Don't Underestimate The Power Of Water

Spring flooding might be a more widespread problem along rivers in the Midwest and Northeast in 2019 due to a number of accumulating factors over the past several months.

The combination of melting snow, additional rain and snow and rising temperatures all play crucial roles in determining how widespread and severe spring river flooding is from March through May in the Midwest and Northeast.

Here's a rundown of the factors that could lead to spring flood issues.

Soaked Since Summer

One of the reasons we're more concerned about spring flooding this year is how wet it has been since last summer.

Parts of the East, Ohio Valley, upper Midwest and southern Plains had their wettest fall - September through November - on record in 2018, according to NOAA's National Centers for Environmental Information. Except for the Florida peninsula, much of the eastern two-thirds of the country was much wetter than average in the fall.

That wet fall followed one of the wettest summers on record in parts of the mid-Atlantic states and Midwest and Plains.

That wet drum beat has marched on through winter.

Dozens of locations in the Plains, Midwest, Northeast and South have had one of the wettest winters-to-date through Feb. 12, according to the Southeast Regional Climate Center.

Saturated Soil

Given all this precipitation, it should be no surprise that soil moisture is about as high as it can get this time of year.

According to an analysis by NOAA's Climate Prediction Center, soil moisture values over vast areas of the Plains, Midwest and East are in the 99th percentile for this time of year. In other words, these soil moisture levels are in the top 1 percent of all values for mid-February.

In some of these areas, the soil contains over 3 inches more moisture than average for this time of year, so the ground cannot absorb much rain or snowmelt before runoff into rivers and streams occurs.

Rivers Already in Flood Stage

Scores of U.S. Geological Survey river and stream gauges from the Plains to the Midwest and East were measuring flow levels in the 90th percentile or higher relative to past records on Feb. 13.

Over 100 river gauges were measuring levels above flood stage, primarily in the Ohio and mid-Mississippi River Valleys, from recent soaking rainfall in February.

Increasing Snowpack

Parts of the Midwest have had one of their snowiest Februaries on record. A healthy snowpack has built over upstate New York and northern New England even though snowfall along parts of the immediate Interstate 95 corridor of the Northeast has been below average.

More important for flood risk, however, is how much water is contained in the snowpack, which is released once it melts.

A NOAA analysis estimated 2 to 6 inches of water is currently locked in the snowpack in parts of the upper Midwest and northern New England.

That may not sound like a big deal, but consider what would happen if an area picks up 2 to 6 inches of rain over the span of a few days. That would likely trigger at least minor nuisance flooding.

Spring Wild Cards

Other important factors that can determine the severity of flooding remain uncertain.

The latest three-month outlook from NOAA's Climate Prediction Center suggested a drier-than-average period through April was possible in the Ohio Valley, but no clear wetter or drier signal in the rest of the Midwest or Northeast.

A heavy rain event during a period of snowmelt, when rainwater plus meltwater magnifies flooding of rivers and streams, is certainly possible through spring.

A sharp, rapid warm spell can melt snowpack quickly, sending a large volume of meltwater into rivers and streams.

This becomes a greater risk when a snowstorm occurs later in the spring, April or May. When temperatures rebound to more typical April or May values, the newly deposited wet, heavy snow can vanish quickly, sending rivers and streams rising.

There are still a lot of unknowns, but the factors spelled out here have already loaded the dice toward a higher spring flood risk in the Midwest and Northeast.