeds to storm surge areas, and warning cones to rainfall amounts, showing either predicted or current figures.
However, Hurricane Harvey has been the epitome of an extreme weather event, not only for the damage it has inflicted on infrastructure but for the unbelievable amounts of rain that have come down, causing a flood event that is unprecedented in U.S. weather history.
On Saturday, so much rain had been dumped on southeastern Texas, the National Weather Service’s (NWS) maps needed to be altered. Because more than 30 inches of rain had fallen in just a couple days, the NWS added a lavender layer to the map to show areas that had already seen “unfathomable” amounts of rain.
The old scale used by the NWS had 13 colors, from light green to dark purple to depict precipitation from 0.1 inches to greater than 15 inches. Well, Harvey’s rainfall amounts trashed the old scale all to pieces. The new scale resets the dark purple color to indicate 15-20 inches of rain — and tacks on “two additional lighter shades of purple to denote 20-30 inches and greater than 30 inches.”
The NWS can assure everyone the new rainfall levels are not “hypothetical,” but real. Any number of Texans along the middle Texas coast and inland areas are living through this extraordinary event and the disheartening news on Monday night is that the region can expect an additional 25 inches of rain in the next day or so.
Houston set a new daily rainfall record Sunday, with 16.07 inches reported at the city’s main airport. On Saturday and Sunday, the NWS said, more than 2 feet of rain (24.44 inches) fell.
Making a change to forecast maps is not totally uncommon. The same thing happened in Australia in 2013. On January 8, 2013, during Australia’s summer, the temperature forecast for the following Monday by Australia’s Bureau of Meteorology was so unprecedented, over 52 degrees Celsius (126 degrees Fahrenheit), that it has had to add a new color to the top of its scale, a suitably incandescent purple, said The Guardian.
