Record atmospheric moisture feeds flooding in Central U.S.

By Dr. Jeff Masters
23 February 2018
(Weather Underground) – An unusually severe winter flood event is underway across the center of the U.S., from Texas to Michigan, thanks to heavy rains that fell during the week, fed by record to near-record atmospheric moisture for this time of year. The most significant flooding thus far has been in Southwest Michigan, Northwest Indiana, and Northeast Illinois, where the heavy rains fell on a snowpack that completely melted, releasing meltwater equivalent to another ½’ – 1” of rain. In East Lansing, Michigan, floodwaters rose on the campus of Michigan State University from the Red Cedar River, causing some classes to be moved on Friday to non-flooded areas. Three drowning deaths have been blamed on the flood thus far, one death each in Michigan, Oklahoma, and Illinois. […]

Record atmospheric moisture fed the flood

Accompanying the exceptional February warmth this week were record levels of February moisture, as a flow of unusually moist air rode northwards from the Gulf of Mexico, where water temperatures were about 1.0°C (1.8°F) above average. Meteorologists use a term called “precipitable water” to discuss how much water vapor is in the atmosphere. Precipitable water is defined as how much rain would fall on the ground if one took a vertical slice of the atmosphere above a given location and condensed all the water vapor into rain. Precipitable water levels tend to be higher when the temperature is warmer, since warm air holds more water vapor. This week, an extraordinarily large number of upper air balloon soundings set all-time records for February moisture. There are 73 radiosonde stations in the contiguous U.S. that take routine measurements twice per day, and six of them set all-time February precipitable water records this week; four of these stations broke their previous February record multiple times. That is a very rare occurrence, as radiosonde data goes back 70 years. Here are the new February precipitable water records set this week:

Detroit, MI, 3 new records: 1.38” at 0Z 21 Feb, 1.36” at 12Z 20 Feb, and 1.29” at 0Z 20 Feb; Old record: 1.15″, 2/23/1985

Lincoln, IL, 2 new records: 1.47″ at 12Z 2/20 and 1.36” at 0Z 2/20; Old record: 1.34″, 2/25/2001

Colombia, MO, 2 new records: 1.44″ at 0Z 2/20 and 1.39” at 12Z 2/19; Old record: 1.33″, 2/21/1997

Shreveport, LA, 3 new records: 1.75″ at 0Z 2/21, 1.69” at 12Z 2/21, and 1.75” at 0Z 2/23; Old record: 1.66″, 2/21/1974

Alpena, MI, 1 new record: 1.11” at 0Z 2/21; Old record: 1.09”, 2/12/1999

Davenport, IA, 1 new record: 1.18” at 12Z 2/21; Old record: 1.09”, 2/25/2001 […]

Global warming plays an important role in causing heavier downpours

An increase in heavy downpours—the upper 1% of heavy rains that are most likely to cause flooding–have been documented across every region of the contiguous U.S. since 1958, and this increase has been partially attributed to the increase in atmospheric moisture due to human-caused global warming. Every degree Centigrade that the air warms up increases the amount of water vapor the air can hold by 7%, due to increased evaporation from the oceans, so record-breaking atmospheric moisture and the resultant major flooding–like the situation observed over the central U.S. this week–are something we will see a lot more of as the climate continues to warm in coming decades. [more]

Record Atmospheric Moisture Feeding Central U.S. Flooding

By Ada Carr and Sean Breslin
23 February 2018
(Weather.com) – For thousands who live near waterways from Texas to Michigan, persistent flooding was expected to continue through the weekend, worsening in some areas before it gets better.
In numerous towns from the South to the Midwest, homes have been turned into islands and school days have been canceled because there’s no way to get to the building. In East Lansing, Michigan, floodwaters rose on the campus of Michigan State University because of the swollen Red Cedar River, causing some classes to be moved to non-flooded areas.
“Be careful if you’re trying to come to campus,” said Lansing Mayor Andy Schor, as reported by the Associated Press. “Changing conditions are affecting not only the roads but sidewalks and walkways.”
At least six Lansing neighborhoods were issued voluntary evacuations in areas where the Grand River was expected to overtake homes, the AP also said. […]Flooding problems were reported in several parts of Indiana, and in Elkhart County, crews in boats rescued residents from a dozen homes along the Baugo Creek, according to the AP.”I ended up grabbing my favorite blanket and stuffed animals,” 15-year-old Madison Schmidt, who was forced to evacuate from her Elkhart home, told the Elkhart Truth. “I got into the boat. Seeing what happened, just almost made me cry.”For this town located 15 miles east of South Bend, it has been decades since flooding of this magnitude has been observed.”This city has not seen flooding like this in the last 45 years,” Mayor Tim Neese told the Elkhart Truth. “We also had record snowfall in addition to consistent rain.” […]In Michigan, residents had to be evacuated in parts of Niles Thursday after the St. Joseph River surpassed a 50-year high, MLive.com reported. The waterway crested at roughly 17.33 feet.”The last time it reached 15 feet in Niles was 5 April 1950,” National Weather Service meteorologist Megan Dodson told MLive.com. [more]

FloFlooding in the Midwest, South Worsens; Water Rises at Michigan State University; Evacuations as Far South as Dallas