Much of the high plains and south central regions of the continental United States have been unusually dry for some time. In particular, parts of Texas and Oklahoma have been in a drought for nearly five years until April and May 2015 when the weather changed to the other extreme.
Large swaths of Texas, Arkansas, Oklahoma, Nebraska, and Lousiana have been soaked by as much as 500 mm (20 inches) of rainfall in the past 30 days, NASA's Earth Observatory reports.
Some meteorologists point to a southerly bend in the jet stream over the American West, driving air masses with lift and turbulence into Gulf of Mexico moisture and producing heavy rainstorms.
Other weather watchers are suggesting connections to El Niño, though it is hard to directly attribute short-term weather events to larger climate patterns without the perspective of time and data analysis. - NASA/EarthObservatory
Several cities are approaching their wettest May on record even though the month has ten days to go.
Fort Smith, Arkansas, has already set a new record with 351.79 mm (13.85 inches) of rain in May. Oklahoma City, with 353.06 mm (13.90 inches), was approaching records for May and for any month on record.
Wichita Falls, Texas, recorded 317.25 mm (12.49 inches) of rain in the first 20 days of the month. On every day from May 5 - 21, at least one weather station in Texas observed 102 mm (4 inches) of rainfall.
The following image depicts satellite-based measurements of rainfall over the continental United States from April 20 to May 19, 2015, as compiled by NASA. Rainfall totals are regional, remotely-sensed estimates, and local amounts can be significantly higher when measured from the ground.
Data taken by Integrated Multi-Satellite Retrievals for GPM (IMERG), a product of the new Global Precipitation Measurement mission. IMERG pulls together precipitation estimates from passive microwave and infrared sensors on several satellites, as well as monthly surface precipitation gauge data, to provide precipitation estimates between 60 degrees North and South latitude. The GPM satellite is the core of the rainfall observatory that includes measurements from NASA, the Japan Aerospace Exploration Agency, and five other national and international partners.
The heavy rainfall in May 2015 has led to flash floods as well as river floods. More than 100 locations reported river flooding on May 20.
April 22 - May 22, 2015 average rainfall. Data: GPM.
End of drought in Texas and Oklahoma
One year ago, 90 percent of Texas was categorized as being in some level of drought, 40 percent of it extreme. At the beginning of 2015, that number was 65 percent. Now it is 30 percent drought, none of it extreme.
May 20, 2014 - May 19, 2015. US South drought statistics. Credit: US DroughtMonitor. Click on image or here for larger version.
In Oklahoma, the percentage of drought was 98 percent as recently as February 2015; it is now down to 51 percent. (EO)
The following map shows improvement over the last 12 months.
US West drought at 60.7%
As visible on the map above, US West did not experience such change.
As of May 19, 2015, 60.7 percent of the region was in some level of drought. In particular, 98.27 percent of California is currently in some level of drought, 46.77 percent of it is in the state of exceptional drought.
Featured image: Average rainfall from April 22 - May 22, 2015 (GPM).