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Epic Rains, Disastrous Floods Plague Texas, Oklahoma
http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2997
Water cascaded through the streets, creeks, and bayous of downtown Austin and Houston on Monday as an upper-level storm inched its way across the southern Great Plains. Slow-moving thunderstorms dumped 6” to 8” across the western Houston metro area between 8:00 and 11:00 p.m., and heavy rains continued well past midnight across much of the south and west metro area, bringing some totals as high as 10+”. Though the Houston flooding came well short of that in 2001’s catastrophic Tropical Storm Allison, countless roads and interstate highways were submerged, and hundreds of homes reportedly took water. This was the latest salvo in a remarkable three-day stretch of torrential rain and destructive flooding across much of Oklahoma and Texas and parts of neighboring states. As of Tuesday morning, the floods had taken at least 8 lives, with at least 12 people missing, and damaged or destroyed many hundreds of buildings.
The scope and intensity of this weekend’s rains resulted from a rich feed of low-level moisture pumping into the region from the Gulf of Mexico, combined with the excruciatingly slow movement of the large-scale storm system. Upper-level winds were largely aligned with the low-level frontal zone, an ideal setup for “training echoes” (successive downpours over the same area). In addition, rains were concentrated by several mesoscale convective vortices, small-scale centers of low-pressure that developed along the frontal bands, in some cases resembling mini-tropical cyclones.
Figure 5. WunderMap analysis of flow at the 200-hPa level (about 39,000 feet) at 1200 GMT on Monday, May 25. A powerful subtropical jet can be seen flowing eastward across Mexico, then northward through the Mississippi Valley. The tornadic supercell at Cuidad Acuna, Mexico, occurred about an hour before the time of this analysis, near the left front corner of a powerful “jet max” (the greenish strip across Mexico). Severe storms tend to occur most often at the left front and right rear of jet maxima, where upward motion is favored. Also evident is the mammoth ridge extending from western Canada into the Arctic Ocean, where record-high temperatures have been observed in recent days. The northwestern ridge and western U.S. trough have persisted through much of May.
Water cascaded through the streets, creeks, and bayous of downtown Austin and Houston on Monday as an upper-level storm inched its way across the southern Great Plains. Slow-moving thunderstorms dumped 6” to 8” across the western Houston metro area between 8:00 and 11:00 p.m., and heavy rains continued well past midnight across much of the south and west metro area, bringing some totals as high as 10+”. Though the Houston flooding came well short of that in 2001’s catastrophic Tropical Storm Allison, countless roads and interstate highways were submerged, and hundreds of homes reportedly took water. This was the latest salvo in a remarkable three-day stretch of torrential rain and destructive flooding across much of Oklahoma and Texas and parts of neighboring states. As of Tuesday morning, the floods had taken at least 8 lives, with at least 12 people missing, and damaged or destroyed many hundreds of buildings.
The scope and intensity of this weekend’s rains resulted from a rich feed of low-level moisture pumping into the region from the Gulf of Mexico, combined with the excruciatingly slow movement of the large-scale storm system. Upper-level winds were largely aligned with the low-level frontal zone, an ideal setup for “training echoes” (successive downpours over the same area). In addition, rains were concentrated by several mesoscale convective vortices, small-scale centers of low-pressure that developed along the frontal bands, in some cases resembling mini-tropical cyclones.
Figure 5. WunderMap analysis of flow at the 200-hPa level (about 39,000 feet) at 1200 GMT on Monday, May 25. A powerful subtropical jet can be seen flowing eastward across Mexico, then northward through the Mississippi Valley. The tornadic supercell at Cuidad Acuna, Mexico, occurred about an hour before the time of this analysis, near the left front corner of a powerful “jet max” (the greenish strip across Mexico). Severe storms tend to occur most often at the left front and right rear of jet maxima, where upward motion is favored. Also evident is the mammoth ridge extending from western Canada into the Arctic Ocean, where record-high temperatures have been observed in recent days. The northwestern ridge and western U.S. trough have persisted through much of May.
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