SIOUX CITY, Iowa (KCAU) — A winter storm impacted parts of Siouxland Wednesday and Thursday, dropping heavy snow in parts of the KCAU 9 viewing area including Sioux Falls, SD which saw a total of 12.6″ of total snow accumulation during the storm. Immediately following the storm – which prompted a slew of Blizzard Warnings, Winter Storm Warnings, and Winter Weather Advisories – temperatures plunged below average with bitterly cold lows and wind chills dropping well below zero.
However, as we head into the weekend, temperatures are once again expected to warm back above the freezing mark and even into the 40s. This will allow for most, if not all of the lighter snow packs, such as here in Sioux City where between 1-3″ of snow fell, to melt and a large amount of the heavier snow packs to our north to also begin the melting process.
In addition to the warmer weather, rain chances are on the rise through Sunday and into Sunday night, helping to further melt snow and provide at least a few tenths of an inch of rain, with the potential for higher totals.
So one of the big concerns people may have is, ‘Where will this rain go? What happens when the snow melts if the ground is still frozen, on top of all that rain?’
Assuming there’s plentiful moisture in the ground, the snow melt, which depending on whether it’s a lighter, fluffier snow (occurs when it’s colder and drier, typically the farther away you get from the 32° mark, the drier and fluffier the snow will be), which will produce less liquid when melted, or a heavier wetter snow (typically what we tend to see when snow falls closer to the 32° mark), which will produce more liquid as it melts, will begin saturating the ground even more.
Rapid snow melt, especially with the heavier, wetter snow, which could translate to, for example, 1 inch of liquid precipitation for every 8 inches of snowfall, coupled with a large snowpack, the ground could easily be saturated, especially if an area has already seen large quantities of precipitation, such as having a year in which they saw above average precipitation. This could definitely lead to flooding, especially if you’re seeing melting snow along with heavy rainfall.
I’ll give you a few different scenarios to help visualize this.
An area has seen above-average precipitation and has a significant surplus of precipitation. They get a significant winter storm that drops very heavy, wet snow (we’ll say 10 inches of snow=1 inch of liquid precipitation), between 12-13.” After a few days, temperatures warm and all that snow begins to melt. They also receive very heavy rainfall and the remainder of the snow is melted off and between 1-1.5″ of rainfall is recorded. In this scenario, the area would very likely see some flooding, since they’ve got a combination of already saturated soils which are likely only partially thawed, along with around 1 inch of liquid added to that soil due to snow melt, and then significant rainfall on top of all that. This is because the ground already has too much moisture within it and is very likely at or near its maximum saturation, meaning it won’t be able to absorb any more liquid and all of the remaining liquid would either pool on the surface or runoff, depending on flatness or slope of the area.
An area has seen normal precipitation and has an average amount of moisture in the ground. They get the same significant winter storm as scenario 1 and also see the same warm-up and rainfall event. In this case, they could see some flooding, but not nearly as significant since the soil/ground is able to absorb more of the snow melt and potentially some of the excessive rainfall. The ground requires more moisture than the already fully saturated ground of the area that has seen above-average precipitation already, to reach its saturation level. Minor ponding and pooling off excess rain/snow melt and/or runoff of the excess liquid is possible in this scenario, but not as significant as in scenario 1.
Similar to the current situation in Siouxland, an area has seen significantly less precipitation than normal and is currently considered in a moderate to severe drought. They also see 12-13″ of heavy, wet snow, followed by a warm-up and period of heavy rainfall. Due to the below-average precipitation and lack of much surplus moisture build-up in the soil/ground, there is a much higher threshold for the amount of liquid that can be absorbed, so the liquid from the snow melt and the accumulated rainfall will likely have little to no problem being absorbed into the dry, possibly partially frozen ground, and flooding is highly unlikely in this situation. It would take significantly more rain and/or snow melt for the ground to reach saturation in this scenario.
Now, since our recent snowfall event brought less in the way of heavy, wet snow, which would yield a higher amount of liquid as it melts, we are still considered to be in a moderate to exceptional drought area-wide, and at this time, rainfall totals for this weekend look to be on the lighter side, the risk of significant, if any flooding, is extremely minimal even in areas like Sioux Falls or Yankton, SD where they say between 7 and 12 inches of snow.
However, if you are concerned about flooding, there are steps you can take to protect yourself and your home from the potential risk. First and foremost, ensure snow is cleared away from your house its foundation, and any basement-level windows or doors you may have. You should also make sure storm drains and downspouts are clear of any debris and snow so they can work properly and do their job of keeping your property safe and dry.
You should also stay up to date with your local forecast so you can be prepared for whatever the weather brings.
For the latest weather updates, visit KCAU 9’s Weather page by clicking here.
And with winter hitting Siouxland, it pays to be prepared. For a variety of resources, click here.