Second Spring Flood Outlook

The second of two planned Spring Flood Outlooks was issued Thursday.

As you have probably guessed, we are under a higher than normal risk of at least moderate flooding over most of the KWWL viewing area. To keep an eye on the latest river levels, click here.

 

We went into the Winter wet… we had above normal rainfall in September (over 13″ in Waterloo for the month!).  Most of our viewing area is 200% above normal as we headed into the winter months.

The beginning of winter was relatively warm and dry but was followed by cold temperatures with several rounds of snow.

As you all keep reminding us, we have had quite a bit of snow over the entire season.

Iowa has had anywhere from 2 to 6 feet of snow fall on the state since the beginning of the winter season.  Which is over 10 inches above normal.

We still have plenty of it left on the ground (our viewing area has 2″ to over a foot!)….

…with plenty of moisture trapped in it.  Our viewing area has mainly 1″ to 4″ of liquid trapped in that snow.

That is running 80% to more than 95% higher than most years.

The speed of melting will be VERY important… the faster it melts the faster it goes into the rivers and the faster the rivers rise. The slower it melts the better for rivers and the towns along them.

The ground is frozen to a depth of 1 to 2 feet over the entire outlook area.

This means that the ground can’t even start to thaw until the snow finally melts and the sun can warm the soil.  This will lead to runoff concerns as snow melts and rain falls, plus river levels are already running high in some areas.

River levels are also be affected by ice jams.

They occur every year, but this year may cause worse flooding if the ice jams occur at the same time as increased snow melt and/or rainfall.

We have the two large storm systems that are expected to track through the region over the next week. They will produce mainly rain over us, but could dump heavy snow to the north. Liquid amounts will be high.

The good news is that the next few weeks are overall dry and cold.

I know, I know… we are “done with the cold”, but in this case, you want it. We want cooler than normal high temperatures, above freezing, during the day in order to melt some snow… and, preferably, we want it to refreeze at night to slow it down even more.  Otherwise, we get the equivalent of a 4″ rain storm dumping into the river basin (all of them) all at once.

The following was put out by the National Weather Service and I include it, because I can’t say it any better.

TO NOTE, EVEN A GRADUAL SNOWMELT WITH LITTLE RAINFALL THIS SPRING
ASSURES AT LEAST MINOR FLOODING FOR MANY RIVERS ACROSS THE REGION.

MAIN POINTS:

* CURRENT CONDITIONS SUPPORT A CHANCE FOR HIGH IMPACT FLOODING THIS
  SPRING, AS WELL AS WIDESPREAD MINOR FLOODING.
* SATURATED SOILS OR FROZEN GROUND WILL CONTRIBUTE TO HIGH AMOUNTS
  OF RUNOFF FROM SNOWMELT AND SPRING-TIME RAINS.
* DUE TO A DEEP SNOWPACK ACROSS MUCH OF THE REGION, SNOWMELT ALONE
  WILL LIKELY CAUSE MOST RIVERS TO REACH LEVELS NEAR OR ABOVE FLOOD
  STAGE. CONFIDENCE IS HIGH ON WIDESPREAD MINOR FLOODING, WITH LOWER
  CONFIDENCE ON THE SEVERITY OF PEAK CRESTS.
* ICE ACTION IN THE RIVERS WILL CONTINUE TO BE A FACTOR IN POTENTIAL
  FLOODING AS MANY RIVERS REMAIN ICE COVERED.
* THE RATE OF THE SNOWMELT AND ADDITIONAL SPRING RAINS WILL BE
  ESSENTIAL TO THE SEVERITY OF FLOODING THAT OCCURS THIS SPRING. A
  FAST SNOWMELT AND ANY SIGNIFICANT SPRING RAINS WILL INCREASE THE
  POTENTIAL FOR HIGH IMPACT FLOODING THIS SEASON.

MANY FACTORS ARE CONSIDERED WHEN DETERMINING THE OVERALL FLOOD RISK
FOR THE UPCOMING SPRING SEASON. THE COMBINATION OF THESE INFLUENCES
FACTOR INTO THE FINAL DETERMINATION. THESE FACTORS ARE DISCUSSED IN
DETAIL BELOW.

Essentially, expect flooding the area, but stay updated on the latest rainfall, snowfall, and temperatures forecasts.

There are currently no outlooks scheduled, but due to the high risk of flooding, there will likely be another look at the situation in a couple of weeks.

Here’s the complete outlook from:

National Weather Service in Des Moines… click here.

National Weather Service in Quad Cities… click here.

National Weather Service in LaCrosse… click here.

Eileen Loan

Eileen Loan

Meteorologist
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