30 September 2016

Historic Rainfall Event in Maryland and Delaware

Posted by Dan Satterfield

In my last post, I wrote about the possibility of a severe flood/rain event in Eastern Virginia/Delaware/Maryland. Unfortunately my forecast was correct, and in short, it’s still raining. The town of Harbeson Delaware had over a foot of rain in 24 hours! Schools were closed, roads washed out, and many other closed.  I mentioned yesterday that the water temps in the Atlantic are at record levels, and it’s hard to not consider that this fact, and the warmest global oceans ever measured played a role in this. Warmer water evaporates more moisture into the air, and warmer air can hold more water.

Below is a map put together by my intern Andrew McCormick at Salisbury University, it shows the MRMS rainfall estimate which is based on rain gauges and dual polarimetric radar estimates.


Image from Andrew McCormick at Salisbury Univ.

Delaware is one of a few states that has a statewide mesonet (Oklahoma and Iowa are others). The DEOS network showed amazing rain totals in southern Delaware, with Harbeson,DE receiving over 12 inches in 24 hours (see below). Now, we can add this event to the other incredible rainfall events in the U.S. this year, like Baton Rouge, Ellicott City, and three previous events of over 7 inches in a few hours that we have experienced here on the Eastern Shore of Maryland/Delaware/Va.


The water vapor imagery below (ctsy. UCAR) shows the strong upper level low over Kentucky. I drew on the two moisture channels that this low steered into the Delmarva region. When a strong storm develops it can take advantage of the extra moisture available in the atmosphere from the record oceans.

Screen Shot 2016-09-30 at 1.28.38 AM

Want to know more about water vapor imagery? Good basic tutorial here. My friend Sheldon Kusselson is an expert on this, and developed new ways of measuring Total Precipitable Water (TPW) in the atmosphere for NOAA. Check out that link for a movie showing the moisture flow into the Mid-Atlantic.

One last image to show you, (from Climate Central) showing the NOAA research data regarding extreme rain events. They’ve been increasing, especially in the Northeast U.S.

Screen Shot 2016-09-30 at 1.35.06 AM

You can read more about the impact these events are having on water quality here.