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.
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.
You can read more about the impact these events are having on water quality here.
Dan Satterfield has worked as an on air meteorologist for 32 years in Oklahoma, Florida and Alabama. Forecasting weather is Dan's job, but all of Earth Science is his passion. This journal is where Dan writes about things he has too little time for on air. Dan blogs about peer-reviewed Earth science for Junior High level audiences and up.
Dan, I’ve been looking at the last image of your 9/30 post, “Heavy Downpours Increasing” from Climate Central.
Which says “Percent increase from 1958-2012in the amount of precipitation falling in very heavy events. Very Heavy Precipitation as the heaviest 1% of all daily events.”
So this could mean that the Northeast went from 1% of its rainfall coming from very heavy events up to 1.7%, or it could be an increase from 10% to 17%. Can’t tell without the underlying numbers.
Similarly, for the Southeast it could be an increase from 4% to 5%, or from 20% to 25.4%.
Unless they mean that in the Northeast 71% of precipitation come from heavy events but that wouldn’t be percent increase.
Can you clarify?
Thanks.
Am pretty sure it’s the amount of precipitation that fell in the top 1% of events. Climate Central is really good at posting their methadology, and Ill check with them.