The summer of 2010 may end up being known as the summer of showers as another round of heavy showers hit the state again this morning. National Weather Service meteorologist Jeff Johnson says central Iowa appears to have been the biggest target this time.
Johnson says there were some “really extreme rates” of rainfall with a rate of six inches-an-hour in Dallas County, and total rainfall reports are two to three inches, along with radar estimates of the those amounts or more. He says a majority of rain fell in and around the Des Moines metro area, which caused flash flooding.
Johnson says there was also some heavy rainfall a little north of Des Moines in Story and Marshal counties. Thousands of people lost power in central and eastern Iowa from the morning storms. Similar storms dropped double-digit rains on eastern Iowa in the last couple of weeks. Johnson says in this case it’s not the speed of the storms, but the payload they are carrying that leads to the large amounts of rain.
“They’re very efficient rainfall producers, the atmosphere is very moisture rich,” Johnson says. He says a typical thunderstorm has lower rates of rainfall, but these have been so heavy in moisture content that they dump a lot of rain very quickly.
Johnson says the moisture is moving in from the south. He says it’s a warm tropical air mass that originates from the southwest monsoon, and it comes over the rockies and on into Iowa and has a “tremendous amount of water potential” that leads to the heavy rainfall. Johnson says things will start drying out soon.
Johnson says the boundary that has been set up over the area will move south and bring some relief from the high heat and humidity and lead to some drier weather into the weekend. Just as they did in eastern Iowa recently, the rains in central Iowa created flash flooding that led to many people finding their cars swamped as they tried to commute to work.
See more about weather watches and warnings on the National Weather Service website.