Why is Ohio seeing more summer downpours than usual?

Yahoo

2 days ago

Central Ohio Weather and Radar
COLUMBUS (WCMH) — The familiar phrase 'when it rains, it pours' applies to our weather in recent weeks. More than 15 inches of rain have fallen on Columbus since May 1, nearly five inches above normal, and double what fell during last year's drought (June-October). Some areas in southern Ohio had upwards of two feet of rain in the past three months, resulting in flooding.
On the evening of July 17, a small shower over northern Fairfield County blew up into a narrow line of torrential rain that spread east along the Licking County border and across Buckeye Lake.
Nearly five inches of rain was measured at Sellers Point, much of it falling in a little more than an hour. Inevitably, low-lying areas were swamped, and water entered the lower floors of several homes and buildings and flooded roads, and closed a portion of State Route 13 just south of Interstate 70 in southern Licking County.
The pattern of storm deluges began at the start of July. On June 30-July 1, 3.85 inches fell at Bainbridge in Ross County. Rockbridge in northern Hocking County received 7.72 inches from June 24 through July 1. On July 9, localized downpours dropped nearly three inches of rain around the Newark area in eastern Licking County.
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Through July 15, a record 3,045 flash flood warnings were issued by the National Weather Service across the U.S., exceeding the 1998 record for an entire year (3,033).
Four historic floods occurred in one week in the eastern part of the country. Catastrophic flooding took more than 135 lives along the Guadalupe River in south-central Texas on July 4. Later in the holiday weekend, up to a foot of rain swamped the Raleigh-Durham, North Carolina, area from the remnants of Tropical Storm Chantal, taking six lives.
On July 7-8, parts of Chicago were soaked with more than 5 inches of rain. Ruidoso, New Mexico, experienced a deadly flash flood after several inches of rain over a burn scar raced downhill, killing three people and carrying a home downstream on July 8.
The New York City area, and neighboring New Jersey and southeastern Pennsylvania region, were swamped with more than six inches of rain on July 14, inundating some subways and flooding neighborhoods and roads. Two people died in New Jersey when their car was swept away in floodwaters.
Reason for excessive rainfalls
Areas east of the Rocky Mountains and south of the Great Lakes have been caught in soggy pattern due to near-record high levels of atmospheric water vapor. The seasonal northward shift of the jet stream around the periphery of high pressure in the Southeast has been the focus for rounds of showers and storms feeding off the extra available energy derived from stagnant tropical moisture.
Frequent disturbances or waves in the mid-level flow drive thunderstorm clusters that tend to congeal into self-sustaining complexes, bringing torrential rain and strong winds. Light steering currents, typical of summer, allows storms to linger longer, or 'train' over the same areas like railroad cars filled with moisture following the same section of track.
In the case of the tragic Texas Hill Country flood, the remnants of Tropical Storm Barry played a major role in the rainfall totals that reached 10 to 20 inches on July 3-4. Successive periods of heavy rain in the past two week, totaling five to 10 inches locally in some events, stalled search and recovery efforts.
Heavy rainfalls increasing in most of U.S.
A recent U.S. study conducted by Climate Central reported that 88 percent (126) of the nation's 144 sampled cities since 1970 have recorded heavier rainfall rates. In the Ohio Valley, the average increase in hourly rainfall intensity was 15 percent, which can add a few additional inches in intense storms, often the difference between ponding and more widespread flooding.
More intense rainfalls falling on complex, hilly terrain and in urban areas with poorer drainage (storm drains, sewers become clogged) promote channeled runoff that is conducive to flash flooding–the nation's deadliest severe weather event.
The primary reason for the long-term wetter trend is warmer air and sea surface temperatures, which causes more moisture to evaporate into the atmosphere. A one degree Fahrenheit rise in the temperature allows the air to store 4 percent more water vapor.
The ocean absorbs about 90 percent of the excess heat generated by greenhouse gas emissions (coal, oil, natural gas) from human activities, which have been steadily increasing globally. Higher ocean temperatures contribute to stronger tropical cyclones capable of bringing copious rain and high winds during and following landfall.
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